public class Person {
  private String name;
  private int age;
  // the usual getters and setters...
    
We're going to provide validation behavior for the
      Person class by implementing the following two
      methods of the
      org.springframework.validation.Validator
      interface: 

        
supports(Class) - Can this
          Validator validate instances of the
          supplied Class?
        
validate(Object,
          org.springframework.validation.Errors) - validates the
          given object and in case of validation errors, registers those with
          the given Errors object
    
 Implementing a Validator is fairly
      straightforward, especially when you know of the
      ValidationUtils helper class that the Spring
      Framework also provides.
    
public class PersonValidator implements Validator {
    * This Validator validates *just* Person instances
    public boolean supports(Class clazz) {
        return Person.class.equals(clazz);
    public void validate(Object obj, Errors e) {
        ValidationUtils.rejectIfEmpty(e, "name", "name.empty");
        Person p = (Person) obj;
        if (p.getAge() < 0) {
            e.rejectValue("age", "negativevalue");
        } else if (p.getAge() > 110) {
            e.rejectValue("age", "too.darn.old");
    
As you can see, the static
      rejectIfEmpty(..) method on the
      ValidationUtils class is used to reject the
      'name' property if it is null or the
      empty string. Have a look at the Javadoc for the
      ValidationUtils class to see what functionality it
      provides besides the example shown previously.
    
While it is certainly possible to implement a single
      Validator class to validate each of the
      nested objects in a rich object, it may be better to encapsulate the
      validation logic for each nested class of object in its own
      Validator implementation. A simple example
      of a 'rich' object would be a
      Customer that is composed of two
      String properties (a first and second name) and a
      complex Address object.
      Address objects may be used independently of
      Customer objects, and so a distinct
      AddressValidator has been implemented. If you want
      your CustomerValidator to reuse the logic contained
      within the AddressValidator class without resorting
      to copy-and-paste, you can dependency-inject or instantiate an
      AddressValidator within your
      CustomerValidator, and use it like so:
    
public class CustomerValidator implements Validator {
    private final Validator addressValidator;
    public CustomerValidator(Validator addressValidator) {
        if (addressValidator == null) {
            throw new IllegalArgumentException(
              "The supplied [Validator] is required and must not be null.");
        if (!addressValidator.supports(Address.class)) {
            throw new IllegalArgumentException(
              "The supplied [Validator] must support the validation of [Address] instances.");
        this.addressValidator = addressValidator;
    * This Validator validates Customer instances, and any subclasses of Customer too
    public boolean supports(Class clazz) {
        return Customer.class.isAssignableFrom(clazz);
    public void validate(Object target, Errors errors) {
        ValidationUtils.rejectIfEmptyOrWhitespace(errors, "firstName", "field.required");
        ValidationUtils.rejectIfEmptyOrWhitespace(errors, "surname", "field.required");
        Customer customer = (Customer) target;
        try {
            errors.pushNestedPath("address");
            ValidationUtils.invokeValidator(this.addressValidator, customer.getAddress(), errors);
        } finally {
            errors.popNestedPath();
    
Validation errors are reported to the
      Errors object passed to the validator. In
      case of Spring Web MVC you can use <spring:bind/>
      tag to inspect the error messages, but of course you can also inspect the
      errors object yourself. More information about the methods it offers can
      be found from the Javadoc.
  
7.3 Resolving codes to error messages

    
We've talked about databinding and validation. Outputting messages
      corresponding to validation errors is the last thing we need to discuss.
      In the example we've shown above, we rejected the name
      and the age field. If we're going to output the error
      messages by using a MessageSource, we will
      do so using the error code we've given when rejecting the field ('name'
      and 'age' in this case). When you call (either directly, or indirectly,
      using for example the ValidationUtils class)
      rejectValue or one of the other
      reject methods from the
      Errors interface, the underlying
      implementation will not only register the code you've passed in, but also
      a number of additional error codes. What error codes it registers is
      determined by the MessageCodesResolver that
      is used. By default, the
      DefaultMessageCodesResolver is used, which for
      example not only registers a message with the code you gave, but also
      messages that include the field name you passed to the reject method. So
      in case you reject a field using rejectValue("age",
      "too.darn.old"), apart from the too.darn.old
      code, Spring will also register too.darn.old.age and
      too.darn.old.age.int (so the first will include the
      field name and the second will include the type of the field); this is
      done as a convenience to aid developers in targeting error messages and
      suchlike.
    
More information on the
      MessageCodesResolver and the default
      strategy can be found online with the Javadocs for MessageCodesResolver and DefaultMessageCodesResolver respectively.
  
7.4 Bean manipulation and the
      BeanWrapper

    
The org.springframework.beans package adheres to
      the JavaBeans standard provided by Sun. A JavaBean is simply a class with
      a default no-argument constructor, which follows a naming convention where
      (by way of an example) a property named bingoMadness
      would have a setter method setBingoMadness(..)
      and a getter method getBingoMadness(). For more
      information about JavaBeans and the specification, please refer to Sun's
      website ( java.sun.com/products/javabeans).
    
One quite important class in the beans package is the
      BeanWrapper interface and its corresponding
      implementation (BeanWrapperImpl). As quoted from
      the Javadoc, the BeanWrapper offers
      functionality to set and get property values (individually or in bulk),
      get property descriptors, and to query properties to determine if they are
      readable or writable. Also, the BeanWrapper
      offers support for nested properties, enabling the setting of properties
      on sub-properties to an unlimited depth. Then, the
      BeanWrapper supports the ability to add
      standard JavaBeans PropertyChangeListeners
      and VetoableChangeListeners, without the
      need for supporting code in the target class. Last but not least, the
      BeanWrapper provides support for the
      setting of indexed properties. The
      BeanWrapper usually isn't used by
      application code directly, but by the
      DataBinder and the
      BeanFactory.




    

    
The way the BeanWrapper works is partly
      indicated by its name: it wraps a bean to perform
      actions on that bean, like setting and retrieving properties.
    
7.4.1 Setting and getting basic and nested properties

      
Setting and getting properties is done using the
        setPropertyValue(s) and
        getPropertyValue(s) methods that both come with a
        couple of overloaded variants. They're all described in more detail in
        the Javadoc Spring comes with. What's important to know is that there
        are a couple of conventions for indicating properties of an object. A
        couple of examples:
      
Table 7.1. Examples of properties

        
Expression
Explanation
name
Indicates the property name
                corresponding to the methods getName()
                or isName() and
                setName(..)
account.name
Indicates the nested property name of
                the property account corresponding e.g. to
                the methods getAccount().setName() or
                getAccount().getName()
account[2]
Indicates the third element of the
                indexed property account. Indexed properties
                can be of type array, list
                or other naturally ordered
                collection
account[COMPANYNAME]
Indicates the value of the map entry indexed by the key
                COMPANYNAME of the Map property
                account
      
Below you'll find some examples of working with the
        BeanWrapper to get and set
        properties.
      
(This next section is not vitally important to you if
        you're not planning to work with the
        BeanWrapper directly. If you're just
        using the DataBinder and the
        BeanFactory and their out-of-the-box
        implementation, you should skip ahead to the section about
        PropertyEditors.)
      
Consider the following two classes:
      
public class Company {
    private String name;
    private Employee managingDirector;
    public String getName() {
        return this.name;
    public void setName(String name) {
        this.name = name;
    public Employee getManagingDirector() {
        return this.managingDirector;
    public void setManagingDirector(Employee managingDirector) {
        this.managingDirector = managingDirector;
      
public class Employee {
    private String name;
    private float salary;
    public String getName() {
        return this.name;
    public void setName(String name) {
        this.name = name;
    public float getSalary() {
        return salary;
    public void setSalary(float salary) {
        this.salary = salary;
      
The following code snippets show some examples of how to retrieve
        and manipulate some of the properties of instantiated
        Companies and Employees:
      
BeanWrapper company = BeanWrapperImpl(new Company());
// setting the company name..
company.setPropertyValue("name", "Some Company Inc.");
// ... can also be done like this:
PropertyValue value = new PropertyValue("name", "Some Company Inc.");
company.setPropertyValue(value);
// ok, let's create the director and tie it to the company:
BeanWrapper jim = BeanWrapperImpl(new Employee());
jim.setPropertyValue("name", "Jim Stravinsky");
company.setPropertyValue("managingDirector", jim.getWrappedInstance());
// retrieving the salary of the managingDirector through the company
Float salary = (Float) company.getPropertyValue("managingDirector.salary");
    
7.4.2 Built-in PropertyEditor
        implementations

      
Spring uses the concept of PropertyEditors to
        effect the conversion between an Object and a
        String. If you think about it, it sometimes might
        be handy to be able to represent properties in a different way than the
        object itself. For example, a Date can be
        represented in a human readable way (as the
        String '2007-14-09'), while
        we're still able to convert the human readable form back to the original
        date (or even better: convert any date entered in a human readable form,
        back to Date objects). This behavior can be
        achieved by registering custom editors, of type
        java.beans.PropertyEditor. Registering
        custom editors on a BeanWrapper or
        alternately in a specific IoC container as mentioned in the previous
        chapter, gives it the knowledge of how to convert properties to the
        desired type. Read more about
        PropertyEditors in the Javadoc of the
        java.beans package provided by Sun.
      
A couple of examples where property editing is used in Spring:
          
setting properties on beans is done using
            PropertyEditors. When mentioning
            java.lang.String as the value of a property of
            some bean you're declaring in XML file, Spring will (if the setter
            of the corresponding property has a
            Class-parameter) use the
            ClassEditor to try to resolve the parameter
            to a Class object.
          
parsing HTTP request parameters in Spring's
            MVC framework is done using all kinds of
            PropertyEditors that you can manually bind in all
            subclasses of the CommandController.
      
Spring has a number of built-in PropertyEditors
        to make life easy. Each of those is listed below and they are all
        located in the
        org.springframework.beans.propertyeditors package.
        Most, but not all (as indicated below), are registered by default by
        BeanWrapperImpl. Where the property editor is
        configurable in some fashion, you can of course still register your own
        variant to override the default one:
      
Table 7.2. Built-in PropertyEditors

        
Class
Explanation
ByteArrayPropertyEditor
Editor for byte arrays. Strings will simply be converted to
                their corresponding byte representations. Registered by default
                by BeanWrapperImpl.
ClassEditor
Parses Strings representing classes to actual classes and
                the other way around. When a class is not found, an
                IllegalArgumentException is thrown.
                Registered by default by
                BeanWrapperImpl.
CustomBooleanEditor
Customizable property editor for
                Boolean properties. Registered by default
                by BeanWrapperImpl, but, can be
                overridden by registering custom instance of it as custom
                editor.
CustomCollectionEditor
Property editor for Collections, converting any source
                Collection to a given target
                Collection type.
CustomDateEditor
Customizable property editor for java.util.Date, supporting
                a custom DateFormat. NOT registered by default. Must be user
                registered as needed with appropriate format.
CustomNumberEditor
Customizable property editor for any Number subclass like
                Integer, Long,
                Float, Double.
                Registered by default by BeanWrapperImpl,
                but can be overridden by registering custom instance of it as a
                custom editor.
FileEditor
Capable of resolving Strings to
                java.io.File objects. Registered by
                default by BeanWrapperImpl. 
InputStreamEditor
One-way property editor, capable of taking a text string
                and producing (via an intermediate
                ResourceEditor and
                Resource) an
                InputStream, so
                InputStream properties may be
                directly set as Strings. Note that the default usage will not
                close the InputStream for you!
                Registered by default by
                BeanWrapperImpl.
LocaleEditor
Capable of resolving Strings to
                Locale objects and vice versa (the String
                format is [language]_[country]_[variant], which is the same
                thing the toString() method of Locale provides). Registered by
                default by BeanWrapperImpl.
PatternEditor
Capable of resolving Strings to JDK 1.5
                Pattern objects and vice versa.
PropertiesEditor
Capable of converting Strings (formatted using the format
                as defined in the Javadoc for the java.lang.Properties class) to
                Properties objects. Registered by default
                by BeanWrapperImpl.
StringTrimmerEditor
Property editor that trims Strings. Optionally allows
                transforming an empty string into a null
                value. NOT registered by default; must be user registered as
                needed.
URLEditor
Capable of resolving a String representation of a URL to an
                actual URL object. Registered by default
                by BeanWrapperImpl.
      
 Spring uses the
        java.beans.PropertyEditorManager to set
        the search path for property editors that might be needed. The search
        path also includes sun.bean.editors, which includes
        PropertyEditor implementations for types
        such as Font, Color, and
        most of the primitive types. Note also that the standard JavaBeans
        infrastructure will automatically discover
        PropertyEditor classes (without you
        having to register them explicitly) if they are in the same package as
        the class they handle, and have the same name as that class, with
        'Editor' appended; for example, one could have the
        following class and package structure, which would be sufficient for the
        FooEditor class to be recognized and used as the
        PropertyEditor for
        Foo-typed properties. 




    

  chank
      FooEditor   // the PropertyEditor for the Foo class

      
Note that you can also use the standard
        BeanInfo JavaBeans mechanism here as well
        (described in not-amazing-detail here). Find below an example of using the
        BeanInfo mechanism for explicitly
        registering one or more PropertyEditor
        instances with the properties of an associated class.
  chank
      FooBeanInfo   // the BeanInfo for the Foo class

      
 Here is the Java source code for the referenced
        FooBeanInfo class. This would associate a
        CustomNumberEditor with the
        age property of the Foo class. 
      
public class FooBeanInfo extends SimpleBeanInfo {
    public PropertyDescriptor[] getPropertyDescriptors() {
        try {
            final PropertyEditor numberPE = new CustomNumberEditor(Integer.class, true);
            PropertyDescriptor ageDescriptor = new PropertyDescriptor("age", Foo.class) {
                public PropertyEditor createPropertyEditor(Object bean) {
                    return numberPE;
            return new PropertyDescriptor[] { ageDescriptor };
        catch (IntrospectionException ex) {
            throw new Error(ex.toString());
      
Registering additional custom
          PropertyEditors

        
When setting bean properties as a string value, a Spring IoC
          container ultimately uses standard JavaBeans
          PropertyEditors to convert these Strings to the
          complex type of the property. Spring pre-registers a number of custom
          PropertyEditors (for example, to convert a
          classname expressed as a string into a real
          Class object). Additionally, Java's standard
          JavaBeans PropertyEditor lookup
          mechanism allows a PropertyEditor for a class
          simply to be named appropriately and placed in the same package as the
          class it provides support for, to be found automatically.
        
If there is a need to register other custom
          PropertyEditors, there are several mechanisms
          available. The most manual approach, which is not normally convenient
          or recommended, is to simply use the
          registerCustomEditor() method of the
          ConfigurableBeanFactory interface,
          assuming you have a BeanFactory
          reference. Another, slightly more convenient, mechanism is to use a
          special bean factory post-processor called
          CustomEditorConfigurer. Although bean factory
          post-processors can be used with
          BeanFactory implementations, the
          CustomEditorConfigurer has a nested property
          setup, so it is strongly recommended that it is used with the
          ApplicationContext, where it may be
          deployed in similar fashion to any other bean, and automatically
          detected and applied.
        
Note that all bean factories and application contexts
          automatically use a number of built-in property editors, through their
          use of something called a BeanWrapper
          to handle property conversions. The standard property editors that the
          BeanWrapper registers are listed in
          the previous section.
          Additionally, ApplicationContexts also override or
          add an additional number of editors to handle resource lookups in a
          manner appropriate to the specific application context type.
        
Standard JavaBeans PropertyEditor
          instances are used to convert property values expressed as strings to
          the actual complex type of the property.
          CustomEditorConfigurer, a bean factory
          post-processor, may be used to conveniently add support for additional
          PropertyEditor instances to an
          ApplicationContext.
        
Consider a user class ExoticType, and
          another class DependsOnExoticType which needs
          ExoticType set as a property:
        
package example;
public class ExoticType {
    private String name;
    public ExoticType(String name) {
        this.name = name;
public class DependsOnExoticType {
    private ExoticType type;
    public void setType(ExoticType type) {
        this.type = type;
        
When things are properly set up, we want to be able to assign the
          type property as a string, which a
          PropertyEditor will behind the scenes
          convert into an actual ExoticType
          instance:
        
<bean id="sample" class="example.DependsOnExoticType">
    <property name="type" value="aNameForExoticType"/>
</bean>
        
The PropertyEditor implementation
          could look similar to this:
        
// converts string representation to ExoticType object
package example;
public class ExoticTypeEditor extends PropertyEditorSupport {
    public void setAsText(String text) {
        setValue(new ExoticType(text.toUpperCase()));
        
Finally, we use CustomEditorConfigurer to
          register the new PropertyEditor with
          the ApplicationContext, which will then
          be able to use it as needed:
        
<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
  <property name="customEditors">
      <entry key="example.ExoticType" value="example.ExoticTypeEditor"/>
  </property>
</bean>
        
Using
            PropertyEditorRegistrars

          
Another mechanism for registering property editors with the
            Spring container is to create and use a
            PropertyEditorRegistrar. This
            interface is particularly useful when you need to use the same set
            of property editors in several different situations: write a
            corresponding registrar and reuse that in each case.
            PropertyEditorRegistrars work in conjunction with
            an interface called
            PropertyEditorRegistry, an interface
            that is implemented by the Spring
            BeanWrapper (and
            DataBinder).
            PropertyEditorRegistrars are particularly
            convenient when used in conjunction with the
            CustomEditorConfigurer (introduced here), which exposes a property called
            setPropertyEditorRegistrars(..):
            PropertyEditorRegistrars added to a
            CustomEditorConfigurer in this fashion can
            easily be shared with DataBinder and
            Spring MVC Controllers. Furthermore,
            it avoids the need for synchronization on custom editors: a
            PropertyEditorRegistrar is expected
            to create fresh PropertyEditor
            instances for each bean creation attempt.
          
Using a PropertyEditorRegistrar
            is perhaps best illustrated with an example. First off, you need to
            create your own
            PropertyEditorRegistrar
            implementation:
          
package com.foo.editors.spring;
public final class CustomPropertyEditorRegistrar implements PropertyEditorRegistrar {
    public void registerCustomEditors(PropertyEditorRegistry registry) {
        // it is expected that new PropertyEditor instances are created
        registry.registerCustomEditor(ExoticType.class, new ExoticTypeEditor());
        // you could register as many custom property editors as are required here...
          
See also the
            org.springframework.beans.support.ResourceEditorRegistrar
            for an example
            PropertyEditorRegistrar
            implementation. Notice how in its implementation of the
            registerCustomEditors(..) method it creates
            new instances of each property editor.
          
Next we configure a
            CustomEditorConfigurer and inject an instance
            of our CustomPropertyEditorRegistrar into
          
<bean class="org.springframework.beans.factory.config.CustomEditorConfigurer">
    <property name="propertyEditorRegistrars">
            <ref bean="customPropertyEditorRegistrar"/>
        </list>
    </property>
</bean>
<bean id="customPropertyEditorRegistrar"
      class="com.foo.editors.spring.CustomPropertyEditorRegistrar"/>
          
Finally, and in a bit of a departure from the focus of this
            chapter, for those of you using Spring's MVC web
            framework, using
            PropertyEditorRegistrars in
            conjunction with data-binding
            Controllers (such as
            SimpleFormController) can be very convenient.
            Find below an example of using a
            PropertyEditorRegistrar in the
            implementation of an initBinder(..)
            method:
          
public final class RegisterUserController extends SimpleFormController {
    private final PropertyEditorRegistrar customPropertyEditorRegistrar;
    public RegisterUserController(PropertyEditorRegistrar propertyEditorRegistrar) {
        this.customPropertyEditorRegistrar = propertyEditorRegistrar;
    protected




    
 void initBinder(HttpServletRequest request, ServletRequestDataBinder binder)
                        throws Exception {
        this.customPropertyEditorRegistrar.registerCustomEditors(binder);
    // other methods to do with registering a User
          
This style of PropertyEditor
            registration can lead to concise code (the implementation of
            initBinder(..) is just one line long!), and
            allows common PropertyEditor
            registration code to be encapsulated in a class and then shared
            amongst as many Controllers as
            needed.
    
 Spring 3 introduces a core.convert package that
      provides a general type conversion system. The system defines an SPI to
      implement type conversion logic, as well as an API to execute type
      conversions at runtime. Within a Spring container, this system can be used
      as an alternative to PropertyEditors to convert externalized bean property
      value strings to required property types. The public API may also be used
      anywhere in your application where type conversion is needed. 
    
7.5.1 Converter SPI

      
 The SPI to implement type conversion logic is simple and strongly
        typed: 
      
package org.springframework.core.convert.converter;
public interface Converter<S, T> {
    T convert(S source);
      
 To create your own Converter, simply implement the interface above.
        Parameterize S as the type you are converting from, and T as the type
        you are converting to. For each call to convert(S), the source argument
        is guaranteed to be NOT null. Your Converter may throw any Exception if
        conversion fails. An IllegalArgumentException should be thrown to report
        an invalid source value. Take care to ensure your Converter
        implementation is thread-safe. 
      
 Several converter implementations are provided in the
        core.convert.support package as a convenience.
        These include converters from Strings to Numbers and other common types.
        Consider StringToInteger as an example Converter
        implementation: 
      
package org.springframework.core.convert.support;
final class StringToInteger implements Converter<String, Integer> {
    public Integer convert(String source) {
        return Integer.valueOf(source);
    
7.5.2 ConverterFactory

      
 When you need to centralize the conversion logic for an entire
        class hierarchy, for example, when converting from String to
        java.lang.Enum objects, implement
        ConverterFactory: 
      
package org.springframework.core.convert.converter;
public interface ConverterFactory<S, R> {
    <T extends R> Converter<S, T> getConverter(Class<T> targetType);
      
 Parameterize S to be the type you are converting from and R to be
        the base type defining the range of classes you can
        convert to. Then implement getConverter(Class<T>), where T is a
        subclass of R. 
      
 Consider the StringToEnum ConverterFactory
        as an example: 
      
package org.springframework.core.convert.support;
final class StringToEnumConverterFactory implements ConverterFactory<String, Enum> {
    public <T extends Enum> Converter<String, T> getConverter(Class<T> targetType) {
        return new StringToEnumConverter(targetType);
    private final class StringToEnumConverter<T extends Enum> implements Converter<String, T> {
        private Class<T> enumType;
        public StringToEnumConverter(Class<T> enumType) {
            this.enumType = enumType;
        public T convert(String source) {
            return (T) Enum.valueOf(this.enumType, source.trim());
    
7.5.3 GenericConverter

      
 When you require a sophisticated Converter implementation, consider
        the GenericConverter interface. With a more flexible but less strongly
        typed signature, a GenericConverter supports converting between multiple
        source and target types. In addition, a GenericConverter makes available
        source and target field context you can use when implementing your
        conversion logic. Such context allows a type conversion to be driven by
        a field annotation, or generic information declared on a field
        signature. 
      
package org.springframework.core.convert.converter;
public interface GenericConverter {
    public Set<ConvertiblePair> getConvertibleTypes();
    Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType);
      
 To implement a GenericConverter, have getConvertibleTypes() return
        the supported source->target type pairs. Then implement
        convert(Object, TypeDescriptor, TypeDescriptor) to implement your
        conversion logic. The source TypeDescriptor provides access to the
        source field holding the value being converted. The target
        TypeDescriptor provides access to the target field where the converted
        value will be set. 
      
 A good example of a GenericConverter is a converter that converts
        between a Java Array and a Collection. Such an
        ArrayToCollectionConverter introspects the field that declares the
        target Collection type to resolve the Collection's element type. This
        allows each element in the source array to be converted to the
        Collection element type before the Collection is set on the target
        field. 
        
 Because GenericConverter is a more complex SPI interface, only
          use it when you need it. Favor Converter or ConverterFactory for basic
          type conversion needs. 
      
ConditionalGenericConverter

        
 Sometimes you only want a Converter to execute if a specific
          condition holds true. For example, you might only want to execute a
          Converter if a specific annotation is present on the target field. Or
          you might only want to execute a Converter if a specific method, such
          as static valueOf method, is defined on the target class.
          ConditionalGenericConverter is an subinterface of GenericConverter
          that allows you to define such custom matching criteria: 
        
public interface ConditionalGenericConverter extends GenericConverter {
    boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType);
        
 A good example of a ConditionalGenericConverter is an
          EntityConverter that converts between an persistent entity identifier
          and an entity reference. Such a EntityConverter might only match if
          the target entity type declares a static finder method e.g.
          findAccount(Long). You would perform such a finder method check in the
          implementation of matches(TypeDescriptor, TypeDescriptor). 
    
7.5.4 ConversionService API

      
 The ConversionService defines a unified API for executing type
        conversion logic at runtime. Converters are often executed behind this
        facade interface: 
      
package org.springframework.core.convert;
public interface ConversionService {
    boolean canConvert(Class<?> sourceType, Class<?> targetType);
    <T> T convert(Object source, Class<T> targetType);
    boolean canConvert(TypeDescriptor sourceType, TypeDescriptor targetType);
    Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType);
      
 Most ConversionService implementations also implement
        ConverterRegistry, which provides an SPI for
        registering converters. Internally, a ConversionService implementation
        delegates to its registered converters to carry out type conversion
        logic. 
      
 A robust ConversionService implementation is provided in the
        core.convert.support package.
        GenericConversionService is the general-purpose
        implementation suitable for use in most environments.
        ConversionServiceFactory provides a convenient
        factory for creating common ConversionService configurations. 
    
7.5.5 Configuring a ConversionService

      
 A ConversionService is a stateless object designed to be
        instantiated at application startup, then shared between multiple
        threads. In a Spring application, you typically configure a
        ConversionService instance per Spring container (or ApplicationContext).
        That ConversionService will be picked up by Spring and then used
        whenever a type conversion needs to be performed by the framework. You
        may also inject this ConversionService into any of your beans and invoke
        it directly. 
        
 If no ConversionService is registered with Spring, the original
          PropertyEditor-based system is used. 
      
 To register a default ConversionService with Spring, add the
        following bean definition with id conversionService: 
      
<bean id="conversionService"
      class="org.springframework.context.support.ConversionServiceFactoryBean"/>
      
 A default ConversionService can convert between strings, numbers,
        enums, collections, maps, and other common types. To supplement or
        override the default converters with your own custom converter(s), set
        the converters property. Property values may implement
        either of the Converter, ConverterFactory, or GenericConverter
        interfaces. 
      
<bean id="conversionService"
      class="org.springframework.context.support.ConversionServiceFactoryBean">
    <property name="converters">
            <bean class="example.MyCustomConverter"/>
        </list>
    </property>
</bean>
      
It is also common to use a ConversionService within a Spring MVC
        application. See Section 7.6.5, “Configuring Formatting in Spring MVC”
        for details on use with
        <mvc:annotation-driven/>.
      
In certain situations you may wish to apply formatting during
        conversion. See Section 7.6.3, “FormatterRegistry SPI” for
        details on using
        FormattingConversionServiceFactoryBean.
    
7.5.6 Using a ConversionService programmatically

      
 To work with a ConversionService instance programmatically, simply
        inject a reference to it like you would for any other bean: 
      
@Service




    

public class MyService {
    @Autowired
    public MyService(ConversionService conversionService) {
        this.conversionService = conversionService;
    public void doIt() {
        this.conversionService.convert(...)
  
7.6 Spring 3 Field Formatting

    
 As discussed in the previous section, core.convert is a general-purpose type
      conversion system. It provides a unified ConversionService API as well as
      a strongly-typed Converter SPI for implementing conversion logic from one
      type to another. A Spring Container uses this system to bind bean property
      values. In addition, both the Spring Expression Language (SpEL) and
      DataBinder use this system to bind field values. For example, when SpEL
      needs to coerce a Short to a
      Long to complete an
      expression.setValue(Object bean, Object value)
      attempt, the core.convert system performs the coercion. 
    
 Now consider the type conversion requirements of a typical client
      environment such as a web or desktop application. In such environments,
      you typically convert from String to support the
      client postback process, as well as back to String to
      support the view rendering process. In addition, you often need to
      localize String values. The more general core.convert
      Converter SPI does not address such formatting
      requirements directly. To directly address them, Spring 3 introduces a
      convenient Formatter SPI that provides a simple and robust alternative to
      PropertyEditors for client environments. 
    
 In general, use the Converter SPI when you need to implement
      general-purpose type conversion logic; for example, for converting between
      a java.util.Date and and java.lang.Long. Use the Formatter SPI when you're
      working in a client environment, such as a web application, and need to
      parse and print localized field values. The ConversionService provides a
      unified type conversion API for both SPIs. 
    
7.6.1 Formatter SPI

      
 The Formatter SPI to implement field formatting logic is simple and
        strongly typed: 
      
package org.springframework.format;
public interface Formatter<T> extends Printer<T>, Parser<T> {
      
 Where Formatter extends from the Printer and Parser building-block
        interfaces: 
      
public interface Printer<T> {
    String print(T fieldValue, Locale locale);
      
import java.text.ParseException;
public interface Parser<T> {
    T parse(String clientValue, Locale locale) throws ParseException;
      
 To create your own Formatter, simply implement the Formatter
        interface above. Parameterize T to be the type of object you wish to
        format, for example, java.util.Date. Implement
        the print() operation to print an instance of T
        for display in the client locale. Implement the
        parse() operation to parse an instance of T from
        the formatted representation returned from the client locale. Your
        Formatter should throw a ParseException or IllegalArgumentException if a
        parse attempt fails. Take care to ensure your Formatter implementation
        is thread-safe. 
      
 Several Formatter implementations are provided in
        format subpackages as a convenience. The
        number package provides a NumberFormatter,
        CurrencyFormatter, and PercentFormatter to format java.lang.Number
        objects using a java.text.NumberFormat. The
        datetime package provides a DateFormatter to format
        java.util.Date objects with a java.text.DateFormat. The
        datetime.joda package provides comprehensive
        datetime formatting support based on the Joda Time library. 
      
 Consider DateFormatter as an example
        Formatter implementation: 
      
package org.springframework.format.datetime;
public final class DateFormatter implements Formatter<Date> {
    private String pattern;
    public DateFormatter(String pattern) {
        this.pattern = pattern;
    public String print(Date date, Locale locale) {
        if (date == null) {
            return "";
        return getDateFormat(locale).format(date);
    public Date parse(String formatted, Locale locale) throws ParseException {
        if (formatted.length() == 0) {
            return null;
        return getDateFormat(locale).parse(formatted);
    protected DateFormat getDateFormat(Locale locale) {
        DateFormat dateFormat = new SimpleDateFormat(this.pattern, locale);
        dateFormat.setLenient(false);
        return dateFormat;
      
 The Spring team welcomes community-driven Formatter contributions;
        see http://jira.springframework.org to contribute. 
    
7.6.2 Annotation-driven Formatting

      
 As you will see, field formatting can be configured by field type
        or annotation. To bind an Annotation to a formatter, implement
        AnnotationFormatterFactory: 
      
package org.springframework.format;
public interface AnnotationFormatterFactory<A extends Annotation> {
    Set<Class<?>> getFieldTypes();
    Printer<?> getPrinter(A annotation, Class<?> fieldType);
    Parser<?> getParser(A annotation, Class<?> fieldType);
      
 Parameterize A to be the field annotationType you wish to associate
        formatting logic with, for example
        org.springframework.format.annotation.DateTimeFormat. Have
        getFieldTypes() return the types of fields the
        annotation may be used on. Have getPrinter()
        return a Printer to print the value of an annotated field. Have
        getParser() return a Parser to parse a
        clientValue for an annotated field. 
      
 The example AnnotationFormatterFactory implementation below binds
        the @NumberFormat Annotation to a formatter. This annotation allows
        either a number style or pattern to be specified: 
      
public final class NumberFormatAnnotationFormatterFactory
        implements AnnotationFormatterFactory<NumberFormat> {
    public Set<Class<?>> getFieldTypes() {
        return new HashSet<Class<?>>(asList(new Class<?>[] {
            Short.class, Integer.class, Long.class, Float.class,
            Double.class, BigDecimal.class, BigInteger.class }));
    public Printer<Number> getPrinter(NumberFormat annotation, Class<?> fieldType) {
        return configureFormatterFrom(annotation, fieldType);
    public Parser<Number> getParser(NumberFormat annotation, Class<?> fieldType) {
        return configureFormatterFrom(annotation, fieldType);
    private Formatter<Number> configureFormatterFrom(NumberFormat annotation,
                                                     Class<?> fieldType) {
        if (!annotation.pattern().isEmpty()) {
            return new NumberFormatter(annotation.pattern());
        } else {
            Style style = annotation.style();
            if (style == Style.PERCENT) {
                return new PercentFormatter();
            } else if (style == Style.CURRENCY) {
                return new CurrencyFormatter();
            } else {
                return new NumberFormatter();
      
 To trigger formatting, simply annotate fields with @NumberFormat: 
      
public class MyModel {
    @NumberFormat(style=Style.CURRENCY)
    private BigDecimal decimal;
      
Format Annotation API

        
 A portable format annotation API exists in the
          org.springframework.format.annotation package.
          Use @NumberFormat to format java.lang.Number fields. Use
          @DateTimeFormat to format java.util.Date, java.util.Calendar,
          java.util.Long, or Joda Time fields. 
        
 The example below uses @DateTimeFormat to format a java.util.Date
          as a ISO Date (yyyy-MM-dd): 
        
public class MyModel {
    @DateTimeFormat(iso=ISO.DATE)
    private Date date;
    
7.6.3 FormatterRegistry SPI

      
 The FormatterRegistry is an SPI for registering formatters and
          converters. FormattingConversionService is
          an implementation of FormatterRegistry suitable for most environments.
          This implementation may be configured programmatically or declaratively
          as a Spring bean using
          FormattingConversionServiceFactoryBean.
          Because this implementation also implements
        ConversionService, it can be directly
        configured for use with Spring's DataBinder and the Spring Expression
        Language (SpEL).
      
 Review the FormatterRegistry SPI below: 
      
package org.springframework.format;
public interface FormatterRegistry extends ConverterRegistry {
    void addFormatterForFieldType(Class<?> fieldType, Printer<?> printer, Parser<?> parser);
    void addFormatterForFieldType(Class<?> fieldType, Formatter<?> formatter);
    void addFormatterForFieldType(Formatter<?> formatter);
    void addFormatterForAnnotation(AnnotationFormatterFactory<?, ?> factory);
      
 As shown above, Formatters can be registered by fieldType or
        annotation.
      
 The FormatterRegistry SPI allows you to configure Formatting rules
        centrally, instead of duplicating such configuration across your
        Controllers. For example, you might want to enforce that all Date fields
        are formatted a certain way, or fields with a specific annotation are
        formatted in a certain way. With a shared FormatterRegistry, you define
        these rules once and they are applied whenever formatting is needed.
    
7.6.4 FormatterRegistrar SPI

      
 The FormatterRegistrar is an SPI for registering formatters and
          converters through the FormatterRegistry:
      
package org.springframework.format;
public interface FormatterRegistrar {
    void registerFormatters(FormatterRegistry registry);
        
 A FormatterRegistrar is useful when registering multiple related
            converters and formatters for a given formatting category, such as Date
            formatting. It can also be useful where declarative registration is
            insufficient. For example when a formatter needs to be indexed under a
            specific field type different from its own <T> or when registering
            a Printer/Parser pair. The next section provides more information on
            converter and formatter registration.
    




    
7.6.5 Configuring Formatting in Spring MVC

      
 In a Spring MVC application, you may configure a custom
        ConversionService instance explicitly as an attribute of the
        annotation-driven element of the MVC namespace. This
        ConversionService will then be used anytime a type conversion is
        required during Controller model binding. If not configured explicitly,
        Spring MVC will automatically register default formatters and converters
        for common types such as numbers and dates. 
      
 To rely on default formatting rules, no custom configuration is
        required in your Spring MVC config XML: 
      
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <mvc:annotation-driven/>
</beans>
      
 With this one-line of configuration, default formatters for Numbers
        and Date types will be installed, including support for the
        @NumberFormat and @DateTimeFormat annotations. Full support for the Joda
        Time formatting library is also installed if Joda Time is present on the
        classpath.
      
 To inject a ConversionService instance with custom formatters and
        converters registered, set the conversion-service attribute and then
        specify custom converters, formatters, or FormatterRegistrars as properties
        of the FormattingConversionServiceFactoryBean: 
      
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <mvc:annotation-driven conversion-service="conversionService"/>
    <bean id="conversionService"
          class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
        <property name="converters">
                <bean class="org.example.MyConverter"/>
        </property>
        <property name="formatters">
                <bean class="org.example.MyFormatter"/>
                <bean class="org.example.MyAnnotationFormatterFactory"/>
        </property>
        <property name="formatterRegistrars">
                <bean class="org.example.MyFormatterRegistrar"/>
        </property>
    </bean>
</beans>
          
 See Section 7.6.4, “FormatterRegistrar SPI” and
            the FormattingConversionServiceFactoryBean
            for more information on when to use FormatterRegistrars.
    
By default, date and time fields that are not annotated with
    @DateTimeFormat are converted from strings
    using the the DateFormat.SHORT style. If you prefer,
    you can change this by defining your own global format.
    
You will need to ensure that Spring does not register default
    formatters, and instead you should register all formatters manually. Use the
    org.springframework.format.datetime.joda.JodaTimeFormatterRegistrar
    or org.springframework.format.datetime.DateFormatterRegistrar
    class depending on whether you use the Joda Time library.
    
For example, the following Java configuration will register a global
    'yyyyMMdd' format. This example does not depend on the
    Joda Time library:
    
@Configuration
public class AppConfig {
  @Bean
  public FormattingConversionService conversionService() {
    // Use the DefaultFormattingConversionService but do not register defaults
    DefaultFormattingConversionService conversionService = new DefaultFormattingConversionService(false);
    // Ensure @NumberFormat is still supported
    conversionService.addFormatterForFieldAnnotation(new NumberFormatAnnotationFormatterFactory());
    // Register date conversion with a specific global format
    DateFormatterRegistrar registrar = new DateFormatterRegistrar();
    registrar.setFormatter(new DateFormatter("yyyyMMdd"));
    registrar.registerFormatters(conversionService);
    return conversionService;
    
If you prefer XML based configuration you can use a
    FormattingConversionServiceFactoryBean. Here is the same
    example, this time using Joda Time:
    
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd>
    <bean id="conversionService" class="org.springframework.format.support.FormattingConversionServiceFactoryBean">
        <property name="registerDefaultFormatters" value="false" />
        <property name="formatters">
            <bean class="org.springframework.format.number.NumberFormatAnnotationFormatterFactory" />
        </property>
        <property name="formatterRegistrars">
          <bean class="org.springframework.format.datetime.joda.JodaTimeFormatterRegistrar">
              <property name="dateFormatter">
                  <bean class="org.springframework.format.datetime.joda.DateTimeFormatterFactoryBean">
                      <property name="pattern" value="yyyyMMdd"/>
                  </bean>
              </property>
          </bean>
      </property>
    </bean>
  </beans>
      
Joda Time provides separate distinct types to represent
      date, time and
      date-time values. The dateFormatter,
      timeFormatter and dateTimeFormatter
      properties of the JodaTimeFormatterRegistrar should
      be used to configure the different formats for each type. The
      DateTimeFormatterFactoryBean provides a
      convenient way to create formatters.
    
If you are using Spring MVC remember to explicitly configure the
    conversion service that is used. For Java based
    @Configuration this means extending the
    WebMvcConfigurationSupport class and overriding
    the mvcConversionService() method. For XML you should
    use the 'conversion-service' attribute of the
    mvc:annotation-driven element. See
    Section 7.6.5, “Configuring Formatting in Spring MVC” for details.

  
7.8 Spring 3 Validation

    
 Spring 3 introduces several enhancements to its validation support.
      First, the JSR-303 Bean Validation API is now fully supported. Second,
      when used programmatically, Spring's DataBinder can now validate objects as
      well as bind to them. Third, Spring MVC now has support for declaratively
      validating @Controller inputs. 
    
7.8.1 Overview of the JSR-303 Bean Validation API

      
 JSR-303 standardizes validation constraint declaration and metadata
        for the Java platform. Using this API, you annotate domain model
        properties with declarative validation constraints and the runtime
        enforces them. There are a number of built-in constraints you can take
        advantage of. You may also define your own custom constraints. 
      
 To illustrate, consider a simple PersonForm model with two
        properties: 
      
public class PersonForm {
    private String name;
    private int age;
      
 JSR-303 allows you to define declarative validation constraints
        against such properties: 
      
public class PersonForm {
    @NotNull
    @Size(max=64)
    private String name;
    @Min(0)
    private int age;
      
 When an instance of this class is validated by a JSR-303 Validator,
        these constraints will be enforced. 
      
 For general information on JSR-303, see the Bean Validation
        Specification. For information on the specific capabilities of
        the default reference implementation, see the Hibernate Validator
        documentation. To learn how to setup a JSR-303 implementation as a
        Spring bean, keep reading. 
    
7.8.2 Configuring a Bean Validation Implementation

      
 Spring provides full support for the JSR-303 Bean Validation API.
        This includes convenient support for bootstrapping a JSR-303
        implementation as a Spring bean. This allows for a
        javax.validation.ValidatorFactory or
        javax.validation.Validator to be injected wherever
        validation is needed in your application. 
      
 Use the LocalValidatorFactoryBean to
        configure a default JSR-303 Validator as a Spring bean: 
      
<bean id="validator"




    

      class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean"/>
      
 The basic configuration above will trigger JSR-303 to initialize
        using its default bootstrap mechanism. A JSR-303 provider, such as
        Hibernate Validator, is expected to be present in the classpath and will
        be detected automatically. 
      
Injecting a Validator

        
 LocalValidatorFactoryBean implements both
          javax.validation.ValidatorFactory and
          javax.validation.Validator, as well as Spring's
          org.springframework.validation.Validator. You may inject
          a reference to either of these interfaces into beans that need to
          invoke validation logic. 
        
 Inject a reference to javax.validation.Validator if
          you prefer to work with the JSR-303 API directly: 
        
import javax.validation.Validator;
@Service
public class MyService {
    @Autowired
    private Validator validator;
        
 Inject a reference to
          org.springframework.validation.Validator if your bean
          requires the Spring Validation API: 
        
import org.springframework.validation.Validator;
@Service
public class MyService {
    @Autowired
    private Validator validator;
      
Configuring Custom Constraints

        
 Each JSR-303 validation constraint consists of two parts. First,
          a @Constraint annotation that declares the constraint and its
          configurable properties. Second, an implementation of the
          javax.validation.ConstraintValidator interface that
          implements the constraint's behavior. To associate a declaration with
          an implementation, each @Constraint annotation references a
          corresponding ValidationConstraint implementation class. At runtime, a
          ConstraintValidatorFactory instantiates the referenced
          implementation when the constraint annotation is encountered in your
          domain model. 
        
 By default, the LocalValidatorFactoryBean
          configures a SpringConstraintValidatorFactory that uses
          Spring to create ConstraintValidator instances. This allows your
          custom ConstraintValidators to benefit from dependency injection like
          any other Spring bean. 
        
 Shown below is an example of a custom @Constraint declaration,
          followed by an associated ConstraintValidator
          implementation that uses Spring for dependency injection: 
        
@Target({ElementType.METHOD, ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Constraint(validatedBy=MyConstraintValidator.class)
public @interface MyConstraint {
        
import javax.validation.ConstraintValidator;
public class MyConstraintValidator implements ConstraintValidator {
    @Autowired;
    private Foo aDependency;
        
 As you can see, a ConstraintValidator implementation may have its
          dependencies @Autowired like any other Spring bean. 
      
Additional Configuration Options

        
 The default LocalValidatorFactoryBean
          configuration should prove sufficient for most cases. There are a
          number of other configuration options for various JSR-303 constructs,
          from message interpolation to traversal resolution. See the JavaDocs
          of LocalValidatorFactoryBean for more
          information on these options. 
    
7.8.3 Configuring a DataBinder

      
 Since Spring 3, a DataBinder instance can be configured with a
        Validator. Once configured, the Validator may be invoked by calling
        binder.validate(). Any validation Errors are automatically
        added to the binder's BindingResult. 
      
 When working with the DataBinder programmatically, this can be used
        to invoke validation logic after binding to a target object: 
      
Foo target = new Foo();
DataBinder binder = new DataBinder(target);
binder.setValidator(new FooValidator());
// bind to the target object
binder.bind(propertyValues);
// validate the target object
binder.validate();
// get BindingResult that includes any validation errors
BindingResult results = binder.getBindingResult();
      
 A DataBinder can also be configured with multiple
      Validator instances
      via dataBinder.addValidators
      and dataBinder.replaceValidators.
      This is useful when combining globally configured JSR-303 Bean Validation
      with a Spring Validator configured
      locally on a DataBinder instance.
      See the section called “Configuring a Validator for use by Spring MVC”.
    
7.8.4 Spring MVC 3 Validation

      
 Beginning with Spring 3, Spring MVC has the ability to
        automatically validate @Controller inputs. In previous versions it was
        up to the developer to manually invoke validation logic. 
      
Triggering @Controller Input Validation

        
 To trigger validation of a @Controller input, simply annotate the
          input argument as @Valid: 
        
@Controller
public class MyController {
    @RequestMapping("/foo", method=RequestMethod.POST)
    public void processFoo(@Valid Foo foo) { /* ... */ }
        
 Spring MVC will validate a @Valid object after binding so-long as
          an appropriate Validator has been configured. 
          
 The @Valid annotation is part of the standard JSR-303 Bean
            Validation API, and is not a Spring-specific construct. 
      
Configuring a Validator for use by Spring MVC

        
 The Validator instance invoked when a @Valid method argument is
          encountered may be configured in two ways. First, you may call
          binder.setValidator(Validator) within a @Controller's @InitBinder
          callback. This allows you to configure a Validator instance per
          @Controller class: 
        
@Controller
public class MyController {
    @InitBinder
    protected void initBinder(WebDataBinder binder) {
        binder.setValidator(new FooValidator());
    @RequestMapping("/foo", method=RequestMethod.POST)
    public void processFoo(@Valid Foo foo) { ... }
        
 Second, you may call setValidator(Validator) on the global
          WebBindingInitializer. This allows you to configure a Validator
          instance across all @Controllers. This can be achieved easily by using
          the Spring MVC namespace: 
        
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <mvc:annotation-driven validator="globalValidator"/>
</beans>
        
 To combine a global and a local validator, configure the
        global validator as shown above and then add a local validator:
        
@Controller
public class MyController {
    @InitBinder
    protected void initBinder(WebDataBinder binder) {
        binder.addValidators(new FooValidator());
      
Configuring a JSR-303 Validator for use by Spring MVC

        
 With JSR-303, a single javax.validation.Validator
          instance typically validates all model objects
          that declare validation constraints. To configure a JSR-303-backed
          Validator with Spring MVC, simply add a JSR-303 Provider, such as
          Hibernate Validator, to your classpath. Spring MVC will detect it and
          automatically enable JSR-303 support across all Controllers. 
        
 The Spring MVC configuration required to enable JSR-303 support
          is shown below: 
        
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:mvc="http://www.springframework.org/schema/mvc"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/mvc
        http://www.springframework.org/schema/mvc/spring-mvc.xsd">
    <!-- JSR-303 support will be detected on classpath and enabled automatically -->
    <mvc:annotation-driven/>
</beans>
        
 With this minimal configuration, anytime a @Valid @Controller
          input is encountered, it will be validated by the JSR-303 provider.
          JSR-303, in turn, will enforce any constraints declared against the
          input. Any ConstraintViolations will automatically be exposed as
          errors in the BindingResult renderable by standard Spring MVC form