import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.core.Version;
import com.fasterxml.jackson.core.type.TypeReference;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.databind.module.SimpleModule;
import org.junit.Test;
import java.io.*;
import java.net.URL;
import java.nio.charset.StandardCharsets;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
public class ObjectMapperReadDemo {
     * Read Object From JSON String
     * 从 JSON 字符串读取对象
     * @throws JsonProcessingException
    @Test
    public void test1() throws JsonProcessingException {
        ObjectMapper objectMapper = new ObjectMapper();
        String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
        System.out.println("************ Read Object From JSON String ************");
        Car car = objectMapper.readValue(carJson, Car.class);
        System.out.println(car);
     * Read Object From JSON Reader
     * 从 JSON Reader 读取对象
     * @throws JsonProcessingException
    @Test
    public void test2() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
        Reader reader = new StringReader(carJson);
        Car car = objectMapper.readValue(reader, Car.class);
        System.out.println(car);
     * Read Object From JSON File
     * 从 JSON 文件读取对象
     * @throws JsonProcessingException
    @Test
    public void test3() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        File file = new File("src/data/car.json");
        Car car = objectMapper.readValue(file, Car.class);
        System.out.println(car);
     * Read Object From JSON via URL
     * 通过 URL 从 JSON 读取对象
     * @throws JsonProcessingException
    @Test
    public void test4() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        URL url = new URL("file:src/data/car.json");
        Car car = objectMapper.readValue(url, Car.class);
        System.out.println(car);
     * Read Object From JSON InputStream
     * 从 JSON InputStream 读取对象
     * @throws JsonProcessingException
    @Test
    public void test5() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        InputStream input = new FileInputStream("src/data/car.json");
        Car car = objectMapper.readValue(input, Car.class);
        System.out.println(car);
     * Read Object From JSON Byte Array
     * 从 JSON 字节数组读取对象
     * @throws JsonProcessingException
    @Test
    public void test6() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : 5 }";
        byte[] bytes = carJson.getBytes(StandardCharsets.UTF_8);
        Car car = objectMapper.readValue(bytes, Car.class);
        System.out.println(car);
     * Read Object Array From JSON Array String
     * 从 JSON 数组字符串读取对象数组
     * @throws JsonProcessingException
    @Test
    public void test7() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]";
        Car[] cars = objectMapper.readValue(jsonArray, Car[].class);
        System.out.println(Arrays.toString(cars));
     * Read Object List From JSON Array String
     * 从 JSON 数组字符串读取对象列表
     * @throws JsonProcessingException
    @Test
    public void test8() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        String jsonArray = "[{\"brand\":\"ford\"}, {\"brand\":\"Fiat\"}]";
        List<Car> cars = objectMapper.readValue(jsonArray, new TypeReference<List<Car>>() {
        System.out.println(cars);
     * Read Map from JSON String
     * 从 JSON 字符串读取 Map
     * @throws JsonProcessingException
    @Test
    public void test9() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        String jsonObject = "{\"brand\":\"ford\", \"doors\":5}";
        Map<String, Object> jsonMap = objectMapper.readValue(jsonObject, new TypeReference<Map<String, Object>>() {
        System.out.println(jsonMap);
     * Ignore Unknown JSON Fields
     * 忽略未知的 JSON 字段
     * @throws JsonProcessingException
    @Test
    public void test10() throws IOException {
        ObjectMapper objectMapper = new ObjectMapper();
        String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : null, \"test\" : 10 }";
         * 确定遇到未知属性（未映射到属性的属性，并且没有“任何设置器”或可以处理它的处理程序）是否会导致失败（通过抛出JsonMappingException ）
         * 的功能。
         * 此设置仅在尝试了所有其他未知属性处理方法后生效，并且属性保持未处理状态。
         * 默认情况下启用功能（意味着如果遇到未知属性将抛出JsonMappingException ）
        objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
        Car car = objectMapper.readValue(carJson, Car.class);
        System.out.println(car);
     * Fail on Null JSON Values for Primitive Types
     * 原始类型的空 JSON 值失败
     * @throws JsonProcessingException
    @Test
    public void test11() throws JsonProcessingException {
        System.out.println("************ Ignore Unknown JSON Fields ************");
        String carJson = "{ \"brand\" : \"Mercedes\", \"doors\" : null}";
        ObjectMapper objectMapper = new ObjectMapper();
         * 确定在反序列化为 Java 基本类型（如“int”或“double”）时遇到 JSON null 是否为错误的功能。
         * 如果是，则抛出 JsonProcessingException 以指示这一点；
         * 如果不是，则使用默认值（'int' 为 0，double 为 0.0，与 JVM 使用的默认值相同）。
         * 默认情况下禁用该功能。
        objectMapper.configure(DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES, true);
        Car car = objectMapper.readValue(carJson, Car.class);
        System.out.println(car);
     * Custom Deserializer
     * 自定义反序列号器
    @Test
    public void test12() throws JsonProcessingException {
        String json = "{ \"brand\" : \"Ford\", \"doors\" : 6 }";
        SimpleModule module = new SimpleModule("CarDeserializer",
                new Version(3, 1, 8, null, null, null));
        module.addDeserializer(Car.class, new StdDeserializer<Car>(Car.class){
            @Override
            public Car deserialize(JsonParser parser, DeserializationContext deserializer) throws IOException, JsonProcessingException {
                Car car = new Car();
                while(!parser.isClosed()){
                    JsonToken jsonToken = parser.nextToken();
                    if(JsonToken.FIELD_NAME.equals(jsonToken)){
                        String fieldName = parser.getCurrentName();
                        System.out.println(fieldName);
                        jsonToken = parser.nextToken();
                        if("brand".equals(fieldName)){
                            car.setBrand(parser.getValueAsString());
                        } else if ("doors".equals(fieldName)){
                            car.setDoors(parser.getValueAsInt());
                return car;
        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(module);
        Car car = mapper.readValue(json, Car.class);
        System.out.println(car);