I am trying to copy and replace a method with a different return type but it seems like the only way I can successfully do it is to have the source code. If I replace the method then instrument the calling method to call the new method I get a VerifyError (Bad type on operand stack). Is there a way to only use the bytecode and not depend on the source code when rebuilding dependent methods?
I am including source code for my example below.
Functioning Example (with source code dependency)
public class OverrideTest {
final ClassPool POOL = ClassPool.getDefault();
class Foo {
public Integer getFoo() { return new Integer(1); }
public String doA() { return getFoo().toString(); }
class FooExt {
public String getFoo() { return "A"; }
@Test
public void d() throws Throwable {
CtClass srcClass = POOL.getCtClass(Foo.class.getName());
CtClass extClass = POOL.getCtClass(FooExt.class.getName());
CtClass d = POOL.makeClass("Derp");
CtClass STRING = POOL.get("java.lang.String");
CtClass INT = POOL.get("java.lang.Integer");
CtMethod doA1 = srcClass.getMethod("doA", Descriptor.ofMethod(STRING, new CtClass[0]));
CtMethod getFoo1 = srcClass.getMethod("getFoo", Descriptor.ofMethod(INT, new CtClass[0]));
CtMethod getFoo = new CtMethod(INT, "getFoo", new CtClass[0], d);
CtMethod doA = new CtMethod(STRING, "doA", new CtClass[0], d);
d.addMethod(doA);
d.addMethod(getFoo);
doA.setBody(doA1, null);
getFoo.setBody(getFoo1, null);
d.setModifiers(d.getModifiers() & ~Modifier.ABSTRACT);
d.removeMethod(getFoo);
CtMethod getFooExt = new CtMethod(STRING, "getFoo", new CtClass[0], d);
d.addMethod(getFooExt);
CtMethod getFooExt1 = extClass.getMethod("getFoo", Descriptor.ofMethod(STRING, new CtClass[0]));
getFooExt.setBody(getFooExt1, null);
doA.setBody("{ return getFoo().toString(); }");
d.setModifiers(d.getModifiers() & ~Modifier.ABSTRACT);
Class<?> c = d.toClass();
Constructor<?> ctor = c.getConstructor();
Object derp = ctor.newInstance();
Method getFoo = derp.getClass().getMethod("getFoo");
Method doA = derp.getClass().getMethod("doA");
Object doResult = doA.invoke(derp);
Object getResult = getFoo.invoke(derp);
assertEquals("A", getResult);
assertEquals("A", doResult);
Non-Functioning Example (VerifyError)
public class OverrideTest {
final ClassPool POOL = ClassPool.getDefault();
class Foo {
public Integer getFoo() { return new Integer(1); }
public String doA() { return getFoo().toString(); }
class FooExt {
public String getFoo() { return "A"; }
@Test
public void d() throws Throwable {
CtClass srcClass = POOL.getCtClass(Foo.class.getName());
CtClass extClass = POOL.getCtClass(FooExt.class.getName());
CtClass d = POOL.makeClass("Derp");
CtClass STRING = POOL.get("java.lang.String");
CtClass INT = POOL.get("java.lang.Integer");
CtMethod doA1 = srcClass.getMethod("doA", Descriptor.ofMethod(STRING, new CtClass[0]));
CtMethod getFoo1 = srcClass.getMethod("getFoo", Descriptor.ofMethod(INT, new CtClass[0]));
CtMethod getFoo = new CtMethod(INT, "getFoo", new CtClass[0], d);
CtMethod doA = new CtMethod(STRING, "doA", new CtClass[0], d);
d.addMethod(doA);
d.addMethod(getFoo);
doA.setBody(doA1, null);
getFoo.setBody(getFoo1, null);
d.setModifiers(d.getModifiers() & ~Modifier.ABSTRACT);
CtMethod tempMethod = new CtMethod(getFoo.getReturnType(), "tempFoo", new CtClass[0], d);
d.addMethod(tempMethod);
doA.instrument(new MethodReplacer(getFoo, tempMethod));
d.removeMethod(getFoo);
CtMethod getFooExt = new CtMethod(STRING, "getFoo", new CtClass[0], d);
d.addMethod(getFooExt);
CtMethod getFooExt1 = extClass.getMethod("getFoo", Descriptor.ofMethod(STRING, new CtClass[0]));
getFooExt.setBody(getFooExt1, null);
doA.instrument(new MethodReplacer(tempMethod, getFooExt));
d.removeMethod(tempMethod);
d.removeMethod(doA);
CtMethod doA2 = new CtMethod(STRING, "doA", new CtClass[0], d);
d.addMethod(doA2);
doA2.setBody(doA, null);
d.setModifiers(d.getModifiers() & ~Modifier.ABSTRACT);
Class<?> c = d.toClass();
Constructor<?> ctor = c.getConstructor();
Object derp = ctor.newInstance();
Method getFoo = derp.getClass().getMethod("getFoo");
Method doA = derp.getClass().getMethod("doA");
Object doResult = doA.invoke(derp);
Object getResult = getFoo.invoke(derp);
assertEquals("A", getResult);
assertEquals("A", doResult);
class MethodReplacer extends ExprEditor {
private CtMethod replacedMethod;
private CtMethod replacement;
MethodReplacer(CtMethod replacedMethod, CtMethod replacement) {
this.replacedMethod = replacedMethod;
this.replacement = replacement;
@Override
public void edit(MethodCall mcall) throws CannotCompileException {
CtClass declaringClass = replacedMethod.getDeclaringClass();
try {
CtMethod m = mcall.getMethod();
if (declaringClass.equals(m.getDeclaringClass()) && m.equals(replacedMethod))
mcall.replace("$_ = " + replacement.getName()+"($$);");
} catch (NotFoundException e) {
throw new RuntimeException("Unable to instrument a dependent method call to " + replacedMethod.getName(), e);
