org.objectweb.asm.ClassVisitor#visitField ( )源码实例Demo

@Override
public Void visitVariable(VariableElement e, ClassVisitor classVisitor) {
  if (e.getModifiers().contains(Modifier.PRIVATE)) {
    return null;
  }

  FieldVisitor fieldVisitor =
      classVisitor.visitField(
          accessFlagsUtils.getAccessFlags(e),
          e.getSimpleName().toString(),
          descriptorFactory.getDescriptor(e),
          signatureFactory.getSignature(e),
          e.getConstantValue());
  visitAnnotations(e, fieldVisitor::visitAnnotation);
  fieldVisitor.visitEnd();

  return null;
}
 

@Override
public void write(ClassVisitor file) {
    FieldVisitor fieldVisitor = file.visitField(modifiers, fieldDescriptor.getName(), fieldDescriptor.getType(), signature, null);
    for(AnnotationCreatorImpl annotation : annotations) {
        AnnotationVisitor av = fieldVisitor.visitAnnotation(DescriptorUtils.extToInt(annotation.getAnnotationType()), annotation.getRetentionPolicy() == RetentionPolicy.RUNTIME);
        for(Map.Entry<String, Object> e : annotation.getValues().entrySet()) {
            AnnotationUtils.visitAnnotationValue(av, e.getKey(), e.getValue());
        }
        av.visitEnd();
    }
    fieldVisitor.visitEnd();
}
 

public void accept(ClassVisitor visitor)
{
	String[] ints = interfaces.getInterfaces().stream().map(i -> i.getName()).toArray(String[]::new);

	visitor.visit(version, access, name.getName(), null, super_class.getName(), ints);
	visitor.visitSource(source, null);

	for (Annotation annotation : annotations.getAnnotations())
	{
		AnnotationVisitor av = visitor.visitAnnotation(annotation.getType().toString(), true);
		annotation.accept(av);
	}

	for (Field field : fields)
	{
		FieldVisitor fv = visitor.visitField(field.getAccessFlags(), field.getName(), field.getType().toString(), null, field.getValue());
		field.accept(fv);
	}

	for (Method method : methods)
	{
		String[] exceptions = method.getExceptions().getExceptions().stream().map(cl -> cl.getName()).toArray(String[]::new);
		if (exceptions.length == 0)
		{
			exceptions = null;
		}

		MethodVisitor mv = visitor.visitMethod(method.getAccessFlags(), method.getName(), method.getDescriptor().toString(), null, exceptions);
		method.accept(mv);
	}

	visitor.visitEnd();
}
 

static void addIsServlet3(ClassVisitor cw) {
  FieldVisitor fv = cw.visitField(ACC_PRIVATE + ACC_FINAL + ACC_STATIC, "$$isServlet3", "Z", null, null);
  fv.visitEnd();

  MethodVisitor mv = cw.visitMethod(ACC_PRIVATE + ACC_STATIC, "$$isServlet3", "()Z", null, null);
  mv.visitCode();
  Label l0 = new Label();
  Label l1 = new Label();
  Label l2 = new Label();
  mv.visitTryCatchBlock(l0, l1, l2, "java/lang/NoSuchMethodException");
  mv.visitLabel(l0);
  mv.visitLineNumber(446, l0);
  mv.visitLdcInsn(Type.getType("Ljavax/servlet/ServletRequest;"));
  mv.visitLdcInsn("startAsync");
  mv.visitInsn(ICONST_0);
  mv.visitTypeInsn(ANEWARRAY, "java/lang/Class");
  mv.visitMethodInsn(INVOKEVIRTUAL, "java/lang/Class", "getMethod",
      "(Ljava/lang/String;[Ljava/lang/Class;)Ljava/lang/reflect/Method;", false);
  mv.visitInsn(POP);
  mv.visitLabel(l1);
  mv.visitLineNumber(447, l1);
  mv.visitInsn(ICONST_1);
  mv.visitInsn(IRETURN);
  mv.visitLabel(l2);
  mv.visitLineNumber(448, l2);
  mv.visitFrame(Opcodes.F_SAME1, 0, null, 1, new Object[] { "java/lang/NoSuchMethodException" });
  mv.visitVarInsn(ASTORE, 0);
  Label l3 = new Label();
  mv.visitLabel(l3);
  mv.visitLineNumber(449, l3);
  mv.visitInsn(ICONST_0);
  mv.visitInsn(IRETURN);
  Label l4 = new Label();
  mv.visitLabel(l4);
  mv.visitLocalVariable("e", "Ljava/lang/NoSuchMethodException;", null, l3, l4, 0);
  mv.visitMaxs(3, 1);
  mv.visitEnd();
}
 

public static void main(String[] args) throws Exception {
	ClassWriter cw = new ClassWriter(0);
	TraceClassVisitor tracer =
			new TraceClassVisitor(cw, new PrintWriter(System.out));
	ClassVisitor cv = tracer;
	String name = "Nerd";
	String generics = null;
	String superName = "java/lang/Object";
	String[] interfaces = null;
	int access = ACC_PUBLIC + ACC_INTERFACE;
	int version = V1_5;
	cv.visit(version, access, name, generics, superName, interfaces);

	int fieldAccess = ACC_PUBLIC + ACC_FINAL + ACC_STATIC;
	String shortDescriptor = Type.SHORT_TYPE.getDescriptor();
	FieldVisitor hair = cv.visitField(fieldAccess, "hair", shortDescriptor,
									  null, new Integer(0));
	hair.visitEnd();

	MethodVisitor playVideoGame =
		cv.visitMethod(ACC_PUBLIC + ACC_ABSTRACT, "playVideoGame",
					   "()V", null, null);
	// no code to define, just finish it up
	playVideoGame.visitEnd();
	cv.visitEnd(); // prints if using tracer
	byte[] b = cw.toByteArray();
	// can define or write to file:
	// defineClass(name, b, 0, b.length)
	// from findClass() in subclass of ClassLoader

	FileOutputStream fos = new FileOutputStream("Nerd.class");
	fos.write(b);
	fos.close();
}
 

public static void main(String[] args) throws Exception {
	ClassWriter cw = new ClassWriter(0);
	TraceClassVisitor tracer =
			new TraceClassVisitor(cw, new PrintWriter(System.out));
	ClassVisitor cv = tracer;
	String name = "Nerd";
	String generics = null;
	String superName = "java/lang/Object";
	String[] interfaces = null;
	int access = ACC_PUBLIC + ACC_INTERFACE;
	int version = V1_5;
	cv.visit(version, access, name, generics, superName, interfaces);

	int fieldAccess = ACC_PUBLIC + ACC_FINAL + ACC_STATIC;
	String shortDescriptor = Type.SHORT_TYPE.getDescriptor();
	FieldVisitor hair = cv.visitField(fieldAccess, "hair", shortDescriptor,
									  null, new Integer(0));
	hair.visitEnd();

	MethodVisitor playVideoGame =
		cv.visitMethod(ACC_PUBLIC + ACC_ABSTRACT, "playVideoGame",
					   "()V", null, null);
	// no code to define, just finish it up
	playVideoGame.visitEnd();
	cv.visitEnd(); // prints if using tracer
	byte[] b = cw.toByteArray();
	// can define or write to file:
	// defineClass(name, b, 0, b.length)
	// from findClass() in subclass of ClassLoader

	FileOutputStream fos = new FileOutputStream("Nerd.class");
	fos.write(b);
	fos.close();
}
 

private static void implementInstanceFields(ClassVisitor classVisitor) {
    classVisitor.visitField(Opcodes.ACC_PRIVATE | Opcodes.ACC_FINAL,
            "waitStrategy",
            Type.getDescriptor(WaitStrategy.class),
            null,
            null);
}
 

public FieldVisitor visitField(ClassVisitor visitor, int access, Object value) {
    return visitor.visitField(access, s_name, s_desc, null, value);
}
 

public void add(ClassVisitor cv) {
  _log.info("Adding field " + _fn.name);
  cv.visitField(_fn.access, _fn.name, _fn.desc, _fn.signature, _fn.value);
  //_fn.accept(cv);
}
 

public void generate(ClassVisitor cw) {
    FieldVisitor fv = cw.visitField(modifiers, name, type.getJVMType().getDescriptor(), null, null);
    generateAnnotations(fv);
    fv.visitEnd();
}
 

public FieldVisitor visitField(ClassVisitor visitor, int access, Object value) {
    return visitor.visitField(access, s_name, s_desc, null, value);
}