Using ASM 5.0.4, I'm trying to find a class' fields and methods having a specific annotation. I like to avoid having to load the class to not worry about dependencies. So far, I can't figure out how to get a hold of the field/method annotations with this approach:
class AnnotationScanner extends ClassVisitor{
public AnnotationVisitor visitAnnotation(String desc, boolean visible){
System.out.println("visitAnnotation: desc="+desc+" visible="+visible);
return super.visitAnnotation(desc,visible);
}
public void visitAttribute(Attribute attr){
System.out.println("visitAttribute: attr="+attr);
super.visitAttribute(attr);
}
public FieldVisitor visitField(int access, String name, String desc, String signature, Object value){
System.out.println("visitField: access="+access+" name="+name+" desc="+desc+" signature="+signature+" value="+value);
return super.visitField(access,name,desc,signature,value);
}
public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions){
System.out.println("visitMethod: access="+access+" name="+name+" desc="+desc+" signature="+signature+" exceptions="+exceptions);
return super.visitMethod(access,name,desc,signature,exceptions);
}
public static void main(String[] args) throws Exception{
for (String arg : args){
FileInputStream in = new FileInputStream(new File(arg));
ClassReader cr = new ClassReader(in);
cr.accept(new AnnotationScanner(Opcodes.ASM4),0);
}
}
}
The entire sample project is on GitHub .
Running it against a simple class
@MyClass(name="annotation scanner")
public class Scannee{
@MyField(name="a string field") public String aStringField;
@MyMethod(name="a method") public void aMethod(){}
}
gives
visitAnnotation: desc=Lorg/springdot/sandbox/asm/MyClass; visible=true
visitField: access=1 name=aStringField desc=Ljava/lang/String; signature=null value=null
visitMethod: access=1 name=<init> desc=()V signature=null exceptions=null
visitMethod: access=1 name=aMethod desc=()V signature=null exceptions=null
but not the annotations of the field and the method.
How can I also get the field and method annotations?
You will need to subclass FieldVisitor
and MethodVisitor
and override the method visitAnnotation
, similar to your ClassVisitor
subclass. For example,
class FieldAnnotationScanner extends FieldVisitor {
public FieldAnnotationScanner() {
super(Opcodes.ASM5);
}
@Override
public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
System.out.println("visitAnnotation: desc="+desc+" visible="+visible);
return super.visitAnnotation(desc, visible);
}
}
class MethodAnnotationScanner extends MethodVisitor {
public MethodAnnotationScanner() {
super(Opcodes.ASM5);
}
@Override
public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
System.out.println("visitAnnotation: desc="+desc+" visible="+visible);
return super.visitAnnotation(desc, visible);
}
}
Then connect them to your AnnotationScanner
in visitField
and visitMethod
. For example, change your code to
@Override
public FieldVisitor visitField(int access, String name, String desc, String signature, Object value){
System.out.println("visitField: access="+access+" name="+name+" desc="+desc+" signature="+signature+" value="+value);
return new FieldAnnotationScanner();
}
@Override
public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions){
System.out.println("visitMethod: access="+access+" name="+name+" desc="+desc+" signature="+signature+" exceptions="+exceptions);
return new MethodAnnotationScanner();
}
The example doesn't show how tho access the name
value of the @MyMethod
annotation ( name="a method"
). To also read the a method
value, you have to add two more Visitors :
static class MethodAnnotationScanner extends MethodVisitor {
MethodAnnotationScanner() {
super(Opcodes.ASM8);
}
@Override
public AnnotationVisitor visitAnnotation(String desc, boolean visible) {
System.out.println("visitMethodAnnotation: type= " + desc);
return new MyAnnotationVisitor();
}
}
static class MethodAnnotationValueScanner extends AnnotationVisitor {
MethodAnnotationValueScanner() {
super(Opcodes.ASM8);
}
@Override
public void visit(String name, Object value) {
System.out.println("visitMethodAnnotationValue: " + name + " = " + value);
super.visit(name, value);
}
}
And insert them by changing retruning the MethodAnnotationScanner
int the visitMethod
:
@Override
public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
System.out.println("visitMethod: access="+access+" name="+name+" desc="+desc+" signature="+signature+" exceptions="+exceptions);
return new MethodAnnotationScanner();
}
You can see the full updated example here: how-to-read-a-java-class-method-annotation-value-with-asm
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