Class ASMifierClassVisitor

A ClassVisitor that prints the ASM code that generates the classes it visits. This class visitor can be used to quickly write ASM code to generate some given bytecode:

• write the Java source code equivalent to the bytecode you want to generate;
• compile it with javac;
• make a ASMifierClassVisitor visit this compiled class (see the main method);
• edit the generated source code, if necessary.

The source code printed when visiting the Hello class is the following:

 import org.objectweb.asm.*;

 public class HelloDump implements Opcodes {

     public static byte[] dump() throws Exception {

         ClassWriter cw = new ClassWriter(0);
         FieldVisitor fv;
         MethodVisitor mv;
         AnnotationVisitor av0;

         cw.visit(49,
                 ACC_PUBLIC + ACC_SUPER,
                 "Hello",
                 null,
                 "java/lang/Object",
                 null);

         cw.visitSource("Hello.java", null);

         {
             mv = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
             mv.visitVarInsn(ALOAD, 0);
             mv.visitMethodInsn(INVOKESPECIAL,
                     "java/lang/Object",
                     "<init>",
                     "()V");
             mv.visitInsn(RETURN);
             mv.visitMaxs(1, 1);
             mv.visitEnd();
         }
         {
             mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC,
                     "main",
                     "([Ljava/lang/String;)V",
                     null,
                     null);
             mv.visitFieldInsn(GETSTATIC,
                     "java/lang/System",
                     "out",
                     "Ljava/io/PrintStream;");
             mv.visitLdcInsn("hello");
             mv.visitMethodInsn(INVOKEVIRTUAL,
                     "java/io/PrintStream",
                     "println",
                     "(Ljava/lang/String;)V");
             mv.visitInsn(RETURN);
             mv.visitMaxs(2, 1);
             mv.visitEnd();
         }
         cw.visitEnd();

         return cw.toByteArray();
     }
 }

 

where Hello is defined by:

 public class Hello {

     public static void main(String[] args) {
         System.out.println("hello");
     }
 }
 

Author: Eric Bruneton Eugene Kuleshov