Class ASMifierClassVisitor

java.lang.Object
org.objectweb.asm.util.AbstractVisitor
org.objectweb.asm.util.ASMifierAbstractVisitor
org.objectweb.asm.util.ASMifierClassVisitor
All Implemented Interfaces:
ClassVisitor
public class ASMifierClassVisitor extends ASMifierAbstractVisitor implements ClassVisitor
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

  • Field Details

    • pw

      protected final PrintWriter pw
      The print writer to be used to print the class.

  • Constructor Details

    • ASMifierClassVisitor

      public ASMifierClassVisitor(PrintWriter pw)
      Constructs a new ASMifierClassVisitor object.
      Parameters:
      pw - the print writer to be used to print the class.

  • Method Details

    • main

      public static void main(String[] args) throws Exception
      Prints the ASM source code to generate the given class to the standard output.

      Usage: ASMifierClassVisitor [-debug] <binary class name or class file name>

      Parameters:
      args - the command line arguments.
      Throws:
      Exception - if the class cannot be found, or if an IO exception occurs.

    • visit

      public void visit(int version, int access, String name, String signature, String superName, String[] interfaces)
      Description copied from interface: ClassVisitor
      Visits the header of the class.
      Specified by:
      visit in interface ClassVisitor
      Parameters:
      version - the class version.
      access - the class's access flags (see Opcodes). This parameter also indicates if the class is deprecated.
      name - the internal name of the class (see getInternalName).
      signature - the signature of this class. May be null if the class is not a generic one, and does not extend or implement generic classes or interfaces.
      superName - the internal of name of the super class (see getInternalName). For interfaces, the super class is Object. May be null, but only for the Object class.
      interfaces - the internal names of the class's interfaces (see getInternalName). May be null.

    • visitSource

      public void visitSource(String file, String debug)
      Description copied from interface: ClassVisitor
      Visits the source of the class.
      Specified by:
      visitSource in interface ClassVisitor
      Parameters:
      file - the name of the source file from which the class was compiled. May be null.
      debug - additional debug information to compute the correspondance between source and compiled elements of the class. May be null.

    • visitOuterClass

      public void visitOuterClass(String owner, String name, String desc)
      Description copied from interface: ClassVisitor
      Visits the enclosing class of the class. This method must be called only if the class has an enclosing class.
      Specified by:
      visitOuterClass in interface ClassVisitor
      Parameters:
      owner - internal name of the enclosing class of the class.
      name - the name of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.
      desc - the descriptor of the method that contains the class, or null if the class is not enclosed in a method of its enclosing class.

    • visitInnerClass

      public void visitInnerClass(String name, String outerName, String innerName, int access)
      Description copied from interface: ClassVisitor
      Visits information about an inner class. This inner class is not necessarily a member of the class being visited.
      Specified by:
      visitInnerClass in interface ClassVisitor
      Parameters:
      name - the internal name of an inner class (see getInternalName).
      outerName - the internal name of the class to which the inner class belongs (see getInternalName). May be null for not member classes.
      innerName - the (simple) name of the inner class inside its enclosing class. May be null for anonymous inner classes.
      access - the access flags of the inner class as originally declared in the enclosing class.

    • visitField

      public FieldVisitor visitField(int access, String name, String desc, String signature, Object value)
      Description copied from interface: ClassVisitor
      Visits a field of the class.
      Specified by:
      visitField in interface ClassVisitor
      Parameters:
      access - the field's access flags (see Opcodes). This parameter also indicates if the field is synthetic and/or deprecated.
      name - the field's name.
      desc - the field's descriptor (see Type).
      signature - the field's signature. May be null if the field's type does not use generic types.
      value - the field's initial value. This parameter, which may be null if the field does not have an initial value, must be an Integer, a Float, a Long, a Double or a String (for int, float, long or String fields respectively). This parameter is only used for static fields. Its value is ignored for non static fields, which must be initialized through bytecode instructions in constructors or methods.
      Returns:
      a visitor to visit field annotations and attributes, or null if this class visitor is not interested in visiting these annotations and attributes.

    • visitMethod

      public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions)
      Description copied from interface: ClassVisitor
      Visits a method of the class. This method must return a new MethodVisitor instance (or null) each time it is called, i.e., it should not return a previously returned visitor.
      Specified by:
      visitMethod in interface ClassVisitor
      Parameters:
      access - the method's access flags (see Opcodes). This parameter also indicates if the method is synthetic and/or deprecated.
      name - the method's name.
      desc - the method's descriptor (see Type).
      signature - the method's signature. May be null if the method parameters, return type and exceptions do not use generic types.
      exceptions - the internal names of the method's exception classes (see getInternalName). May be null.
      Returns:
      an object to visit the byte code of the method, or null if this class visitor is not interested in visiting the code of this method.

    • createASMifierMethodVisitor

      protected ASMifierMethodVisitor createASMifierMethodVisitor()

    • visitAnnotation

      public AnnotationVisitor visitAnnotation(String desc, boolean visible)
      Description copied from class: ASMifierAbstractVisitor
      Prints the ASM code that generates the given annotation.
      Specified by:
      visitAnnotation in interface ClassVisitor
      Overrides:
      visitAnnotation in class ASMifierAbstractVisitor
      Parameters:
      desc - the class descriptor of the annotation class.
      visible - true if the annotation is visible at runtime.
      Returns:
      a visitor to visit the annotation values.

    • visitEnd

      public void visitEnd()
      Description copied from class: ASMifierAbstractVisitor
      Prints the ASM code to end the visit.
      Specified by:
      visitEnd in interface ClassVisitor
      Overrides:
      visitEnd in class ASMifierAbstractVisitor