org.logicalcobwebs.asm.util
Class DumpClassVisitor

java.lang.Object
  org.logicalcobwebs.asm.util.PrintClassVisitor
      org.logicalcobwebs.asm.util.DumpClassVisitor

All Implemented Interfaces:

ClassVisitor

public class DumpClassVisitor
extends PrintClassVisitor

A PrintClassVisitor 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 DumpClassVisitor 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.logicalcobwebs.asm.*;
 import java.io.FileOutputStream;

 public class Dump implements Constants {

 public static void main (String[] args) throws Exception {

 ClassWriter cw = new ClassWriter(false);
 CodeVisitor cv;

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

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

 FileOutputStream os = new FileOutputStream("Dumped.class");
 os.write(cw.toByteArray());
 os.close();
 }
 }
 

where Hello is defined by:

 public class Hello {

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

Field Summary

Fields inherited from class org.logicalcobwebs.asm.util.PrintClassVisitor

buf, pw, text

Constructor Summary

DumpClassVisitor(java.io.PrintWriter pw)
Constructs a new DumpClassVisitor object.

Method Summary

(package private) void	appendAccess(int access) Appends a string representation of the given access modifiers to buf.
(package private) static void	appendConstant(java.lang.StringBuffer buf, java.lang.Object cst) Appends a string representation of the given constant to the given buffer.
static void	main(java.lang.String[] args) Prints the ASM source code to generate the given class to the standard output.
void	visit(int access, java.lang.String name, java.lang.String superName, java.lang.String[] interfaces, java.lang.String sourceFile) Visits the header of the class.
void	visitAttribute(Attribute attr) Visits a non standard attribute of the class.
void	visitEnd() Visits the end of the class.
void	visitField(int access, java.lang.String name, java.lang.String desc, java.lang.Object value, Attribute attrs) Visits a field of the class.
void	visitInnerClass(java.lang.String name, java.lang.String outerName, java.lang.String innerName, int access) Visits information about an inner class.
CodeVisitor	visitMethod(int access, java.lang.String name, java.lang.String desc, java.lang.String[] exceptions, Attribute attrs) Visits a method of the class.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DumpClassVisitor

public DumpClassVisitor(java.io.PrintWriter pw)

Constructs a new DumpClassVisitor object.

Parameters:

pw - the print writer to be used to print the class.

Method Detail

main

public static void main(java.lang.String[] args)
                 throws java.lang.Exception

Prints the ASM source code to generate the given class to the standard output.

Usage: DumpClassVisitor <fully qualified class name>

Parameters:

args - the command line arguments.

Throws:

java.lang.Exception - if the class cannot be found, or if an IO exception occurs.

visit

public void visit(int access,
                  java.lang.String name,
                  java.lang.String superName,
                  java.lang.String[] interfaces,
                  java.lang.String sourceFile)

Description copied from interface: ClassVisitor

Visits the header of the class.

Parameters:

access - the class's access flags (see Constants). This parameter also indicates if the class is deprecated.

name - the internal name of the class (see getInternalName).

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 java.lang.Object class.

interfaces - the internal names of the class's interfaces (see getInternalName). May be null.

sourceFile - the name of the source file from which this class was compiled. May be null.

visitInnerClass

public void visitInnerClass(java.lang.String name,
                            java.lang.String outerName,
                            java.lang.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.

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.

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 void visitField(int access,
                       java.lang.String name,
                       java.lang.String desc,
                       java.lang.Object value,
                       Attribute attrs)

Description copied from interface: ClassVisitor

Visits a field of the class.

Parameters:

access - the field's access flags (see Constants). This parameter also indicates if the field is synthetic and/or deprecated.

name - the field's name.

desc - the field's descriptor (see Type).

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. 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.

attrs - the non standard method attributes, linked together by their next field. May be null.

visitMethod

public CodeVisitor visitMethod(int access,
                               java.lang.String name,
                               java.lang.String desc,
                               java.lang.String[] exceptions,
                               Attribute attrs)

Description copied from interface: ClassVisitor

Visits a method of the class. This method must return a new CodeVisitor instance (or null) each time it is called, i.e., it should not return a previously returned visitor.

Parameters:

access - the method's access flags (see Constants). This parameter also indicates if the method is synthetic and/or deprecated.

name - the method's name.

desc - the method's descriptor (see Type).

exceptions - the internal names of the method's exception classes (see getInternalName). May be null.

attrs - the non standard method attributes, linked together by their next field. 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.

visitAttribute

public void visitAttribute(Attribute attr)

Description copied from interface: ClassVisitor

Visits a non standard attribute of the class. This method must visit only the first attribute in the given attribute list.

Parameters:

attr - a non standard class attribute. Must not be null.

visitEnd

public void visitEnd()

Description copied from interface: ClassVisitor

Visits the end of the class. This method, which is the last one to be called, is used to inform the visitor that all the fields and methods of the class have been visited.

Specified by:

visitEnd in interface ClassVisitor

Overrides:

visitEnd in class PrintClassVisitor

appendAccess

void appendAccess(int access)

Appends a string representation of the given access modifiers to buf.

Parameters:

access - some access modifiers.

appendConstant

static void appendConstant(java.lang.StringBuffer buf,
                           java.lang.Object cst)

Appends a string representation of the given constant to the given buffer.

Parameters:

buf - a string buffer.

cst - an Integer, Float, Long, Double or String object. May be null.