org.objectweb.asm.util Documentation Differences

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Provides some ASM class visitors that can be useful for programming and debugging purposes. These class visitors are normally not used by applications at runtime. This is why they are bundled in an optional asm-util.jar library that is separated from (but requires) the asm.jar library, which contains the core ASM framework. @since ASM 1.3.2

A PrintClassVisitorClassVisitor that prints the ASM code that that generates the classes itit visits. This class visitor can be used to quickly quickly write ASM code to generategenerate some given bytecode:

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

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

 import org.objectweb.asm.*;
 import java.io.FileOutputStream;

 public class DumpHelloDump implements ConstantsOpcodes {

 public static void main (Stringpublic static byte[] argsdump() throws Exception {

         ClassWriter cw = new ClassWriter(false0);
 CodeVisitor        FieldVisitor fv;
         MethodVisitor mv;
      cv   AnnotationVisitor av0;

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

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

         {
 cv            mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "main""<init>", "([Ljava/lang/String";()V"", null, null);
 cv.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
        cv mv.visitLdcInsnvisitVarInsn("hello"ALOAD, 0);
 cv            mv.visitMethodInsn(INVOKEVIRTUALINVOKESPECIAL,
       "              "java/iolang/PrintStream"Object",
 "println"                    "<init>",
 "(Ljava/lang/String                    ";()V"");
 cv            mv.visitInsn(RETURN);
 cv            mv.visitMaxs(21, 1);
             mv.visitEnd();
         }
         {
 cv            mv = cw.visitMethod(ACC_PUBLIC + ACC_STATIC,
         "            &ltquot;initmain&gtquot;",
             "        "([Ljava/lang/String;)V"",
                     null,
                     null);
 cv            mv.visitVarInsnvisitFieldInsn(ALOADGETSTATIC,
 0                    "java/lang/System",
                     "out",
                     "Ljava/io/PrintStream;");
             mv.visitLdcInsn("hello");
 cv            mv.visitMethodInsn(INVOKESPECIALINVOKEVIRTUAL,
           "          "java/langio/Object"PrintStream",
           "          &ltquot;initprintln&gtquot;",
               "      "(Ljava/lang/String;)V"");
 cv            mv.visitInsn(RETURN);
 cv            mv.visitMaxs(12, 1);
 }
 cw           mv.visitEnd();


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


  os       return cw.closetoByteArray();
     }
 }


 

where Hello is defined by:

 public class Hello {

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

@author Eric Bruneton,Bruneton @author Eugene Kuleshov

Constructs a new ASMifierClassVisitor object. @param pw the print writer to be used to print the class.

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

Usage: ASMifierClassVisitor [-debug] <fully qualifiedqualified class name or class file name> @param args the command line arguments. @throws Exception if the class cannot be found, or if an IO exception occurs.

A ClassAdapter that checks that its methods are properly properly used. MoreMore precisely this class adapter checks each method call individually, basedbased only on its arguments, but does not check the the sequence of method calls. For example, the invalid sequence visitField(ACC_PUBLIC, "i", "I", null) visitField(ACC_PUBLIC, "i", "D", null) will not be detected by this class adapter. @author Eric Bruneton

Constructs a new CheckClassAdapter object. @param cv the class visitor to which this adapter must delegate calls.

Checks a given class.

Usage: CheckClassAdapter CheckClassAdapter <fully qualifiedqualified class name or class file name> @param args the command line arguments. @throws Exception if the class cannot be found, or if an IO exception occurs.

A PrintClassVisitorClassVisitor that prints a disassembled disassembled view of the classes itit visits. This class visitor can be used alone (see the the main method) to disassemble a class. It can also be used in in the middle of classclass visitor chain to trace the class that is visited at a a given point in thisthis chain. This may be uselful for debugging purposes.

The trace printed whenwhen visiting the Hello class is the following:

 // compiled from Helloclass version 49.java
0 (49)
 // access flags 33
 public class Hello {

  // compiled publicfrom: staticHello.java

 main ([Ljava /lang/String;)V
 access flags  1
 GETSTATIC java/lang/System outpublic Ljava/io/PrintStream<;
init> ()V
    LDC "hello"
ALOAD 0
    INVOKEVIRTUAL INVOKESPECIAL java/iolang/PrintStreamObject println<init> (Ljava/lang/String;)V
     RETURN
     MAXSTACK = 2
1
     MAXLOCALS = 1

   public// <init>access ()V
flags 9
   public ALOADstatic 0
main ([Ljava/lang/String;)V
     INVOKESPECIALGETSTATIC java/lang/ObjectSystem out Ljava/io/PrintStream;
     LDC &ltquot;inithello&gtquot;
     INVOKEVIRTUAL java/io/PrintStream println (Ljava/lang/String;)V
     RETURN
     MAXSTACK = 1
2
     MAXLOCALS = 1

1
 }
 

where Hello is defined by:

 public class Hello {

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

@author Eric Bruneton,Bruneton @author Eugene Kuleshov

Constructs a new TraceClassVisitor object. @param cv the class visitorClassVisitor to which this adapter mustvisitor delegatedelegates calls. May May be null. @param pw the print writer to be used to print the class.

Prints a disassembled view of the given class to the standard output.

Usage: TraceClassVisitor [-debug] <fully qualified class name or classclass file name > @param args the command line arguments. @throws Exception if the class cannot be found, or if an IO exception occurs.

The ClassVisitor to which this visitor delegates delegates calls. May bebe null.