'bcel'에 해당되는 글 1건

  1. 2009.04.29 BCEL in Java 6

BCEL in Java 6

eclipse 2009.04.29 20:15


Java 6 have bcel packages, so I made interesting code to print "Hello World" every first-experience java developers have to meet.
There are no library have to include. That's my favorite!! 

BCEL tutorial is below web site.
http://jakarta.apache.org/bcel/manual.html


 



import com.sun.org.apache.bcel.internal.Constants;
import com.sun.org.apache.bcel.internal.generic.ArrayType;
import com.sun.org.apache.bcel.internal.generic.ClassGen;
import com.sun.org.apache.bcel.internal.generic.ConstantPoolGen;
import com.sun.org.apache.bcel.internal.generic.InstructionFactory;
import com.sun.org.apache.bcel.internal.generic.InstructionList;
import com.sun.org.apache.bcel.internal.generic.MethodGen;
import com.sun.org.apache.bcel.internal.generic.ObjectType;
import com.sun.org.apache.bcel.internal.generic.PUSH;
import com.sun.org.apache.bcel.internal.generic.Type;

public class SimpleHelloWorldBuilder {
public static void main(String[] args) throws Exception {
// public HellowWorld extends java.lang.Object
ClassGen classGen = new ClassGen("HelloWorld", "java.lang.Object", "", Constants.ACC_PUBLIC
| Constants.ACC_SUPER, null);
ConstantPoolGen constantPoolGen = classGen.getConstantPool();
InstructionList instructionList = new InstructionList();

// public static void main
MethodGen methodGen = new MethodGen(Constants.ACC_PUBLIC | Constants.ACC_STATIC, Type.VOID,
// (String[] args)
new Type[] {new ArrayType(Type.STRING, 1)}, new String[] {"args"}, "main", "HelloWorld", instructionList, constantPoolGen);

InstructionFactory instructionFactory = new InstructionFactory(classGen);
classGen.addEmptyConstructor(Constants.ACC_PUBLIC);
// System.out.println
ObjectType printStream = new ObjectType("java.io.PrintStream");
instructionList.append(instructionFactory.createFieldAccess("java.lang.System", "out", printStream, Constants.GETSTATIC));
// "Hello world!!"
instructionList.append(new PUSH(constantPoolGen, "Hello World!!"));
instructionList.append(instructionFactory.createInvoke("java.io.PrintStream", "println", Type.VOID,
new Type[] {Type.STRING}, Constants.INVOKEVIRTUAL));

classGen.addMethod(methodGen.getMethod());
instructionList.dispose();

classGen.getJavaClass().dump("build/HelloWorld.class");
}
}



After running this class, I can find "build/HelloWorld.class". 
By using jad, I can see the decompiled class.
// Decompiled by Jad v1.5.8g. Copyright 2001 Pavel Kouznetsov.
// Jad home page: http://www.kpdus.com/jad.html
// Decompiler options: packimports(3) 
// Source File Name:   

import java.io.PrintStream;

public class HelloWorld
{

    public HelloWorld()
    {
    }

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


Posted by 김용환 '김용환'
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