| /*** |
| * ASM examples: examples showing how ASM can be used |
| * Copyright (c) 2000-2011 INRIA, France Telecom |
| * All rights reserved. |
| * |
| * Redistribution and use in source and binary forms, with or without |
| * modification, are permitted provided that the following conditions |
| * are met: |
| * 1. Redistributions of source code must retain the above copyright |
| * notice, this list of conditions and the following disclaimer. |
| * 2. Redistributions in binary form must reproduce the above copyright |
| * notice, this list of conditions and the following disclaimer in the |
| * documentation and/or other materials provided with the distribution. |
| * 3. Neither the name of the copyright holders nor the names of its |
| * contributors may be used to endorse or promote products derived from |
| * this software without specific prior written permission. |
| * |
| * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" |
| * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE |
| * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE |
| * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE |
| * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR |
| * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF |
| * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS |
| * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN |
| * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) |
| * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF |
| * THE POSSIBILITY OF SUCH DAMAGE. |
| */ |
| import java.io.FileOutputStream; |
| import java.io.PrintStream; |
| |
| import org.objectweb.asm.ClassWriter; |
| import org.objectweb.asm.MethodVisitor; |
| import org.objectweb.asm.Opcodes; |
| import org.objectweb.asm.Type; |
| import org.objectweb.asm.commons.GeneratorAdapter; |
| import org.objectweb.asm.commons.Method; |
| |
| /** |
| * @author Eric Bruneton |
| */ |
| public class Helloworld extends ClassLoader implements Opcodes { |
| |
| public static void main(final String args[]) throws Exception { |
| |
| // Generates the bytecode corresponding to the following Java class: |
| // |
| // public class Example { |
| // public static void main (String[] args) { |
| // System.out.println("Hello world!"); |
| // } |
| // } |
| |
| // creates a ClassWriter for the Example public class, |
| // which inherits from Object |
| ClassWriter cw = new ClassWriter(0); |
| cw.visit(V1_1, ACC_PUBLIC, "Example", null, "java/lang/Object", null); |
| |
| // creates a MethodWriter for the (implicit) constructor |
| MethodVisitor mw = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, |
| null); |
| // pushes the 'this' variable |
| mw.visitVarInsn(ALOAD, 0); |
| // invokes the super class constructor |
| mw.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V"); |
| mw.visitInsn(RETURN); |
| // this code uses a maximum of one stack element and one local variable |
| mw.visitMaxs(1, 1); |
| mw.visitEnd(); |
| |
| // creates a MethodWriter for the 'main' method |
| mw = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "main", |
| "([Ljava/lang/String;)V", null, null); |
| // pushes the 'out' field (of type PrintStream) of the System class |
| mw.visitFieldInsn(GETSTATIC, "java/lang/System", "out", |
| "Ljava/io/PrintStream;"); |
| // pushes the "Hello World!" String constant |
| mw.visitLdcInsn("Hello world!"); |
| // invokes the 'println' method (defined in the PrintStream class) |
| mw.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", |
| "(Ljava/lang/String;)V"); |
| mw.visitInsn(RETURN); |
| // this code uses a maximum of two stack elements and two local |
| // variables |
| mw.visitMaxs(2, 2); |
| mw.visitEnd(); |
| |
| // gets the bytecode of the Example class, and loads it dynamically |
| byte[] code = cw.toByteArray(); |
| |
| FileOutputStream fos = new FileOutputStream("Example.class"); |
| fos.write(code); |
| fos.close(); |
| |
| Helloworld loader = new Helloworld(); |
| Class<?> exampleClass = loader.defineClass("Example", code, 0, |
| code.length); |
| |
| // uses the dynamically generated class to print 'Helloworld' |
| exampleClass.getMethods()[0].invoke(null, new Object[] { null }); |
| |
| // ------------------------------------------------------------------------ |
| // Same example with a GeneratorAdapter (more convenient but slower) |
| // ------------------------------------------------------------------------ |
| |
| cw = new ClassWriter(ClassWriter.COMPUTE_MAXS); |
| cw.visit(V1_1, ACC_PUBLIC, "Example", null, "java/lang/Object", null); |
| |
| // creates a GeneratorAdapter for the (implicit) constructor |
| Method m = Method.getMethod("void <init> ()"); |
| GeneratorAdapter mg = new GeneratorAdapter(ACC_PUBLIC, m, null, null, |
| cw); |
| mg.loadThis(); |
| mg.invokeConstructor(Type.getType(Object.class), m); |
| mg.returnValue(); |
| mg.endMethod(); |
| |
| // creates a GeneratorAdapter for the 'main' method |
| m = Method.getMethod("void main (String[])"); |
| mg = new GeneratorAdapter(ACC_PUBLIC + ACC_STATIC, m, null, null, cw); |
| mg.getStatic(Type.getType(System.class), "out", |
| Type.getType(PrintStream.class)); |
| mg.push("Hello world!"); |
| mg.invokeVirtual(Type.getType(PrintStream.class), |
| Method.getMethod("void println (String)")); |
| mg.returnValue(); |
| mg.endMethod(); |
| |
| cw.visitEnd(); |
| |
| code = cw.toByteArray(); |
| loader = new Helloworld(); |
| exampleClass = loader.defineClass("Example", code, 0, code.length); |
| |
| // uses the dynamically generated class to print 'Helloworld' |
| exampleClass.getMethods()[0].invoke(null, new Object[] { null }); |
| } |
| } |