Java ASM 简单例子

###Test的代码比较简单 public class Test { /** * @param args */ public static void main(String[] args) { test01(); }

static void test01() {
	System.out.println("Hello In Test01!");
}

}

###对Test.class进行处理，添加test03的生成及调用 import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException;

import org.objectweb.asm.ClassAdapter;
import org.objectweb.asm.ClassReader;
import org.objectweb.asm.ClassVisitor;
import org.objectweb.asm.ClassWriter;
import org.objectweb.asm.MethodAdapter;
import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;
public class Test_08 {
	/**
	 * @param args
	 * @throws IOException
	 */
	public static void main(String[] args) throws IOException {
		FileInputStream fis = new FileInputStream("D:\\Test.class");
		ClassReader reader = new ClassReader(fis);
		ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
		reader.accept(new MyClassVisivator(cw), 0);
		writeToFile(cw.toByteArray(), "D:\\Test.class");
	}

	static void writeToFile(byte[] bytes, String fileName) {
		try {
			(new File(fileName)).createNewFile();
		} catch (IOException e1) {
			e1.printStackTrace();
		}
		FileOutputStream fos = null;
		try {
			fos = new FileOutputStream(fileName);
			fos.write(bytes);
			fos.flush();
		} catch (Exception e) {
		}finally{
			try {
				if (fos != null) {
					fos.close();
				}
			} catch (IOException e) {
				e.printStackTrace();
			}
		}
	}

	static class MyClassVisivator extends ClassAdapter {
		ClassVisitor mCv;
		public MyClassVisivator(ClassVisitor cv) {
			super(cv);
			mCv = cv;
		}

		@Override
		public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
			MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions);
			if ("main".equals(name)) {
				MyMethodVisitor mmv = new MyMethodVisitor(mv);
				return mmv;
			}
			return mv;
		}

		@Override
		public void visitEnd() {
			MethodVisitor mv = mCv.visitMethod(Opcodes.ACC_STATIC, "test03", "()V", null, null);
			if (mv != null) {
				mv.visitCode();
				mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
				mv.visitLdcInsn("Hello In Test03!");
				mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V");
				mv.visitInsn(Opcodes.RETURN);
				mv.visitMaxs(0, 0);
				mv.visitEnd();
			}
		}
	}

	static class MyMethodVisitor extends MethodAdapter {
		MethodVisitor mMv;
		public MyMethodVisitor(MethodVisitor mv) {
			super(mv);
			mMv = mv;
		}

		@Override
		public void visitInsn(int opcode) {
			if (opcode == Opcodes.RETURN) {
				System.out.println("Debug");
				mv.visitMethodInsn(Opcodes.INVOKESTATIC, "Test", "test03", "()V");
			}
			super.visitInsn(opcode);
		}

		@Override
		public void visitEnd() {
			super.visitEnd();
		}
	}
}

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