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(); }

1static void test01() {
2	System.out.println("Hello In Test01!");
3}
4
5}

###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;

1import org.objectweb.asm.ClassAdapter;
2import org.objectweb.asm.ClassReader;
3import org.objectweb.asm.ClassVisitor;
4import org.objectweb.asm.ClassWriter;
5import org.objectweb.asm.MethodAdapter;
6import org.objectweb.asm.MethodVisitor;
7import org.objectweb.asm.Opcodes;
8public class Test_08 {
9	/**
10	 * @param args
11	 * @throws IOException 
12	 */
13	public static void main(String[] args) throws IOException {
14		FileInputStream fis = new FileInputStream("D:\\Test.class");
15		ClassReader reader = new ClassReader(fis);
16		ClassWriter cw = new ClassWriter(ClassWriter.COMPUTE_FRAMES);
17		reader.accept(new MyClassVisivator(cw), 0);
18		writeToFile(cw.toByteArray(), "D:\\Test.class");
19	}
20	
21	static void writeToFile(byte[] bytes, String fileName) {
22		try {
23			(new File(fileName)).createNewFile();
24		} catch (IOException e1) {
25			e1.printStackTrace();
26		}
27		FileOutputStream fos = null;
28		try {
29			fos = new FileOutputStream(fileName);
30			fos.write(bytes);
31			fos.flush();
32		} catch (Exception e) {
33		}finally{
34			try {
35				if (fos != null) {
36					fos.close();
37				}
38			} catch (IOException e) {
39				e.printStackTrace();
40			}
41		}
42	}
43	
44	static class MyClassVisivator extends ClassAdapter {
45		ClassVisitor mCv;
46		public MyClassVisivator(ClassVisitor cv) {
47			super(cv);
48			mCv = cv;
49		}
50		
51		@Override
52		public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) {
53			MethodVisitor mv = super.visitMethod(access, name, desc, signature, exceptions);
54			if ("main".equals(name)) {
55				MyMethodVisitor mmv = new MyMethodVisitor(mv);
56				return mmv;
57			}
58			return mv;
59		}
60		
61		@Override
62		public void visitEnd() {
63			MethodVisitor mv = mCv.visitMethod(Opcodes.ACC_STATIC, "test03", "()V", null, null);
64			if (mv != null) {
65				mv.visitCode();
66				mv.visitFieldInsn(Opcodes.GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
67				mv.visitLdcInsn("Hello In Test03!");
68				mv.visitMethodInsn(Opcodes.INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V");
69				mv.visitInsn(Opcodes.RETURN);
70				mv.visitMaxs(0, 0);
71				mv.visitEnd();
72			}
73		}
74	}
75	
76	static class MyMethodVisitor extends MethodAdapter {
77		MethodVisitor mMv;
78		public MyMethodVisitor(MethodVisitor mv) {
79			super(mv);
80			mMv = mv;
81		}
82		
83		@Override
84		public void visitInsn(int opcode) {
85			if (opcode == Opcodes.RETURN) {
86				System.out.println("Debug");
87				mv.visitMethodInsn(Opcodes.INVOKESTATIC, "Test", "test03", "()V");
88			}
89			super.visitInsn(opcode);
90		}
91		
92		@Override
93		public void visitEnd() {
94			super.visitEnd();
95		}
96	}
97}

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