使用ASM实现AOP功能，根据现有的CLASS类文件，动态生成它的代理类文件，并在所有的方法前后添加拦截处理，具体如下：
- 生成被代理类的子类,并重写所有方法（除java.lang.Object类定义的方法和main）,增加before和after拦截。
- 重新定义被代理类的所有属性（不包括属性的赋值及父类属性）。
jdk自带的代理（InvocationHandler）的不足:
- jdk只能代理接口（被代理的类必须实现至少一个接口）。
- jdk提供的代理方法，不能拦截同一类中方法的调用。如A.method1(){this.method2();}
- 此时method2将不会被拦截。
下面是简单的被代理类及父类(也可以不要父类)：
public class Service{ public String name; public void insert(Object o) {} } public class RoleService extends Service{ public String roleName; public String executeOuter(Integer name) { System.out.println("executeOuter call super.query()"); return query(); } public String query() { System.out.println("execute (RoleService): query"); return "query result (RoleService)"; } }
核心类ClassAdapter用于生成一个类的子类，并为所有代理类方法添加拦截方法，如下：
public class ClassAdapter extends ClassVisitor implements Opcodes{ public static final String INIT = "<init>"; private ClassWriter classWriter; private String originalClassName; private String enhancedClassName; private Class<?> originalClass; public ClassAdapter(String enhancedClassName, Class<?> targetClass, ClassWriter writer) { super(Opcodes.ASM4,writer); this.classWriter = writer; this.originalClassName = targetClass.getName(); this.enhancedClassName = enhancedClassName; this.originalClass = targetClass; } @Override public void visit(int version, int access, String name, String signature, String superName, String[] interfaces) { cv.visit(version, Opcodes.ACC_PUBLIC, toAsmCls(enhancedClassName), signature, name,interfaces); } @Override public FieldVisitor visitField(int access, String name, String desc, String signature, Object value) { // 拷贝所有属性 可使用java反射给属性赋值（生成class后newInstance在赋值） return super.visitField(access, name, desc, signature, value); } @Override public MethodVisitor visitMethod(int access, String name, String desc, String signature, String[] exceptions) { // 删除所有方法 return null; } private static String toAsmCls(String className) { return className.replace('.', '/'); } private static void doBefore(MethodVisitor mWriter,String methodInfo) { mWriter.visitFieldInsn(GETSTATIC,"java/lang/System","out","Ljava/io/PrintStream;"); mWriter.visitLdcInsn("before method : " + methodInfo); mWriter.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V"); // 或者直接调用静态方法 // mWriter.visitLdcInsn(methodInfo); // mWriter.visitMethodInsn(INVOKESTATIC,toAsmCls(TxHandler.class.getName()),"before","(Ljava/lang/String;)V"); } private static void doAfter(MethodVisitor mWriter,String methodInfo) { mWriter.visitFieldInsn(GETSTATIC,"java/lang/System","out","Ljava/io/PrintStream;"); mWriter.visitLdcInsn("after method : " + methodInfo); mWriter.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V"); } public static boolean needOverride(Method m) { // object类本身的方法不做重写 if (m.getDeclaringClass().getName().equals(Object.class.getName())) { return false; } // "main" 方法不做重写 if (Modifier.isPublic(m.getModifiers()) && Modifier.isStatic(m.getModifiers()) && m.getReturnType().getName().equals("void") && m.getName().equals("main")) { return false; } return true; } @Override public void visitEnd() { // 如果originalClass定义了私有成员变量，那么直接在visitMethod中复制originalClass的<init>会报错。 // 创建<init>并调用父类的<init> // 调用originalClassName的<init>方法，否则class不能实例化 MethodVisitor mvInit = classWriter.visitMethod(ACC_PUBLIC, INIT, "()V", null, null); // pushes the 'this' variable mvInit.visitVarInsn(ALOAD, 0); mvInit.visitMethodInsn(INVOKESPECIAL, toAsmCls(originalClassName), INIT, "()V"); mvInit.visitInsn(RETURN); // this code uses a maximum of one stack element and one local variable mvInit.visitMaxs(0, 0); mvInit.visitEnd(); // 获取所有方法，并重写(main方法 和 Object的方法除外) Method[] methods = originalClass.getMethods(); for(Method m : methods) { if(!needOverride(m)) { continue; } // mt.toString() == ()Ljava/lang/String Type mt = Type.getType(m); // 生成打印信息 StringBuilder methodInfo = new StringBuilder(originalClassName); methodInfo.append(".").append(m.getName()); methodInfo.append("|"); Class<?>[] paramTypes = m.getParameterTypes(); for(Class<?> t : paramTypes) { methodInfo.append(t.getName()).append(","); } if(paramTypes.length > 0) { methodInfo.deleteCharAt(methodInfo.length() - 1); } // 方法 description MethodVisitor mWriter = classWriter.visitMethod(ACC_PUBLIC, m.getName(), mt.toString(), null, null); // insert code here (before) doBefore(mWriter,methodInfo.toString()); int i = 0; // 如果不是静态方法 load this对象 if(!Modifier.isStatic(m.getModifiers())) { mWriter.visitVarInsn(ALOAD, i++); } //StringBuilder sb = new StringBuilder(m.getName()); // load 出方法的所有参数 for(Class<?> tCls : m.getParameterTypes()) { Type t = Type.getType(tCls); //sb.append(loadCode(t)).append(","); mWriter.visitVarInsn(loadCode(t), i++); // long和double 用64位表示，要后移一个位置，否则会报错 if(t.getSort() == Type.LONG || t.getSort() == Type.DOUBLE) { i++; } } // 方法所属类全名 String declaringCls = toAsmCls(m.getDeclaringClass().getName()); // super.xxx(); mWriter.visitMethodInsn(INVOKESPECIAL,declaringCls,m.getName(),mt.toString()); // 处理返回值类型 Type rt = Type.getReturnType(m); // 没有返回值 if(rt.toString().equals("V")) { doAfter(mWriter,methodInfo.toString()); mWriter.visitInsn(RETURN); } // 把return xxx() 转变成 ： Object o = xxx(); return o; // store/load 存储并载入变量 else { int storeCode = storeCode(rt); int loadCode = loadCode(rt); int returnCode = rtCode(rt); mWriter.visitVarInsn(storeCode, i); doAfter(mWriter,methodInfo.toString()); mWriter.visitVarInsn(loadCode, i); mWriter.visitInsn(returnCode); } mWriter.visitMaxs(i, ++i); mWriter.visitEnd(); } cv.visitEnd(); } public static int storeCode(Type type) { int sort = type.getSort(); switch (sort) { case Type.ARRAY: sort = ASTORE; break; case Type.BOOLEAN: sort = ISTORE; break; case Type.BYTE: sort = ISTORE; break; case Type.CHAR: sort = ISTORE; break; case Type.DOUBLE: sort = DSTORE; break; case Type.FLOAT: sort = FSTORE; break; case Type.INT: sort = ISTORE; break; case Type.LONG: sort = LSTORE; break; case Type.OBJECT: sort = ASTORE; break; case Type.SHORT: sort = ISTORE; break; default: break; } return sort; } public static int loadCode(Type type) { int sort = type.getSort(); switch (sort) { case Type.ARRAY: sort = ALOAD; break; case Type.BOOLEAN: sort = ILOAD; break; case Type.BYTE: sort = ILOAD; break; case Type.CHAR: sort = ILOAD; break; case Type.DOUBLE: sort = DLOAD; break; case Type.FLOAT: sort = FLOAD; break; case Type.INT: sort = ILOAD; break; case Type.LONG: sort = LLOAD; break; case Type.OBJECT: sort = ALOAD; break; case Type.SHORT: sort = ILOAD; break; default: break; } return sort; } public static int rtCode(Type type) { int sort = type.getSort(); switch (sort) { case Type.ARRAY: sort = ARETURN; break; case Type.BOOLEAN: sort = IRETURN; break; case Type.BYTE: sort = IRETURN; break; case Type.CHAR: sort = IRETURN; break; case Type.DOUBLE: sort = DRETURN; break; case Type.FLOAT: sort = FRETURN; break; case Type.INT: sort = IRETURN; break; case Type.LONG: sort = LRETURN; break; case Type.OBJECT: sort = ARETURN; break; case Type.SHORT: sort = IRETURN; break; default: break; } return sort; } }
具体调用类如下：
public class AsmFactory { public static final String SUFIX = "$EnhancedByCc"; public static BytecodeLoader classLoader = new BytecodeLoader(); /** * 根据字节码加载class */ public static class BytecodeLoader extends ClassLoader { public Class<?> defineClass(String className, byte[] byteCodes) { return super.defineClass(className, byteCodes, 0, byteCodes.length); } } /** * 返回代理类 */ @SuppressWarnings("unchecked") protected static <T> Class<T> getEnhancedClass(Class<T> clazz){ String enhancedClassName = clazz.getName() + SUFIX; try { return (Class<T>) classLoader.loadClass(enhancedClassName); } catch (ClassNotFoundException classNotFoundException) { ClassReader reader = null; try { reader = new ClassReader(clazz.getName()); } catch (IOException ioexception) { throw new RuntimeException(ioexception); } ClassWriter writer = new ClassWriter(ClassWriter.COMPUTE_MAXS); ClassVisitor visitor = new ClassAdapter(enhancedClassName, clazz, writer); reader.accept(visitor, 0); byte[] byteCodes = writer.toByteArray(); writeClazz(enhancedClassName, byteCodes); Class<T> result = (Class<T>) classLoader.defineClass( enhancedClassName, byteCodes); return result; } } public static void writeClazz(String name, byte[] data) { try { File file = new File("D:/com/" + name + ".class"); FileOutputStream fout = new FileOutputStream(file); fout.write(data); fout.close(); } catch (Exception e) { e.printStackTrace(); } } public static void main(String[] args) throws InstantiationException, IllegalAccessException { Class<RoleService> rsCls = getEnhancedClass(RoleService.class); rsCls.newInstance().executeOuter(1); } }
