前言:
代理模式是常用的java设计模式,它的特征是代理类与委托类有同样的接口,代理类主要负责为委托类预处理消息、过滤消息、把消息转发给委托类,以及事后处理消息等。代理类与委托类之间通常会存在关联关系,一个代理类的对象与一个委托类的对象关联,代理类的对象本身并不真正实现服务,而是通过调用委托类的对象的相关方法,来提供特定的服务。
JAVA各种动态代理实现的比较
接口
interface AddInterface{
int add(int a, int b);
} interface SubInterface{
int sub(int a, int b);
}
实现类
class Arithmetic implements AddInterface, SubInterface{
@Override
public int sub(int a, int b) {
return a-b;
} @Override
public int add(int a, int b) {
return a+b;
}
}
方式1: JDK自带的动态代理
实现方式
Java在JDK1.3后引入的动态代理机制,使我们可以在运行期动态的创建代理类。使用动态代理实现AOP需要有四个角色:被代理的类,被代理类的接口,织入器,和InvocationHandler,而织入器使用接口反射机制生成一个代理类,然后在这个代理类中织入代码。被代理的类是AOP里所说的目标,InvocationHandler是切面,它包含了Advice和Pointcut。
InvocationHandler接口的实现
class JdkDPQueryHandler implements InvocationHandler{
private Arithmetic real;
public JdkDPQueryHandler(Arithmetic real){
this.real = real;
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
System.out.println(method);
System.out.println("the method: " + methodName + "开始, 参数: "+Arrays.asList(args));
Object result = method.invoke(real, args);
System.out.println("the method: "+methodName+"结束, 结果: " + result);
return result;
}
}
创建代理类并且调用代理类
public class Main{
private static int a = 4, b = 2; public static Object createJDKProxy(Arithmetic real){
Object proxyArithmetic = Proxy.newProxyInstance(real.getClass().getClassLoader(),
real.getClass().getInterfaces(), new JdkDPQueryHandler(real));
return proxyArithmetic;
} public static void main(String[] args){
Arithmetic real = new Arithmetic();
Object proxyArithmetic = createJDKProxy(real);
((AddInterface)proxyArithmetic).add(a, b);
((SubInterface)proxyArithmetic).sub(a, b);
}
}
方式2:动态字节码生成(cglib)
实现方式
接口InvocationHandler(jdk中)和接口MethodInterceptor(cglib中)对比
public interface MethodInterceptor extends Callback {
public Object intercept(Object obj, java.lang.reflect.Method method, Object[] args,MethodProxy proxy) throws Throwable;
}
public interface InvocationHandler {
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable;
}
实现1
MethodInterceptor接口的实现
class CglibDPQueryInterceptor implements MethodInterceptor{
private Arithmetic real;
public CglibDPQueryInterceptor(Arithmetic real){
this.real = real;
} @Override
public Object intercept(Object target, Method method, Object[] args, MethodProxy proxy) throws Throwable {
String methodName = method.getName();
System.out.println(method);
System.out.println("the method: " + methodName + "开始, 参数: "+Arrays.asList(args));
//Object result = method.invoke(real, args);//两种方式都是可以得
Object result = proxy.invoke(real, args);
System.out.println("the method: "+methodName+"结束, 结果: " + result);
return result;
}
}
创建代理类并调用代理类
public class Main{
private static int a = 4, b = 2;
public static Object createCglibProxy(Arithmetic real){
Enhancer enhancer = new Enhancer();
enhancer.setCallback(new CglibDPQueryInterceptor(real));
enhancer.setInterfaces(real.getClass().getInterfaces());
return enhancer.create();
} public static void main(String[] args){
Arithmetic real = new Arithmetic();
Object proxyArithmetic = createCglibProxy(real);
((AddInterface)proxyArithmetic).add(a, b);
((SubInterface)proxyArithmetic).sub(a, b);
}
}
注意了,MethodProxy在对执行函数的时候,提供了2个方法
public Object invoke (Object obj, Object[] args) throws Throwable
public Object invokeSuper(Object obj, Object[] args) throws Throwable
其中,javadoc上说这个invoke()方法可以用于相同类中的其他对象的方法执行,也就是说这个方法中的obj需要传入相同一个类的另一个对象(上述方法中就是传入了Arithmetic类的不同对象),否则会进入无限递归循环(测试之后还真是出现了*Error)。仔细的想一想就会发现,public Object intercept(Object target, Method method, Object[] args, MethodProxy proxy)中的target是实现的代理类对象,通过target调用add()方法时会触发intercept()方法被调用,如果在intercept()方法中再调用method.invoke(target, args),就相当于add()方法中又调用add()方法,导致无限的递归循环。但是如果执行method.invoke(real, args)则不会,因为real和target是同一个类不同对象,real是真实逻辑主题,target是真实主题real的代理。
下面一个例子来模拟一下:
interface SolveInterface{
void solve();
} class Real implements SolveInterface{
public void solve(){
System.out.println("Real Solve!");
}
} class Target extends Real{
private Object obj; public void setObject(Object obj){
this.obj = obj;
} private void invoke(){
try {
Method method = SolveInterface.class.getMethod("solve", new Class[]{});
method.invoke(obj, new Class[]{});
} catch (Exception e) {
e.printStackTrace();
}
}
public void solve(){
System.out.println("Target Solve!");
invoke();
}
}
public class Main{public static void main(String[] args) throws Exception{
Target target = new Target();
target.setObject(new Real());//正确
//target.setObject(target);//发生循环调用
target.solve();
}
}
其实Method的invoke()方法会根据obj的类型去调用对应的solve()方法,也就是多态性。
实现2
MethodInterceptor接口的实现
class CglibDPQueryInterceptor implements MethodInterceptor{ @Override
public Object intercept(Object target, Method method, Object[] args, MethodProxy proxy) throws Throwable {
String methodName = method.getName();
System.out.println(method);
System.out.println("the method: " + methodName + "开始, 参数: "+Arrays.asList(args));
// 打印类信息 :target.getClass();省略
Object result = proxy.invokeSuper(target, args);
System.out.println("the method: "+methodName+"结束, 结果: " + result);
return result;
}
}
创建代理类并调用代理类
public class Main{
private static int a = 4, b = 2;
public static Object createCglibProxy(){
Enhancer enhancer = new Enhancer();
enhancer.setCallback(new CglibDPQueryInterceptor());
enhancer.setSuperclass(Arithmetic.class);
return enhancer.create();
} public static void main(String[] args){
Arithmetic real = new Arithmetic(); Object proxyArithmetic = createCglibProxy(); ((AddInterface)proxyArithmetic).add(a, b);
((SubInterface)proxyArithmetic).sub(a, b);
}
}
注意了,实现2中Enhancer 没有设置接口,因为设置了Superclass了(也就是代理类的父类是Arithmetic),我们的代理类会继承它,而Arithmetic已经实现了我们的接口。为了证明这一点,可以在MethodInterceptor的 intercept方法中打印 target.getClass()的类信息,你会发现cglib的两种方式代理类的父类是不同的。如下:
(如果需要打印类信息代码,请参考:http://www.cnblogs.com/hujunzheng/p/5132943.html)
实现1:
public class com.test.Arithmetic$$EnhancerByCGLIB$$4fa786eb extends java.lang.Object
实现2:
public class com.test.Arithmetic$$EnhancerByCGLIB$$4fa786eb extends com.test.Arithmetic
方式3:javassist生成动态代理(代理工厂创建 或者 动态代码创建)
Javassist是一个编辑字节码的框架,可以让你很简单地操作字节码。它可以在运行期定义或修改Class。使用Javassist实现AOP的原理是在字节码加载前直接修改需要切入的方法。这比使用Cglib实现AOP更加高效,并且没太多限制,实现原理如下图:
实现1:
接口的实现
class JavassistDPQueryHandler implements MethodHandler{ @Override
public Object invoke(Object target, Method method, Method proxy, Object[] args) throws Throwable {
String methodName = method.getName();
System.out.println(method);
System.out.println("the method: " + methodName + "开始, 参数: "+Arrays.asList(args));
Object result = proxy.invoke(target, args);
System.out.println("the method: "+methodName+"结束, 结果: " + result);
return result;
}
}
创建代理类并调用代理类
public class Main{
private static int a = 4, b = 2;
public static Object createJavassistProxy() throws Exception{
ProxyFactory factory = new ProxyFactory();
factory.setSuperclass(Arithmetic.class);
factory.setHandler(new JavassistDPQueryHandler());
return factory.createClass().newInstance();
} public static void main(String[] args) throws Exception{
Arithmetic real = new Arithmetic(); Object proxyArithmetic = createJavassistProxy(); ((AddInterface)proxyArithmetic).add(a, b);
((SubInterface)proxyArithmetic).sub(a, b);
}
}
注意:MethodHandler接口中invoke方法的定义,如下:
public Object invoke(Object target, Method method, Method proxy, Object[] args)
method代表调用方法的Method对象,proxy是代理类产生并代替method的对象,否则用method.invoke(target, args)会产生无限循环调用。
实现2:
(来自:http://cuishen.iteye.com/blog/421464),代码注释很详细,仔细研究一下就会懂了!
javassist使用动态java代码常见代理过程和前文的方法略有不同。javassist内部可以通过动态java代码,生成字节码。这种方式创建的动态代理可以非常灵活,甚至可以在运行时产生业务逻辑。
//自定义拦截器接口
interface InterceptorHandler { /**
* 调用动态代理对象的方法将反射本方法,可在本方法实现中添加类似AOP的事前事后操作,只有在本方法体中加入如下代码
* 被代理的方法才会被执行,返回值将返回给代理最后返回给程序
* @param obj Object 被代理的对象
* @param method Method 被代理对象的方法
* @param args Object[] 被代理对象的方法的参数
* @return Object 被代理对象的方法执行后的返回值
* @throws Throwable
*/
public Object invoke(Object obj, Method method, Object[] args) throws Throwable;
}
//拦截器的实现
class InterceptorHandlerImpl implements InterceptorHandler{
@Override
public Object invoke(Object obj, Method method, Object[] args) throws Throwable {
String methodName = method.getName();
System.out.println(method);
System.out.println("the method: " + methodName + "开始, 参数: "+Arrays.asList(args));
Object result = method.invoke(obj, args);
System.out.println("the method: "+methodName+"结束, 结果: " + result);
return result;
}
} class MyProxyImpl {
/** 动态代理类的类名后缀 */
private final static String PROXY_CLASS_NAME_SUFFIX = "$MyProxy_";
/** 拦截器接口 */
private final static String INTERCEPTOR_HANDLER_INTERFACE = "com.test.InterceptorHandler";
/** 动态代理类的类名索引,防止类名重复 */
private static int proxyClassIndex = 1; /**
* 暴露给用户的动态代理接口,返回某个接口的动态代理对象,注意本代理实现需和com.cuishen.myAop.InterceptorHandler拦截器配合
* 使用,即用户要使用本动态代理,需先实现com.cuishen.myAop.InterceptorHandler拦截器接口
* @param interfaceClassName String 要动态代理的接口类名, e.g test.StudentInfoService
* @param classToProxy String 要动态代理的接口的实现类的类名, e.g test.StudentInfoServiceImpl
* @param interceptorHandlerImplClassName String 用户提供的拦截器接口的实现类的类名
* @return Object 返回某个接口的动态代理对象
* @throws InstantiationException
* @throws IllegalAccessException
* @throws NotFoundException
* @throws CannotCompileException
* @throws ClassNotFoundException
* @see com.cuishen.myAop.InterceptorHandler
*/
public static Object newProxyInstance(String interfaceClassName, String classToProxy, String interceptorHandlerImplClassName) throws InstantiationException, IllegalAccessException, NotFoundException, CannotCompileException, ClassNotFoundException {
Class interfaceClass = Class.forName(interfaceClassName);
Class interceptorHandlerImplClass = Class.forName(interceptorHandlerImplClassName);
return dynamicImplementsInterface(classToProxy, interfaceClass, interceptorHandlerImplClass);
} /**
* 动态实现要代理的接口
* @param classToProxy String 要动态代理的接口的实现类的类名, e.g test.StudentInfoServiceImpl
* @param interfaceClass Class 要动态代理的接口类, e.g test.StudentInfoService
* @param interceptorHandlerImplClass Class 用户提供的拦截器接口的实现类
* @return Object 返回某个接口的动态代理对象
* @throws NotFoundException
* @throws CannotCompileException
* @throws InstantiationException
* @throws IllegalAccessException
*/
private static Object dynamicImplementsInterface(String classToProxy, Class interfaceClass, Class interceptorHandlerImplClass) throws NotFoundException, CannotCompileException, InstantiationException, IllegalAccessException {
ClassPool cp = ClassPool.getDefault();
String interfaceName = interfaceClass.getName();
//动态指定代理类的类名
String proxyClassName = interfaceName + PROXY_CLASS_NAME_SUFFIX + proxyClassIndex++;
//要实现的接口的包名+接口名
String interfaceNamePath = interfaceName; CtClass ctInterface = cp.getCtClass(interfaceNamePath);
CtClass cc = cp.makeClass(proxyClassName);
cc.addInterface(ctInterface);
Method [] methods = interfaceClass.getMethods();
for(int i = 0; i < methods.length; i++) {
Method method = methods[i];
dynamicImplementsMethodsFromInterface(classToProxy, cc, method, interceptorHandlerImplClass, i);
}
return (Object)cc.toClass().newInstance();
} /**
* 动态实现接口里的方法
* @param classToProxy String 要动态代理的接口的实现类的类名, e.g test.StudentInfoServiceImpl
* @param implementer CtClass 动态代理类的包装
* @param methodToImpl Method 动态代理类里面要实现的接口方法的包装
* @param interceptorClass Class 用户提供的拦截器实现类
* @param methodIndex int 要实现的方法的索引
* @throws CannotCompileException
*/
private static void dynamicImplementsMethodsFromInterface(String classToProxy, CtClass implementer, Method methodToImpl, Class interceptorClass, int methodIndex) throws CannotCompileException {
String methodCode = generateMethodCode(classToProxy, methodToImpl, interceptorClass, methodIndex);
CtMethod cm = CtNewMethod.make(methodCode, implementer);
implementer.addMethod(cm);
} /**
* 动态组装方法体,当然代理里面的方法实现并不是简单的方法拷贝,而是反射调用了拦截器里的invoke方法,并将接收到的参数进行传递
* @param classToProxy String 要动态代理的接口的实现类的类名, e.g test.StudentInfoServiceImpl
* @param methodToImpl Method 动态代理类里面要实现的接口方法的包装
* @param interceptorClass Class 用户提供的拦截器实现类
* @param methodIndex int 要实现的方法的索引
* @return String 动态组装的方法的字符串
*/
private static String generateMethodCode(String classToProxy, Method methodToImpl, Class interceptorClass, int methodIndex) {
String methodName = methodToImpl.getName();
String methodReturnType = methodToImpl.getReturnType().getName();
Class[] parameters = methodToImpl.getParameterTypes();
Class[] exceptionTypes = methodToImpl.getExceptionTypes();
StringBuffer exceptionBuffer = new StringBuffer();
//组装方法的Exception声明
if(exceptionTypes.length > 0) exceptionBuffer.append(" throws ");
for(int i = 0; i < exceptionTypes.length; i++) {
if(i != exceptionTypes.length - 1) exceptionBuffer.append(exceptionTypes[i].getName()).append(",");
else exceptionBuffer.append(exceptionTypes[i].getName());
}
StringBuffer parameterBuffer = new StringBuffer();
//组装方法的参数列表
for(int i = 0; i < parameters.length; i++) {
Class parameter = parameters[i];
String parameterType = parameter.getName();
//动态指定方法参数的变量名
String refName = "a" + i;
if(i != parameters.length - 1) parameterBuffer.append(parameterType).append(" " + refName).append(",");
else parameterBuffer.append(parameterType).append(" " + refName);
}
StringBuffer methodDeclare = new StringBuffer();
//方法声明,由于是实现接口的方法,所以是public
methodDeclare.append("public ").append(methodReturnType).append(" ").append(methodName).append("(").append(parameterBuffer).append(")").append(exceptionBuffer).append(" {\n");
String interceptorImplName = interceptorClass.getName();
//方法体
methodDeclare.append(INTERCEPTOR_HANDLER_INTERFACE).append(" interceptor = new ").append(interceptorImplName).append("();\n");
//反射调用用户的拦截器接口
methodDeclare.append("Object returnObj = interceptor.invoke(Class.forName(\"" + classToProxy + "\").newInstance(), Class.forName(\"" + classToProxy + "\").getMethods()[" + methodIndex + "], ");
//传递方法里的参数
if(parameters.length > 0) methodDeclare.append("new Object[]{");
for(int i = 0; i < parameters.length; i++) {
//($w) converts from a primitive type to the corresponding wrapper type: e.g.
//Integer i = ($w)5;
if(i != parameters.length - 1) methodDeclare.append("($w)a" + i + ",");
else methodDeclare.append("($w)a" + i);
}
if(parameters.length > 0) methodDeclare.append("});\n");
else methodDeclare.append("null);\n");
//对调用拦截器的返回值进行包装
if(methodToImpl.getReturnType().isPrimitive()) {
if(methodToImpl.getReturnType().equals(Boolean.TYPE)) methodDeclare.append("return ((Boolean)returnObj).booleanValue();\n");
else if(methodToImpl.getReturnType().equals(Integer.TYPE)) methodDeclare.append("return ((Integer)returnObj).intValue();\n");
else if(methodToImpl.getReturnType().equals(Long.TYPE)) methodDeclare.append("return ((Long)returnObj).longValue();\n");
else if(methodToImpl.getReturnType().equals(Float.TYPE)) methodDeclare.append("return ((Float)returnObj).floatValue();\n");
else if(methodToImpl.getReturnType().equals(Double.TYPE)) methodDeclare.append("return ((Double)returnObj).doubleValue();\n");
else if(methodToImpl.getReturnType().equals(Character.TYPE)) methodDeclare.append("return ((Character)returnObj).charValue();\n");
else if(methodToImpl.getReturnType().equals(Byte.TYPE)) methodDeclare.append("return ((Byte)returnObj).byteValue();\n");
else if(methodToImpl.getReturnType().equals(Short.TYPE)) methodDeclare.append("return ((Short)returnObj).shortValue();\n");
} else {
methodDeclare.append("return (" + methodReturnType + ")returnObj;\n");
}
methodDeclare.append("}");
System.out.println(methodDeclare.toString());
return methodDeclare.toString();
} } public class Main{
public static void main(String[] args) throws Exception{
//分别对应 代理类要实现的接口类名, 需要代理类的类名, 用户自定义拦截器实现类的类名
Object proxyArithmetic = MyProxyImpl.newProxyInstance("com.test.ArithmeticInterface", "com.test.Arithmetic",
"com.test.InterceptorHandlerImpl");
((ArithmeticInterface)proxyArithmetic).add(a, b);
((ArithmeticInterface)proxyArithmetic).sub(a, b);
}
}
打印一下动态实现接口的代码如下:
public int add(int a0,int a1) {
com.test.InterceptorHandler interceptor = new com.test.InterceptorHandlerImpl();
Object returnObj = interceptor.invoke(Class.forName("com.test.Arithmetic").newInstance(), Class.forName("com.test.Arithmetic").getMethods()[0], new Object[]{($w)a0,($w)a1});
return ((Integer)returnObj).intValue();
}
public int sub(int a0,int a1) {
com.test.InterceptorHandler interceptor = new com.test.InterceptorHandlerImpl();
Object returnObj = interceptor.invoke(Class.forName("com.test.Arithmetic").newInstance(), Class.forName("com.test.Arithmetic").getMethods()[1], new Object[]{($w)a0,($w)a1});
return ((Integer)returnObj).intValue();
}