public interface ICalculator {
//加法运算
public int add(int a,int b);
//减法
public int subtract(int a,int b);
//乘法
public int multiply(int a,int b);
//除法
public int devide(int a,int b);
}
public class CalculatorImpl implements ICalculator{
@Override
public int add(int a, int b) {
return a + b;
}
@Override
public int subtract(int a, int b) {
return a - b;
}
@Override
public int multiply(int a, int b) {
return a * b;
}
@Override
public int devide(int a, int b) {
return a / b;
}
}
如何在不改动原来计算器类内部代码的情况下记录计算器各个方法使用的总次数呢?
public class TestHandler implements InvocationHandler {
private Object targetObject;
private int useTimes;
//绑定委托对象,并返回代理类
public Object bind(Object targetObject){
this.targetObject = targetObject;
return Proxy.newProxyInstance(targetObject.getClass().getClassLoader(),targetObject.getClass().getInterfaces(),this);
}
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
//do something
before();
Object result = method.invoke(targetObject,args);
after();
return result;
}
private void before(){
System.out.println("we can do something before calculate.");
}
private void after(){
useTimes++;
System.out.println("已使用:"+useTimes+"次");
}
}
别看代码好像有点多,其实主要的方法就是invoke方法,里面的Object result = method.invoke(targetObject,args);相当于继续用原来的参数执行原来方法。这里的before和after为自定义的函数,可以在目标代码执行前后做一些我们想要做的事情,比如这里的使用次数统计。
在bind方法里,传入目标代理对象,并返回一个代理类实例。接下来我们看看如何使用:
public class TestProxy {
public static void main(String[] args) {
TestHandler proxy = new TestHandler();
ICalculator calculator = (ICalculator)proxy.bind(new CalculatorImpl());
int result = calculator.add(1,2);
System.out.println("result is:"+result);
result = calculator.subtract(3,2);
System.out.println("result is:"+result);
result = calculator.multiply(4,6);
System.out.println("result is:"+result);
result = calculator.devide(6,2);
System.out.println("result is:"+result);
}
}
我们先定义一个TestHandler,然后通过bind方法来获得一个代理实例,之后我们就可以直接使用这个实例了。运行结果如下:
we can do something before calculate.
已使用:1次
result is:3
we can do something before calculate.
已使用:2次
result is:1
we can do something before calculate.
已使用:3次
result is:24
we can do something before calculate.
已使用:4次
result is:3
这样我们就实现了不修改CalculatorImpl内部代码的情况下对代码进行扩展。
public class CGLibProxy implements MethodInterceptor {
private int useTimes;
private Object target;
public Object getInstance(Object target){
this.target=target;
Enhancer enhancer =new Enhancer();
enhancer.setSuperclass(this.target.getClass());
enhancer.setCallback(this);
return enhancer.create();
}
@Override
public Object intercept(Object o, Method method, Object[] objects, MethodProxy methodProxy) throws Throwable {
before();
Object result = methodProxy.invokeSuper(o,objects);
after();
return result;
}
private void before(){
System.out.println("we can do something before calculate.");
}
private void after(){
useTimes++;
System.out.println("已使用:"+useTimes+"次");
}
}
测试一下:
public class TestCGLibProxy {
public static void main(String[] args) {
CGLibProxy cgLibProxy = new CGLibProxy();
ICalculator calculator = (ICalculator) cgLibProxy.getInstance(new CalculatorImpl());
int result = calculator.add(1,2);
System.out.println("result is:"+result);
result = calculator.subtract(3,2);
System.out.println("result is:"+result);
result = calculator.multiply(4,6);
System.out.println("result is:"+result);
result = calculator.devide(6,2);
System.out.println("result is:"+result);
}
}
运行结果如下:
we can do something before calculate.
已使用:1次
result is:3
we can do something before calculate.
已使用:2次
result is:1
we can do something before calculate.
已使用:3次
result is:24
we can do something before calculate.
已使用:4次
result is:3
现在我们得到了同样的结果。(需要导入两个包,cglib-2.2.2.jar asm-3.3.jar)