动态代理理解

    从这张图上看，动态代理也可以用在真正类外面包裹一层普通处理类来实现， 这样做的坏处是

不能扩展，每一个真正类都需要自己的一个代理类，而动态代理可以用一个Proxy类对所有的有接口实现的真正类进行代理。

public class DPMain {
    
    public static PDQueryStatus create(DPQueryStatusImpl dpqs) {
        //定义转发处理类
        DPInvocationHandler handler = new DPInvocationHandler(dpqs);
        //定义了一个
        Class<?>[] interfaces=new Class[] { PDQueryStatus.class };
        
        Object result = Proxy.newProxyInstance(dpqs.getClass().getClassLoader(), 
                                               interfaces,   
                                               handler); 

          //核心在这里，handler可以对interfaces接口数组中的方法进行转发处理
        //Class<?> proxy=Proxy.getProxyClass(dpqs.getClass().getClassLoader(), 
//                                           interfaces); 

        //System.out.println("Proxy class name: "+proxy.getCanonicalName());
//        System.out.println("Proxy's super class name: "+proxy.getSuperclass().getName());
//        System.out.println();
        
        return (PDQueryStatus) result;
    }
    
    /**
     * @param args
     */
    public static void main(String[] args) {
        try {
            PDQueryStatus query = DPMain.create(new DPQueryStatusImpl());
            DPFileStatus status = query.getFileStatus("/tmp/testDP");
            System.out.println(status);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

public class DPFileStatus {    
    private String filename;
    private long time;
    
    public DPFileStatus(String filename) {
        this.filename=filename;
        this.time=(new Date()).getTime();
    }

    public String getFilename() {
        return filename;
    }
    
    public void setFilename(String filename) {
        this.filename = filename;
    }
    
    public long getTime() {
        return time;
    }
    
    public void setTime(long time) {
        this.time = time;
    }
    
    public String toString() {
        return "File: "+filename+" Create at "+(new Date(time)); 
    }
}

public interface PDQueryStatus {
    DPFileStatus getFileStatus(String filename);
}

public class DPInvocationHandler implements InvocationHandler {
    private DPQueryStatusImpl dpqs;

    public DPInvocationHandler(DPQueryStatusImpl dpqs) {
        this.dpqs = dpqs;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args)
            throws Throwable {
        Object ret = null;
        String msg1 = MessageFormat.format("Calling method {0}({1})", 
                                           method.getName(), 
                                           Arrays.toString(args));
        System.out.println(msg1);

        ret = method.invoke(dpqs, args);

        String msg2 = MessageFormat.format("Method {0} returned with ({1})",
                method.getName(), ret.toString());
        System.out.println(msg2);
        return ret;
    }
}

public class DPQueryStatusImpl implements PDQueryStatus {
    @Override
    public DPFileStatus getFileStatus(String filename) {
        DPFileStatus status=new DPFileStatus(filename);
        System.out.println("Method getFileStatus Called, return: "+status);
        return status;
    }
}