ダイナミックプロキシクラスの使用例

任意メソッド起動時の前後でデバックメッセージを出す方法です。

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DebugProxy.java(Sunのサイトより引用)
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import java.lang.reflect.*;

public class DebugProxy implements java.lang.reflect.InvocationHandler {

    private Object obj;

    public static Object newInstance( Object obj ) {
        return java.lang.reflect.Proxy.newProxyInstance(
                   obj.getClass().getClassLoader(),
                   obj.getClass().getInterfaces(),
                   new DebugProxy( obj ) );
    }

    private DebugProxy( Object obj ) {
        this.obj = obj;
    }

    public Object invoke( Object proxy, Method m, Object[] args )
    throws Throwable {
        Object result;
        try {
            System.out.println( "*** before method " + m.getName() );
            result = m.invoke( obj, args );
        } catch ( InvocationTargetException e ) {
            throw e.getTargetException();
        } catch ( Exception e ) {
            throw new RuntimeException( "unexpected invocation exception: " +
                                        e.getMessage() );
        } finally {
            System.out.println( "*** after method " + m.getName() + "\n" );
        }

        return result;
    }
}

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MyInterface.java
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/**
* $Id: Proxy.html,v 1.1 2009/06/22 16:11:53 kishi Exp kishi $
*/
public interface MyInterface {

    public void doSomething();
    public void doExecute();

}
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MyInterfaceImpl.java
::::::::::::::
import java.util.*;

/**
* $Id: Proxy.html,v 1.1 2009/06/22 16:11:53 kishi Exp kishi $
*/
public class MyInterfaceImpl implements MyInterface {

    public void doSomething() {
        System.out.println( this.getClass().getName() + " is saying: " + new Date() );
    }
    public void doExecute() {
        for ( int i = 0;i < 15;i++ ) {
            System.out.printf( "%2d\n", i );
        }
    }

    /**
    * 単体試験用メインメソッド
    */
    public static void main( String[] args ) {

        MyInterface myObj = ( MyInterface ) DebugProxy.newInstance( new MyInterfaceImpl() );
        myObj.doSomething();
        myObj.doExecute();

    }

}

■実行結果
$ java -cp . MyInterfaceImpl
*** before method doSomething
MyInterfaceImpl is saying: Fri Feb 17 18:50:54 JST 2006
*** after method doSomething

*** before method doExecute
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*** after method doExecute