本文承接上一篇文章，解釋不使用requestFacade, responseFacade為什麼不好，使用requestFacade, responseFacade為什麼可以解決問題。

• 不使用requestFacade, responseFacade為什麼不好：

public class Test {
    public static void main(String[] args){
        //上轉型，Response例項轉換為ServletResponse例項，
        //相對應於將Response例項的引數傳給service(ServletRequest res,ServletResponse response)
 

        ServletResponse b=new Response();
        b.sayhello();
        //相對應於在service(ServletRequest res,ServletResponse response)方法體中將
        //ServletRequest例項的b轉換為Response例項型的，從而訪問類Response有的而ServletRequest沒有的sendStaticResource方法
        //從而造成不安全
        Response res=(Response) b;//把
        res.sendStaticResource();
    }
}
class
 
 Response implements ServletResponse{
    @Override
    public void sayhello() {
        System.out.println("Response...");
    }
    public void sendStaticResource(){
        System.out.println("sendStaticResource");
    }

}
interface ServletResponse{
    public void sayhello();
}

• 使用requestFacade, responseFacade為什麼可以解決問題

public class Test2 {
    public static void main(String[] args){
        //上轉型，在ResponseFacade內部把Response例項轉換為ServletResponse例項，
        ResponseFacade b=new ResponseFacade(new Response()) ;

        //相對應於將Response例項的引數傳給service(ServletRequest res,ServletResponse response)
        ServletResponse c=b;

        //1、相對應於在service(ServletRequest res,ServletResponse response)方法體中將
        //2、ServletRequest例項的c轉換為ResponseFacade例項型的，再把裡面的ServletResponse例項的response取出，記做res.response
        //3、將res.response轉為Response型，從而訪問sendStaticResource方法
        //按照上面3步，在第二步中res.response為private，從而無法做到第2、3步，使sendStaticResource不能被訪問到
        ResponseFacade res=(ResponseFacade) c;
        Response res2=(Response)res.response;//報錯The field ResponseFacade.response is not visible
        res2.sendStaticResource();
    }
}
class ResponseFacade implements ServletResponse{
    private ServletResponse response=null;
    public ResponseFacade(Response response){
        this.response=response;
    }

    @Override
    public void sayhello() {
        System.out.println("ResponseFacade...");
    }
}