三十五、拦截过滤器模式 ( Intercepting Filter )

拦截过滤器模式(Intercepting Filter Pattern)用于对应用程序的请求或响应做一些预处理/后处理

定义过滤器,并在把请求传给实际目标应用程序之前应用在请求上

过滤器可以做认证/授权/记录日志,或者跟踪请求,然后把请求传给相应的处理程序

拦截过滤器模式涉及以下实体:

  • 过滤器(Filter) - 过滤器在请求处理程序执行请求之前或之后,执行某些任务。
  • 过滤器链(Filter Chain) - 过滤器链带有多个过滤器,并在 Target 上按照定义的顺序执行这些过滤器。
  • Target - Target 对象是请求处理程序。
  • 过滤管理器(Filter Manager) - 过滤管理器管理过滤器和过滤器链。
  • 客户端(Client) - Client 是向 Target 对象发送请求的对象。

实现

 

1、 定义类FilterChainFilterManagerTargetClient作为表示实体的各种对象;
2、 定义类AuthenticationFilterDebugFilter表示实体过滤器;
3、 定义类InterceptingFilterDemo使用Client来演示拦截过滤器设计模式;

范例

1. 创建过滤器接口 Filter

Filter.java

// author: pottercoding.cn 程序员波特,程序员编程资料站(pottercoding.cn)
// Copyright © 2015-2065 pottercoding.cn. All rights reserved.
package com.pottercoding.gof;
public interface Filter {
   public void execute(String request);

2. 创建实体过滤器

AuthenticationFilter.java

// author: pottercoding.cn 程序员波特,程序员编程资料站(pottercoding.cn)
// Copyright © 2015-2065 pottercoding.cn. All rights reserved.
package com.pottercoding.gof;
public class AuthenticationFilter implements Filter {
   public void execute(String request){
      System.out.println("Authenticating request: " + request);
   }

DebugFilter.java

// author: pottercoding.cn 程序员波特,程序员编程资料站(pottercoding.cn)
// Copyright © 2015-2065 pottercoding.cn. All rights reserved.
package com.pottercoding.gof;
public class DebugFilter implements Filter {
   public void execute(String request){
      System.out.println("request log: " + request);
   }

3. 创建 Target

Target.java

// author: pottercoding.cn 程序员波特,程序员编程资料站(pottercoding.cn)
// Copyright © 2015-2065 pottercoding.cn. All rights reserved.
package com.pottercoding.gof;
public class Target {
   public void execute(String request){
      System.out.println("Executing request: " + request);
   }

4. 创建过滤器链

FilterChain.java

// author: pottercoding.cn 程序员波特,程序员编程资料站(pottercoding.cn)
// Copyright © 2015-2065 pottercoding.cn. All rights reserved.
package com.pottercoding.gof;
import java.util.ArrayList;
import java.util.List;
public class FilterChain {
   private List<Filter> filters = new ArrayList<Filter>();
   private Target target;
   public void addFilter(Filter filter){
      filters.add(filter);
   }
   public void execute(String request){
      for (Filter filter : filters) {
         filter.execute(request);
      }
      target.execute(request);
   }
   public void setTarget(Target target){
      this.target = target;
   }

5. 创建过滤管理器

FilterManager.java

// author: pottercoding.cn 程序员波特,程序员编程资料站(pottercoding.cn)
// Copyright © 2015-2065 pottercoding.cn. All rights reserved.
package com.pottercoding.gof;
public class FilterManager {
   FilterChain filterChain;
   public FilterManager(Target target){
      filterChain = new FilterChain();
      filterChain.setTarget(target);
   }
   public void setFilter(Filter filter){
      filterChain.addFilter(filter);
   }
   public void filterRequest(String request){
      filterChain.execute(request);
   }

6. 创建客户端 Client

Client.java

// author: pottercoding.cn 程序员波特,程序员编程资料站(pottercoding.cn)
// Copyright © 2015-2065 pottercoding.cn. All rights reserved.
package com.pottercoding.gof;
public class Client {
   FilterManager filterManager;
   public void setFilterManager(FilterManager filterManager){
      this.filterManager = filterManager;
   }
   public void sendRequest(String request){
      filterManager.filterRequest(request);
   }

7. 使用 Client 来演示拦截过滤器设计模式

FrontControllerPatternDemo.java

// author: pottercoding.cn 程序员波特,程序员编程资料站(pottercoding.cn)
// Copyright © 2015-2065 pottercoding.cn. All rights reserved.
package com.pottercoding.gof;
public class InterceptingFilterDemo {
   public static void main(String[] args) {
      FilterManager filterManager = new FilterManager(new Target());
      filterManager.setFilter(new AuthenticationFilter());
      filterManager.setFilter(new DebugFilter());
      Client client = new Client();
      client.setFilterManager(filterManager);
      client.sendRequest("HOME");
   }

编译运行以上 Java 范例,输出结果如下

$ javac -d . src/main/com.pottercoding/gof/InterceptingFilterDemo.java
$ java  com.pottercoding.gof.InterceptingFilterDemo
Authenticating request: HOME
request log: HOME
Executing request: HOME