SPRING与设计模式---责任链模式

系统管理员 2022-04-14 02:12 652阅读 0赞

# SPRING与设计模式---责任链模式 #

2018年02月24日 16:17:20 [json20080301][] 阅读数：822更多

个人分类： [架构][Link 1][设计模式][Link 2]

所属专栏： [SpringSecurity4源码解读][SpringSecurity4]

SPRING与设计模式---责任链模式

使用场景：当你想让一个以上的对象有机会能够处理某个请求的时候，就使用责任链模式。

spring框架中的应用：

spring安全框架security使用责任链模式，框架使用者可以动态地添加删除责任（处理request请求）。

UML类图：

![20180224201327531][]

活动图：

![20180304193709908][]

源码解析：currentPosition表示责任链的要处理请求链条节点的位置，使用additionalFilters来依次处理request请求。additionalFilters中的每个Filter成员都承担某一项具体职责，并且每个Filter都会被执行到。 责任链条的成员执行完自己的职责后，会回调链条的处理请求方法，责任链条会找到下一个链条成员来执行职责，直到链条尾端。

1.  `private static class VirtualFilterChain implements FilterChain {`
2.  `private final FilterChain originalChain; //链条中的节点全部执行完后，处理request请求的对象`
3.  `private final List<Filter> additionalFilters; //请求实际执行者，`
4.  `private final FirewalledRequest firewalledRequest;`
5.  `private final int size;`
6.  `private int currentPosition = 0; //链条移动的位置，当currentPosition==size,到达链条的尾端。`
7.  `private VirtualFilterChain(FirewalledRequest firewalledRequest,`
8.  `FilterChain chain, List<Filter> additionalFilters) {`
9.  `this.originalChain = chain;`
10. `this.additionalFilters = additionalFilters;`
11. `this.size = additionalFilters.size();`
12. `this.firewalledRequest = firewalledRequest;`
13. `}`
14.  
15. `public void doFilter(ServletRequest request, ServletResponse response)`
16. `throws IOException, ServletException {`
17. `if (currentPosition == size) { //到达链条尾端`
18. `if (logger.isDebugEnabled()) {`
19. `logger.debug(UrlUtils.buildRequestUrl(firewalledRequest)`
20. `+ " reached end of additional filter chain; proceeding with original chain");`
21. `}`
22.  
23. `// Deactivate path stripping as we exit the security filter chain`
24. `this.firewalledRequest.reset();`
25.  
26. `originalChain.doFilter(request, response);`
27. `}`
28. `else {`
29. `currentPosition++; //依次移动链条指针到具体节点`
30.  
31. `Filter nextFilter = additionalFilters.get(currentPosition - 1);`
32.  
33. `if (logger.isDebugEnabled()) {`
34. `logger.debug(UrlUtils.buildRequestUrl(firewalledRequest)`
35. `+ " at position " + currentPosition + " of " + size`
36. `+ " in additional filter chain; firing Filter: '"`
37. `+ nextFilter.getClass().getSimpleName() + "'");`
38. `}`
39.  
40. `nextFilter.doFilter(request, response, this);//将链条本身的对象传递给链条成员`
41. `}`
42. `}`
43. `}`

链条成员Filter会执行chain.doFilter(request, response )方法，而chain是链条本身的引用，这样成员就将请求又重新交给了链条。看SecurityContextHolderAwareRequestFilter源码：

public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain)
          throws IOException, ServletException {
       chain.doFilter(this.requestFactory.create((HttpServletRequest) req,
             (HttpServletResponse) res), res);
    }

[json20080301]: https://me.csdn.net/json20080301
[Link 1]: https://blog.csdn.net/json20080301/article/category/6799557
[Link 2]: https://blog.csdn.net/json20080301/article/category/7464684
[SpringSecurity4]: https://blog.csdn.net/column/details/19809.html
[20180224201327531]: /images/20220414/9eb721495e8d405db1db96d239155f64.png
[20180304193709908]: /images/20220414/bf2ee98bf45748608399d31269653d7b.png