职责链模式

职责链模式

责任链（Chain of Responsibility）模式：为了避免请求发送者与多个请求处理者耦合在一起，于是将所有请求的处理者通过前一对象记住其下一个对象的引用而连成一条链；当有请求发生时，可将请求沿着这条链传递，直到有对象处理它为止。

案例

实习一个tomcat的过滤器链 A -> B -> C -> 目标方法 -> C -> B -> A

目标方法：

public class My {public void hello(){System.out.println("hello world");}
}

request和response：

public class HttpRequest {String msg;public HttpRequest(String msg) {this.msg = msg;}
}

public class HttpResponse {String content;public HttpResponse(String content) {this.content = content;}
}

过滤器：

public interface Filter {void doFilter(HttpRequest request,HttpResponse response,FilterChain chain);
}

public class HttpFilter implements Filter{@Overridepublic void doFilter(HttpRequest request, HttpResponse response, FilterChain chain) {System.out.println("HttpFilter正在执行");chain.doFilter(request,response,chain);System.out.println("HttpFilter已返回");}
}

public class CharacterFilter implements Filter{@Overridepublic void doFilter(HttpRequest request, HttpResponse response, FilterChain chain) {System.out.println("CharacterFilter 正在执行");chain.doFilter(request,response,chain);System.out.println("CharacterFilter 已返回");}
}

public class EncodingFilter implements Filter{@Overridepublic void doFilter(HttpRequest request, HttpResponse response, FilterChain chain) {System.out.println("EncodingFilter 正在执行");chain.doFilter(request,response,chain);System.out.println("EncodingFilter 已返回");}
}

过滤器链：

public class FilterChain implements Filter{private int cursor = 0;private List<Filter> filters = new ArrayList<>();private My target;public FilterChain(My target) {this.target = target;}public void addFilter(Filter filter){filters.add(filter);}@Overridepublic void doFilter(HttpRequest request, HttpResponse response, FilterChain chain) {if(cursor < filters.size()){Filter filter = filters.get(cursor);cursor++;filter.doFilter(request,response,chain);}else{target.hello();}}
}

测试：

public class Main {public static void main(String[] args) {My my = new My();FilterChain filterChain = new FilterChain(my);filterChain.addFilter(new HttpFilter());filterChain.addFilter(new CharacterFilter());filterChain.addFilter(new EncodingFilter());filterChain.doFilter(new HttpRequest("request"),new HttpResponse("response"),filterChain);}
}