网页设计 参考网站/国外域名购买

环境：Java8

Servlet中Filter使用的设计模式是责任链设计模式。我们可以定义一组Filter然后对数据进行依次的处理。责任链设计模式属于行为型模式。UML图如下：

Filter执行流程如下：

接下来我们来实现一个Filter

Filter.java接口

public interface Filter {void doFilter(Request request, Response response, FilterChain chain) ;}

FilterChain.java 关键的调用链

public class FilterChain implements Filter{private List<Filter> filters = new ArrayList<>() ;private int position = 0 ;public void doFilter(Request request, Response response, FilterChain chain) {if (position > filters.size() - 1) {return ;}Filter filter = filters.get(this.position++) ;filter.doFilter(request, response, this) ;}// 构建需要调用的Filter链public FilterChain addFilter(Filter filter) {this.filters.add(filter) ;return this ;}}

Filter相关子类

public class LoginFilter implements Filter {@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {System.out.println("LoginFilter entry...") ;chain.doFilter(request, response, chain) ;System.out.println("LoginFilter over...") ;}}

public class CharFilter implements Filter {@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {System.out.println("CharFilter entry...") ;chain.doFilter(request, response, chain) ;System.out.println("CharFilter over...") ;}}

public class GrantFilter implements Filter {@Overridepublic void doFilter(Request request, Response response, FilterChain chain) {System.out.println("GrantFilter entry...") ;chain.doFilter(request, response, chain) ;System.out.println("GrantFilter over...") ;}}

客户端

public static void main(String[] args) {LoginFilter loginFilter = new LoginFilter() ;CharFilter charFilter = new CharFilter() ;GrantFilter grantFilter = new GrantFilter() ;FilterChain chain = new FilterChain() ;chain.addFilter(loginFilter).addFilter(charFilter).addFilter(grantFilter) ;Request request = new Request() ;Response response = new Response() ;chain.doFilter(request, response, null) ;}

运行结果

按照添加Filter顺序，请求时先添加的先执行，返回时后添加的Filter先执行。java web中的Filter不也是这样么！！！

完毕！！！

关注+转发