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详解Servlet之Filter实现原理
发布时间：2025-11-04 14:19:12 来源：码上建站 作者：IT科技
环境：Java8
Servlet中Filter使用的详解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实现处理。责任链设计模式属于行为型模式。服务器租用原理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,详解 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 { @Override public 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 { @Override public 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 { @Override public 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，请求时先添加的实现先执行，高防服务器返回时后添加的原理Filter先执行。java web中的详解Filter不也是这样么!!!
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