1.说明：对过滤器的理解我们不要从请求作为起点，而是项目本身的资源作为过滤的起点，然后根据其要过滤的项目资源（url），在根据他的模式，就可以知道它要过滤的是啥资源了，然后看它的方法，就可以知道它过滤是处理些什么逻辑，当然，最后还需要把该请求传下去，如果是后面还有过滤器就继续过滤，如果没有，就到了servlet或者jsp了，而过滤的顺序与其注册的顺序是一致的。
2.创建一个过滤器
a.步骤：
1）建一个过滤器，根据需求写好逻辑方法
2）进行注册（xml或者直接注释进行注册）
b.代码
package com.guolvqi;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.annotation.WebFilter;/** * Servlet Filter implementation class fristFilter */ //代表过滤映射为/downloadServlet的项目资源@WebFilter("/downloadServlet")public class fristFilter implements Filter { /** * @see Filter#destroy() */ public void destroy() { // TODO Auto-generated method stub } /** * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain) */ public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { System.out.println("过滤器实施了"); chain.doFilter(request, response); } /** * @see Filter#init(FilterConfig) */ public void init(FilterConfig fConfig) throws ServletException { // TODO Auto-generated method stub }}
3.Filter的生命周期
4.过滤器的api
5.过滤器的配置
5.案例：使用Filter进行字符编码转换
1）servlet
package com.anli;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.annotation.WebFilter;import javax.servlet.annotation.WebServlet;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;/** * Servlet implementation class TestFilter */@WebServlet("/TestFilter")public class TestFilter extends HttpServlet { private static final long serialVersionUID = 1L; /** * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) */ protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub response.getWriter().append("其内容为通过了过滤器设置编码才能正常显示的"); } /** * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) */ protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { // TODO Auto-generated method stub doGet(request, response); }} 2）Filter
package com.guolvqi;import java.io.IOException;import javax.servlet.Filter;import javax.servlet.FilterChain;import javax.servlet.FilterConfig;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.annotation.WebFilter;import javax.servlet.annotation.WebInitParam;/** * Servlet Filter implementation class fristFilter */@WebFilter(urlPatterns= {"/*"}, initParams= { @WebInitParam(name="encoding",value="utf-8"),@WebInitParam(name="encoding1",value="utf-8")})public class fristFilter implements Filter { String enconding; /** * @see Filter#destroy() */ public void destroy() { enconding=null; } /** * @see Filter#doFilter(ServletRequest, ServletResponse, FilterChain) */ public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { if(enconding!=null) { //这边的设置既可以是输入的时候输入中文，也可以是输出的时候是中文 request.setCharacterEncoding(enconding); response.setCharacterEncoding(enconding); } chain.doFilter(request, response); } /** * @see Filter#init(FilterConfig) */ public void init(FilterConfig fConfig) throws ServletException { enconding=fConfig.getInitParameter("encoding"); }} 3）测试：
