作用：过滤response和request对象的内容
使用：
Filter是J2EE的一个接口，自定义Filter需要实现该接口，并重写所有的方法.
Filter提供的方法：
init()
doFilter()
destory()
在web.xml中的配置：
* 实现步骤:
* 创建Java类,实现Filter接口,并且重写所有方法.
* 在web.xml文件中进行配置.
<filter>
<filter-name>MyFilter1</filter-name>
<filter-class>filter.MyFilter1</filter-class>
</filter>
<filter-mapping>
<filter-name>MyFilter1</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
案例：使用filter解决中文乱码：
Myfilter.java
package filter; 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.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; //解决全站中文乱码 public class Myfilter1 implements Filter{ @Override public void destroy() { } @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { //进行Request和Response对象的类型强转 HttpServletRequest request = (HttpServletRequest)req; HttpServletResponse response = (HttpServletResponse)res; //解决中文乱码问题1.请求的中文乱码Get 和 Post 2.响应中文乱码 request.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=utf-8"); //3.创建自定义的Request //4.放行 chain.doFilter(request, response); } @Override public void init(FilterConfig arg0) throws ServletException { } }
ServletTest.java
package filter; import java.io.IOException; import java.io.PrintWriter; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class ServletTest extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //获取表单信息 String username = request.getParameter("username"); String password = request.getParameter("password"); System.out.println(username + "--" + password); response.getWriter().println("中文doPost正常"); } }
web.xml配置文件
<filter>
<filter-name>Myfilter1</filter-name>
<filter-class>filter.Myfilter1</filter-class>
</filter>
<filter-mapping>
<filter-name>Myfilter1</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
index.jsp
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <base href="<%=basePath%>"> <title>My JSP 'index.jsp' starting page</title> <meta http-equiv="pragma" content="no-cache"> <meta http-equiv="cache-control" content="no-cache"> <meta http-equiv="expires" content="0"> <meta http-equiv="keywords" content="keyword1,keyword2,keyword3"> <meta http-equiv="description" content="This is my page"> </head> <body> //表单 <form action="servlet/ServletTest" method="post"> 用户名：<input type="text" name="username"><br> 密码：<input type="password" name="password"><br> <input type="submit" value="提交"> </form> </body> </html>
此处action的路径有三种写法：
1.相对路径："servlet/ServletTest"
2.绝对路径："/Filter/servlet/ServletTest"
3.获取路径：${pageContext.request.contextPath }