j2ee学习笔记 Filter过滤器

2022-12-29 20:53:55

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="">

    <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 }

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