Servlet过滤器

一、实验目的：

1. 了解过滤器的作用；

2. 掌握过滤器的开发与部署的步骤；

3. 了解过滤器链。

二、实验环境：

MyEclipse10+Tomcat 7.0+Java EE 6.0

三、实验内容：

编写一个过滤器改变请求编码

【步骤 1】编写一个 loginform.html 文件，代码如下：

<!DOCTYPE html>

<html>

  <head>

    <title>使用过滤器改变请求编码</title>

    <meta http-equiv="Content-Type" content="text/html;charset=GB2312">

  </head>



  <body>

     <div align="center">

            <h2>请输入用户名和口令</h2>

            <form action="servlet/CheckParamServlet" method="post">

             <table>

               <tr>

                 <td>用户名:</td>

                 <td><input type="text" name="name" ></td>

               </tr>

               <tr>

                 <td>口令:</td>

                 <td><input type="password" name="pass"></td>

               </tr>

               <tr>

                 <td></td>

                 <td>

                 <input type="submit" name="ok" value="提交">

                 <input name="cancel" type="reset" value="重置">

                 </td>

               </tr>

             </table>

          </form>

     </div>

  </body>

</html>

【步骤 2】编写处理请求参数的 Servlet，新建CheckParamServlet.java文件，包名为servlet，代码如下：

//CheckParamServlet.java

package servlet;



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 CheckParamServlet extends HttpServlet {



       /**

        * Constructor of the object.

        */

       public CheckParamServlet() {

              super();

       }



       /**

        * Destruction of the servlet. <br>

        */

       public void destroy() {

              super.destroy(); // Just puts "destroy" string in log

              // Put your code here

       }



       /**

        * The doGet method of the servlet. <br>

        *

        * This method is called when a form has its tag value method equals to get.

        *

        * @param request the request send by the client to the server

        * @param response the response send by the server to the client

        * @throws ServletException if an error occurred

        * @throws IOException if an error occurred

        */

       public void doGet(HttpServletRequest request, HttpServletResponse response)

                     throws ServletException, IOException {



              String name=request.getParameter("name");

              String pass=request.getParameter("pass");

              response.setContentType("text/html;charset=gb2312");

              PrintWriter out=response.getWriter();

              out.println("<html><head><title>Param Test</title></head>");

              out.println("<h3 align=center>你的用户名为："+name+"</h3>");

              out.println("<h3 align=center>您的口令为："+pass+"</h3>");

              out.println("</body></html>");

       }



       /**

        * The doPost method of the servlet. <br>

        *

        * This method is called when a form has its tag value method equals to post.

        *

        * @param request the request send by the client to the server

        * @param response the response send by the server to the client

        * @throws ServletException if an error occurred

        * @throws IOException if an error occurred

        */

       public void doPost(HttpServletRequest request, HttpServletResponse response)

                     throws ServletException, IOException {



              doGet(request, response);

       }



       /**

        * Initialization of the servlet. <br>

        *

        * @throws ServletException if an error occurs

        */

       public void init() throws ServletException {

              // Put your code here

       }



}

下面通过编写一个过滤器改变请求编码。

【步骤 3】新建EnCodingFilter.java文件，包名为filter，过滤器代码如下：

//EnCodingFilter.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;



public class EnCodingFilter implements Filter {

       protected String encoding=null;

       protected FilterConfig config;

       public void init(FilterConfig filterConfig) throws ServletException {

              this.config = filterConfig;

              //得到在web.xml中配置的编码

              this.encoding = filterConfig.getInitParameter("Encoding");

       }

       public void doFilter (ServletRequest request,ServletResponse response,FilterChain chain)

              throws IOException,ServletException {

              if(request.getCharacterEncoding()==null) {

                     //得到指定的编码

                     String encode=getEncoding();

                     if(encode!=null) {

                            //设置request的编码

                            request.setCharacterEncoding(encode);

                            response.setCharacterEncoding(encode);

                     }

              }

              chain.doFilter(request, response);

       }

       protected String getEncoding() {

              return encoding;

       }

       public void destroy() {

       }

}

【步骤 4】修改 web.xml 文件，加入下面代码：

<servlet>

    <servlet-name>CheckParamServlet</servlet-name>

    <servlet-class>servlet.CheckParamServlet</servlet-class>

  </servlet>

<filter>

     <filter-name>EnCodingFilter</filter-name>

     <filter-class>filter.EnCodingFilter</filter-class>

     <init-param>

            <param-name>Encoding</param-name>

            <param-value>gb2312</param-value>

     </init-param>

  </filter>

<servlet-mapping>

    <servlet-name>CheckParamServlet</servlet-name>

    <url-pattern>/servlet/CheckParamServlet</url-pattern>

  </servlet-mapping>

<filter-mapping>

     <filter-name>EnCodingFilter</filter-name>

     <url-pattern>/*</url-pattern>

  </filter-mapping>

运行结果：