Servlet(2)：Requset/Response Encoding and Filter

Requset/Response Encoding

表单提交分GET和POST，接下来分开讨论。

（1）GET/URL提交的数据

在 Tomcat中，默认情况下使用"URIEncoding"的值（tomcat8.0后是UTF-8，之前是ISO-8859-1）对URL提交的数据和表单中GET方式提交的数据进行解码。由于浏览器已经进行了一次编码（UTF-8），所以后台什么都不需要做。

     @Override

     protected void doGet(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

         // 不需要设置 request.setCharacterEncoding()

         // request.setCharacterEncoding("UTF-8");

         // 设置response的Character

         response.setContentType("text/html");

         response.setCharacterEncoding("UTF-8");

         // 也可以直接写成

         // response.setContentType("text/html;charset=UTF-8");

     }

URIEncoding 是对所有 GET 方式的请求的数据进行统一的重新编码（解码），而 useBodyEncodingForURI 则是根据响应该请求的页面的request.setCharacterEncoding 参数对数据进行的重新编码（解码），不同的页面可以有不同的重新编码（解码）的编码。

所以，如果要修改编码格式，可以使用下面两个方法：

<Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" URIEncoding="GBK" />

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

或

<Connector port="8080" protocol="HTTP/1.1" connectionTimeout="20000" redirectPort="8443" useBodyEncodingForURI="true" />

request.setCharacterEncoding("GBK");

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

（2）POST提交的数据

由于"URIEncoding"只对GET方式有效，所以POST时必须设置request.setCharacterEncoding

request.setCharacterEncoding("UTF-8");

response.setContentType("text/html;charset=UTF-8");

（3）综合以上讨论，如果使用Tomcat8以上，UTF-8编码的项目，则不需要修改server.xml，再在每个servlet中加上下面代码即可。

request.setCharacterEncoding("UTF-8");

response.setCharacterEncoding("UTF-8");

（4）[Add] HttpServletRequest的常用方法

getRequestURL：返回客户端发出请求时的完整URL
getRequestURI：返回请求行中的资源名部分
getQueryString：返回请求行中的参数部分
getPathInfo：返回请求URL中的额外路径信息。额外路径信息是请求URL中的位于Servlet的路径之后和查询参数之前的内容，它以“/”开头
getRemoteAddr：返回发出请求的客户机的IP地址。
getRemoteHost：返回发出请求的客户机的完整主机名
getRemotePort：返回客户机所使用的网络端口号
getLocalAddr：返回WEB服务器的IP地址
getLocalName：方法返回WEB服务器的主机名

Filter

Filter也称之为过滤器，它是Servlet技术中最实用的技术，Web开发人员通过Filter技术，对web服务器管理的所有web资源：例如Jsp, Servlet, 静态图片文件或静态 html 文件等进行拦截，从而实现一些特殊的功能。例如实现URL级别的权限访问控制、过滤敏感词汇、压缩响应信息等一些高级功能。

它主要用于对用户请求进行预处理，也可以对HttpServletResponse进行后处理。使用Filter的完整流程：Filter对用户请求进行预处理，接着将请求交给Servlet进行处理并生成响应，最后Filter再对服务器响应进行后处理。

上面的如果每个Servlet中都添加Encode的代码会非常麻烦，可以用Filter解决。以下是代码。

 package com.mytest.servlettest.servlet;

 import java.io.IOException;

 import java.io.PrintWriter;

 import javax.servlet.ServletException;

 import javax.servlet.annotation.WebServlet;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 /**

  * Servlet implementation class Login

  */

 @WebServlet("/login")

 public class Login extends HttpServlet {

     private static final long serialVersionUID = 1L;

     /**

      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

      */

     @Override

     protected void doGet(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

         response.setContentType("text/html");

         PrintWriter out = response.getWriter();

         out.println("<!DOCTYPE html>");

         out.println("<html>");

         out.println("<head>");

         out.println("<title>Login Page</title>");

         out.println("</head>");

         out.println("<body>");

         out.println("<form action=\"welcome\" method=\"POST\">");

         out.println("帐号: <input type=\"text\" name=\"userId\"/><br/>");

         out.println("密码: <input type=\"password\" name=\"password\"/><br/>");

         out.println("<input type=\"submit\" value=\"提交\"/>");

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

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

         System.out.println("[login]" + request.getCharacterEncoding());

         System.out.println("[login]" + response.getCharacterEncoding());

     }

     /**

      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

      */

     @Override

     protected void doPost(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

         doGet(request, response);

     }

 }

 package com.mytest.servlettest.servlet;

 import java.io.IOException;

 import java.io.PrintWriter;

 import javax.servlet.ServletException;

 import javax.servlet.annotation.WebServlet;

 import javax.servlet.http.HttpServlet;

 import javax.servlet.http.HttpServletRequest;

 import javax.servlet.http.HttpServletResponse;

 /**

  * Servlet implementation class Welcome

  */

 @WebServlet("/welcome")

 public class Welcome extends HttpServlet {

     private static final long serialVersionUID = 1L;

     /**

      * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

      */

     @Override

     protected void doGet(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

         response.setContentType("text/html");

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

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

         PrintWriter out = response.getWriter();

         out.println("<!DOCTYPE html>");

         out.println("<html>");

         out.println("<head>");

         out.println("<title>Login Page</title>");

         out.println("</head>");

         out.println("<body>");

         if ("123".equals(password)) {

             out.println("欢迎您, " + userId);

         } else {

             out.println("您的帐号或密码错误!");

         }

         out.println("<a href = \"login\">返回</a>");

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

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

         System.out.println("[welcome]" + request.getCharacterEncoding());

         System.out.println("[welcome]" + response.getCharacterEncoding());

     }

     /**

      * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

      */

     @Override

     protected void doPost(HttpServletRequest request, HttpServletResponse response)

             throws ServletException, IOException {

         doGet(request, response);

     }

 }

 package com.mytest.servlettest.filter;

 import javax.servlet.*;

 import java.io.IOException;

 /**

  * Created by Administrator on 2017/9/4.

  */

 public class CharacterEncodingFilter implements Filter {

     private String encoding;

     public void setEncoding(String encoding) {

         this.encoding = encoding;

     }

     @Override

     public void init(FilterConfig filterConfig) throws ServletException {

         encoding = filterConfig.getInitParameter("encoding");

         if (encoding == null || encoding == "") {

             encoding = "UTF-8";

         }

     }

     @Override

     public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {

         servletRequest.setCharacterEncoding(encoding);

         servletResponse.setCharacterEncoding(encoding);

         filterChain.doFilter(servletRequest, servletResponse);

     }

     @Override

     public void destroy() {

     }

 }

 <?xml version="1.0" encoding="UTF-8"?>

 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

          xmlns="http://xmlns.jcp.org/xml/ns/javaee"

          xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"

          id="WebApp_ID" version="3.1">

     <filter>

         <filter-name>characterEncodingFilter</filter-name>

         <filter-class>com.mytest.servlettest.filter.CharacterEncodingFilter</filter-class>

         <init-param>

             <param-name>encoding</param-name>

             <param-value>UTF-8</param-value>

         </init-param>

     </filter>

     <filter-mapping>

         <filter-name>characterEncodingFilter</filter-name>

         <url-pattern>/*</url-pattern>

     </filter-mapping>

     <welcome-file-list>

         <welcome-file>login</welcome-file>

     </welcome-file-list>

 </web-app>

推荐使用Spring的CharacterEncodingFilter

 <filter>

     <filter-name>characterEncodingFilter</filter-name>

     <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>

     <init-param>

         <param-name>encoding</param-name>

         <param-value>UTF-8</param-value>

     </init-param>

     <init-param>

         <param-name>forceEncoding</param-name>

         <param-value>true</param-value>

     </init-param>

 </filter>

 <filter-mapping>

     <filter-name>characterEncodingFilter</filter-name>

     <url-pattern>/*</url-pattern>

 </filter-mapping>

CharacterEncodingFilter

巴特西

Servlet(2)：Requset/Response Encoding and Filter

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