Servlet：Requset/Response Encoding and Filter
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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。
1 @Override 2 protected void doGet(HttpServletRequest request, HttpServletResponse response) 3 throws ServletException, IOException { 4 5 // 不需要设置 request.setCharacterEncoding() 6 // request.setCharacterEncoding("UTF-8"); 7 // 设置response的Character 8 response.setContentType("text/html"); 9 response.setCharacterEncoding("UTF-8"); 10 // 也可以直接写成 11 // response.setContentType("text/html;charset=UTF-8"); 12 }
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");
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。
1 package com.mytest.servlettest.servlet; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 6 import javax.servlet.ServletException; 7 import javax.servlet.annotation.WebServlet; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 12 /** 13 * Servlet implementation class Login 14 */ 15 @WebServlet("/login") 16 public class Login extends HttpServlet { 17 18 private static final long serialVersionUID = 1L; 19 20 /** 21 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 22 */ 23 @Override 24 protected void doGet(HttpServletRequest request, HttpServletResponse response) 25 throws ServletException, IOException { 26 27 response.setContentType("text/html"); 28 29 PrintWriter out = response.getWriter(); 30 out.println("<!DOCTYPE html>"); 31 out.println("<html>"); 32 out.println("<head>"); 33 out.println("<title>Login Page</title>"); 34 out.println("</head>"); 35 out.println("<body>"); 36 out.println("<form action=\"welcome\" method=\"POST\">"); 37 out.println("帐号: <input type=\"text\" name=\"userId\"/><br/>"); 38 out.println("密码: <input type=\"password\" name=\"password\"/><br/>"); 39 out.println("<input type=\"submit\" value=\"提交\"/>"); 40 out.println("</body>"); 41 out.println("</html>"); 42 43 System.out.println("[login]" + request.getCharacterEncoding()); 44 System.out.println("[login]" + response.getCharacterEncoding()); 45 } 46 47 /** 48 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 49 */ 50 @Override 51 protected void doPost(HttpServletRequest request, HttpServletResponse response) 52 throws ServletException, IOException { 53 doGet(request, response); 54 } 55 }
1 package com.mytest.servlettest.servlet; 2 3 import java.io.IOException; 4 import java.io.PrintWriter; 5 6 import javax.servlet.ServletException; 7 import javax.servlet.annotation.WebServlet; 8 import javax.servlet.http.HttpServlet; 9 import javax.servlet.http.HttpServletRequest; 10 import javax.servlet.http.HttpServletResponse; 11 12 /** 13 * Servlet implementation class Welcome 14 */ 15 @WebServlet("/welcome") 16 public class Welcome extends HttpServlet { 17 18 private static final long serialVersionUID = 1L; 19 20 /** 21 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response) 22 */ 23 @Override 24 protected void doGet(HttpServletRequest request, HttpServletResponse response) 25 throws ServletException, IOException { 26 27 response.setContentType("text/html"); 28 29 String userId = request.getParameter("userId"); 30 String password = request.getParameter("password"); 31 32 PrintWriter out = response.getWriter(); 33 out.println("<!DOCTYPE html>"); 34 out.println("<html>"); 35 out.println("<head>"); 36 out.println("<title>Login Page</title>"); 37 out.println("</head>"); 38 out.println("<body>"); 39 if ("123".equals(password)) { 40 out.println("欢迎您, " + userId); 41 } else { 42 out.println("您的帐号或密码错误!"); 43 } 44 out.println("<a href = \"login\">返回</a>"); 45 out.println("</body>"); 46 out.println("</html>"); 47 48 System.out.println("[welcome]" + request.getCharacterEncoding()); 49 System.out.println("[welcome]" + response.getCharacterEncoding()); 50 } 51 52 /** 53 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response) 54 */ 55 @Override 56 protected void doPost(HttpServletRequest request, HttpServletResponse response) 57 throws ServletException, IOException { 58 doGet(request, response); 59 } 60 }
1 package com.mytest.servlettest.filter; 2 3 import javax.servlet.*; 4 import java.io.IOException; 5 6 /** 7 * Created by Administrator on 2017/9/4. 8 */ 9 public class CharacterEncodingFilter implements Filter { 10 11 private String encoding; 12 13 public void setEncoding(String encoding) { 14 this.encoding = encoding; 15 } 16 17 @Override 18 public void init(FilterConfig filterConfig) throws ServletException { 19 encoding = filterConfig.getInitParameter("encoding"); 20 if (encoding == null || encoding == "") { 21 encoding = "UTF-8"; 22 } 23 } 24 25 @Override 26 public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException { 27 servletRequest.setCharacterEncoding(encoding); 28 servletResponse.setCharacterEncoding(encoding); 29 filterChain.doFilter(servletRequest, servletResponse); 30 } 31 32 @Override 33 public void destroy() { 34 } 35 }
1 <?xml version="1.0" encoding="UTF-8"?> 2 <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 3 xmlns="http://xmlns.jcp.org/xml/ns/javaee" 4 xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" 5 id="WebApp_ID" version="3.1"> 6 <filter> 7 <filter-name>characterEncodingFilter</filter-name> 8 <filter-class>com.mytest.servlettest.filter.CharacterEncodingFilter</filter-class> 9 <init-param> 10 <param-name>encoding</param-name> 11 <param-value>UTF-8</param-value> 12 </init-param> 13 </filter> 14 <filter-mapping> 15 <filter-name>characterEncodingFilter</filter-name> 16 <url-pattern>/*</url-pattern> 17 </filter-mapping> 18 <welcome-file-list> 19 <welcome-file>login</welcome-file> 20 </welcome-file-list> 21 </web-app>
推荐使用Spring的CharacterEncodingFilter
1 <filter> 2 <filter-name>characterEncodingFilter</filter-name> 3 <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class> 4 <init-param> 5 <param-name>encoding</param-name> 6 <param-value>UTF-8</param-value> 7 </init-param> 8 <init-param> 9 <param-name>forceEncoding</param-name> 10 <param-value>true</param-value> 11 </init-param> 12 </filter> 13 <filter-mapping> 14 <filter-name>characterEncodingFilter</filter-name> 15 <url-pattern>/*</url-pattern> 16 </filter-mapping>
CharacterEncodingFilter
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