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
