getCharacterEncoding与编码过滤器

本文探讨了在Java Web应用中request.getCharacterEncoding()总是返回null的原因,并通过配置自定义过滤器来设置请求编码为UTF-8,从而解决了这一常见问题。

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request.getCharacterEncoding() always returns null

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>Insert title here</title>
</head>
<body>
<%
out.println("Current request encoded with: " +request.getCharacterEncoding());
out.println("Current response encoded with: " +response.getCharacterEncoding());
%>
</body>
</html>
以上程序在页面输出2个utf-8

package yangxian;

import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class AServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
   
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        System.out.println(request.getCharacterEncoding());
    }

}

<body>
   <form action="/b3log130614/zhuhuan" method="post">
    <input type="text" name="name"> 
    <input type="submit">
</form>
</body>

以上程序输出utf-8,但这是因为

<filter>
    <filter-name>EncodingFilter</filter-name>
    <filter-class>org.b3log.latke.servlet.filter.EncodingFilter</filter-class>
    <init-param>
      <param-name>requestEncoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name>responseEncoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>EncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
一下程序选自国内开源项目b3log

package org.b3log.latke.servlet.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 final class EncodingFilter implements Filter {


    private String requestEncoding = "UTF-8";

    private String responseEncoding = "UTF-8";

    @Override
    public void init(final FilterConfig filterConfig) throws ServletException {
        requestEncoding = filterConfig.getInitParameter("requestEncoding");
        responseEncoding = filterConfig.getInitParameter("responseEncoding");
    }

    @Override
    public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain)
        throws IOException, ServletException {
        request.setCharacterEncoding(requestEncoding);
        response.setCharacterEncoding(responseEncoding);
        
        chain.doFilter(request, response);
    }

    @Override
    public void destroy() {}
}

如果在web.xml里面把这个过滤器注释掉,则输出null

源代码:http://pan.baidu.com/share/link?shareid=2215279416&uk=3878681452


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