httpclient 接收参数乱码

源：http://www.blogjava.net/thinkbase/archive/2006/10/31/HttpClientPOST_UTF8.html
评：
Apache HttpClient ( http://jakarta.apache.org/commons/httpclient/ ) 是一个纯 Java 的HTTP 协议的客户端编程工具包, 对 HTTP 协议的支持相当全面, 更多细节也可以参考IBM 网站上的这篇文章 HttpClient入门 ( http://www-128.ibm.com/developerworks/cn/opensource/os-httpclient/ ).

问题分析
不过在实际使用中, 还是发现按照最基本的方式调用 HttpClient 时, 并不支持 UTF-8 编码, 在网络上找过一些文章, 也不得要领, 于是查看了 commons-httpclient-3.0.1 的一些代码, 首先在 PostMethod 中找到了 generateRequestEntity() 方法:
    /**
     * Generates a request entity from the post parameters, if present.  Calls
     * {@link EntityEnclosingMethod#generateRequestBody()} if parameters have not been set.
     *
     * @since 3.0
     */
    protected RequestEntity generateRequestEntity() {
        if (!this.params.isEmpty()) {
            // Use a ByteArrayRequestEntity instead of a StringRequestEntity.
            // This is to avoid potential encoding issues.  Form url encoded strings
            // are ASCII by definition but the content type may not be.  Treating the content
            // as bytes allows us to keep the current charset without worrying about how
            // this charset will effect the encoding of the form url encoded string.
            String content = EncodingUtil.formUrlEncode(getParameters(), getRequestCharSet());
            ByteArrayRequestEntity entity = new ByteArrayRequestEntity(
                EncodingUtil.getAsciiBytes(content),
                FORM_URL_ENCODED_CONTENT_TYPE
            );
            return entity;
        } else {
            return super.generateRequestEntity();
        }
    }

原来使用 NameValuePair 加入的 HTTP 请求的参数最终都会转化为 RequestEntity 提交到 HTTP 服务器, 接着在 PostMethod 的父类 EntityEnclosingMethod 中找到了如下的代码:
    /**
     * Returns the request's charset.  The charset is parsed from the request entity's
     * content type, unless the content type header has been set manually.
     *
     * @see RequestEntity#getContentType()
     *
     * @since 3.0
     */
    public String getRequestCharSet() {
        if (getRequestHeader("Content-Type") == null) {
            // check the content type from request entity
            // We can't call getRequestEntity() since it will probably call
            // this method.
            if (this.requestEntity != null) {
                return getContentCharSet(
                    new Header("Content-Type", requestEntity.getContentType()));
            } else {
                return super.getRequestCharSet();
            }
        } else {
            return super.getRequestCharSet();
        }
    }


解决方案
从上面两段代码可以看出是 HttpClient 是如何依据 "Content-Type" 获得请求的编码(字符集), 而这个编码又是如何应用到提交内容的编码过程中去的. 按照这个原来, 其实我们只需要重载 getRequestCharSet() 方法, 返回我们需要的编码(字符集)名称, 就可以解决 UTF-8 或者其它非默认编码提交 POST 请求时的乱码问题了.

测试
首先在 Tomcat 的 ROOT WebApp 下部署一个页面 test.jsp, 作为测试页面, 主要代码片段如下:
<%@ page contentType="text/html;charset=UTF-8"%>
<%@ page session="false" %>
<%
request.setCharacterEncoding("UTF-8");
String val = request.getParameter("TEXT");
System.out.println(">>>> The result is " + val);
%>


接着写一个测试类, 主要代码如下:
    public static void main(String[] args) throws Exception, IOException {
        String url = "http://localhost:8080/test.jsp";
        PostMethod postMethod = new UTF8PostMethod(url);
        //填入各个表单域的值
        NameValuePair[] data = {
                new NameValuePair("TEXT", "中文"),
        };
        //将表单的值放入postMethod中
        postMethod.setRequestBody(data);
        //执行postMethod
        HttpClient httpClient = new HttpClient();
        httpClient.executeMethod(postMethod);
    }
   
    //Inner class for UTF-8 support
    public static class UTF8PostMethod extends PostMethod{
        public UTF8PostMethod(String url){
            super(url);
        }
        @Override
        public String getRequestCharSet() {
            //return super.getRequestCharSet();
            return "UTF-8";
        }
    }


运行这个测试程序, 在 Tomcat 的后台输出中可以正确打印出 ">>>> The result is 中文" .

代码下载
本文所提到的所有代码, 以及测试程序(可直接导入 eclipse)提供打包下载: att:HttpClient POST 的 UTF-8 编码问题.httpClientUTF8.tar.bz2

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