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前段时间遇到一个问题，在spring mvc 服务端接收post请求时，通过html 表单提交的时候，服务端能够接收到参数的值。但是使用httpclient4.3构造post请求，却无法接收到参数的值。
spring 代码：
@RequestMapping(value = "login.do", method = RequestMethod.POST)
@ResponseBody
public String login(String username, String password) throws Exception {
return username + ":" + password;
}表单代码：
name: httpclient4.3发送post代码：
@Test
public void testMultipartPost() throws IOException {
HttpPost httpPost = new HttpPost("http://localhost:8080/test/login.do");
try {
HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();
CloseableHttpClient httpClient = httpClientBuilder.build();
RequestConfig config = RequestConfig.custom().setConnectTimeout(200000).setSocketTimeout(200000).build();
httpPost.setConfig(config);
MultipartEntityBuilder multipartEntityBuilder = MultipartEntityBuilder.create();
multipartEntityBuilder.setCharset(Charset.forName("UTF-8"));
multipartEntityBuilder.addTextBody("username", "taozi");
multipartEntityBuilder.addTextBody("password", "123");
HttpEntity httpEntity = multipartEntityBuilder.build();
httpPost.setEntity(httpEntity);
HttpResponse response = httpClient.execute(httpPost);
System.out.println(EntityUtils.toString(response.getEntity()));
} finally {
httpPost.releaseConnection();
}
}一直在查找原因，为什么通过httpclient4.3构造的post请求，服务端无法接收到传输的参数。比较与html的差异，发现httpclient构造的请求使用的是multipart形式。而表单上传使用的是默认形式的编码，x-www-form-urlencoded，所以表单能够成功。现在找到问题了，将httpclient的构造代码，改为x-www-form-urlencoded编码上传，
@Test
public void testUrlencodedPost() throws IOException {
HttpPost httpPost = new HttpPost("http://localhost:8080/test/login.do");
try {
CloseableHttpClient client = HttpClients.createDefault();
List params = new ArrayList();
params.add(new BasicNameValuePair("username", "taozi"));
params.add(new BasicNameValuePair("password", "123"));
HttpEntity httpEntity = new UrlEncodedFormEntity(params, "UTF-8");
httpPost.setEntity(httpEntity);
CloseableHttpResponse response = client.execute(httpPost);
System.out.println(EntityUtils.toString(response.getEntity()));
} finally {
httpPost.releaseConnection();
}
} 现在服务端能够正常的接收到请求了，现在总结一下表单两种编码的形式
application/x-www-form-urlencoded 空格转换为 "+" 加号，特殊符号转换为 ASCII HEX 值
multipart/form-data 不对字符进行编码，使用二进制数据传输，一般用于上传文件，非文本的数据传输。
spring mvc如果要接收 multipart/form-data 传输的数据，应该在spring上下文配置
这样服务端就既可以接收multipart/form-data 传输的数据，也可以接收application/x-www-form-urlencoded传输的文本数据了。