关于httpclient定制对象RequestEntity和RequestBody引发的问题

在处理自动提交表单的业务中往往要用到httpclient的poseMethod提交数据，httpclient3.1采用RequestEntity接口替代以前的RequestBody。
RequestEntity ：

HttpClient client = new HttpClient();
PostMethod post = new PostMethod(redirectUrl);
		Part[] parts = {
				new StringPart("user", “aaa”),
				new StringPart("password", "bbb")
				};
		post.setRequestEntity(new MultipartRequestEntity(parts, post.getParams()));
client.executeMethod(post);
String result = post.getResponseBodyAsString();

RequestBody:

HttpClient client = new HttpClient();
PostMethod post = new PostMethod(redirectUrl);
		NameValuePair[] pairs = {
			new NameValuePair("user", “aaa”),
                        new NameValuePair("password", “bbb”)
                        };
		post.setRequestBody(pairs);
client.executeMethod(post);
String result = post.getResponseBodyAsString();

在某些网站用RequestEntity方式请求有会失败，改成RequestBody就可以,可能就是这个原因。