http Request-Line

以下代码通过jdk自带的HttpURLConnection获取百度对关键字"angry brids"的搜索结果。

        URL baiduSearch = new URL("http://www.baidu.com/s?wd=angry birds");
        HttpURLConnection connection = (HttpURLConnection) baiduSearch.openConnection();
        connection.setRequestMethod("POST");
        connection.setDoInput(true);
        ... ...
        connection.setRequestProperty("Host", "www.baidu.com");
        connection.getOutputStream().flush();
        InputStream inputStream = connection.getInputStream();

但是用wireshark抓包发现http请求的参数不符合预期。
请求行(Request-Line)是POST /s?wd=angry bird HTTP/1.1，按照RFC2616的定义
   Request-Line = Method SP Request-URI SP HTTP-Version CRLF
预期的结果是

Method	Request-URI	HTTP-Version
POST	/s?wd=angry bird	HTTP/1.1

而实际由于查询参数"angry birds"中的空格，请求是

Method	Request-URI	HTTP-Version
POST	/s?wd=angry	bird HTTP/1.1

见下图红框内容

因此需要在构造url的时候对path "s?wd=angry birds"部分做编码，可以使用jdk的java.net.URLEncoder。