HttpURLConnection设置host请求头无效

问题与解决方案

由于业务需要在调用第三方SDK时需要设置host请求头为对方的域名，在测试时发现代码设置后依然无法生效。查找资料后发现是从JDK6的6u23版本开始就对HTTP的部分请求头做了限制，如下：

private static final String[] restrictedHeaders = {
    /* Restricted by XMLHttpRequest2 */
    //"Accept-Charset",
    //"Accept-Encoding",
    "Access-Control-Request-Headers",
    "Access-Control-Request-Method",
    "Connection", /* close is allowed */
    "Content-Length",
    //"Cookie",
    //"Cookie2",
    "Content-Transfer-Encoding",
    //"Date",
    "Expect",
    "Host",
    "Keep-Alive",
    "Origin",
    // "Referer", 
    // "TE",
    "Trailer",
    "Transfer-Encoding",
    "Upgrade",
    //"User-Agent",
    "Via"
    allowRestrictedHeaders = ((Boolean)java.security.AccessController.doPrivileged(
        new sun.security.action.GetBooleanAction(
            "sun.net.http.allowRestrictedHeaders"))).booleanValue();