Java HTTPclient中没有SSLContext的Handshake_failure

Question

我感到自己遇到了一个奇怪的问题，我编写了一个没有SSLContext的核心java http客户端，当我运行该程序以调用REST服务时，它因以下异常而开始失败。但是，当我将SSLContext添加到客户端时，它通过并且看到响应。

Initial Code without SSLContext :
String url = "https://URL";
    URL obj = new URL(url);
    HttpsURLConnection con = (HttpsURLConnection) obj.openConnection();     
    con.setRequestMethod("POST");           
    con.setRequestProperty("CONTENT-TYPE", "application/json"); 
    String request = "{ json Request }";    
    con.setDoOutput(true);
    DataOutputStream wr = new DataOutputStream(con.getOutputStream());
    wr.write(request.getBytes());
    wr.flush();
    wr.close();
    int responseCode = con.getResponseCode();
    System.out.println("Response Code : " + responseCode);

例外：         javax.net.ssl.SSLHandshakeException：收到致命警报：handshake_failure

During SSL debugging it is found that client server sends TSLv1.2 during ClientHello, however i dont see a ServerHello in return.
But when the below SSL code error disappeared

SSLContext sc = SSLContext.getInstance("TLSv1.2"); 
        sc.init(null, null, new java.security.SecureRandom());
        con.setSSLSocketFactory(sc.getSocketFactory());

帮助我了解如果未设置SSLContext以及添加SSLContext时的行为会发生什么情况。