从HttpUrlConnection对象获取头 [英] Get header from HttpUrlConnection object

问题描述

我想向servlet发送请求并从响应中读取标头。所以我尝试使用它：

I want to send request to servlet and read headers from response. So I try it using this:

  URL url = new URL(contextPath + "file_operations");
    HttpURLConnection conn = null;
    try {
        conn = (HttpURLConnection) url.openConnection();
        conn.setDoOutput(true);
        conn.setDoInput(true);
        conn.setRequestMethod("POST");
        conn.setRequestProperty("charset", "utf-8");
        conn.setUseCaches(false);
        conn.setConnectTimeout(1000 * 5);
        conn.connect();

        conn.getHeaderField("MyHeader")
        .....

但收到的标题总是 null 。 Servlet运行正常（我尝试使用独立的HTTP客户端使用servlet）

But received headers are always null. Servlet works fine (i tried work with servlet using standalone HTTP client)

推荐答案

确保在尝试之前获得成功的响应获取标题。这是你如何检查你的回复：

Make sure you are getting the successful response before you try to fetch the headers. This is how you can check for your response:

int status = conn.getResponseCode();

if (status == HttpURLConnection.HTTP_OK) {
          String = conn.getHeaderField("MyHeader");

    }

还要确保Servlet响应不是重定向响应，如果重定向所有会话信息，包括标题将丢失。

Also make sure the Servlet response is not a redirect response, if redirected all the session information, including headers will be lost.

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