Java代理中的Java NullPointerException

Question

我正在开发Java代理。我有一个NullPointerException错误，我认为应该不会发生。

这是调试控制台消息：

java.lang.NullPointerException
    at sun.net.www.http.HttpClient.parseHTTPHeader(HttpClient.java:719)
    at sun.net.www.http.HttpClient.parseHTTP(HttpClient.java:646)
    at COM.ibm.JEmpower.applet.http.HttpURLConnection.getInputStream(HttpURLConnection.java:411)
    at COM.ibm.JEmpower.applet.http.HttpURLConnection.getHeaderField(HttpURLConnection.java:703)
    at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:399)
    at JavaAgent.NotesMain(JavaAgent.java:16)
    at lotus.domino.AgentBase.runNotes(Unknown Source)
    at lotus.domino.NotesThread.run(Unknown Source)

这是Java代理中的代码

import lotus.domino.*;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.Date;
public class JavaAgent extends AgentBase {

    public void NotesMain() {
      String strAux = "[A Working URL]";
      try {
          Session session = getSession();
          AgentContext agentContext = session.getAgentContext();

          // (Your code goes here)

          HttpURLConnection httpCon = (HttpURLConnection) new URL(strAux).openConnection();

          httpCon.setRequestMethod("HEAD");
          httpCon.setConnectTimeout(20000);  
          httpCon.setReadTimeout(20000);

          httpCon.connect();

          System.out.println(HttpCon.getURL().toString());

          int responsecode = httpCon.getResponseCode();
          System.out.println("Response code is " + responsecode + " - " + httpCon.getResponseMessage());
      } catch(Exception e) {
          e.printStackTrace();
      }
    }

}

基本上，错误指向System.out.println("Response code is " + httpCon.getResponseCode() + " - " + httpCon.getResponseMessage());。

事实是，URL是有效的链接，因为我已经通过在浏览器中进行访问尝试了它。

此错误的可能原因是什么？在我创建用于测试的本地Notes数据库上，它的效果不佳。但是，在注释中未开发的普通Java程序中，它可以工作。

Answer 1

在发送任何内容之前获取响应代码毫无意义。您应该先发送请求，然后获取响应代码，然后根据需要获取响应