java.lang.IllegalStateException : Already connected for setRequestProperty method : Java 错误

Question

我创建了一个类，我正在创建一个 HttpURLConnection对象并将该对象传递给另一个方法，如果它满足以下条件:

在这门课中，我通过了 username , password和 senderId使用 proxy 连接到某个 URL当连接不为空时。

下面是Java类的完整代码:

public class SMSGenerator {
   public static HttpURLConnection sendSingleSMS(HttpURLConnection lconnection, String username,
       String password, String senderId,
       String mobileNo, String message) {
   try {
       String smsservicetype = "singlemsg"; // For single message.
       String query = "username=" + URLEncoder.encode(username)
               + "&password=" + URLEncoder.encode(password)
               + "&smsservicetype=" + URLEncoder.encode(smsservicetype)
               + "&content=" + URLEncoder.encode(message) + "&mobileno="
               + URLEncoder.encode(mobileNo) + "&senderid="
               + URLEncoder.encode(senderId);

       lconnection.setRequestProperty("Content-length", String.valueOf(query.length()));
       lconnection.setRequestProperty("Content-Type",
               "application/x-www-form-urlencoded");
       lconnection.setRequestProperty("User-Agent",
               "Mozilla/4.0 (compatible; MSIE 5.0; Windows 98; DigExt)");

       // open up the output stream of the connection
       DataOutputStream output = new DataOutputStream(lconnection.getOutputStream());

       // write out the data
       int queryLength = query.length();
       output.writeBytes(query);
       // output.close();

       // get ready to read the response from the cgi script
       DataInputStream input = new DataInputStream(lconnection.getInputStream());

       // read in each character until end-of-stream is detected
       for (int c = input.read(); c != -1; c = input.read()) {
           System.out.print((char) c);
       }
       input.close();
   } catch (Exception e) {
       System.out.println("Something bad just happened.");
       e.printStackTrace();
   }
   return lconnection;
}
public static boolean sendSMS(String mobilenumber, String msg) throws MalformedURLException, IOException {
   boolean flag = false;
   Proxy proxy = new Proxy(Proxy.Type.HTTP, new InetSocketAddress("xxxxxxxxxx", xx));
   URL surl = new URL("xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx");
   HttpURLConnection connection = null;
   connection = (HttpURLConnection) surl.openConnection(proxy);
   connection.setDoInput(true);
   connection.setDoOutput(true);
   connection.setRequestMethod("POST");
   HttpURLConnection.setFollowRedirects(true);
   System.out.println("Response code " + connection.getResponseMessage());
   System.out.println("code : " + connection.getResponseCode() + " " + HttpURLConnection.HTTP_NOT_FOUND);
   if ("OK".equals(connection.getResponseMessage())) {
       System.out.println("in");
       SMSGenerator.sendSingleSMS(connection, "username", "password", "SMS", mobilenumber, msg);
//             System.out.println("Sent successful SMS");
       flag = true;

   } else if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
       System.out.println("Hiiii");
   } else if (connection.getResponseCode() == HttpURLConnection.HTTP_BAD_GATEWAY) {
       System.out.println("Hi 1");
   } else if (connection.getResponseCode() == HttpURLConnection.HTTP_INTERNAL_ERROR) {
       System.out.println("Hi 2");
   }
//        System.out.println("");
   return flag;
}
public static void main(String[] args) throws IOException {
   new SMSGenerator().sendSMS("xxxxxxxxxx", "ManojYest1");
}
}

这段代码的问题在于，如果我检查 if条件为:connection != null然后它建立连接并正确调用该方法。但是，如果我用 responseCode 检查条件作为connection.getResponseCode() == HttpURLConnection.HTTP_OK然后出现以下错误:

java.lang.IllegalStateException: Already connected
   at sun.net.www.protocol.http.HttpURLConnection.setRequestProperty(HttpURLConnection.java:3013)

我该如何解决这个错误？

Answer 1

因为不应该那样使用连接。您正在尝试执行以下操作:

"Open" Connection
Get Response
|-> Connect (if not already connected)
|-> Read response data
setRequestProperty
|-> Check connected state - Oops! Already connected!

这不是您应该使用 UrlConnection 的方式。相反，它希望您执行以下操作:

"Open" Connection
setRequestProperty
|-> Check connected state - Not Connected
getOutputStream
|-> Connect
|-> Create and return output stream
Write request to output stream
Get Response
|-> Connect (if not already connected)
|-> Send (empty) request
|-> Read response data

您是否需要知道在发送数据之前 会收到 OK 响应？或者您只是想验证您是否已成功连接到端点？

openConnection 不会导致连接对象实际连接 到目标 URL...