Java HTTPUrlConnection 超时不起作用

Question

我编写了一个程序，它通过随机代理打开到网站的 httpurl 连接。我的 httpurl 连接称为 conn。现在我知道，其中一些代理可能太慢了，所以我使用 conn.setConnectTimeout(40000) 和 conn.setReadTimeout(40000) 将连接超时设置为 40000 毫秒)。

这样做之后，我得到了这段代码:

long diff = 0;
    long starttime = 0;
    long endtime = 0;

    try
    {
        starttime = System.currentTimeMillis();
        conn.connect();

        endtime = System.currentTimeMillis();

        diff = endtime - starttime;

        if (endtime <= starttime + conn.getConnectTimeout())
        {
            //Trying to read sourecode
            InputStreamReader isrConn = new InputStreamReader(conn.getInputStream());
            BufferedReader brConn = new BufferedReader(isrConn);

            line = brConn.readLine();

            while (line != null)
            {

                response += line + "\t";
                try
                {
                    line = brConn.readLine();
                } catch (IOException e)
                {
                    printError("Reading sourcecode failed.");
                }

            }
        }
        else
        {
            response = "blabla.";
        }




    // If conn.connect failed   
    } catch (IOException e)
    {
        endtime = System.currentTimeMillis();
        diff = endtime - starttime;

        response = "Message: "+e.getMessage() +" MyTimeout:"+ conn.getConnectTimeout() +" Actual time passed:  "+ diff;
               e.printStackTrace();


    }

连接失败的原因有很多，所以在很多情况下，我会到达最后一个 catch-block 并获得以下输出:

---

消息:连接超时:connect MyTimeout:40000 实际耗时:21012

消息:连接超时:connect MyTimeout:40000 实际耗时:21016

消息:连接超时:connect MyTimeout:40000 实际耗时:21010

消息:连接超时:connect MyTimeout:40000 实际耗时:21009

---

所以我的问题是:我已将超时设置为 40000 毫秒，但我在大约 21000 毫秒后收到“连接超时”响应，有人知道这是为什么吗？

编辑:我使用的是 Windows 7，我现在将 e.printStackTrace() 添加到 catch-block，如评论中所述。谢谢到目前为止。现在的输出是(示例):

java.net.ConnectException: Connection timed out: connect
    at java.net.DualStackPlainSocketImpl.waitForConnect(Native Method)
    at java.net.DualStackPlainSocketImpl.socketConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.doConnect(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connectToAddress(Unknown Source)
    at java.net.AbstractPlainSocketImpl.connect(Unknown Source)
    at java.net.PlainSocketImpl.connect(Unknown Source)
    at java.net.Socket.connect(Unknown Source)
    at sun.net.NetworkClient.doConnect(Unknown Source)
    at sun.net.www.http.HttpClient.openServer(Unknown Source)
    at sun.net.www.http.HttpClient$1.run(Unknown Source)
    at sun.net.www.http.HttpClient$1.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.net.www.http.HttpClient.privilegedOpenServer(Unknown Source)
    at sun.net.www.http.HttpClient.openServer(Unknown Source)
    at sun.net.www.http.HttpClient.<init>(Unknown Source)
    at sun.net.www.http.HttpClient.New(Unknown Source)
    at sun.net.www.http.HttpClient.New(Unknown Source)
    at sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(Unknown Source)
    at sun.net.www.protocol.http.HttpURLConnection.plainConnect(Unknown Source)
    at sun.net.www.protocol.http.HttpURLConnection.connect(Unknown Source)
    at TestThread.getSourcePage(TestThread.java:361)
    at TestThread.aChecker(TestThread.java:216)
    at TestThread.getNextProxy(TestThread.java:169)
    at TestThread.getNextC(TestThread.java:157)
    at TestThread.aChecker(TestThread.java:273)
    at TestThread.getNextProxy(TestThread.java:169)
    at TestThread.aChecker(TestThread.java:295)
    at TestThread.getNextProxy(TestThread.java:169)
    at TestThread.getNextC(TestThread.java:157)
    at TestThread.run(TestThread.java:103)
    at java.lang.Thread.run(Unknown Source)

Message: Connection timed out: connect MyTimeout:40000 Actual time passed:  21015

Answer 1

查看您得到的异常:
最大的线索:您得到了 java.net.ConnectException根据 javadoc，java.net.ConnectException 表示连接被远程拒绝，原因是没有进程正在监听端口。

public class ConnectException
extends SocketException

Signals that an error occurred while attempting to connect a socket to a remote address and port. 
Typically, the connection was refused remotely (e.g., no process is listening on the remote 
address/port)

您在 HttpUrlConnection 中配置的内容:
连接超时(假定远程端口接受连接)。如果连接超时到期，您将收到 java.net.SocketTimeoutException 而不是 java.net.ConnectException。

那么，是什么导致了 java.net.ConnectException？
我尝试了以下测试用例:

   +------------+------------+----------------+------------------+---------------------------------+ 
   | Valid Host | Valid Port | Valid Proxy IP | Valid Proxy Port | Exception                       | 
   +------------+------------+----------------+------------------+---------------------------------+ 
#1 | yes        | yes        | -NA-           | -NA-             | -- none --                      |
#2 | yes        | no         | -NA-           | -NA-             | java.net.ConnectException       |
   +------------+------------+----------------+------------------+---------------------------------+ 
#3 | yes        | yes        | yes            | yes              | -- none --                      |
#4 | yes        | no         | yes            | yes              | java.net.SocketTimeoutException |
#5 | yes        | yes        | yes            | no               | java.net.ConnectException       |
   +------------+------------+----------------+------------------+---------------------------------+ 

• 案例 #1、#3 是所有配置都正确的快乐路径
• 在案例 #4 中，我们得到一个 java.net.SocketTimeoutException，因为 java 进程能够建立连接(到代理端口)，但没有获取任何数据作为目标主机的端口读取号码无效
• 在案例 #2、#5 中，我们得到 java.net.ConnectException，因为 java 进程尝试写入/读取的端口无效
• 连接超时值不适用于没有进程监听 java 进程尝试连接的端口的情况。这就是为什么您在超时到期之前获得 ConnectException 的原因


消息:连接被拒绝:连接 MyTimeout:10000 实际耗时:6549
java.net.ConnectException:连接被拒绝:连接
在 java.net.DualStackPlainSocketImpl.waitForConnect( native 方法)
在 java.net.DualStackPlainSocketImpl.socketConnect(DualStackPlainSocketImpl.java:85)
....
....


结论:

• 您尝试连接的某些代理肯定已关闭。因此 java 进程抛出 java.net.ConnectException
• 最好捕获java.net.ConnectException并将代理标记为无效/关闭