查找主机时如何设置套接字的超时时间？

Question

在我的单元测试中，我使用 commons httpclient 请求错误的远程网站，最大超时时间为：

@Test(timeout = 10000)
public void should_not_be_accessible_if_configuration_is_incorrect() throws Exception {
     // use httpclient to visit an invalid remote http web site
}

但是在某些计算机上可能会抛出这样的异常：

java.lang.Exception: test timed out after 10000 milliseconds
at java.net.Inet4AddressImpl.lookupAllHostAddr(Native Method)
at java.net.InetAddress$1.lookupAllHostAddr(InetAddress.java:894)
at java.net.InetAddress.getAddressesFromNameService(InetAddress.java:1286)
at java.net.InetAddress.getAllByName0(InetAddress.java:1239)
at java.net.InetAddress.getAllByName(InetAddress.java:1155)
at java.net.InetAddress.getAllByName(InetAddress.java:1091)
at org.apache.http.impl.conn.SystemDefaultDnsResolver.resolve(SystemDefaultDnsResolver.java:44)
at org.apache.http.impl.conn.HttpClientConnectionOperator.connect(HttpClientConnectionOperator.java:102)
at org.apache.http.impl.conn.PoolingHttpClientConnectionManager.connect(PoolingHttpClientConnectionManager.java:314)
at org.apache.http.impl.execchain.MainClientExec.establishRoute(MainClientExec.java:357)
at org.apache.http.impl.execchain.MainClientExec.execute(MainClientExec.java:218)
at org.apache.http.impl.execchain.ProtocolExec.execute(ProtocolExec.java:194)
at org.apache.http.impl.execchain.RetryExec.execute(RetryExec.java:85)
at org.apache.http.impl.execchain.RedirectExec.execute(RedirectExec.java:108)
at org.apache.http.impl.client.InternalHttpClient.doExecute(InternalHttpClient.java:186)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:82)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:106)
at org.apache.http.impl.client.CloseableHttpClient.execute(CloseableHttpClient.java:57)

似乎它阻塞了方法： java.net.Inet4AddressImpl.lookupAllHostAddr()

我想知道有没有办法为它设置最大超时时间？

Answer 1

您可以通过此处描述的超时属性来控制Java的DNS超时：

com.example.jndi.dns.timeout.initial
com.example.jndi.dns.timeout.retries

Answer 2

一种解决方案是在不同的线程上执行 DNS 解析，该线程仅在一定时间内完成。

这是一个可以帮助您执行此操作的简单实用程序：

public class TimeSliceExecutor {

  public static class TimeSliceExecutorException extends RuntimeException {
    public TimeSliceExecutorException(String message, Throwable cause) {
      super(message, cause);
    }
  }

  public static void execute(Runnable runnable, long timeoutInMillis) {
    ExecutorService executor = Executors.newSingleThreadExecutor();
    try {
      Future<?> future = executor.submit(runnable);
      getFuture(future, timeoutInMillis);
    }
    finally {
      if (executor != null) {
        executor.shutdown();
      }
    }
  }

  public static <T> T execute(Callable<T> callable, long timeoutInMillis) {
    ExecutorService executor = Executors.newSingleThreadExecutor();
    try {
      Future<T> future = executor.submit(callable);
      return getFuture(future, timeoutInMillis);
    }
    finally {
      if (executor != null) {
        executor.shutdown();
      }
    }
  }

  public static <T> T getFuture(Future<T> future, long timeoutInMillis) {
    try {
      return future.get(timeoutInMillis, TimeUnit.MILLISECONDS);
    }
    catch (InterruptedException ex) {
      Thread.currentThread().interrupt();
      throw new TimeSliceExecutorException("Interrupton exception", ex);
    }
    catch (ExecutionException ex) {
      throw new TimeSliceExecutorException("Execution exception", ex);
    }
    catch (TimeoutException ex) {
      throw new TimeSliceExecutorException(String.format("%dms timeout reached", timeoutInMillis), ex);
    }
  }
}

然后沿着这些线构建套接字：

private Socket buildSocket() throws IOException {
  final Socket socket = new Socket();
  socket.setSoTimeout(socketTimeout);
  socket.connect(new InetSocketAddress(resolveHost(host, dnsTimeout), port), connectionTimeout);
  return socket;
}

private static InetAddress resolveHost(String host, long timeout) throws IOException {
  try {
    return TimeSliceExecutor.execute(() -> InetAddress.getByName(host), timeout);
  }
  catch (TimeSliceExecutor.TimeSliceExecutorException ex) {
    throw new UnknownHostException(host);
  }
}