1

下面的程序执行 DNS 查找。除了主机名和 dns 的一种特定组合外，它运行良好：

import javax.naming.directory.InitialDirContext;
import javax.naming.NamingException;
import java.util.Hashtable;

public final class StackOverflow {
 public static void main(String args[]) throws NamingException {
  Hashtable<String, Object> env = new Hashtable<String, Object>();
  env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
  env.put("java.naming.provider.url", "dns://ns.dnssek.org");
  System.out.println(new InitialDirContext(env).getAttributes("dnsseccert.us", new String[]{"NS","A"}));
 }
}

我试图设置超时：

env.put("com.sun.jndi.dns.timeout.initial", "220");

但是它的行为很奇怪。当它抛出时，它有时适用于小值：

DNS error [Root exception is java.net.SocketTimeoutException: Receive timed out];

但在大多数情况下，程序只是冻结并挂在内存中。

其他人有同样的问题并解决了吗？是否有任何其他设置我可以尝试阻止它？我可以尝试其他一些替代java.naming.factory.initial吗？

4

2 回答 2

4

我花了几个小时，但我终于找到了一个可以接受的解决方案。我下载了com.sun.jndi.dns包的源代码，并在DnsClient类中添加了一行：

...
Tcp(InetAddress server, int port, int timeout) throws IOException {
    sock = new Socket(server, port);
    sock.setSoTimeout(timeout);  // <-- missing timeout
    sock.setTcpNoDelay(true);
    out = new java.io.BufferedOutputStream(sock.getOutputStream());
    in = new java.io.BufferedInputStream(sock.getInputStream());
}
...

我设置了套接字的超时。实际上，我还在 Tcp 构造函数中添加了一个参数并修改了它的调用，因此它现在由com.sun.jndi.dns.timeout.initial的值初始化。

于 2013-01-30T20:37:32.383 回答
0

请尝试同时设置com.sun.jndi.dns.timeout.initial和com.sun.jndi.dns.timeout.retries值。例如，我看到以下一致的超时：

$ cat StackOverflow.java 
import javax.naming.directory.InitialDirContext;
import javax.naming.NamingException;
import java.util.Hashtable;

public final class StackOverflow {
 public static void main(String args[]) throws NamingException {
  Hashtable<String, Object> env = new Hashtable<String, Object>();
  env.put("java.naming.factory.initial", "com.sun.jndi.dns.DnsContextFactory");
  env.put("java.naming.provider.url", "dns://ns.dnssek.org");

  env.put("com.sun.jndi.dns.timeout.initial", "220");
  env.put("com.sun.jndi.dns.timeout.retries", "1");

  System.out.println(new InitialDirContext(env).getAttributes("dnsseccert.us", new String[]{"NS","A"}));
 }
}

$ java -version
java version "11" 2018-09-25
Java(TM) SE Runtime Environment 18.9 (build 11+28)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11+28, mixed mode)

$ java StackOverflow
Exception in thread "main" javax.naming.CommunicationException: DNS error [Root exception is java.net.SocketTimeoutException: Receive timed out]; remaining name    'dnsseccert.us'
    at jdk.naming.dns/com.sun.jndi.dns.DnsClient.query(DnsClient.java:313)
    at jdk.naming.dns/com.sun.jndi.dns.Resolver.query(Resolver.java:81)
    at jdk.naming.dns/com.sun.jndi.dns.DnsContext.c_getAttributes(DnsContext.java:434)
    at java.naming/com.sun.jndi.toolkit.ctx.ComponentDirContext.p_getAttributes(ComponentDirContext.java:235)
    at java.naming/com.sun.jndi.toolkit.ctx.PartialCompositeDirContext.getAttributes(PartialCompositeDirContext.java:141)
    at java.naming/com.sun.jndi.toolkit.ctx.PartialCompositeDirContext.getAttributes(PartialCompositeDirContext.java:129)
    at java.naming/javax.naming.directory.InitialDirContext.getAttributes(InitialDirContext.java:142)
    at StackOverflow.main(StackOverflow.java:14)
    Caused by: java.net.SocketTimeoutException: Receive timed out
    at java.base/java.net.PlainDatagramSocketImpl.receive0(Native Method)
    at java.base/java.net.AbstractPlainDatagramSocketImpl.receive(AbstractPlainDatagramSocketImpl.java:181)
    at java.base/java.net.DatagramSocket.receive(DatagramSocket.java:814)
    at jdk.naming.dns/com.sun.jndi.dns.DnsClient.doUdpQuery(DnsClient.java:423)
    at jdk.naming.dns/com.sun.jndi.dns.DnsClient.query(DnsClient.java:212)
    ... 7 more

您当然会想要配置在您自己的环境中有意义的超时和重试值。上述值仅用于演示目的。

于 2019-07-17T14:12:07.013 回答