Question

以下程序执行DNS查找。除了主机名和dns的一个特定组合之外，它的效果很好：

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");

然而它表现得很奇怪。当它抛出时，它有时适用于小值：

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

但是大多数时候程序只是冻结并挂起在内存中。

让其他人遇到同样的问题并解决了吗？有没有其他设置我可以尝试阻止它？还有其他的替代 java.naming.factory.initial 我可以试试吗？

Answer 1

花了我几个小时，但我终于找到了一个可以接受的解决方案。我下载了包 com.sun.jndi.dns 的源代码，并在类 DnsClient 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());
}
...

我设置套接字的timout。我实际上还在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 中的值初始化。

Answer 2

请尝试同时设置com.sun.jndi.dns.timeout.initial和com.sun.jndi.dns.timeout.retries的值。例如，我看到与以下内容一致的超时：

$ 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

您当然要配置在您自己的环境中有意义的超时和重试值。以上数值仅供参考。

DNS查询在java中与DnsContextFactory冻结

2 个答案: