hadoop DNSDomainNameResolver 源码
haddop DNSDomainNameResolver 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/DNSDomainNameResolver.java
/**
* Licensed to the Apache Software Foundation (ASF) under one
* or more contributor license agreements. See the NOTICE file
* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance
* with the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.apache.hadoop.net;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import javax.naming.NamingException;
import java.net.InetAddress;
import java.net.UnknownHostException;
/**
* DNSDomainNameResolver wraps up the default DNS service for forward/reverse
* DNS lookup. It also provides a function to resolve a host name to all of
* fully qualified domain names belonging to the IPs from this host name
*/
public class DNSDomainNameResolver implements DomainNameResolver {
private final static Logger LOG =
LoggerFactory.getLogger(DNSDomainNameResolver.class.getName());
@Override
public InetAddress[] getAllByDomainName(String domainName)
throws UnknownHostException {
return InetAddress.getAllByName(domainName);
}
@Override
public String getHostnameByIP(InetAddress address) {
String host = address.getCanonicalHostName();
if (host != null && host.length() != 0
&& host.charAt(host.length()-1) == '.') {
host = host.substring(0, host.length()-1);
}
// Protect against the Java behaviour of returning the IP address as a string from a cache
// instead of performing a reverse lookup.
if (host != null && host.equals(address.getHostAddress())) {
LOG.debug("IP address returned for FQDN detected: {}", address.getHostAddress());
try {
return DNS.reverseDns(address, null);
} catch (NamingException lookupFailure) {
LOG.warn("Failed to perform reverse lookup: {}", address);
}
}
return host;
}
@Override
public String[] getAllResolvedHostnameByDomainName(
String domainName, boolean useFQDN) throws UnknownHostException {
InetAddress[] addresses = getAllByDomainName(domainName);
String[] hosts = new String[addresses.length];
if (useFQDN) {
for (int i = 0; i < addresses.length; i++) {
hosts[i] = getHostnameByIP(addresses[i]);
}
} else {
for (int i = 0; i < addresses.length; i++) {
hosts[i] = addresses[i].getHostAddress();
}
}
return hosts;
}
}
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