org.apache.hadoop.fs.FsUrlStreamHandlerFactory.java Source code

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Here is the source code for org.apache.hadoop.fs.FsUrlStreamHandlerFactory.java

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/**
 * 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.fs;

import java.io.IOException;
import java.net.URLStreamHandlerFactory;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.classification.InterfaceStability;
import org.apache.hadoop.conf.Configuration;

/**
 * Factory for URL stream handlers.
 * 
 * There is only one handler whose job is to create UrlConnections. A
 * FsUrlConnection relies on FileSystem to choose the appropriate FS
 * implementation.
 * 
 * Before returning our handler, we make sure that FileSystem knows an
 * implementation for the requested scheme/protocol.
 */
@InterfaceAudience.Private
@InterfaceStability.Unstable
public class FsUrlStreamHandlerFactory implements URLStreamHandlerFactory {

    private static final Logger LOG = LoggerFactory.getLogger(FsUrlStreamHandlerFactory.class);

    /**
     * These are the protocols with MUST NOT be exported, as doing so
     * would conflict with the standard URL handlers registered by
     * the JVM. Many things will break.
     */
    public static final String[] UNEXPORTED_PROTOCOLS = { "http", "https" };

    // The configuration holds supported FS implementation class names.
    private Configuration conf;

    // This map stores whether a protocol is know or not by FileSystem
    private Map<String, Boolean> protocols = new ConcurrentHashMap<String, Boolean>();

    // The URL Stream handler
    private java.net.URLStreamHandler handler;

    public FsUrlStreamHandlerFactory() {
        this(new Configuration());
    }

    public FsUrlStreamHandlerFactory(Configuration conf) {
        this.conf = new Configuration(conf);
        // force init of FileSystem code to avoid HADOOP-9041
        try {
            FileSystem.getFileSystemClass("file", conf);
        } catch (IOException io) {
            throw new RuntimeException(io);
        }
        this.handler = new FsUrlStreamHandler(this.conf);
        for (String protocol : UNEXPORTED_PROTOCOLS) {
            protocols.put(protocol, false);
        }
    }

    @Override
    public java.net.URLStreamHandler createURLStreamHandler(String protocol) {
        LOG.debug("Creating handler for protocol {}", protocol);
        if (!protocols.containsKey(protocol)) {
            boolean known = true;
            try {
                Class<? extends FileSystem> impl = FileSystem.getFileSystemClass(protocol, conf);
                LOG.debug("Found implementation of {}: {}", protocol, impl);
            } catch (IOException ex) {
                known = false;
            }
            protocols.put(protocol, known);
        }
        if (protocols.get(protocol)) {
            LOG.debug("Using handler for protocol {}", protocol);
            return handler;
        } else {
            // FileSystem does not know the protocol, let the VM handle this
            LOG.debug("Unknown protocol {}, delegating to default implementation", protocol);
            return null;
        }
    }

}