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Apache Hadoop MapReduce Streaming
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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.streaming;

import java.io.*;

import org.apache.hadoop.classification.InterfaceAudience;
import org.apache.hadoop.fs.FileUtil;

/**
 * Maps a relative pathname to an absolute pathname using the PATH environment.
 */
@InterfaceAudience.Private
public class PathFinder {
  String pathenv; // a string of pathnames
  String pathSep; // the path separator
  String fileSep; // the file separator in a directory

  /**
   * Construct a PathFinder object using the path from java.class.path
   */
  public PathFinder() {
    pathenv = System.getProperty("java.class.path");
    pathSep = System.getProperty("path.separator");
    fileSep = System.getProperty("file.separator");
  }

  /**
   * Construct a PathFinder object using the path from the specified system
   * environment variable.
   */
  public PathFinder(String envpath) {
    pathenv = System.getenv(envpath);
    pathSep = System.getProperty("path.separator");
    fileSep = System.getProperty("file.separator");
  }

  /**
   * Appends the specified component to the path list
   */
  public void prependPathComponent(String str) {
    pathenv = str + pathSep + pathenv;
  }

  /**
   * Returns the full path name of this file if it is listed in the path
   */
  public File getAbsolutePath(String filename) {
    if (pathenv == null || pathSep == null || fileSep == null) {
      return null;
    }
    int val = -1;
    String classvalue = pathenv + pathSep;

    while (((val = classvalue.indexOf(pathSep)) >= 0)
        && classvalue.length() > 0) {
      // Extract each entry from the pathenv
      String entry = classvalue.substring(0, val).trim();
      File f = new File(entry);

      if (f.isDirectory()) {
        // this entry in the pathenv is a directory.
        // see if the required file is in this directory
        f = new File(entry + fileSep + filename);
      }
      // see if the filename matches and we can read it
      if (f.isFile() && FileUtil.canRead(f)) {
        return f;
      }
      classvalue = classvalue.substring(val + 1).trim();
    }
    return null;
  }

  public static void main(String args[]) throws IOException {
    if (args.length < 1) {
      System.out.println("Usage: java PathFinder ");
      System.exit(1);
    }
    PathFinder finder = new PathFinder("PATH");
    File file = finder.getAbsolutePath(args[0]);
    if (file != null) {
      System.out.println("Full path name = " + file.getCanonicalPath());
    }
  }
}