ExternalMapReduce.java 文件源码

public void map(WritableComparable key, Writable value,
                OutputCollector<WritableComparable, IntWritable> output,
                Reporter reporter)
  throws IOException {
  //check for classpath
  String classpath = System.getProperty("java.class.path");
  if (classpath.indexOf("testjob.jar") == -1) {
    throw new IOException("failed to find in the library " + classpath);
  }
  if (classpath.indexOf("test.jar") == -1) {
    throw new IOException("failed to find the library test.jar in" 
        + classpath);
  }
  //fork off ls to see if the file exists.
  // java file.exists() will not work on 
  // Windows since it is a symlink
  String[] argv = new String[7];
  argv[0] = "ls";
  argv[1] = "files_tmp";
  argv[2] = "localfilelink";
  argv[3] = "dfsfilelink";
  argv[4] = "tarlink";
  argv[5] = "ziplink";
  argv[6] = "test.tgz";
  Process p = Runtime.getRuntime().exec(argv);
  int ret = -1;
  try {
    ret = p.waitFor();
  } catch(InterruptedException ie) {
    //do nothing here.
  }
  if (ret != 0) {
    throw new IOException("files_tmp does not exist");
  }
}