Hadoop2.2.0源碼系列--Job類

獲取Job對象

Job的構造函數

最直接的獲取Job對象的方式

@Deprecated
  public Job() throws IOException {
    this(new Configuration());
  }

  @Deprecated
  public Job(Configuration conf) throws IOException {
    this(new JobConf(conf));
  }

  @Deprecated
  public Job(Configuration conf, String jobName) throws IOException {
    this(conf);
    setJobName(jobName);
  }

  Job(JobConf conf) throws IOException {
    super(conf, null);
    // propagate existing user credentials to job
    this.credentials.mergeAll(this.ugi.getCredentials());
    this.cluster = null;
  }

  Job(JobStatus status, JobConf conf) throws IOException {
    this(conf);
    setJobID(status.getJobID());
    this.status = status;
    state = JobState.RUNNING;
  }

五個構造方法，但是不鼓勵使用缺省構造函數或Configuration類來構造Job對象。常用JobConf對象來構造Job對象。

獲取Job對象的實例化方法

除了通過構造函數，Job類中還提供了通過一些靜態方法來獲取Job的事例對象，一個例子如下：

/**
   * Creates a new {@link Job} with no particular {@link Cluster} .
   * A Cluster will be created with a generic {@link Configuration}.
   * 
   * @return the {@link Job} , with no connection to a cluster yet.
   * @throws IOException
   */
  public static Job getInstance() throws IOException {
    // create with a null Cluster
    return getInstance(new Configuration());
  }