hadoop - 如何将系统属性传递给hadoop中的映射函数

Question

有没有办法将系统参数（类似于-Dmy_param = XXX）传递给hadoop map reduce框架中的映射函数。通过 .setJarByClass() 向 hadoop 集群提交作业。在映射器中，我必须创建配置，所以我想让它可配置，所以我认为通过属性文件的标准方式就可以了。只是在设置属性的位置传递参数。另一种方法是将属性文件添加到提交的 jar 中。有人有经验如何解决这个问题吗？

Answer 1

如果您尚未在工作中使用它，您可以尝试使用 GenericOptionsParser、Tool 和 ToolRunner 来运行 Hadoop Job。

注意： MyDriver 扩展了 Configured 并实现了 Tool。而且，要运行你的工作，请使用这个

hadoop -jar somename.jar MyDriver -D your.property=value arg1 arg2

有关更多信息，请查看此链接。

这是我为您准备的一些示例代码：

public class MyDriver extends Configured implements Tool {

  public static class MyDriverMapper extends Mapper<LongWritable, Text, LongWritable, NullWritable> {

    protected void map(LongWritable key, Text value, Context context)
      throws IOException, InterruptedException {
      // In the mapper you can retrieve any configuration you've set
      // while starting the job from the terminal as shown below

      Configuration conf = context.getConfiguration();
      String yourPropertyValue = conf.get("your.property");
    }
  }

  public static class MyDriverReducer extends Reducer<LongWritable, NullWritable, LongWritable, NullWritable> {

    protected void reduce(LongWritable key, Iterable<NullWritable> values, Context context) 
      throws IOException, InterruptedException {
      // --- some code ---
    }
  }

  public static void main(String[] args) throws Exception {
    int exitCode = ToolRunner.run(new MyDriver(), args);
    System.exit(exitCode);
  }

  @Override
  public int run(String[] args) throws Exception {
    Configuration conf = getConf();
    // if you want you can get/set to conf here too.
    // your.property can also be file location and after
    // you retrieve the properties and set them one by one to conf object.

    // --other code--//
    Job job = new Job(conf, "My Sample Job");
    // --- other code ---//
    return (job.waitForCompletion(true) ? 0 : 1);
  }
}