如何在hadoop中将系统属性传递给map函数

Question

有没有一种方法可以将系统参数（类似于-Dmy_param=XXX）传递到hadoop map reduce框架中的map函数。向hadoop集群提交作业是通过.setJarByClass（）完成的。在mapper中，我必须创建配置，所以我想使其可配置，所以认为通过属性文件的标准方式是可以的。只是在设置属性的地方传递参数。另一种方法是将属性文件添加到提交的jar中。有人有解决问题的经验吗？

Answer 1

如果您还没有在作业中使用它，您可以尝试GenericOptionsParser、Tool和ToolRunner来运行Hadoop作业。

注意：MyDriver扩展了Configured并实现了Tool。并且，要运行您的作业，请使用此

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

有关详细信息，请查看此链接。

以下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);
  }
}