hadoop权威指南--气温最大值所遇到的--内部类为静态的问题

老的API：

public class MaxTemperature {
  
  public static  class  MaxTemperatureMapper extends MapReduceBase implements Mapper<LongWritable, Text, Text, IntWritable> {
    private  static final  int MISSING = 9999;
    @Override
    public void map(LongWritable key, Text value, OutputCollector<Text, IntWritable> output, Reporter reporter)
        throws IOException {
      String line = value.toString();
      String year = line.substring(15, 19);
      int airTemperature;
      if(line.charAt(87) == '+') {
        airTemperature = Integer.parseInt(line.substring(88,92));
      } else {
        airTemperature = Integer.parseInt(line.substring(87, 92));
      }
      String  quality = line.substring(92, 93);
      if(airTemperature != MISSING && quality.matches("[01459]")) {
        output.collect(new Text(year), new IntWritable(airTemperature));
      }
    }
  }
  
  public static class MaxTemperatureReducer  extends  MapReduceBase implements  Reducer<Text,IntWritable, Text, IntWritable>{

    @Override
    public void reduce(Text key, Iterator<IntWritable> values, OutputCollector<Text, IntWritable> output, Reporter reporter)
        throws IOException {
      
      int maxvalue = Integer.MIN_VALUE;
      while (values.hasNext()) {
        maxvalue = Math.max(maxvalue, values.next().get());
      }
      output.collect(key, new IntWritable(maxvalue));
      
    }
    
  } 
  public static void main(String[] args) throws IOException {
    if (args.length != 2) {
      System.err.println("Usage: MaxTemperature <input path> <output path>");
    }
    JobConf  conf  = new JobConf(MaxTemperature.class);
    conf.setJobName("Max temperature");
    
    FileInputFormat.addInputPath(conf, new Path(args[0]));
    FileOutputFormat.setOutputPath(conf, new Path(args[1]));
    conf.setMapperClass(MaxTemperatureMapper.class);
    conf.setReducerClass(MaxTemperatureReducer.class);
    conf.setOutputKeyClass(Text.class);
    conf.setOutputValueClass(IntWritable.class);
    
    JobClient.runJob(conf);
  }
  
}

 新的api：

public class NewMaxTemperature {

  public static  class NewMaxTemperatureMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
    private static final int MISSING = 9999;

    public void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, IntWritable>.Context context)
        throws IOException, InterruptedException {
      String line = value.toString();
      String year = line.substring(15, 19);
      int airTemperature;
      if (line.charAt(87) == '+') {
        airTemperature = Integer.parseInt(line.substring(88, 92));
      } else {
        airTemperature = Integer.parseInt(line.substring(87, 92));
      }
      String quality = line.substring(92, 93);
      if (airTemperature != MISSING && quality.matches("[01459]")) {
        context.write(new Text(year), new IntWritable(airTemperature));
      }
    }
  }

  public static class NewMaxTemperatureReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
    @Override
    public void reduce(Text key, Iterable<IntWritable> values,
        Reducer<Text, IntWritable, Text, IntWritable>.Context context) throws IOException, InterruptedException {
      int maxvalue = Integer.MIN_VALUE;
      while (values.iterator().hasNext()) {
        maxvalue = Math.max(maxvalue, values.iterator().next().get());
      }
      context.write(key, new IntWritable(maxvalue));
    }

  }

  public static void main(String[] args) throws IOException, InterruptedException, ClassNotFoundException {
    if (args.length != 2) {
      System.err.println("Usage: MaxTemperature <input path> <output path>");
    }
    Configuration conf = new Configuration();
    String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
    HashMap<String, String> params = ParamsUtil.getJobParameters(otherArgs);
    Job job = Job.getInstance(new Cluster(conf), conf);
    job.setJarByClass(NewMaxTemperature.class);
    job.setMapperClass(NewMaxTemperatureMapper.class);
    job.setReducerClass(NewMaxTemperatureReducer.class);

    job.setMapOutputKeyClass(Text.class);
    job.setMapOutputValueClass(IntWritable.class);
    job.setOutputKeyClass(Text.class);
    job.setOutputValueClass(IntWritable.class);

    String reduceTasksNum = params.get("r");
    if (reduceTasksNum == null) {
      System.out.println("No reduce tasks num");
      System.exit(-1);
    }

    String input = params.get("input");
    if (input == null) {
      System.out.println("No input");
      System.exit(-1);
    }

    String output = params.get("output");
    if (output == null) {
      System.out.println("No output");
      System.exit(-1);
    }
    String name = params.get("name");
    if (name == null || "".equals(name)) {
      name = "MaxTemperature Test";
    }
    job.setNumReduceTasks(Integer.valueOf(reduceTasksNum));
    FileInputFormat.setInputPaths(job, input);
    FileOutputFormat.setOutputPath(job, new Path(output));
    job.setJobName(name);
    job.waitForCompletion(true);
  }

}

 在运行新的程序时，刚开始内部类没有用静态修饰，运行时报错：

WARN org.apache.hadoop.mapred.Child: Exception running child : java.lang.RuntimeException: java.lang.NoSuchMethodException: com.renren.dp.mapred.NewMaxTemperature$NewMaxTemperatureMapper.<init>()
	at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:123)
	at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:612)
	at org.apache.hadoop.mapred.MapTask.run(MapTask.java:328)
	at org.apache.hadoop.mapred.Child$4.run(Child.java:217)
	at java.security.AccessController.doPrivileged(Native Method)
	at javax.security.auth.Subject.doAs(Subject.java:396)
	at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:742)
	at org.apache.hadoop.mapred.Child.main(Child.java:211)
Caused by: java.lang.NoSuchMethodException: com.renren.dp.mapred.NewMaxTemperature$NewMaxTemperatureMapper.<init>()
	at java.lang.Class.getConstructor0(Class.java:2706)
	at java.lang.Class.getDeclaredConstructor(Class.java:1985)
	at org.apache.hadoop.util.ReflectionUtils.newInstance(ReflectionUtils.java:117)
	... 7 more
原因是：hadoop在调用map和reduce类时采用的反射调用，内部类不是静态的，没有获取到内部类的实例，因为必须要获取外部类的实例，new NewMaxTemperature（）.new NewMaxTemperatureMapper();如果是静态的内部类的话：直接new NewMaxTemperatureMapper() 得出实例。 在新api中封装了参数解析类： public class ParamsUtil {
	public static HashMap<String, String> getJobParameters(String[] args) {
		Options options = new Options();
		for (String arg : args) {
			if (arg.startsWith("-")) {
				Option option = OptionBuilder.hasArg(true).create(
						arg.substring(1));
				option.setArgName(arg.substring(1));
				options.addOption(option);
			}
		}
		PosixParser posixerParser = new PosixParser();
		CommandLine cmd = null;
		try {
			cmd = posixerParser.parse(options, args);
			HashMap<String, String> params = new HashMap<String, String>();
			for (Option op : cmd.getOptions()) {
				params.put(op.getArgName(), op.getValue());
				System.out.println("Params:" + op.getArgName() + "="
						+ op.getValue());
			}
			return params;
		} catch (org.apache.commons.cli.ParseException e) {
			e.printStackTrace();
			System.exit(0);
		}
		return null;
	}