Hadoop 找不到映射器 class

Question

我是 Hadoop 的新手，我想运行一个 MapReduce 作业。但是，我得到了 hadoop 找不到映射器 class 的错误。这是错误：

INFO mapred.JobClient: Task Id : attempt_201608292140_0023_m_000000_0, Status : FAILED
java.lang.RuntimeException: java.lang.ClassNotFoundException: TransMapper1
    at org.apache.hadoop.conf.Configuration.getClass(Configuration.java:857)
    at org.apache.hadoop.mapreduce.JobContext.getMapperClass(JobContext.java:199)
    at org.apache.hadoop.mapred.MapTask.runNewMapper(MapTask.java:718)
    at org.apache.hadoop.mapred.MapTask.run(MapTask.java:364)
    at org.apache.hadoop.mapred.Child.run(Child.java:255)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)

我检查了我的jar文件的权限，没问题。这里是jar文件的权限：

-rwxrwxrwx.

这是启动 mapreduce 作业的代码：

import java.io.File;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.NullWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

public class mp{

public static void main(String[] args) throws Exception {

    Job job1 = new Job();
    job1.setJarByClass(mp.class);
    FileInputFormat.addInputPath(job1, new Path(args[0]));                  
    String oFolder = args[0] + "/output";
    FileOutputFormat.setOutputPath(job1, new Path(oFolder));
    job1.setMapperClass(TransMapper1.class);
    job1.setReducerClass(TransReducer1.class);
    job1.setMapOutputKeyClass(LongWritable.class);
    job1.setMapOutputValueClass(DnaWritable.class);
    job1.setOutputKeyClass(LongWritable.class);
    job1.setOutputValueClass(Text.class);
}
}

这里是映射器 class (TransMapper1):

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.io.DoubleWritable;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;

public class TransMapper1 extends  Mapper<LongWritable, Text, LongWritable, DnaWritable> {

    @Override
    public void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {

        String line = value.toString();
        StringTokenizer tokenizer = new StringTokenizer(line);
        LongWritable bamWindow = new LongWritable(Long.parseLong(tokenizer.nextToken()));
        LongWritable read = new LongWritable(Long.parseLong(tokenizer.nextToken()));
        LongWritable refWindow = new LongWritable(Long.parseLong(tokenizer.nextToken()));
        IntWritable chr = new IntWritable(Integer.parseInt(tokenizer.nextToken()));
        DoubleWritable dist = new DoubleWritable(Double.parseDouble(tokenizer.nextToken()));
        DnaWritable dnaW = new DnaWritable(bamWindow,read,refWindow,chr,dist);
        context.write(bamWindow,dnaW);
    }
}

我正在使用以下命令编译包：

javac -classpath $MR_HADOOPJAR ${rootPath}mp/src/*.java
jar cvfm $mpJar $MR_MANIFEST ${rootPath}mp/src/*.class

这是 jar -tf mp/src/mp.jar 命令的结果：

META-INF/
META-INF/MANIFEST.MF
mnt/miczfs/tide/mp/src/DnaWritable.class
mnt/miczfs/tide/mp/src/mp.class
mnt/miczfs/tide/mp/src/TransMapper1.class
mnt/miczfs/tide/mp/src/TransMapper2.class
mnt/miczfs/tide/mp/src/TransReducer1.class
mnt/miczfs/tide/mp/src/TransReducer2.class

我运行用这个来完成工作：

mpJar=${rootPath}mp/src/mp.jar
mp_exec=mp
export HADOOP_CLASSPATH=$mpJar
hadoop $mp_exec <input path>

此外，我也试过这个命令：

hadoop jar $mp_exec <input path>

我将创建 jar 文件的方式更改为以下命令：

jar cf $mpJar $MR_MANIFEST ${rootPath}mp/src/*.class

通过此更改，错误已更改为：

Exception in thread "main" java.lang.ClassNotFoundException: mp
    at java.net.URLClassLoader.findClass(URLClassLoader.java:381)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:424)
    at java.lang.ClassLoader.loadClass(ClassLoader.java:357)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:348)
    at org.apache.hadoop.util.RunJar.main(RunJar.java:153)

所以，之前我的问题是程序找不到映射器class，现在找不到主要的class！！！有什么想法吗？？

谢谢大家

Answer 1

HADOOP_CLASSPATH 必须指定 JAR 文件所在的文件夹，因此无法找到 class 定义。

Answer 2

运行来自 hadoop 命令的 Mapreduce 作业需要 jar 文件、主类和其他参数..

Usage: hadoop jar <jar> [mainClass] args...

所以运行您的应用程序 jar 的命令应该是：

hadoop jar $mpJar $mp_exec <inputpath>

Hadoop 找不到映射器 class

Hadoop can not find the mapper class

java

hadoop

mapreduce

mapper