错误:java.lang.NullPointermap reduce程序的异常错误

Question

i map.java 类我尝试通过这个发送文件名

context.write（new Text（stringWord）， new Text（fileName））

回避.java

 import java.io.IOException;
 import org.apache.hadoop.io.*;
 import org.apache.hadoop.mapreduce.*;
 public class Reduce extends Reducer<Text, Text, Text, Text> {
@Override
public void reduce(Text key, Iterable<Text> values, Context context)
throws IOException, InterruptedException {
    int sum = 0;
    MapWritable occurenceInFile = new MapWritable();
    for (Text val : values) {
        if(occurenceInFile.containsKey(val)) {
            occurenceInFile.put(val, new IntWritable(1));
        } else {
            IntWritable occurence = (IntWritable) occurenceInFile.get(val);
            occurenceInFile.put(val, new IntWritable(occurence.get() + 1));
        }
        sum += 1;
    }
    String result = key.toString() + " (";
    boolean flag = false;
    for (Writable filenameWritable : occurenceInFile.keySet()) {
        if (flag) {
            result += ", ";
        }
        String filename = ((Text) filenameWritable).toString();
        result += filename + "=" + ((IntWritable) occurenceInFile.get(filenameWritable)).toString();
        flag = true;
    }
    result += ")nTotal occurence of "" + key + "": " + Integer.toString(sum);
    context.write(key, new Text(result));
}
}

错误代码此错误代码显示在 STDERR 中

Error: java.lang.NullPointerException
at Reduce.reduce(Reduce.java:18)
at Reduce.reduce(Reduce.java:6)
at org.apache.hadoop.mapreduce.Reducer.run(Reducer.java:180)
at org.apache.hadoop.mapred.ReduceTask.runNewReducer(ReduceTask.java:656)
at org.apache.hadoop.mapred.ReduceTask.run(ReduceTask.java:394)
at org.apache.hadoop.mapred.YarnChild$2.run(YarnChild.java:172)
at java.security.AccessController.doPrivileged(Native Method)
at javax.security.auth.Subject.doAs(Subject.java:415)
at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1657)
at org.apache.hadoop.mapred.YarnChild.main(YarnChild.java:166)

我开始编写字数统计程序，但我仍然不知道如何修复此错误。

Answer 1

我想行号#18是这个：

occurenceInFile.put(val, new IntWritable(occurence.get() + 1));

因此，在上一行读取occurence变量值可能是null 。另一种变体是occurence.get()值为 null .

因此，很难确切地建议导致它的原因，但您应该调试程序并找到为什么occurenceInFile.get(val);可以返回null值。