进行hdfs的上下载的时候，出现了空指针异常的问题

Question

在进行hdfs的上下载的时候，运行idea出现了空指针异常的问题

package com.ykd;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
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.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;

import java.io.IOException;

public class UseDemo_1 {
    public static void main(String[] args) throws IOException, ClassNotFoundException, InterruptedException {
        //1-声明  Job对象，把mian方法所在的类加载进来
        Job job = Job.getInstance(new Configuration(), UseDemo_1.class.getSimpleName());
        //2-关联   mapper类  reduce 类
        job.setMapperClass(DepMapper.class);
        job.setReducerClass(DepReducer.class);
        //3-分别  设置  mapper 输出的 key-value数据类型
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(IntWritable.class);
        //设置 reduce 输出的 key-value数据类型
        job.setMapOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);

        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));

        job.waitForCompletion(true);    //在这里出现问题
    }

    static class DepMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
        IntWritable valu = new IntWritable(1);
        Text outKey = new Text();
        @Override
        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            String str = new String(value.getBytes(), 0, value.getLength(), "GBK");
            String[] arrs = str.trim().split(",");
            if (null != arrs && arrs.length > 10 && arrs[10] != null) {
                System.out.println("第11个位置上的值是=" + arrs[10]);
                if (arrs[10].equals("非营运")) {
                    outKey.set("乘用车辆");
                    context.write(outKey, valu);
                } else {
                    outKey.set("商用车辆");
                    context.write(outKey, valu);
                }
            }
        }
    }

    static class DepReducer extends Reducer<Text, IntWritable, Text, DoubleWritable> {
        IntWritable valu = new IntWritable();
        DoubleWritable dw = new DoubleWritable();
        double all = 0;
        @Override
        protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable ele : values) {
                sum += ele.get();
            }
            all += sum;
            double rs = sum / all;
            dw.set(rs);
            context.write(key, dw);
        }

    }
}

报错内容：

log4j:WARN No appenders could be found for logger (org.apache.hadoop.metrics2.lib.MutableMetricsFactory).
log4j:WARN Please initialize the log4j system properly.
log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.
Exception in thread "main" java.lang.NullPointerException
    at java.lang.ProcessBuilder.start(ProcessBuilder.java:1012)
    at org.apache.hadoop.util.Shell.runCommand(Shell.java:483)
    at org.apache.hadoop.util.Shell.run(Shell.java:456)
    at org.apache.hadoop.util.Shell$ShellCommandExecutor.execute(Shell.java:722)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:815)
    at org.apache.hadoop.util.Shell.execCommand(Shell.java:798)
    at org.apache.hadoop.fs.RawLocalFileSystem.setPermission(RawLocalFileSystem.java:731)
    at org.apache.hadoop.fs.RawLocalFileSystem.mkOneDirWithMode(RawLocalFileSystem.java:489)
    at org.apache.hadoop.fs.RawLocalFileSystem.mkdirsWithOptionalPermission(RawLocalFileSystem.java:530)
    at org.apache.hadoop.fs.RawLocalFileSystem.mkdirs(RawLocalFileSystem.java:507)
    at org.apache.hadoop.fs.FilterFileSystem.mkdirs(FilterFileSystem.java:305)
    at org.apache.hadoop.mapreduce.JobSubmissionFiles.getStagingDir(JobSubmissionFiles.java:133)
    at org.apache.hadoop.mapreduce.JobSubmitter.submitJobInternal(JobSubmitter.java:144)
    at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1290)
    at org.apache.hadoop.mapreduce.Job$10.run(Job.java:1287)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1657)
    at org.apache.hadoop.mapreduce.Job.submit(Job.java:1287)
    at org.apache.hadoop.mapreduce.Job.waitForCompletion(Job.java:1308)
    at com.ykd.CarTypeDemo_5.main(CarTypeDemo_5.java:38)

Process finished with exit code 1

我重新配置过环境，也跟着网上资料尝试过他们的方法，也清理过缓存，还是没有解决这个问题。希望各位可以帮我看一下这个问题。

Answer 1

望采纳！点击该回答右侧的“采纳”按钮即可采纳！！！

我猜原因可能是某些对象没有正确初始化。

你可以尝试在这些对象使用前加上非空判断，或者检查是否存在某些配置参数或路径写错的情况。

例如，你可以在主函数的开头加上非空判断，以确保 args 数组不为空：

if (args == null || args.length < 2) {
System.out.println("请输入输入路径和输出路径");
return;
}

此外，你可以在 FileInputFormat.addInputPath 和 FileOutputFormat.setOutputPath 函数

调用之前加上非空判断，以确保 args[0] 和 args[1] 不为空。

在程序运行时，你还可以添加断点来调试程序，并检查对象的值是否正确。

如果你仍然无法解决问题，你可以尝试打印出调用堆栈信息来帮助查找问题。你可以使用下面的代码来打印堆栈信息：

e.printStackTrace();

我希望这些建议能帮助你解决空指针异常的问题