创建一个maven工程

pom.xml引入如下依赖
<dependency>
  <groupId>org.apache.hadoop</groupId>
  <artifactId>hadoop-client</artifactId>
  <version>2.9.2</version>
</dependency>

复制hadoop环境下面的配置文件到resources目录

复制四个配置文件

编写HDFS客户端

package com.zhanghh.train;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.io.IOUtils;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;

import java.io.*;

/**
 * Hello world!
 *
 */
public class HdfsTest {
    Configuration conf;
    FileSystem fs;

    @Before
    public void before() throws Exception {
        //加载配置,默认会加载classpath下面的四个配置
        conf = new Configuration(true);
        //根据配置获取FileSystem API
        fs = FileSystem.get(conf);
    }

    @After
    public void after() throws Exception {
        fs.close();
    }

    /**
     * 创建目录
     * @throws Exception
     */
    @Test
    public void mkdir() throws Exception {
        Path path = new Path("/tmp");
        if (fs.exists(path)){
            fs.delete(path,true);
        }
        fs.mkdirs(path);
    }

    /**
     * 上传本地文件到HDFS指定文件
     * @throws Exception
     */
    @Test
    public void uploadFile() throws Exception {
        Path path = new Path("/tmp/test.txt");
        if(fs.exists(path)){
            fs.delete(path,false);
        }
        FSDataOutputStream outputStream = fs.create(path);
        File file = new File("C:\\Users\\zhanghh\\Desktop\\test.txt");
        InputStream inputStream = new BufferedInputStream(new FileInputStream(file));
        IOUtils.copyBytes(inputStream,outputStream,conf,true);
    }

    /**
     * 下载HDFS上的文件
     * @throws Exception
     */
    @Test
    public void downFile() throws Exception {
        Path path = new Path("/tmp/test.txt");
        FSDataInputStream inputStream = fs.open(path);
        BufferedOutputStream outputStream = new BufferedOutputStream(new FileOutputStream(new File("C:\\Users\\zhanghh\\Desktop\\222.txt")));
        IOUtils.copyBytes(inputStream,outputStream,conf,true);
    }

    /**
     * 查看文件存放的block位置信息
     * @throws Exception
     */
    @Test
    public void blockLoction() throws Exception {
        Path path = new Path("/tmp/test.txt");
        FileStatus fss=fs.getFileStatus(path);
        BlockLocation[] locations = fs.getFileBlockLocations(fss, 0, fss.getLen());
        for (BlockLocation obj:locations) {
            System.out.println(obj);
        }
    }

    /**
     * 删除文件
     * @throws Exception
     */
    @Test
    public void delete() throws Exception{
        Path path = new Path("/tmp");
        if (fs.exists(path)){
            fs.delete(path,true);
        }
    }
}

mapperReduce编写一个wordCount简单计算

package com.zhanghh.train;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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;

/**
 * <pre>
 * MR测试类
 * </pre>
 *
 * @author zhanghh
 * @create 2019/8/25
 */
public class MapperReduceTest {
    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration(true);
        Job job = Job.getInstance(conf);
        job.setJarByClass(MyWordCount.class); //设置程序入口
        job.setJobName("zhanghh_job");  //任务名称

        Path inputPath = new Path("/tmp/test.txt");
        FileInputFormat.addInputPath(job, inputPath); //输入路径

        Path outputPath = new Path("/tmp/output");
        if (outputPath.getFileSystem(conf).exists(outputPath)) {
            outputPath.getFileSystem(conf).delete(outputPath, true);
        }
        FileOutputFormat.setOutputPath(job, outputPath); //输出路径

        job.setMapperClass(MyWordCount.MyMapper.class);  //mapper类
        job.setMapOutputKeyClass(Text.class);            //mapper输出的key类型
        job.setMapOutputValueClass(IntWritable.class);   //mapper输出的value类型
        job.setReducerClass(MyWordCount.MyReducer.class);//reducer类

        // Submit the job, then poll for progress until the job is complete
        job.waitForCompletion(true);    //提交任务,等待job完成
    }
}

----------------------------------------------------------------------------------------------------------
package com.zhanghh.train;

import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;

import java.io.IOException;
import java.util.StringTokenizer;

/**
 * <pre>
 * 单词统计
 * </pre>
 *
 * @author zhanghh
 * @create 2019/8/27
 */
public class MyWordCount {

    public static class MyMapper extends Mapper<Object, Text, Text, IntWritable> {
        private IntWritable one=new IntWritable(1);
        private Text word = new Text();
        @Override
        protected void map(Object key, Text value, Context context) throws IOException, InterruptedException {
            StringTokenizer itr = new StringTokenizer(value.toString());
            while (itr.hasMoreTokens()){
                word.set(itr.nextToken());
                context.write(word,one);
            }
        }
    }

    public static class MyReducer extends Reducer<Text,IntWritable,Text,IntWritable> {
        private IntWritable result=new IntWritable();
        @Override
        protected void reduce(Text key, Iterable<IntWritable> values, Context context) throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable val:values) {
                 sum +=val.get();
            }
            result.set(sum);
            context.write(key,result);
        }
    }
}