1、hdfs java demo

首先是添加相关的依赖包

<project xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>org.luozheng.hadoop</groupId>
    <artifactId>Hadoop-Hdfs-01</artifactId>
    <version>0.0.1-SNAPSHOT</version>


    <properties>
        <hadoop.version>3.0.1</hadoop.version>

    </properties>


    <dependencies>

        <!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-client -->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>${hadoop.version}</version>
        </dependency>
        
        <!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-hdfs -->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-hdfs</artifactId>
            <version>${hadoop.version}</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-common -->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-common</artifactId>
            <version>${hadoop.version}</version>
            <scope>provided</scope>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.codehaus.woodstox/woodstox-core-lgpl -->
        <dependency>
            <groupId>org.codehaus.woodstox</groupId>
            <artifactId>woodstox-core-lgpl</artifactId>
            <version>4.4.1</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.25</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-log4j12 -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-log4j12</artifactId>
            <version>1.7.25</version>
            <scope>test</scope>
        </dependency>

        <!-- https://mvnrepository.com/artifact/log4j/log4j -->
        <dependency>
            <groupId>log4j</groupId>
            <artifactId>log4j</artifactId>
            <version>1.2.17</version>
        </dependency>


        <!-- https://mvnrepository.com/artifact/commons-collections/commons-collections -->
        <dependency>
            <groupId>commons-collections</groupId>
            <artifactId>commons-collections</artifactId>
            <version>3.2.2</version>
        </dependency>

        <!-- https://mvnrepository.com/artifact/org.apache.commons/commons-configuration2 -->
        <dependency>
            <groupId>org.apache.commons</groupId>
            <artifactId>commons-configuration2</artifactId>
            <version>2.2</version>
        </dependency>
    </dependencies>
</project>

为啥会有这么多依赖，我也不知道，没找到官方配置，反正都是报错后一个个加的。
测试程序：

package org.luozheng.hadoop;

import java.io.FileInputStream;
import java.io.IOException;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.util.Progressable;

public class FileSystemApp {

    public static void main(String[] args) {
        try {
            // 1、获取hadoop文件系统操作对象
            Configuration config = new Configuration();
            String fsRootUrl = config.get("fs.defaultFS");
            System.out.println("fs.defaultFS = " + fsRootUrl);
            FileSystem fileSystem = FileSystem.newInstance(config);
            System.out.println("" + fileSystem);
            // 2、把本地文件上传到文件系统
            String localFilePath = "/home/luozheng/eclipseworkspace/Hadoop-Hdfs-01/src/main/java/org/luozheng/hadoop/FileSystemApp.java";
            FileInputStream inStream = new FileInputStream(localFilePath);
            String dstUrl = fsRootUrl + "/user/luozheng/hadooptest/FileSystemApp.java";
            Path dstPath = new Path(dstUrl);
            FSDataOutputStream outStream = fileSystem.create(dstPath, new Progressable() {
                public void progress() {
                    //System.out.println(".");
                }
            });

            // IOUtils.copyBytes(inStream, outStream, config);
            IOUtils.copyBytes(inStream, outStream, 4096, true);
            System.err.println("file upload successful !!!");

            // 3、文件下载
            FSDataInputStream dstInstream = fileSystem.open(dstPath);
            IOUtils.copyBytes(dstInstream, System.out, config, true);
            System.err.println("file download successful !!!");
        } catch (IllegalArgumentException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {

        }

    }

}

2、mapreducer java demo

package org.luozheng.hadoop;

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

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 WordCountMapper extends Mapper<LongWritable, Text, Text, IntWritable> {

    private final static IntWritable one = new IntWritable(1);
    private Text word = new Text();

    @Override
    protected void map(LongWritable key, Text value, Mapper<LongWritable, Text, Text, IntWritable>.Context context)
            throws IOException, InterruptedException {
        System.out.println("[luozheng] map key=" + key.get() + ",value=" + value.toString());
        StringTokenizer itr = new StringTokenizer(value.toString());
        while (itr.hasMoreTokens()) {
            word.set(itr.nextToken());
            // 轉換成另外的一個map，其key爲字符，value为字符出现的次数
            context.write(word, one);
        }

    }

}

package org.luozheng.hadoop;

import java.io.IOException;

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

public class WordCountReducer extends Reducer<Text,IntWritable,Text,IntWritable> {

    private IntWritable result = new IntWritable();
    
    @Override
    protected void reduce(Text key, Iterable<IntWritable> values,
            Reducer<Text, IntWritable, Text, IntWritable>.Context context) throws IOException, InterruptedException {
        System.out.println("[luozheng] reduce key=" + key.toString() + ",value=" + values);
        int sum = 0;
        for(IntWritable value : values) {
            sum += value.get();
        }
        result.set(sum);
        context.write(key, result);
    }

    
}

package org.luozheng.hadoop;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.mapred.JobConf;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.util.Tool;

/**
 * input -> map -> reducer -> output
 * @author root
 */
@SuppressWarnings("rawtypes")
public class AbstractMapReducer extends Configured implements Tool{
    
    private Class mapperClazz = null;
    private Class mapOutKeyClazz = null;
    private Class mapOutValueClazz = null;
    private Class reducerClazz = null;
    
    /**
     * AbstractMapReducer构造函数
     * @param mapperClazz MapperClass
     * @param mapOutKeyClazz MapOutputKeyClass
     * @param mapOutValueClazz MapOutputValueClass
     * @param reducerClazz ReducerClass
     */
    public AbstractMapReducer(Class mapperClazz, Class mapOutKeyClazz, Class mapOutValueClazz, Class reducerClazz) {
        setConf(new Configuration());
        this.mapperClazz = mapperClazz;
        this.mapOutKeyClazz = mapOutKeyClazz;
        this.mapOutValueClazz = mapOutValueClazz;
        this.reducerClazz = reducerClazz;
    }

    @SuppressWarnings({ "unchecked"})
    public int run(String[] args) throws Exception {
        if(args.length < 2) {
            System.out.println("[luozheng] please input handle data file and result file!");
            return -1;
        }
        
        // 第一步，创建JobConf
        JobConf jobConf = new JobConf(getConf());
//      jobConf.setJarByClass(this.getClass());
//      // 第二步，设置mapper
//      jobConf.setMapperClass(mapperClazz);
//      jobConf.setMapOutputKeyClass(mapOutKeyClazz);
//      jobConf.setMapOutputValueClass(mapOutValueClazz);
//      // 第三步，设置reducer
//      jobConf.setReducerClass(reducerClazz);
        // 第四步，基于JobConf创建一个Job
        Job job = Job.getInstance(jobConf, this.getClass().getName());
        job.setJarByClass(this.getClass());
        // 第二步，设置mapper
        job.setMapperClass(mapperClazz);
        job.setMapOutputKeyClass(mapOutKeyClazz);
        job.setMapOutputValueClass(mapOutValueClazz);
        // 第三步，设置reducer
        job.setReducerClass(reducerClazz);
        // 第一个参数为要处理的数据文件名
        FileInputFormat.addInputPath(job, new Path(args[0]));
        // 第二个参数为结果放置的路径
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        // 参数true的意思是是否输出处理的日志
        return (job.waitForCompletion(true)?0:-1);
    }
    
    
    
    
    

}

package org.luozheng.hadoop;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.util.ToolRunner;

public class WordCountMapReducer extends AbstractMapReducer{

    public WordCountMapReducer() {
        super(WordCountMapper.class, Text.class, IntWritable.class, WordCountReducer.class);
        System.out.println("====>" + WordCountMapper.class.isAssignableFrom(Mapper.class));
    }

    public static void main(String[] args) throws Exception {
        WordCountMapReducer mapReducer = new WordCountMapReducer();
        String hdfsRootUrl = mapReducer.getConf().get("fs.defaultFS");
        System.out.println(hdfsRootUrl);
        args = new String[] {
                hdfsRootUrl + "/user/luozheng/hadooptest/test",
                hdfsRootUrl + "/user/luozheng/hadooptest/test-luozheng-output"
        };
        
        Configuration configuration = new Configuration();
        int result = ToolRunner.run(configuration, mapReducer, args);
        System.out.println("[luozheng] result = " + result);
    }

}