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Hadoop 教程

前期准备

IDEA安装
- ~~IDEA2020.3.3~~
JDK安装
- ~~jdk18绿色版~~
IDEA中JDK配置
VMware安装
Hadoop 虚拟机
- 待补充

HDFS启动

1 2	shell复制代码cd app/hadoop-2.6.0-cdh5.7.0/sbin/ ./start-dfs.sh

在这里插入图片描述

Hadoop启动失败解决方法

重新编辑本机的hosts文件

1	bash复制代码sudo vim /etc/hosts

将 hadoop000 与 localhost 均改为本机ip

Hadoop Shell命令

浏览器可视化文件系统

路径遍历
- hadoop fs -ls [路径]
查看文件
- hadoop fs -cat [文件路径]
- eg：hadoop fs -cat /hadoopruochen/test/ruochen.txt
新建文件夹
- hadoop fs -mkdir -p [路径]
- -p：递归新建
- eg：hadoop fs -mkdir -p /hadoopruochen/test
传文件到 Hadoop
- hadoop fs -put [文件路径] [hadoop路径]
- eg：hadoop fs -put ruochen.txt /hadoopruochen/test
下载 Hadoop 文件到本地
- hadoop fs -get [hadoop文件路径] [本地路径]
- eg：hadoop fs -get /hadoopruochen/test/ruochen.txt haha.txt
移动文件
- hadoop fs -mv [源路径] [目的路径]
- eg：hadoop fs -mv /hadoopruochen/test/ruochen.txt /user
删除文件
- hadoop fs -rm [-r] [文件]
- eg：hadoop fs -rm /hadoopruochen
- eg：hadoop fs -rm -r /hadoopruochen

Java 操作 HDFS API

5.1. 新建项目

新建一个空项目，我这里起名为BigData
新建一个module
Finish 即可
pom.xml如下

xml复制代码<?xml version="1.0" encoding="UTF-8"?>

<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>com.neusoft</groupId>
    <artifactId>hadoopdemo</artifactId>
    <version>1.0-SNAPSHOT</version>

    <name>hadoopdemo</name>
    <!-- FIXME change it to the project's website -->
    <url>http://www.example.com</url>

    <properties>
        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <maven.compiler.source>1.7</maven.compiler.source>
        <maven.compiler.target>1.7</maven.compiler.target>
        <hadoop.version>2.6.0-cdh5.7.0</hadoop.version>
    </properties>
    <repositories>
        <repository>
            <id>cloudera</id>
            <url>https://repository.cloudera.com/artifactory/cloudera-repos/</url>
        </repository>
    </repositories>

    <dependencies>
        <!--        添加hadoop依赖-->
        <dependency>
            <groupId>org.apache.hadoop</groupId>
            <artifactId>hadoop-client</artifactId>
            <version>${hadoop.version}</version>
        </dependency>
        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
            <plugins>
                <!-- clean lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#clean_Lifecycle -->
                <plugin>
                    <artifactId>maven-clean-plugin</artifactId>
                    <version>3.1.0</version>
                </plugin>
                <!-- default lifecycle, jar packaging: see https://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_jar_packaging -->
                <plugin>
                    <artifactId>maven-resources-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.0</version>
                </plugin>
                <plugin>
                    <artifactId>maven-surefire-plugin</artifactId>
                    <version>2.22.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-jar-plugin</artifactId>
                    <version>3.0.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-install-plugin</artifactId>
                    <version>2.5.2</version>
                </plugin>
                <plugin>
                    <artifactId>maven-deploy-plugin</artifactId>
                    <version>2.8.2</version>
                </plugin>
                <!-- site lifecycle, see https://maven.apache.org/ref/current/maven-core/lifecycles.html#site_Lifecycle -->
                <plugin>
                    <artifactId>maven-site-plugin</artifactId>
                    <version>3.7.1</version>
                </plugin>
                <plugin>
                    <artifactId>maven-project-info-reports-plugin</artifactId>
                    <version>3.0.0</version>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>
</project>

5.2. 测试

5.2.1 新建文件夹

接下来，我们使用 Java 连接 hdfs，并新建一个文件夹
在test下新建HDFSApp.java，如下
通过测试方法连接HDFS，并新建一个/ruochen/test2文件夹，代码如下

java复制代码package com.neusoft.hdfs;

import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
import org.apache.hadoop.conf.Configuration;

import java.net.URI;

public class HDFSApp {
    Configuration configuration = null;
    FileSystem fileSystem = null;
    public static final String HDFS_PATH = "hdfs://192.168.10.128:8020";

    @Test
    public void mkdir() throws Exception {
        fileSystem.mkdirs(new Path("/ruochen/test2"));
    }

    // Java 连接hdfs 需要先建立一个连接
    // 测试方法执行之前要执行的操作
    @Before
    public void setUp() throws Exception {
        System.out.println("开始建立与HDFS的连接");
        configuration = new Configuration();
        fileSystem = FileSystem.get(new URI(HDFS_PATH), configuration, "hadoop");
    }

    // 测试之后要执行的代码
    @After
    public void tearDown() {
        configuration = null;
        fileSystem = null;
        System.out.println("关闭与HDFS的连接");
    }
}

然后运行mkdir()函数，运行完后我们可以看到已经新建了一个文件夹

5.2.2 新建文件

新建文件代码如下

java复制代码    // 创建文件
    @Test
    public void create() throws Exception {
        Path path = new Path("/ruochen/test1/hello.txt");
        FSDataOutputStream outputStream = fileSystem.create(path);
        outputStream.write("hello world".getBytes());
        outputStream.flush();
        outputStream.close();
    }

运行结束后，我们通过shell脚本查看一下

5.2.3 修改文件名称

Java代码如下

java复制代码   // rename文件
   @Test
   public void rename() throws Exception {
       Path oldPath = new Path("/ruochen/test1/hello.txt");
       Path newPath = new Path("/ruochen/test1/xixi.txt");
       fileSystem.rename(oldPath, newPath);
   }

运行结果如下

5.2.4 查看文件

Java代码如下

java复制代码    // 查看文件
    @Test
    public void cat() throws Exception {
        Path path = new Path("/ruochen/test1/xixi.txt");
        FSDataInputStream inputStream = fileSystem.open(path);
        IOUtils.copyBytes(inputStream, System.out, 1024);
        inputStream.close();
    }

运行结果

5.2.5 上传文件

Java 代码如下

java复制代码    // 上传文件
    @Test
    public void upload() throws Exception {
        Path localPath = new Path("cifar-10-python.tar.gz");
        Path hdfsPath = new Path("/");
        fileSystem.copyFromLocalFile(localPath, hdfsPath);
    }

运行完成后，我们可以看到 hdfs 已经成功显示刚才上传的文件

5.2.6 下载文件

Java 代码

java复制代码    // 下载文件
    @Test
    public void download() throws Exception {
        Path hdfsPath = new Path("/hadoop-2.6.0-cdh5.7.0.tar.gz");
        Path localPath = new Path("./down/hadoop-2.6.0-cdh5.7.0.tar.gz");
        fileSystem.copyToLocalFile(false, hdfsPath, localPath, true);
    }

运行完后我们可以看到当前目录 down 下已经有了刚刚下载的文件

Java 实现 WordCount

这里要注意在 main 下操作，test下是用来测试的

新建一个 WordCountApp 类
Java 代码如下

java复制代码package com.neusoft;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
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;

/**
 * 词频统计
 */
public class WordCountApp {
    /**
     * map 阶段
     */
    public static class MyMapper extends Mapper<LongWritable, Text, Text, LongWritable> {
        LongWritable one = new LongWritable(1);

        @Override
        protected void map(LongWritable key, Text value, Context context) throws IOException, InterruptedException {
            // 分
            String line = value.toString();
            // 拆分
            String[] s = line.split(" ");
            for (String word : s) {
                // 输出
                context.write(new Text(word), one);
            }
        }
    }

    /**
     * reduce 阶段
     */
    public static class MyReducer extends Reducer<Text, LongWritable, Text, LongWritable> {
        @Override
        protected void reduce(Text key, Iterable<LongWritable> values, Context context) throws IOException, InterruptedException {
            long sum = 0;
            // 合并统计
            for (LongWritable value : values) {
                // 求和
                sum += value.get();
            }
            context.write(key, new LongWritable(sum));
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration configuration = new Configuration();
        Job job = Job.getInstance(configuration, "wordcount");
        job.setJarByClass(WordCountApp.class);

        // 设置 map 相关参数
        FileInputFormat.setInputPaths(job, new Path(args[0]));
        job.setMapperClass(MyMapper.class);
        job.setMapOutputKeyClass(Text.class);
        job.setMapOutputValueClass(LongWritable.class);

        // 设置 reduce 相关参数
        job.setReducerClass(MyReducer.class);
        job.setOutputKeyClass(MyReducer.class);
        job.setOutputValueClass(LongWritable.class);

        Path outPath = new Path(args[1]);
        FileSystem fileSystem = FileSystem.get(configuration);
        if (fileSystem.exists(outPath)) {
            // 删除文件
            fileSystem.delete(outPath, true);
            System.out.println("输出路径已存在, 已被删除");
        }
        FileOutputFormat.setOutputPath(job, outPath);

        // 控制台输出详细信息
        // 输出：1  不输出：0
        System.exit(job.waitForCompletion(true) ? 0 : 1);
    }
}

打包程序
打包完成后，将 jar 包上传到 hadoop 虚拟机
首先通过shell命令将输出文件夹删除，不然重复执行会报错

1	shell复制代码hadoop fs -rm -r /output/wc

然后执行下列操作

1	shell复制代码hadoop jar hadoopdemo-1.0-SNAPSHOT.jar com.neusoft.WordCountApp hdfs://hadoop000:8020/ruochenchen.txt hdfs://hadoop000:8020/output/wc