[大数据] 使用Java连接Hadoop进行编程

开发: C++知识库 Java知识库 JavaScript Python PHP知识库人工智能区块链大数据移动开发嵌入式开发工具数据结构与算法开发测试游戏开发网络协议系统运维
教程: HTML教程 CSS教程 JavaScript教程 Go语言教程 JQuery教程 VUE教程 VUE3教程 Bootstrap教程 SQL数据库教程 C语言教程 C++教程 Java教程 Python教程 Python3教程 C#教程
数码: 电脑笔记本显卡显示器固态硬盘硬盘耳机手机 iphone vivo oppo 小米华为单反装机图拉丁

-> 大数据 -> 使用Java连接Hadoop进行编程 -> 正文阅读

[大数据]使用Java连接Hadoop进行编程

文章目录

实验环境

hadoop版本：3.3.2
jdk版本：1.8
hadoop安装系统：ubuntu18.04
编程环境：IDEA
编程主机：windows

实验内容

测试Java远程连接hadoop

创建maven工程，引入以下依赖：

			<dependency>
                <groupId>org.testng</groupId>
                <artifactId>testng</artifactId>
                <version>RELEASE</version>
                <scope>compile</scope>
            </dependency>
            <dependency>
                <groupId>org.apache.hadoop</groupId>
                <artifactId>hadoop-common</artifactId>
            </dependency>
            <dependency>
                <groupId>org.apache.hadoop</groupId>
                <artifactId>hadoop-hdfs</artifactId>
                <version>3.3.2</version>
            </dependency>
            <dependency>
                <groupId>org.apache.hadoop</groupId>
                <artifactId>hadoop-common</artifactId>
                <version>3.3.2</version>
            </dependency>
            <dependency>
                <groupId>org.apache.hadoop</groupId>
                <artifactId>hadoop-core</artifactId>
                <version>1.2.1</version>
            </dependency>

虚拟机的/etc/hosts配置
在这里插入图片描述

hdfs-site.xml配置


<configuration>
        <property>
                <name>dfs.replication</name>
                <value>1</value>
        </property>
        <property>
                <name>dfs.namenode.name.dir</name>
                <value>file:/root/rDesk/hadoop-3.3.2/tmp/dfs/name</value>
        </property>
        <property>
                <name>dfs.datanode.http.address</name>
                <value>VM-12-11-ubuntu:50010</value>
        </property>
        <property>
                <name>dfs.client.use.datanode.hostname</name>
                <value>true</value>
        </property>
        <property>
                <name>dfs.datanode.data.dir</name>
                <value>file:/root/rDesk/hadoop-3.3.2/tmp/dfs/data</value>
        </property>
</configuration>

在这里插入图片描述

core-site.xml配置

<configuration>
  <property>
          <name>hadoop.tmp.dir</name>
          <value>file:/root/rDesk/hadoop-3.3.2/tmp</value>
          <description>Abase for other temporary directories.</description>
  </property>
  <property>
          <name>fs.defaultFS</name>
          <value>hdfs://VM-12-11-ubuntu:9000</value>
  </property>
</configuration>

在这里插入图片描述

启动hadoop

sbin/start-dfs.sh

主机的hosts（C:\Windows\System32\drivers\etc）文件配置
在这里插入图片描述

尝试连接到虚拟机的hadoop并读取文件内容，这里我读取hdfs下的/root/iinput文件内容
在这里插入图片描述

；

Java代码：

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.DistributedFileSystem;

public class TestConnectHadoop {
    public static void main(String[] args) throws Exception {

        String hostname = "VM-12-11-ubuntu";
        String HDFS_PATH = "hdfs://" + hostname + ":9000";
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", HDFS_PATH);
        conf.set("fs.hdfs.impl", DistributedFileSystem.class.getName());
        conf.set("dfs.client.use.datanode.hostname", "true");

        FileSystem fs = FileSystem.get(conf);
        FileStatus[] fileStatuses = fs.listStatus(new Path("/"));
        for (FileStatus fileStatus : fileStatuses) {
            System.out.println(fileStatus.toString());
        }
        FileStatus fileStatus = fs.getFileStatus(new Path("/root/iinput"));
        System.out.println(fileStatus.getOwner());
        System.out.println(fileStatus.getGroup());

        System.out.println(fileStatus.getPath());
        FSDataInputStream open = fs.open(fileStatus.getPath());
        byte[] buf = new byte[1024];
        int n = -1;
        StringBuilder sb = new StringBuilder();
        while ((n = open.read(buf)) > 0) {
            sb.append(new String(buf, 0, n));
        }
        System.out.println(sb);
    }
}

运行结果：
在这里插入图片描述

编程实现一个类“MyFSDataInputStream”，该类继承“org.apache.hadoop.fs.FSDataInputStream",要求如下：

①实现按行读取HDFS中指定文件的方法”readLine（）“，如果读到文件末尾，则返回为空，否则返回文件一行的文本

思路：emmm我的思路比较简单，只适用于该要求，仅作参考。
将所有的数据读取出来存储起来，然后根据换行符进行拆分，将拆分的字符串数组存储起来，用于readline返回

Java代码

import org.apache.hadoop.fs.FSDataInputStream;

import java.io.IOException;
import java.io.InputStream;

public class MyFSDataInputStream extends FSDataInputStream {

    private String data = null;

    private String[] lines = null;

    private int count = 0;

    private FSDataInputStream in;

    public MyFSDataInputStream(InputStream in) throws IOException {
        super(in);
        this.in = (FSDataInputStream) in;
        init();
    }

    private void init() throws IOException {
        byte[] buf = new byte[1024];
        int n = -1;
        StringBuilder sb = new StringBuilder();
        while ((n = this.in.read(buf)) > 0) {
            sb.append(new String(buf, 0, n));
        }
        data = sb.toString();
        lines = data.split("\n");
    }
    
    /**
     * 实现按行读取HDFS中指定文件的方法”readLine（）“，如果读到文件末尾，则返回为空，否则返回文件一行的文本
     */
    public String read_line() {
        return count < lines.length ? lines[count++] : null;
    }

}

测试类：

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.DistributedFileSystem;

public class TestConnectHadoop {
    public static void main(String[] args) throws Exception {

        String hostname = "VM-12-11-ubuntu";
        String HDFS_PATH = "hdfs://" + hostname + ":9000";
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", HDFS_PATH);
        conf.set("fs.hdfs.impl", DistributedFileSystem.class.getName());
        conf.set("dfs.client.use.datanode.hostname", "true");
        FileSystem fs = FileSystem.get(conf);
        FileStatus fileStatus = fs.getFileStatus(new Path("/root/iinput"));
        System.out.println(fileStatus.getOwner());
        System.out.println(fileStatus.getGroup());
        System.out.println(fileStatus.getPath());
        FSDataInputStream open = fs.open(fileStatus.getPath());
        MyFSDataInputStream myFSDataInputStream = new MyFSDataInputStream(open);
        String line = null;
        int count = 0;
        while ((line = myFSDataInputStream.read_line()) != null ) {
            System.out.printf("line %d is: %s\n", count++, line);
        }
        System.out.println("end");

    }
}

运行结果：
在这里插入图片描述

②实现缓存功能，即利用”MyFSDataInputStream“读取若干字节数据时，首先查找缓存，如果缓存中有所需要数据，则直接由缓存提供，否则从HDFS中读取数据

import org.apache.hadoop.fs.FSDataInputStream;

import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;

public class MyFSDataInputStream extends FSDataInputStream {

    private BufferedInputStream buffer;

    private String[] lines = null;

    private int count = 0;

    private FSDataInputStream in;

    public MyFSDataInputStream(InputStream in) throws IOException {
        super(in);
        this.in = (FSDataInputStream) in;
        init();
    }

    private void init() throws IOException {
        byte[] buf = new byte[1024];
        int n = -1;
        StringBuilder sb = new StringBuilder();
        while ((n = this.in.read(buf)) > 0) {
            sb.append(new String(buf, 0, n));
        }
        //缓存数据读取
        buffer = new BufferedInputStream(this.in);
        lines = sb.toString().split("\n");
    }

    /**
     * 实现按行读取HDFS中指定文件的方法”readLine（）“，如果读到文件末尾，则返回为空，否则返回文件一行的文本
     */
    public String read_line() {
        return count < lines.length ? lines[count++] : null;
    }

    @Override
    public int read() throws IOException {
        return this.buffer.read();
    }
    
    public int readWithBuf(byte[] buf, int offset, int len) throws IOException {
        return this.buffer.read(buf, offset, len);
    }
    
    public int readWithBuf(byte[] buf) throws IOException {
        return this.buffer.read(buf);
    }
}