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利用Java连接Hadoop进行编程

作者：wr456wr

这篇文章主要介绍了利用Java连接Hadoop进行编程，文章围绕主题展开详细的内容介绍，具有一定的参考价值，感兴趣的小伙伴可以参考一下

实验环境

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

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>

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>

启动hadoop

sbin/start-dfs.sh

主机的hosts（C:\Windows\System32\drivers\etc）文件配置

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

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：

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：

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);
    }
}

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