利用Java连接Hadoop进行编程

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:


                org.testng
                testng
                RELEASE
                compile
            
            
                org.apache.hadoop
                hadoop-common
            
            
                org.apache.hadoop
                hadoop-hdfs
                3.3.2
            
            
                org.apache.hadoop
                hadoop-common
                3.3.2
            
            
                org.apache.hadoop
                hadoop-core
                1.2.1
            

虚拟机的/etc/hosts配置

利用Java连接Hadoop进行编程_第1张图片

hdfs-site.xml配置


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

利用Java连接Hadoop进行编程_第2张图片

core-site.xml配置


  
          hadoop.tmp.dir
          file:/root/rDesk/hadoop-3.3.2/tmp
          Abase for other temporary directories.
  
  
          fs.defaultFS
          hdfs://VM-12-11-ubuntu:9000
  

利用Java连接Hadoop进行编程_第3张图片

启动hadoop

sbin/start-dfs.sh

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

利用Java连接Hadoop进行编程_第4张图片

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

利用Java连接Hadoop进行编程_第5张图片

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:

利用Java连接Hadoop进行编程_第6张图片

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:

利用Java连接Hadoop进行编程_第7张图片

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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