Hadoop学习之hdfs的操作

1.将HDFS中的文件复制到本地

java 复制代码

package com.shujia.hdfs;

import org.apache.hadoop.conf.Configuration;
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 java.io.IOException;

public class Demo02Download {
    FileSystem fileSystem;

    // 创建执行对象
    // @Before: 前置通知, 在方法执行之前执行
    @Before
    public void getFileSystem() throws IOException {
        Configuration entries = new Configuration();
        entries.set("fs.defaultFS", "hdfs://master:9000");
        fileSystem = FileSystem.get(entries);
    }

    // 实现文件复制到本地
    // @Test的作用，省略了public static void main(String[] args) {，表示测试类的方法
    @Test
    public void getData() throws IOException {
        String hdfsPath = "/NOTICE.txt";
        String localPath = "data/";
        // 将HDFS中的文件复制到本地
        fileSystem.copyToLocalFile(new Path(hdfsPath),new Path(localPath));
    }


    // @After: 后置通知, 在方法执行之后执行 。
    @After
    public void close() throws IOException {
        fileSystem.close();
    }

}

2.上传数据到HDFS中

java 复制代码

package com.shujia.hdfs;

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

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class Demo04PutData {
    public static void main(String[] args) throws IOException, URISyntaxException, InterruptedException {
        /*
            上传数据到HDFS中
         */
        putData();
        putData2();
    }

    public static void putData() throws IOException {
        // 没有设置用户信息
        Configuration entries = new Configuration();
        entries.set("fs.defaultFS","hdfs://master:9000");
        FileSystem fileSystem = FileSystem.get(entries);
        // 从本地上传文件到HDFS上
        fileSystem.copyFromLocalFile(new Path("hadoop/data/students.txt"),new Path("/data/"));
        fileSystem.close();
    }

    public static void putData2() throws IOException, URISyntaxException, InterruptedException {
        // 设置了用户信息
        Configuration entries = new Configuration();
        entries.set("fs.defaultFS","hdfs://master:9000");
        /*
            FileSystem get(final URI uri, final Configuration conf,final String user)
         */
        URI uri = new URI("hdfs://master:9000");
        // 获取FileSystem的实体类对象（传递uri到get函数中吗，会更改上传到HDFS中文件的用户信息）
        FileSystem fileSystem = FileSystem.get(uri,entries,"root");
        fileSystem.copyFromLocalFile(new Path("hadoop/data/students.txt"),new Path("/data/"));
        fileSystem.close();
    }
}

3.在HDFS上创建文件目录

java 复制代码

package com.shujia.hdfs;

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

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class Demo05MakeDir {
    public static void main(String[] args) throws IOException, URISyntaxException, InterruptedException {
        /*
            上传数据到HDFS中
         */
        mkdir();
    }


    public static void mkdir() throws IOException, URISyntaxException, InterruptedException {
        // 设置了用户信息
        Configuration entries = new Configuration();
        entries.set("fs.defaultFS","hdfs://master:9000");

        URI uri = new URI("hdfs://master:9000");
        FileSystem fileSystem = FileSystem.get(uri,entries,"root");

        fileSystem.mkdirs(new Path("/api"));
//        fileSystem.mkdirs(new Path("/api/1/2"));

        fileSystem.close();
    }
}

4.删除HDFS上的文件目录

java 复制代码

package com.shujia.hdfs;

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

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class Demo06Delete {
    public static void main(String[] args) throws IOException, URISyntaxException, InterruptedException {
        delete();
    }
    public static void delete() throws IOException, URISyntaxException, InterruptedException {
        // 设置了用户信息
        Configuration entries = new Configuration();
        entries.set("fs.defaultFS","hdfs://master:9000");

        URI uri = new URI("hdfs://master:9000");
        FileSystem fileSystem = FileSystem.get(uri,entries,"root");

//        fileSystem.delete(new Path("/api/1/2"));
        //TODO 参数recursive:如果path是一个目录并设置为true，则删除该目录，否则抛出异常。
        //               在文件的情况下，递归可以设置为true或false。
        fileSystem.delete(new Path("/api"),true);
        fileSystem.close();
    }
}

5.查看HDFS文件系统中文件和目录的元数据

java 复制代码

package com.shujia.hdfs;

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

import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;

public class Demo07Liststatus {
    public static void main(String[] args) throws IOException, URISyntaxException, InterruptedException {
        getBlockLocation();
    }

    public static void getBlockLocation() throws IOException, URISyntaxException, InterruptedException {

        Configuration entries = new Configuration();
        entries.set("fs.defaultFS","hdfs://master:9000");

        URI uri = new URI("hdfs://master:9000");
        FileSystem fileSystem = FileSystem.get(uri,entries,"root");

        FileStatus fileStatus = fileSystem.getFileStatus(new Path("/hadoop-3.1.3.tar.gz"));
        System.out.println("路径:"+fileStatus.getPath());
        System.out.println("长度:"+fileStatus.getLen());
        System.out.println("副本数:"+fileStatus.getReplication());
        /*
            获取一个文件的文件指定开始和结束的部分数据所在的Block块位置
            BlockLocation[] getFileBlockLocations(FileStatus file,
                    long start, long len)
         */
        BlockLocation[] fileBlockLocations = fileSystem.getFileBlockLocations(fileStatus, 0, fileStatus.getLen());
        for (BlockLocation fileBlockLocation : fileBlockLocations) {
            System.out.println("整个长度："+fileBlockLocation.getLength());
            System.out.println("偏移量，从文件的什么位置开始："+fileBlockLocation.getOffset());
            System.out.println("整个主机："+fileBlockLocation.getHosts());
            System.out.println("整个名称："+fileBlockLocation.getNames());
        }
        fileSystem.close();
    }


    public static void getFileStatus() throws IOException, URISyntaxException, InterruptedException {

        Configuration entries = new Configuration();
        entries.set("fs.defaultFS","hdfs://master:9000");

        URI uri = new URI("hdfs://master:9000");
        FileSystem fileSystem = FileSystem.get(uri,entries,"root");

        // getFileStatus()获取FileStatus对象
        // FileStatus对象封装了文件系统中文件和目录的元数据，包括文件的长度、块大小、备份数、修改时间、所有者以及权限等信息。
        FileStatus fileStatus = fileSystem.getFileStatus(new Path("/hadoop-3.1.3.tar.gz"));
        System.out.println("路径:"+fileStatus.getPath());
        System.out.println("长度:"+fileStatus.getLen());
        System.out.println("副本数:"+fileStatus.getReplication());
        fileSystem.close();
    }



    public static void listStatus() throws IOException, URISyntaxException, InterruptedException {
        // 没有设置用户信息
        Configuration entries = new Configuration();
        entries.set("fs.defaultFS","hdfs://master:9000");

        URI uri = new URI("hdfs://master:9000");
        FileSystem fileSystem = FileSystem.get(uri,entries,"root");


        // listStatus()获取FileStatus对象数组，遍历根目录下的所有文件和目录的元数据
        FileStatus[] fileStatuses = fileSystem.listStatus(new Path("/"));
        for (FileStatus fileStatus : fileStatuses) {
            // 判断其是否为文件（检查这个抽象路径名表示的文件是否是普通文件），若为目录则输出其路径
            if (fileStatus.isFile()) {
                long blockSize = fileStatus.getBlockSize();
                System.out.println(fileStatus.getPath());
                System.out.println("Block块大小:"+blockSize);
                System.out.println("长度:"+fileStatus.getLen());
            }else {
                System.out.println(fileStatus.getPath());
            }
        }
        fileSystem.close();
    }
}