Hadoop Java API操作HDFS文件系统（Mac）

1、下载Hadoop的压缩包 tar.gz   https://mirrors.tuna.tsinghua.edu.cn/apache/hadoop/common/stable/

2、关联jar包

　　在eclipse中新建项目中，建lib文件夹，把要用的jar包拷贝进来，jar包在解压好的 hadoop-2.9.1/share/hadoop中

　　我们这里不拷贝，选择关联你所存放在电脑上的路径

　　在项目上右键选择 Bulid Path > Add Libraries > User Library > ok > new > 命名 > ok > Add External JARs > 选择jar包

　　  

　　

      

　　然后会看到项目下多了个包

　　

3、开始写代码

package bigdata.hdfs;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.net.URI;
import java.util.Iterator;
import java.util.Map.Entry;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.BlockLocation;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.LocatedFileStatus;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.RemoteIterator;
import org.junit.Before;
import org.junit.Test;

/* 客户端操作hdfs时，需要一个用户身份，
 * 默认情况下，hdfs客户端会从jvm中获取一个参数来作为自己的用户身份：-DHADOOP_USER_NAME=hadoop,
 * 解决方法方法有两种：
 * 1、设置外部参数；
 * 2、在代码中写明，用get方法时，选择三个参数的，将用户名传进去；
 */
public class HdfsClientDemo {
	FileSystem fs = null;

	@Before
	public void init() throws Exception {
		Configuration conf = new Configuration();
		//这里要识别master的话，需要修改本机hosts文件
		conf.set("fs.defaultFS", "hdfs://master:9000");
		//拿到一个文件操作系统的客户端实例对象
		fs = FileSystem.get(new URI("hdfs://master:9000"), conf, "wang");
	}

	// 上传
	@Test
	public void testUpload() throws Exception {
		fs.copyFromLocalFile(new Path("/Users/wang/Desktop/upload.jpg"),new Path("/upload_copy.jpg"));
		fs.close();
	}

	//下载
	@Test
	public void testDownload() throws Exception {
		fs.copyToLocalFile(new Path("/upload_copy.jpg"), new Path("/Users/wang/Desktop/download.jpg"));
		fs.close();
	}

	@Test
	public void testUpload2() throws Exception {
		//以流的方式上传
		FSDataOutputStream outputStream = fs.create(new Path("/liu.txt"));
		FileInputStream inputStream = new FileInputStream("/Users/wang/Desktop/");
		org.apache.commons.io.IOUtils.copy(inputStream, outputStream);
	}

	@Test
	public void testDownload2() throws Exception {
		//以流的方式下载
		FSDataInputStream InputStream= fs.open(new Path("/a.txt"));
		//指定读取文件的指针的起始位置
		InputStream.seek(12);
		FileOutputStream OutputStream = new FileOutputStream("/Users/wang/Desktop/a.txt");
		org.apache.commons.io.IOUtils.copy(InputStream, OutputStream);
	}

	//打印参数
	@Test
	public void testConf() {
		Configuration conf = new Configuration();
		Iterator<Entry<String, String>> it = conf.iterator();
		while(it.hasNext()) {
			Entry<String, String> en = it.next();
			System.out.println(en.getKey()+':'+en.getValue());
		}
	}

	@Test
	public void testLs() throws Exception{
		//递归列出所有文件，返回一个迭代器对象
		RemoteIterator<LocatedFileStatus> listFiles = fs.listFiles(new Path("/"), true);
		while (listFiles.hasNext()) {
			LocatedFileStatus fileStatus = listFiles.next();
			System.out.println("blocksize:"+fileStatus.getBlockSize());
			System.out.println("owner:"+fileStatus.getOwner());
			System.out.println("Replication:"+fileStatus.getReplication());
			System.out.println("Permission:"+fileStatus.getPermission());
			System.out.println("Name:"+fileStatus.getPath().getName());
			BlockLocation[] blockLocations = fileStatus.getBlockLocations();
			for(BlockLocation b:blockLocations) {
				System.out.println("块起始偏移量"+b.getOffset());
				System.out.println("块长度"+b.getLength());
				String[] hosts = b.getHosts();
				//块所在的datanode节点
				for(String host:hosts) {
					System.out.println("datanode:"+host);
				}
			}
			System.out.println("--------------------");
		}
	}

	@Test
	public void testLs2() throws Exception {
		//只列出一个层级
		FileStatus[] listStatus = fs.listStatus(new Path("/"));
		for(FileStatus file:listStatus) {
			System.out.print("name:"+file.getPath().getName()+",");
			System.out.println((file.isFile()?"file":"directory"));
		}
	}
}