前面项目中我们是创建的java项目来演示的，但是hadoop相关的依赖太多了，不方便，本文通过maven项目来演示HDFS的java API操作

创建maven项目

相关的依赖

<dependencies>
	<dependency>
		<groupId>org.apache.hadoop</groupId>
		<artifactId>hadoop-hdfs</artifactId>
		<version>2.5.0</version>
	</dependency>

	<dependency>
		<groupId>org.apache.hadoop</groupId>
		<artifactId>hadoop-client</artifactId>
		<version>2.5.1</version>
	</dependency>

	<dependency>
		<groupId>org.apache.hadoop</groupId>
		<artifactId>hadoop-common</artifactId>
		<version>2.5.0</version>
	</dependency>

	<dependency>
		<groupId>junit</groupId>
		<artifactId>junit</artifactId>
		<version>4.12</version>
	</dependency>
</dependencies>

CRUD 操作

package com.sxt.test;

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

import org.apache.commons.io.IOUtils;
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;


public class HdfsTest {

	FileSystem fs = null;
	
	Configuration conf = null;
	
	@Before
	public void test() throws Exception {
		// 1.加载配置文件
		conf = new Configuration(true);
		// 2.获取FileSystem对象
		fs = FileSystem.get(new URI("hdfs://hadoop-node01:9000"),conf,"root");
	}
	/**
	 * 上传文件
	 * @throws IOException 
	 * @throws IllegalArgumentException 
	 */
	@Test
	public void updateFile() throws IllegalArgumentException, IOException{
		fs.copyFromLocalFile(true, true, new Path("c:/unintall.log"), new Path("/"));
		fs.close();
	}
	
	/**
	 * 下载文件
	 * @throws Exception
	 */
	@Test
	public void testDownload() throws Exception {
		fs.copyToLocalFile(new Path("/a.txt"), new Path("c:/tools"));
		fs.close();
	}
	
	
	/**
	 * 打印参数
	 */
	@Test
	public void testConf(){
		Iterator<Entry<String, String>> it = conf.iterator();
		while(it.hasNext()){
			Entry<String, String> ent = it.next();
			System.out.println(ent.getKey() + " : " + ent.getValue());
		}
	}

	/**
	 * 创建文件夹
	 * @throws Exception
	 */
	@Test
	public void testMkdir() throws Exception {
		boolean mkdirs = fs.mkdirs(new Path("/testmkdir/aaa/bbb"));
		System.out.println(mkdirs);
		
	}
	
	/**
	 * 删除文件夹
	 * @throws Exception
	 */
	@Test
	public void testDelete() throws Exception {
		// recursive 是否递归删除
		boolean flag = fs.delete(new Path("/testmkdir/aaa"), true);
		System.out.println(flag);
		
	}
	
	/**
	 * 递归列出指定目录下所有子文件夹中的文件
	 * @throws Exception
	 */
	@Test
	public void testLs() throws Exception {
		
		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());
			System.out.println("------------------");
			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());
				//块所在的datanode节点
				String[] datanodes = b.getHosts();
				for(String dn:datanodes){
				System.out.println("datanode:" + dn);
				}
			}	
		}		
	}
	
	
	/**
	 * 获取文件的类型
	 * @throws Exception
	 */
	@Test
	public void testLs2() throws Exception {		
		FileStatus[] listStatus = fs.listStatus(new Path("/"));
		for(FileStatus file :listStatus){
			System.out.println("name: " + file.getPath().getName());
			System.out.println((file.isFile()?"file":"directory"));
		}
	}
	/**
	 * 通过流的方式将文件上传到HDFS系统中
	 * @throws Exception
	 * @throws IOException
	 */
	@Test
	public void testStreamUpload() throws Exception, IOException{
		// 输出流
		FSDataOutputStream out = fs.create(new Path("/dpb.txt"), true);
		// 字节输入流
		InputStream in = new FileInputStream("c:/tools/aaaaa.txt");
		IOUtils.copy(in, out);
		in.close();
		out.close();
	}
	
	/**
	 * 通过流的方式获取HDFS上的数据
	 * @throws Exception 
	 * @throws IllegalArgumentException 
	 */
	@Test
	public void testStreamDownload() throws IllegalArgumentException, Exception{
		FSDataInputStream in = fs.open(new Path("/dpb.txt"));
		OutputStream out = new FileOutputStream("c:/tools/a1.txt");
		IOUtils.copy(in, out);
		out.close();
		in.close();
	}
	
	/**
	 * 获取HDFS中的文件的一部分内容
	 * @throws Exception 
	 * @throws IllegalArgumentException 
	 */
	@Test
	public void testRandomAccess() throws IllegalArgumentException, Exception{
		FSDataInputStream in = fs.open(new Path("/dpb.txt"));
		in.seek(4);
		OutputStream out = new FileOutputStream("c:/tools/a2.txt");
		IOUtils.copy(in, out);
		out.close();
		in.close();
	}
	
	/**
	 * 显示HDFS上文件的内容
	 * @throws IOException 
	 * @throws IllegalArgumentException 
	 */
	@Test
	public void testCat() throws IllegalArgumentException, IOException{
		FSDataInputStream in = fs.open(new Path("/dpb.txt"));
		// 将输出的目的地执行控制台即可~
		IOUtils.copy(in, System.out);
	}
}

只放出最后一个方法的输出。其他方法执行效果请各自尝试