After building a high-availability HDFS cluster, Java can be used in Eclipse to operate HDFS and read and write files.

Connecting HDFS with Eclipse

1. Place hadoop-eclipse-plugin-2.6.0.rar in the installation directory of eclipse, as follows:

2. Restart eclipse and click Open Perspective in the upper right corner of eclipse

3. Select the map/reduce view and click open

4. Right-click new Hadoop Location in the margin of the Map/Reduce Locations view below

5. Fill in a NameNode node in Host. My name is Noe1. If you do not modify the hosts file of the system, you will make a mistake. Fill in port 8020.

6. Modify the hosts file: C: Windows System32 drivers etc

7. After opening the hosts file, edit and add the routing of the four nodes of HDFS

8. Elipse connects the HDFS view:

9. Create a new dynamic web project to test HDFS:

In fact, the configuration files core-site.xml and hdfs-site.xml are copied from the installation directory of hadoop in node1 node.

Test source code:

package com.hpe.hadoop.hdfs;

import java.io.FileNotFoundException;
import java.io.IOException;

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.FileUtil;
import org.apache.hadoop.fs.HdfsBlockLocation;
import org.apache.hadoop.fs.Path;

import com.sun.xml.bind.v2.schemagen.xmlschema.List;

/**
 * 1,see file
 * 2,Create a new folder
 * 3,Upload files
 * 4,Download File
 * 5,Delete files
 * 6,Internal mobility
 * 7,Internal replication
 * 8,rename
 * 9,Create new files
 * 10,Writing file
 * 11,Read the contents of the document
 * @author eversec
 *
 */
public class TestHDFS {
	public static void main(String[] args) throws IOException {
		//Create configuration objects before operating HDFS
		Configuration conf = new Configuration(true);
		//Create objects that operate on HDFS
		FileSystem fs = FileSystem.get(conf);
		//View the contents of the file system
		List list = listFileSystem(fs,"/");
		
		//create folder
		createDir(fs,"/test/abc");
		
		//Upload files
		uploadFileToHDFS(fs,"d:/test.txt","/test/abc/");
		
		//Download File
		downLoadFileFromHDFS(fs,"/test/abc/test.txt","d:/");
		
		//Delete...
		
		//rename
		renameFile(fs,"/test/abc/test.txt","/test/abc/Angelababy.txt");
		
		//Internal Mobile Internal Replication
		innerCopyAndMoveFile(fs,conf,"/test/abc/Angelababy.txt","/");
		
		//Create a new file
		createNewFile(fs,"/test/abc/hanhong");
		
		//Writing file
		writeToHDFSFile(fs,"/test/abc/hanhong","hello world");
		//Additional writing
		appendToHDFSFile(fs,"/test/abc/hanhong","\nhello world");
		
		//Read the contents of the document
		readFromHDFSFile(fs,"/test/abc/hanhong");
		
		//Location of data acquisition
		getFileLocation(fs,"/test/abc/hanhong");
	}

	private static void getFileLocation(FileSystem fs, String string) throws IOException {
		FileStatus fileStatus = fs.getFileStatus(new Path(string));
		long len = fileStatus.getLen();
		BlockLocation[] fileBlockLocations = fs.getFileBlockLocations(fileStatus, 0, len);
		String[] hosts = fileBlockLocations[0].getHosts();
		for (String string2 : hosts) {
			System.out.println(string2);
		}
		
		HdfsBlockLocation blockLocation = (HdfsBlockLocation)fileBlockLocations[0];
		long blockId = blockLocation.getLocatedBlock().getBlock().getBlockId();
		System.out.println(blockId);
	}

	private static void readFromHDFSFile(FileSystem fs, String string) throws IllegalArgumentException, IOException {
		FSDataInputStream inputStream = fs.open(new Path(string));
		
		FileStatus fileStatus = fs.getFileStatus(new Path(string));
		
		
		
		long len = fileStatus.getLen();
		
		byte[] b = new byte[(int)len];
		int read = inputStream.read(b);
		while(read != -1){
			System.out.println(new String(b));
			read = inputStream.read(b);
		}
		
		
	}

	private static void appendToHDFSFile(FileSystem fs, String filePath, String content) throws IllegalArgumentException, IOException {
		FSDataOutputStream append = fs.append(new Path(filePath));
		append.write(content.getBytes("UTF-8"));
		append.flush();
		append.close();
	}

	private static void writeToHDFSFile(FileSystem fs, String filePath, String content) throws IllegalArgumentException, IOException {
		 FSDataOutputStream outputStream = fs.create(new Path(filePath));
		 outputStream.write(content.getBytes("UTF-8"));
		 outputStream.flush();
		 outputStream.close();
	}

	private static void createNewFile(FileSystem fs, String string) throws IllegalArgumentException, IOException {
		fs.createNewFile(new Path(string));
	}

	private static void innerCopyAndMoveFile(FileSystem fs, Configuration conf,String src, String dest) throws IOException {
		Path srcPath = new Path(src);
		Path destPath = new Path(dest);
		
		//Internal copy
//		FileUtil.copy(srcPath.getFileSystem(conf), srcPath, destPath.getFileSystem(conf), destPath,false, conf);
		//Internal mobility
		FileUtil.copy(srcPath.getFileSystem(conf), srcPath, destPath.getFileSystem(conf), destPath,true, conf);
	}

	private static void renameFile(FileSystem fs, String src, String dest) throws IOException {
		Path srcPath = new Path(src);
		Path destPath = new Path(dest);
		
		fs.rename(srcPath, destPath);
	
	}

	private static void downLoadFileFromHDFS(FileSystem fs, String src, String dest) throws IOException {
		Path srcPath = new Path(src);
		Path destPath = new Path(dest);
		//copyToLocal
//		fs.copyToLocalFile(srcPath, destPath);
		//moveToLocal
		fs.copyToLocalFile(true,srcPath, destPath);
	}

	private static void uploadFileToHDFS(FileSystem fs, String src, String dest) throws IOException {
		Path srcPath = new Path(src);
		Path destPath = new Path(dest);
		//copyFromLocal
//		fs.copyFromLocalFile(srcPath, destPath);
		//moveFromLocal
		fs.copyFromLocalFile(true,srcPath, destPath);
	}

	private static void createDir(FileSystem fs, String string) throws IllegalArgumentException, IOException {
		Path path = new Path(string);
		if(fs.exists(path)){
			fs.delete(path, true);
		}
		fs.mkdirs(path);
	}

	private static List listFileSystem(FileSystem fs, String path) throws FileNotFoundException, IOException {
		Path ppath = new Path(path);
		
		FileStatus[] listStatus = fs.listStatus(ppath);
		
		for (FileStatus fileStatus : listStatus) {
			System.out.println(fileStatus.getPath());
		}
		
		return null;
	}
}