实验二：熟悉常用的HDFS操作

实验目的

1、理解HDFS在Hadoop体系结构中的角色
2、熟悉使用HDFS操作常用的Shell命令
3、熟悉HDFS操作常用的Java API

实验平台

1、操作系统：Windows
2、Hadoop版本：3.1.3
3、JDK版本：1.8
4、Java IDE：Eclipse

实验步骤

1、编程实现以下功能，并利用Hadoop提供的Shell命令完成相同任务
1）向 HDFS 中上传任意文本文件，如果指定的文件在 HDFS 中已经存在，则由用户来指定是追加到原有文件末尾还是覆盖原有的文件；
Shell 命令
检查文件是否存在，可以使用如下命令:

cd /usr/local/hadoop
./bin/hdfs dfs -test -e text.txt

执行完上述命令不会输出结果，需要继续输入命令查看结果：

echo $?

如果结果显示文件已经存在，则用户可以选择追加到原来文件末尾或者覆盖原来文件，
具体命令如下：

cd /usr/local/hadoop
./bin/hdfs dfs -appendToFile local.txt text.txt #追加到原文件末尾
./bin/hdfs dfs -copyFromLocal -f local.txt text.txt #覆盖原来文件，第一种命令形式
./bin/hdfs dfs -cp -f file:///home/hadoop/local.txt text.txt#覆盖原来文件，第二种命令形式

实际上，也可以不用上述方法，而是采用如下命令来实现：

if $(hdfs dfs -test -e text.txt);
then $(hdfs dfs -appendToFile local.txt text.txt);
else $(hdfs dfs -copyFromLocal -f local.txt text.txt);
fi

上述代码可视为一行代码，在终端中输入第一行代码后，代码不会立即被执行，可以继续输入第 2 行代码和第 3 行代码，直到输入 fi 以后，上述代码才会真正执行。另外，上述代码中，直接使用了 hdfs 命令，而没有给出命令的路径，因为，这里假设已经配置了 PATH环境变量，把 hdfs 命令的路径“/usr/local/hadoop/bin”写入了 PATH 环境变量中。

Java 代码
我们这里需要一个jar包来实现scphttp://www.ganymed.ethz.ch/ssh2/
项目目录结构如下：

HDFSApi.java

package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;

import HDFSApi.SCP;

public class HDFSApi {
	 
	 public static boolean test(Configuration conf, String path) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 	return fs.exists(new Path(path));
	 }
	 
	 public static void copyFromLocalFile(Configuration conf, String localFilePath, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path localPath = new Path(localFilePath);
		 Path remotePath = new Path(remoteFilePath);
		 
		 fs.copyFromLocalFile(false, true, localPath, remotePath);
		 fs.close();
	 }
	 
	 public static void appendToFile(Configuration conf, String localFilePath, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 
		 FileInputStream in = new FileInputStream(localFilePath);
		 
		 FSDataOutputStream out = fs.append(remotePath);
		 
		 byte[] data = new byte[1024];
		 int read = -1;
		 while ( (read = in.read(data)) > 0 ) {
			 out.write(data, 0, read);
		 }
		 out.close();
		 in.close();
		 fs.close();
	 }
	
	public static void main(String[] args) throws IOException {
		
		SCP.get();//通过SCP将linux上的文件下载到windows上
		
		Configuration conf = new Configuration();
		conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String localFilePath = "D:\local.txt"; // 本地路径
		String remoteFilePath = "/user/hadoop/text.txt"; // HDFS 路径
		String choice = "append"; // 若文件存在则追加到文件末尾
		// String choice = "overwrite"; // 若文件存在则覆盖
		try {
			
			Boolean fileExists = false;
			if (HDFSApi.test(conf, remoteFilePath)) {
				fileExists = true;
				System.out.println(remoteFilePath + " 已存在.");
			} else {
				System.out.println(remoteFilePath + " 不存在.");
			}
			
			if ( !fileExists) { // 文件不存在，则上传
				HDFSApi.copyFromLocalFile(conf, localFilePath, remoteFilePath);
				System.out.println(localFilePath + " 已上传至 " + remoteFilePath);
			} else if ( choice.equals("overwrite") ) { // 选择覆盖
				HDFSApi.copyFromLocalFile(conf, localFilePath, remoteFilePath);
				System.out.println(localFilePath + " 已覆盖 " + remoteFilePath);
			} else if ( choice.equals("append") ) { // 选择追加
				HDFSApi.appendToFile(conf, localFilePath, remoteFilePath);
				System.out.println(localFilePath + " 已追加至 " + remoteFilePath);
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

SCP.java

package HDFSApi;
import java.io.IOException;
import ch.ethz.ssh2.Connection;
import ch.ethz.ssh2.SCPClient;
public class SCP {
	public static void get() throws IOException{
		Connection conn = new Connection("192.168.43.200");
		conn.connect();
		boolean isAuthenticated = conn.authenticateWithPassword("root", "123456");
		if (isAuthenticated == false)
			throw new IOException("Authentication failed.");
		SCPClient client = new SCPClient(conn);
		client.get("/root/local.txt", "D:\");
		conn.close();
	}
}

log4j.properties

log4j.rootLogger=info,consolePrint,errorFile,logFile

log4j.appender.consolePrint.Encoding = UTF-8
log4j.appender.consolePrint = org.apache.log4j.ConsoleAppender
log4j.appender.consolePrint.Target = System.out
log4j.appender.consolePrint.layout = org.apache.log4j.PatternLayout
log4j.appender.consolePrint.layout.ConversionPattern=%d %p [%c] - %m%n

log4j.appender.logFile.Encoding = UTF-8
log4j.appender.logFile = org.apache.log4j.DailyRollingFileAppender
log4j.appender.logFile.File = D:/eclipse/log4j_properties_runlog/WorldCount_demo_run.log
log4j.appender.logFile.Append = true
log4j.appender.logFile.Threshold = info
log4j.appender.logFile.layout = org.apache.log4j.PatternLayout
log4j.appender.logFile.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

log4j.appender.errorFile.Encoding = UTF-8
log4j.appender.errorFile = org.apache.log4j.DailyRollingFileAppender
log4j.appender.errorFile.File = D:/eclipse/log4j_properties_runlog/WorldCount_demo_error.log
log4j.appender.errorFile.Append = true
log4j.appender.errorFile.Threshold = ERROR
log4j.appender.errorFile.layout = org.apache.log4j.PatternLayout
log4j.appender.errorFile.layout.ConversionPattern =%-d{yyyy-MM-dd HH:mm:ss}  [ %t:%r ] - [ %p ]  %m%n

2）从 HDFS 中下载指定文件，如果本地文件与要下载的文件名称相同，则自动对下载的文件重命名
shell命令

if $(hdfs dfs -test -e file:///home/hadoop/text.txt);
then $(hdfs dfs -copyToLocal text.txt ./text2.txt);
else $(hdfs dfs -copyToLocal text.txt ./text.txt);
fi

Java代码

HDFSApi

package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;

public class HDFSApi {
	 
	public static void copyToLocal(Configuration conf, String remoteFilePath, String localFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 File f = new File(localFilePath);
		 
		 if (f.exists()) {
			 System.out.println(localFilePath + " 已存在.");
			 Integer i = 0;
			 while (true) {
				 f = new File(localFilePath + "_" + i.toString());
				 if (!f.exists()) {
					 localFilePath = localFilePath + "_" + i.toString();
					 break;
				 }
				 i++;
			 }
			 System.out.println("将重新命名为: " + localFilePath);
		 }
		 
		 // 下载文件到本地
		 Path localPath = new Path(localFilePath);
		 fs.copyToLocalFile(remotePath, localPath);
		 fs.close();
	 }
	 
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String localFilePath = "D://text.txt"; // 本地路径
		String remoteFilePath = "/user/hadoop/text.txt"; // HDFS 路径
		try {
			HDFSApi.copyToLocal(conf, remoteFilePath, localFilePath);
			System.out.println("下载完成");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

（3）将 HDFS 中指定文件的内容输出到终端中
shell命令

hdfs dfs -cat text.txt

java命令

package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;
	public class HDFSApi {
	 
	 public static void cat(Configuration conf, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 FSDataInputStream in = fs.open(remotePath);
		 BufferedReader d = new BufferedReader(new InputStreamReader(in));
		 String line = null;
		 while ( (line = d.readLine()) != null ) {
			 System.out.println(line);
		 }
		 d.close();
		 in.close();
		 fs.close();
	 }
	 
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteFilePath = "/user/hadoop/text.txt"; // HDFS 路径
		try {
			System.out.println("读取文件: " + remoteFilePath);
			HDFSApi.cat(conf, remoteFilePath);
			System.out.println("n 读取完成");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

（4）显示 HDFS 中指定的文件的读写权限、大小、创建时间、路径等信息；
shell命令

 hdfs dfs -ls -h text.txt

Java代码

package HDFSApi;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;
import java.text.SimpleDateFormat;
public class HDFSApi {
	 
	 public static void ls(Configuration conf, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 FileStatus[] fileStatuses = fs.listStatus(remotePath);
		 for (FileStatus s : fileStatuses) {
			 System.out.println("路径: " + s.getPath().toString());
			 System.out.println("权限: " + s.getPermission().toString());
			 System.out.println("大小: " + s.getLen());
			 
			 Long timeStamp = s.getModificationTime();
			 SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
			 String date = format.format(timeStamp); 
			 System.out.println("时间: " + date);
		 }
		 fs.close();
	 }
	 
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		 conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteFilePath = "/user/hadoop/text.txt"; // HDFS 路径
		try {
			System.out.println("读取文件信息: " + remoteFilePath);
			HDFSApi.ls(conf, remoteFilePath);
			System.out.println("n 读取完成");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

（5）给定 HDFS 中某一个目录，输出该目录下的所有文件的读写权限、大小、创建时
间、路径等信息，如果该文件是目录，则递归输出该目录下所有文件相关信息；
shell命令

cd /usr/local/hadoop
./bin/hdfs dfs -ls -R -h /user/hadoop

java代码

package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;
import java.text.SimpleDateFormat;
public class HDFSApi {
	 
	public static void lsDir(Configuration conf, String remoteDir) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path dirPath = new Path(remoteDir);
		 
		 RemoteIterator remoteIterator = fs.listFiles(dirPath, true);
		 
		while (remoteIterator.hasNext()) {
			 FileStatus s = remoteIterator.next();
			 System.out.println("路径: " + s.getPath().toString());
			 System.out.println("权限: " + s.getPermission().toString());
			 System.out.println("大小: " + s.getLen());
			 
			 Long timeStamp = s.getModificationTime();
			 SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
			 String date = format.format(timeStamp); 
			 System.out.println("时间: " + date);
			 System.out.println();
		}
		 fs.close();
	} 
	 
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		 conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteDir = "/user/hadoop"; // HDFS 路径
		try {
			System.out.println("(递归)读取目录下所有文件的信息: " + remoteDir);
			HDFSApi.lsDir(conf, remoteDir);
			System.out.println("读取完成");
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

（6）提供一个 HDFS 内的文件的路径，对该文件进行创建和删除操作。如果文件所在
目录不存在，则自动创建目录；
shell命令

if $(hdfs dfs -test -d dir1/dir2);
then $(hdfs dfs -touchz dir1/dir2/filename);
else $(hdfs dfs -mkdir -p dir1/dir2 && hdfs dfs -touchz dir1/dir2/filename);
fi
hdfs dfs -rm dir1/dir2/filename #删除文件

java代码

package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;
public class HDFSApi {
	 
	public static boolean test(Configuration conf, String path) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 return fs.exists(new Path(path));
	}
	 
	public static boolean mkdir(Configuration conf, String remoteDir) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path dirPath = new Path(remoteDir);
		 boolean result = fs.mkdirs(dirPath);
		 fs.close();
		 return result;
	}
	 
	public static void touchz(Configuration conf, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 FSDataOutputStream outputStream = fs.create(remotePath);
		 outputStream.close();
		 fs.close();
	}
	 
	 
	public static boolean rm(Configuration conf, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 boolean result = fs.delete(remotePath, false);
		 fs.close();
		 return result;
	}
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		 conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteFilePath = "/user/hadoop/input/text.txt"; // HDFS 路径
		String remoteDir = "/user/hadoop/input"; // HDFS 路径对应的目录
		try {
			
			if ( HDFSApi.test(conf, remoteFilePath) ) {
				HDFSApi.rm(conf, remoteFilePath); // 删除
				System.out.println("删除路径: " + remoteFilePath);
			} else {
				if ( !HDFSApi.test(conf, remoteDir) ) { // 若目录不存在，则进行创建
					HDFSApi.mkdir(conf, remoteDir);
					System.out.println("创建文件夹: " + remoteDir);
				}
				HDFSApi.touchz(conf, remoteFilePath);
				System.out.println("创建路径: " + remoteFilePath);
			}
		} catch (Exception e) {
				e.printStackTrace();
		}
	}
}

（7）提供一个 HDFS 的目录的路径，对该目录进行创建和删除操作。创建目录时，如
果目录文件所在目录不存在，则自动创建相应目录；删除目录时，由用户指定
当该目录不为空时是否还删除该目录；
shell命令
创建目录的命令如下：

 hdfs dfs -mkdir -p dir1/dir2

删除目录的命令如下：

hdfs dfs -rmdir dir1/dir2

上述命令执行以后，如果目录非空，则会提示 not empty，删除操作不会执行。如果要
强制删除目录，可以使用如下命令：

hdfs dfs -rm -R dir1/dir2

java代码

package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;
public class HDFSApi {
	 
	public static boolean test(Configuration conf, String path) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 return fs.exists(new Path(path));
	}
	 
	public static boolean isDirEmpty(Configuration conf, String remoteDir) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path dirPath = new Path(remoteDir);
		 RemoteIterator remoteIterator = fs.listFiles(dirPath, true);
		 return !remoteIterator.hasNext();
	}
	 
	public static boolean mkdir(Configuration conf, String remoteDir) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path dirPath = new Path(remoteDir);
		 boolean result = fs.mkdirs(dirPath);
		 fs.close();
		 return result;
	}
	 
	 
	public static boolean rmDir(Configuration conf, String remoteDir) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path dirPath = new Path(remoteDir);
		 
		 boolean result = fs.delete(dirPath, true);
		 fs.close();
		 return result;
	}
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		 conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteDir = "/user/hadoop/input"; // HDFS 目录
		Boolean forceDelete = false; // 是否强制删除
		try {
			
			if ( !HDFSApi.test(conf, remoteDir) ) {
				HDFSApi.mkdir(conf, remoteDir); // 创建目录
				System.out.println("创建目录: " + remoteDir);
			} else {
				if ( HDFSApi.isDirEmpty(conf, remoteDir) || forceDelete ) { // 目录为空或强制删除
					HDFSApi.rmDir(conf, remoteDir);
					System.out.println("删除目录: " + remoteDir);
				} else { // 目录不为空
					System.out.println("目录不为空，不删除: " + remoteDir);
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

（8）向HDFS中指定的文件追加内容，由用户指定内容追加到原有文件的开头或结尾；
shell命令
追加到原文件末尾的命令如下：

 hdfs dfs -appendToFile local.txt text.txt

追加到原文件的开头，在 HDFS 中不存在与这种操作对应的命令，因此，无法使用一条
命令来完成。可以先移动到本地进行操作，再进行上传覆盖，具体命令如下：

hdfs dfs -get text.txt
cat text.txt >> local.txt
hdfs dfs -copyFromLocal -f local.txt text.txt

java代码

package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;
public class HDFSApi {
	 
	public static boolean test(Configuration conf, String path) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 return fs.exists(new Path(path));
	}
	 
	 public static void appendContentToFile(Configuration conf, String content, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 
		 FSDataOutputStream out = fs.append(remotePath);
		 out.write(content.getBytes());
		 out.close();
		 fs.close();
	}
	 
	 public static void appendToFile(Configuration conf, String localFilePath, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 
		 FileInputStream in = new FileInputStream(localFilePath);
		 
		 FSDataOutputStream out = fs.append(remotePath);
		 
		 byte[] data = new byte[1024];
		 int read = -1;
		 if(in!=null){
			while ( (read = in.read(data)) > 0 ) {
					out.write(data, 0, read);
			}
		 }
		 out.close();
		 in.close();
		 fs.close();
	}
	 
	 public static void moveToLocalFile(Configuration conf, String remoteFilePath, String localFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 Path localPath = new Path(localFilePath);
		 fs.moveToLocalFile(remotePath, localPath);
	}
	 
	 
	 public static void touchz(Configuration conf, String remoteFilePath) throws IOException { 
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 FSDataOutputStream outputStream = fs.create(remotePath);
		 outputStream.close();
		 fs.close();
	 }
 
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		 conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteFilePath = "/user/hadoop/text.txt"; // HDFS 文件
		String content = "新追加的内容n";
		//String choice = "after"; //追加到文件末尾
		 String choice = "before"; // 追加到文件开头
		try {
			
			if ( !HDFSApi.test(conf, remoteFilePath) ) {
				System.out.println("文件不存在: " + remoteFilePath);
			} else {
				if ( choice.equals("after") ) { // 追加在文件末尾
					HDFSApi.appendContentToFile(conf, content, remoteFilePath);
					System.out.println("已追加内容到文件末尾" + remoteFilePath);
				} else if ( choice.equals("before") ) { // 追加到文件开头
					
					
					String localTmpPath = "/user/hadoop/tmp.txt";
					// 移动到本地
					HDFSApi.moveToLocalFile(conf, remoteFilePath, localTmpPath);
					 // 创建一个新文件
					HDFSApi.touchz(conf, remoteFilePath); 
					 // 先写入新内容
					HDFSApi.appendContentToFile(conf, content, remoteFilePath);
					 // 再写入原来内容
					HDFSApi.appendToFile(conf, localTmpPath, remoteFilePath); 
					System.out.println("已追加内容到文件开头: " + remoteFilePath);
				}
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

注：这里选择追加到末尾没有问题，如果追加到头部会产生一个问题

Failed to replace a bad datanode on the existing pipeline due to no more good datanodes being available to try.

FSDataOutputStream out = fs.append(remotePath);
1）：如果集群中的文件是空文件，则能追加进去。
2）：如果集群中的文件有内容，则追加的时候会报错。
原因是因为hadoop环境中只有两个datanode slave1,slave2，太少的datanode节点导致追加操作错误太多。
解决方法
1、我们将datanode扩展至三个或以上，我们可以将master也加入datanode，这样就有了三个节点。

stop-all.sh  #停下hadoop
vi /usr/local/hadoop/etc/hadoop/workers  #增加master节点

start-all.sh  #启动hadoop

2、在管道中没有可用datanode时，生成新的datanode
我们需要在java代码中添加conf

conf.set("dfs.client.block.write.replace-datanode-on-failure.enable", "true");
 

conf.set("dfs.client.block.write.replace-datanode-on-failure.policy", "NEVER");

（9）删除 HDFS 中指定的文件
shell命令

hdfs dfs -rm text.txt

java代码

package HDFSApi;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;
public class HDFSApi {
	 
	public static boolean rm(Configuration conf, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 boolean result = fs.delete(remotePath, false);
		 fs.close();
		 return result;
	}
	 
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		 conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteFilePath = "/user/hadoop/text.txt"; // HDFS 文件
		try {
			if ( HDFSApi.rm(conf, remoteFilePath) ) {
				System.out.println("文件删除: " + remoteFilePath);
			} else {
				System.out.println("操作失败（文件不存在或删除失败）");
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

（10）在 HDFS 中，将文件从源路径移动到目的路径
shell命令

hdfs dfs -mv text.txt text2.txt

java代码

package HDFSApi;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.*;
import java.io.*;
public class HDFSApi {
	 
	 public static boolean mv(Configuration conf, String remoteFilePath, String remoteToFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path srcPath = new Path(remoteFilePath);
		 Path dstPath = new Path(remoteToFilePath);
		 boolean result = fs.rename(srcPath, dstPath);
		 fs.close();
		 return result;
	}
	 
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		 conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteFilePath = "hdfs:///user/hadoop/text.txt"; // 源文件 HDFS 路径
		String remoteToFilePath = "hdfs:///user/hadoop/new.txt"; // 目的 HDFS 路径
		try {
			if ( HDFSApi.mv(conf, remoteFilePath, remoteToFilePath) ) {
				System.out.println(" 将文件 " + remoteFilePath + " 移动到 " + remoteToFilePath);
			} else {
				System.out.println("操作失败(源文件不存在或移动失败)");
			}
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

（二）编程实现一个类“MyFSDataInputStream”

该类继承“org.apache.hadoop.fs.FSDataInputStream”，要求如下：实现按行读取 HDFS 中指定文件的方法“readLine()”，如果读到文件末尾，则返回空，否则返回文件一行的文本。

package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.*;
public class MyFSDataInputStream extends FSDataInputStream {
	public MyFSDataInputStream(InputStream in) {
		super(in);
	}
	
	public static String readline(BufferedReader br) throws IOException {
		char[] data = new char[1024];
		int read = -1;
		int off = 0; 
		// 循环执行时，br 每次会从上一次读取结束的位置继续读取
		//因此该函数里，off 每次都从 0 开始
		while ( (read = br.read(data, off, 1)) != -1 ) {
			if (String.valueOf(data[off]).equals("n") ) {
				off += 1;
				break;
			}
			off += 1;
		}
		if (off > 0) {
			return String.valueOf(data);
		} else {
			return null;
		}
	}
	
	public static void cat(Configuration conf, String remoteFilePath) throws IOException {
		 FileSystem fs = FileSystem.get(conf);
		 Path remotePath = new Path(remoteFilePath);
		 FSDataInputStream in = fs.open(remotePath);
		 BufferedReader br = new BufferedReader(new InputStreamReader(in));
		 String line = null;
		 while ( (line = MyFSDataInputStream.readline(br)) != null ) {
			 System.out.println(line);
		 }
		 br.close();
		 in.close();
		 fs.close();
	}
	
	public static void main(String[] args) {
		Configuration conf = new Configuration();
		 conf.set("fs.default.name","hdfs://192.168.43.200:9000");
		String remoteFilePath = "/user/hadoop/text.txt"; // HDFS 路径
		try {
			MyFSDataInputStream.cat(conf, remoteFilePath);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
}

（三）输出 HDFS 中指定文件的文本到终端中

查看 Java 帮助手册或其它资料，用“java.net.URL”和“org.apache.hadoop.fs.FsURLSt
reamHandlerFactory”编程完成输出 HDFS 中指定文件的文本到终端中。

package HDFSApi;
import org.apache.hadoop.fs.*;
import org.apache.hadoop.io.IOUtils;
import java.io.*;
import java.net.URL;
public class HDFSApi {
	static{ 
		URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory()); 
	 }
	 
	public static void main(String[] args) throws Exception {
		String remoteFilePath = "hdfs://192.168.43.200:9000/user/hadoop/text.txt"; // HDFS 文件
		InputStream in = null; 
		 try{ 
			 
			 in = new URL(remoteFilePath).openStream(); 
		 	IOUtils.copyBytes(in,System.out,4096,false); 
		 } finally{ 
			 IOUtils.closeStream(in); 
		 } 
	}
}

实验二：熟悉常用的HDFS操作

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