Hadoop实验——熟悉常用的HDFS操作

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一，编程实现以下指定功能，并利用Hadoop提供的Shell命令完成相同任务：

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，由用户指定是追加到原有文件末尾还是覆盖原有的文件

Shell命令实现:1.先到Hadoop主文件夹cd /usr/local/hadoop2.启动Hadoop服务

sbin/start-dfs.shsbin/start-yarn.sh

3.创建两个任意文本文件用于实验

echo "hello world" > local.txtecho "hello hadoop" >text.txt

4.创建用户工作目录(HDFS默认工作目录格式为/user/当前用户)

hadoop fs -mkdir -p /user/当前用户名

5.检查文件是否存在

hadoop fs -test -e text.txtecho $?

6.上传本地文件到HDFS系统
hadoop fs -put text.txt

7.追加到文件末尾的指令
hadoop fs -appendToFile local.txt text.txt

8.查看HDFS文件的内容
hadoop fs -cat text.txt

9.覆盖原有文件的指令(覆盖之后再执行一遍上一步)
hadoop fs -copyFromLocal -f local.txt text.txt

10.以上步骤也可以用如下命令实现

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

package cn.edu.zucc.hdfs;import java.io.FileInputStream;import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataOutputStream;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;public class CopyFromLocalFile {/**    * 判断路径是否存在 */public static boolean test(Configuration conf, String path) {       try (FileSystem fs = FileSystem.get(conf)) {           return fs.exists(new Path(path));

       } catch (IOException e) {           e.printStackTrace();           return false;       }   }   /**    * 复制文件到指定路径 若路径已存在，则进行覆盖    */   public static void copyFromLocalFile(Configuration conf,           String localFilePath, String remoteFilePath) {       Path localPath = new Path(localFilePath);       Path remotePath = new Path(remoteFilePath);       try (FileSystem fs = FileSystem.get(conf)) {           /* fs.copyFromLocalFile 第一个参数表示是否删除源文件，第二个参数表示是否覆盖 */           fs.copyFromLocalFile(false, true, localPath, remotePath);       } catch (IOException e) {           e.printStackTrace();       }   }   /**    * 追加文件内容    */   public static void appendToFile(Configuration conf, String localFilePath,           String remoteFilePath) {       Path remotePath = new Path(remoteFilePath);       try (FileSystem fs = FileSystem.get(conf);               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();       } catch (IOException e) {           e.printStackTrace();       }   }   /**    * 主函数    */   public static void main(String[] args) {       Configuration conf = new Configuration();       conf.set("fs.defaultFS", "hdfs://localhost:9000");       String localFilePath = "/usr/local/hadoop/text.txt"; // 本地路径       String remoteFilePath = "/user/tiny/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 {           /* 判断文件是否存在 */           boolean fileExists = false;           if (CopyFromLocalFile.test(conf, remoteFilePath)) {               fileExists = true;               System.out.println(remoteFilePath + " 已存在.");           } else {               System.out.println(remoteFilePath + " 不存在.");           }           /* 进行处理 */           if (!fileExists) { // 文件不存在，则上传               CopyFromLocalFile.copyFromLocalFile(conf, localFilePath,                       remoteFilePath);               System.out.println(localFilePath + " 已上传至 " + remoteFilePath);           } else if (choice.equals("overwrite")) { // 选择覆盖               CopyFromLocalFile.copyFromLocalFile(conf, localFilePath,                       remoteFilePath);               System.out.println(localFilePath + " 已覆盖 " + remoteFilePath);           } else if (choice.equals("append")) { // 选择追加               CopyFromLocalFile.appendToFile(conf, localFilePath,                       remoteFilePath);               System.out.println(localFilePath + " 已追加至 " + remoteFilePath);           }       } catch (Exception e) {           e.printStackTrace();       }   }}

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命令实现:

if $(hadoop fs -test -e /usr/local/hadoop/text.txt);then $(hadoop fs -copyToLocal text.txt ./text.txt); else $(hadoop fs -copyToLocal text.txt ./text2.txt); fi

package cn.edu.zucc.hdfs;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.*;import org.apache.hadoop.fs.FileSystem;import java.io.*;public class CopyToLocal {    /**     * 下载文件到本地 判断本地路径是否已存在，若已存在，则自动进行重命名     */    public static void copyToLocal(Configuration conf, String remoteFilePath,            String localFilePath) {        Path remotePath = new Path(remoteFilePath);        try (FileSystem fs = FileSystem.get(conf)) {            File f = new File(localFilePath);            /* 如果文件名存在，自动重命名(在文件名后面加上 _0, _1 ...) */            if (f.exists()) {                System.out.println(localFilePath + " 已存在.");                Integer i = Integer.valueOf(0);                while (true) {                    f = new File(localFilePath + "_" + i.toString());                    if (!f.exists()) {                        localFilePath = localFilePath + "_" + i.toString();                        break;                    } else {                        i++;                        continue;                    }                }                System.out.println("将重新命名为: " + localFilePath);            }            // 下载文件到本地    

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，由用户指定是追加到原有文件末尾还是覆盖原有的文件

Shell命令实现:1.先到Hadoop主文件夹cd /usr/local/hadoop

2.启动Hadoop服务

sbin/start-dfs.shsbin/start-yarn.sh

3.创建两个任意文本文件用于实验

echo "hello world" > local.txtecho "hello hadoop" >text.txt

4.创建用户工作目录(HDFS默认工作目录格式为/user/当前用户)

hadoop fs -mkdir -p /user/当前用户名

5.检查文件是否存在

hadoop fs -test -e text.txtecho $?

6.上传本地文件到HDFS系统
hadoop fs -put text.txt

7.追加到文件末尾的指令
hadoop fs -appendToFile local.txt text.txt

8.查看HDFS文件的内容
hadoop fs -cat text.txt

9.覆盖原有文件的指令(覆盖之后再执行一遍上一步)
hadoop fs -copyFromLocal -f local.txt text.txt

10.以上步骤也可以用如下命令实现

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

 package cn.edu.zucc.hdfs;import java.io.FileInputStream;import java.io.IOException;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataOutputStream;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;public class CopyFromLocalFile {   /**    * 判断路径是否存在    */   public static boolean test(Configuration conf, String path) {       try (FileSystem fs = FileSystem.get(conf)) {           return fs.exists(new Path(path));       } catch (IOException e) {           e.printStackTrace();           return false;       }   }   /**    * 复制文件到指定路径 若路径已存在，则进行覆盖    */   public static void copyFromLocalFile(Configuration conf,           String localFilePath, String remoteFilePath) {       Path localPath = new Path(localFilePath);       Path remotePath = new Path(remoteFilePath);       try (FileSystem fs = FileSystem.get(conf)) {           /* fs.copyFromLocalFile 第一个参数表示是否删除源文件，第二个参数表示是否覆盖 */           fs.copyFromLocalFile(false, true, localPath, remotePath);       } catch (IOException e) {           e.printStackTrace();       }   }   /**    * 追加文件内容    */   public static void appendToFile(Configuration conf, String localFilePath,           String remoteFilePath) {       Path remotePath = new Path(remoteFilePath);       try (FileSystem fs = FileSystem.get(conf);               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();       } catch (IOException e) {           e.printStackTrace();       }   }   /**    * 主函数    */   public static void main(String[] args) {       Configuration conf = new Configuration();       conf.set("fs.defaultFS", "hdfs://localhost:9000");       String localFilePath = "/usr/local/hadoop/text.txt"; // 本地路径       String remoteFilePath = "/user/tiny/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 {           /* 判断文件是否存在 */           boolean fileExists = false;           if (CopyFromLocalFile.test(conf, remoteFilePath)) {               fileExists = true;               System.out.println(remoteFilePath + " 已存在.");           } else {               System.out.println(remoteFilePath + " 不存在.");           }           /* 进行处理 */           if (!fileExists) { // 文件不存在，则上传               CopyFromLocalFile.copyFromLocalFile(conf, localFilePath,                       remoteFilePath);               System.out.println(localFilePath + " 已上传至 " + remoteFilePath);           } else if (choice.equals("overwrite")) { // 选择覆盖               CopyFromLocalFile.copyFromLocalFile(conf, localFilePath,                       remoteFilePath);               System.out.println(localFilePath + " 已覆盖 " + remoteFilePath);           } else if (choice.equals("append")) { // 选择追加               CopyFromLocalFile.appendToFile(conf, localFilePath,                       remoteFilePath);               System.out.println(localFilePath + " 已追加至 " + remoteFilePath);           }       } catch (Exception e) {           e.printStackTrace();       }   }}

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命令实现:

if $(hadoop fs -test -e /usr/local/hadoop/text.txt);then $(hadoop fs -copyToLocal text.txt ./text.txt); else $(hadoop fs -copyToLocal text.txt ./text2.txt); fi

package cn.edu.zucc.hdfs;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.*;import org.apache.hadoop.fs.FileSystem;import java.io.*;public class CopyToLocal {    /**     * 下载文件到本地 判断本地路径是否已存在，若已存在，则自动进行重命名     */    public static void copyToLocal(Configuration conf, String remoteFilePath,            String localFilePath) {        Path remotePath = new Path(remoteFilePath);        try (FileSystem fs = FileSystem.get(conf)) {            File f = new File(localFilePath);            /* 如果文件名存在，自动重命名(在文件名后面加上 _0, _1 ...) */            if (f.exists()) {                System.out.println(localFilePath + " 已存在.");                Integer i = Integer.valueOf(0);                while (true) {                    f = new File(localFilePath + "_" + i.toString());                    if (!f.exists()) {                        localFilePath = localFilePath + "_" + i.toString();                        break;                    } else {                        i++;                        continue;                    }                }                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);        } catch (IOException e) {            // TODO Auto-generated catch block            e.printStackTrace();        }    }    /**     * 主函数     */    public static void main(String[] args) {        Configuration conf = new Configuration();        conf.set("fs.defaultFS", "hdfs://localhost:9000");        String localFilePath = "/usr/local/hadoop/text.txt"; // 本地路径        String remoteFilePath = "/user/tiny/text.txt"; // HDFS路径        try {            CopyToLocal.copyToLocal(conf, remoteFilePath, localFilePath);            System.out.println("下载完成");        } catch (Exception e) {            e.printStackTrace();        }    }}

http://www.jianshu.com/p/0663d74b79b5

Path localPath = new Path(localFilePath); fs.copyToLocalFile(remotePath, localPath); } catch (IOException e) { // TODO Auto-generated catch block e.printStackTrace(); } } /** * 主函数 */ public static void main(String[] args) { Configuration conf = new Configuration(); conf.set("fs.defaultFS", "hdfs://localhost:9000"); String localFilePath = "/usr/local/hadoop/text.txt"; // 本地路径 String remoteFilePath = "/user/tiny/text.txt"; // HDFS路径 try { CopyToLocal.copyToLocal(conf, remoteFilePath, localFilePath); System.out.println("下载完成"); } catch (Exception e) { e.printStackTrace(); } }}

      http://www.jianshu.com/p/0663d74b79b5
 

           

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