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【大数据计算】(一) HDFS操作方法和基础编程

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1. HDFS操作常用Shell命令

1.1 查看命令使用方法

  • 启动Hadoop
start-dfs.sh
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  • 查看各种命令
hdfs dfs -help
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1.2 HDFS目录操作

1.2.1 目录操作方法

  • 查看HDFS下所有的目录
hdfs dfs -ls
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  • 创建一个input_test的目录
hdfs dfs -mkdir input_test
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  • 删除input_test的目录
hdfs dfs -rm -r input_test
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1.2.2 文件操作方法

  • 查看HDFS中一个文件in0.txt的内容
hdfs dfs -cat in0.txt
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  • 把HDFS中的in0.txt文件内容下载到本地系统/home/zqc/download
hdfs dfs -get in0.txt /home/zqc/download
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  • 文件上传到HDFS out文件夹中
hdfs dfs -put /home/zqc/score.txt out
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  • 把文件从HDFS的一个目录复制到另外一个目录
hdfs dfs -cp out/score.txt wordcount/input
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2. 利用HDFS的Web管理界面

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3. HDFS编程实践

  1. 在IDEA中创建项目
  2. 为项目添加需要用到的JAR包
  3. 编写Java应用程序
  4. 编译运行程序
  5. 应用程序的部署

3.1 题目1

编写 FileUtils 类,其中包含文件下载与上传函数的实现,要求如下: A. 函数UploadFile()向HDFS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;

B. 函数DownloadFile()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;

C. 在本地Download文件夹中创建文本文件 localfile.txt ,在main函数中编写逻辑实现将其上传到hdfs的input文件夹中;

import java.io.*;
import java.util.Scanner;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;

public class FileUtils {
    public static void appendToFile(Configuration conf, String LocalPath, String UploadPath) {
        Path uploadpath = new Path(UploadPath);
        try (FileSystem fs = FileSystem.get(conf); FileInputStream in = new FileInputStream(LocalPath);) {
            FSDataOutputStream out = fs.append(uploadpath);
            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();
        }
    }

    public static void coverFile(Configuration conf, String LocalPath, String UploadPath) {
        Path uploadpath = new Path(UploadPath);
        try (FileSystem fs = FileSystem.get(conf); FileInputStream in = new FileInputStream(LocalPath);) {
            FSDataOutputStream out = fs.create(uploadpath);
            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();
        }
    }

    public static void UploadFile(Configuration conf, String LocalPath, String UploadPath) {
        try {
            FileSystem fs = FileSystem.get(conf);
            Path localpath = new Path(LocalPath);
            Path uploadpath = new Path(UploadPath);
            if (fs.exists(uploadpath)) {
                System.out.println("File \"" + UploadPath + "\" exist!");
                System.out.println("1. append\t2. cover");
                Scanner sc = new Scanner(System.in);
                String s = sc.nextLine();
                if (s.equals("1")) {
                    try {
                        appendToFile(conf, LocalPath, UploadPath);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                } else {
                    try {
                        coverFile(conf, LocalPath, UploadPath);
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            } else {
                System.out.println("File \"" + UploadPath + "\" not exist!");
                InputStream in = new FileInputStream(LocalPath);
                OutputStream out = fs.create(uploadpath);
                IOUtils.copyBytes(in, out, 4096, true);
                System.out.println("File uploaded successfully!");
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void DownloadFile(Configuration conf, String LocalPath, String DownloadPath) {
        Path downloadpath = new Path(DownloadPath);
        try (FileSystem fs = FileSystem.get(conf)) {
            File f = new File(LocalPath);
            if (f.exists()) {
                System.out.println(LocalPath + " exits!");
                Integer i = Integer.valueOf(0);
                while (true) {
                    f = new File(LocalPath + "_" + i.toString());
                    if (!f.exists()) {
                        LocalPath = LocalPath + "_" + i.toString();
                        break;
                    } else {
                        i++;
                        continue;
                    }
                }
                System.out.println("rename: " + LocalPath);
            }
            Path localpath = new Path(LocalPath);
            fs.copyToLocalFile(downloadpath, localpath);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) {
        Configuration conf = new Configuration();
        conf.set("dfs.client.block.write.replace-datanode-on-failure.enable", "true");
        conf.set("dfs.client.block.write.replace-datanode-on-failure.policy", "NEVER");
        conf.set("fs.defaultFS", "hdfs://localhost:9000");
        conf.set("fs.hdfs.impl", "org.apache.hadoop.hdfs.DistributedFileSystem");
        String LocalPath = "/home/zqc/Downloads/localfile.txt";
        String UploadPath = "/user/zqc/input/localfile.txt";
//        String DownloadPath = "/user/hadoop/input/score.txt";
        UploadFile(conf, LocalPath, UploadPath);
//        DownloadFile(conf, LocalPath, DownloadPath);
//        try { 
//            String CreateDir = "/home/zqc/Downloads/";
//            String FileName = "localfile.txt";
//            String HDFSDir = "/user/hadoop/input";
//            File file = new File(CreateDir, FileName);
//            if (file.createNewFile()) {
//                FileSystem hdfs = FileSystem.get(conf);
//                Path localpath = new Path(CreateDir + FileName);
//                Path hdfspath = new Path(HDFSDir);
//                hdfs.copyFromLocalFile(localpath, hdfspath);
//            }
//        } catch (Exception e) {
//            e.printStackTrace();
//        }

    }
}
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3.2 题目2

A. 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。

B. 在main函数中编写逻辑实现按行读取input文件夹中的file.txt (查看附件)文件,将长度超过15个字符的行在控制台中打印出来;

import java.io.*;
import java.net.URI;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

public class ReadLine {
    public class MyFSDataInputStream extends FSDataInputStream {
        public MyFSDataInputStream(InputStream in) {
            super(in);
        }
    }

    public static String readline(Configuration conf, String filepath) throws IOException {
        Path path = new Path(filepath);
        FileSystem fs = FileSystem.get(URI.create("hdfs://localhost:9000"), conf);
        FSDataInputStream in = fs.open(path);
        BufferedReader d = new BufferedReader(new InputStreamReader(in));
        String line = null;
        while ((line = d.readLine()) != null) {
            System.out.println(line);
        }
        d.close();
        in.close();
        return null;
    }

    public static void main(String[] args) throws IOException {
        Configuration conf = new Configuration();
        conf.set("fs.defaultFS", "hdfs://localhost:9000");
        conf.set("fs.hdfs.impl", "org.apache.hadoop.hdfs.DistributedFileSystem");
        String filepath = "/user/zqc/input/file.txt";
        try {
            Path path = new Path(filepath);
            FileSystem fs = FileSystem.get(URI.create("hdfs://localhost:9000"), conf);
            FSDataInputStream in = fs.open(path);
            BufferedReader d = new BufferedReader(new InputStreamReader(in));
            String line = null;
            while ((line = d.readLine()) != null) {
                if (line.length() > 15) {
                    System.out.println(line);
                }
            }
            d.close();
            in.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}
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