【大数据计算】(一) HDFS操作方法和基础编程

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

• 查看各种命令

hdfs dfs -help

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

• 创建一个input_test的目录

hdfs dfs -mkdir input_test

• 删除input_test的目录

hdfs dfs -rm -r input_test

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

• 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

• 文件上传到HDFS out文件夹中

hdfs dfs -put /home/zqc/score.txt out

• 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

2. 利用HDFS的Web管理界面

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();
// }

    }
}

3.2 题目2