用 Java 读取 HDFS 和本地文件

Question

我想读取文件路径，无论它们是 HDFS 还是本地文件。目前，我通过前缀为 file:// 的本地路径和前缀为 hdfs:// 的 HDFS 路径并编写如下代码

Configuration configuration = new Configuration();
FileSystem fileSystem = null;
if (filePath.startsWith("hdfs://")) {
  fileSystem = FileSystem.get(configuration);
} else if (filePath.startsWith("file://")) {
  fileSystem = FileSystem.getLocal(configuration).getRawFileSystem();
}

从这里我使用 FileSystem 的 API 来读取文件。

请告诉我是否有比这更好的方法？

Answer 1

这有意义吗，

public static void main(String[] args) throws IOException {

    Configuration conf = new Configuration();
    conf.addResource(new Path("/hadoop/projects/hadoop-1.0.4/conf/core-site.xml"));
    conf.addResource(new Path("/hadoop/projects/hadoop-1.0.4/conf/hdfs-site.xml"));

    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    System.out.println("Enter the file path...");
    String filePath = br.readLine();

    Path path = new Path(filePath);
    FileSystem fs = path.getFileSystem(conf);
    FSDataInputStream inputStream = fs.open(path);
    System.out.println(inputStream.available());
    fs.close();
}

如果你走这条路，你不必检查。直接从 Path 获取 FileSystem，然后随心所欲。

Answer 2

您可以通过以下方式获取FileSystem：

Configuration conf = new Configuration();
Path path = new Path(stringPath);
FileSystem fs = FileSystem.get(path.toUri(), conf);

你不需要判断路径是以hdfs://还是file://开头的。此 API 将完成这项工作。

Answer 3

请检查下面的代码 sn-p 列出来自 HDFS 路径的文件；即以hdfs:// 开头的路径字符串。如果您可以提供 Hadoop 配置和本地路径，它还将列出本地文件系统中的文件；即以file://开头的路径字符串。

    //helper method to get the list of files from the HDFS path
    public static List<String> listFilesFromHDFSPath(Configuration hadoopConfiguration, String hdfsPath,
                                                     boolean recursive)
    {
        //resulting list of files
        List<String> filePaths = new ArrayList<String>();
        FileSystem fs = null;

        //try-catch-finally all possible exceptions
        try
        {
            //get path from string and then the filesystem
            Path path = new Path(hdfsPath);  //throws IllegalArgumentException, all others will only throw IOException
            fs = path.getFileSystem(hadoopConfiguration);

            //resolve hdfsPath first to check whether the path exists => either a real directory or o real file
            //resolvePath() returns fully-qualified variant of the path
            path = fs.resolvePath(path);


            //if recursive approach is requested
            if (recursive)
            {
                //(heap issues with recursive approach) => using a queue
                Queue<Path> fileQueue = new LinkedList<Path>();

                //add the obtained path to the queue
                fileQueue.add(path);

                //while the fileQueue is not empty
                while (!fileQueue.isEmpty())
                {
                    //get the file path from queue
                    Path filePath = fileQueue.remove();

                    //filePath refers to a file
                    if (fs.isFile(filePath))
                    {
                        filePaths.add(filePath.toString());
                    }
                    else   //else filePath refers to a directory
                    {
                        //list paths in the directory and add to the queue
                        FileStatus[] fileStatuses = fs.listStatus(filePath);
                        for (FileStatus fileStatus : fileStatuses)
                        {
                            fileQueue.add(fileStatus.getPath());
                        } // for
                    } // else

                } // while

            } // if
            else        //non-recursive approach => no heap overhead
            {
                //if the given hdfsPath is actually directory
                if (fs.isDirectory(path))
                {
                    FileStatus[] fileStatuses = fs.listStatus(path);

                    //loop all file statuses
                    for (FileStatus fileStatus : fileStatuses)
                    {
                        //if the given status is a file, then update the resulting list
                        if (fileStatus.isFile())
                            filePaths.add(fileStatus.getPath().toString());
                    } // for
                } // if
                else        //it is a file then
                {
                    //return the one and only file path to the resulting list
                    filePaths.add(path.toString());
                } // else

            } // else

        } // try
        catch(Exception ex) //will catch all exception including IOException and IllegalArgumentException
        {
            ex.printStackTrace();

            //if some problem occurs return an empty array list
            return new ArrayList<String>();
        } //
        finally
        {
            //close filesystem; not more operations
            try
            {
                if(fs != null)
                    fs.close();
            } catch (IOException e)
            {
                e.printStackTrace();
            } // catch

        } // finally


        //return the resulting list; list can be empty if given path is an empty directory without files and sub-directories
        return filePaths;
    } // listFilesFromHDFSPath

如果您真的想使用 java.io.File API，那么以下方法将帮助您仅列出本地文件系统中的文件；即以file://开头的路径字符串。

    //helper method to list files from the local path in the local file system
    public static List<String> listFilesFromLocalPath(String localPathString, boolean recursive)
    {
        //resulting list of files
        List<String> localFilePaths = new ArrayList<String>();

        //get the Java file instance from local path string
        File localPath = new File(localPathString);


        //this case is possible if the given localPathString does not exit => which means neither file nor a directory
        if(!localPath.exists())
        {
            System.err.println("\n" + localPathString + " is neither a file nor a directory; please provide correct local path");

            //return with empty list
            return new ArrayList<String>();
        } // if


        //at this point localPath does exist in the file system => either as a directory or a file


        //if recursive approach is requested
        if (recursive)
        {
            //recursive approach => using a queue
            Queue<File> fileQueue = new LinkedList<File>();

            //add the file in obtained path to the queue
            fileQueue.add(localPath);

            //while the fileQueue is not empty
            while (!fileQueue.isEmpty())
            {
                //get the file from queue
                File file = fileQueue.remove();

                //file instance refers to a file
                if (file.isFile())
                {
                    //update the list with file absolute path
                    localFilePaths.add(file.getAbsolutePath());
                } // if
                else   //else file instance refers to a directory
                {
                    //list files in the directory and add to the queue
                    File[] listedFiles = file.listFiles();
                    for (File listedFile : listedFiles)
                    {
                        fileQueue.add(listedFile);
                    } // for
                } // else

            } // while
        } // if
        else        //non-recursive approach
        {
            //if the given localPathString is actually a directory
            if (localPath.isDirectory())
            {
                File[] listedFiles = localPath.listFiles();

                //loop all listed files
                for (File listedFile : listedFiles)
                {
                    //if the given listedFile is actually a file, then update the resulting list
                    if (listedFile.isFile())
                        localFilePaths.add(listedFile.getAbsolutePath());
                } // for
            } // if
            else        //it is a file then
            {
                //return the one and only file absolute path to the resulting list
                localFilePaths.add(localPath.getAbsolutePath());
            } // else
        } // else


        //return the resulting list; list can be empty if given path is an empty directory without files and sub-directories
        return localFilePaths;
    } // listFilesFromLocalPath

Answer 4

这项工作。

package com.leerhdfs;

//import org.apache.commons.io.IOUtils;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.util.Progressable;

import java.io.*;
import java.net.URI;
import java.nio.charset.StandardCharsets;

public class ReadWriteHDFSExample {

public static void main(String[] args) throws IOException {

    Path inFile = new Path(args[0]);
    String destinosrc = args[1];
    
    //InputStream in = new BufferedInputStream(new FileInputStream(localsrc));
    Configuration conf = new Configuration();
    
    
    FileSystem fs = FileSystem.get(URI.create(destinosrc), conf);
    FSDataInputStream in = fs.open(inFile);
   
    
    //Progressable ir viendo aumento 10%, 20%, 30%
    OutputStream out = fs.create(new Path(destinosrc), new Progressable() {
        
        public void progress() {
            System.out.println("Leyendo y escribiendo...");
            
        }
    });
    
    IOUtils.copyBytes(in ,out, 4096, true);
       in.close();
  }

}