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Hdfs读取文件到本地总结

2024-08-06 03:49:28   225人阅读

总结了一下三个方法：hdfs自带 按字节复制 按行复制 （在java io里还有字符复制，暂且不提）

因为hdfs自带的，不知道为什么有些场合不能用，每次能下载的个数还不一定，所以就考虑自己按照java的方式来复制，就出现第2、3种方法。

有时间好好研究一下IO，比如针对特殊文件，文件复制会出现大小不一样的情况。这里

	// void downloadFromHdfs(String hdfsSrc , String localDst)	// String hdfsDst = "hdfs://54.0.88.53:8020/user/flume/SyslogNetwork/";	// String localDir = "D://flume//";//下载单个文件	public static boolean downloadFromHdfs(String hdfsSrc, String localDst) {		Configuration conf = new Configuration();		Path dst = new Path(hdfsSrc);		try {			Path Src = http://www.mamicode.com/new Path(hdfsSrc);" download successed.");		} catch (IOException e) {			// TODO Auto-generated catch block			e.printStackTrace();			System.out.print(" download failed.");			return false;		}		return true;	}//下载目录下所有文件，方法1：  IOUtils.copyBytes或者copyToLocal	public static boolean downFromHdfsDir(String hdfsSrc, String localDst)			throws IOException {		Configuration conf = new Configuration();		Path dstpath = new Path(hdfsSrc);		int i = 1;		FileSystem fs = FileSystem.get(URI.create(hdfsSrc), conf);		try {			String subPath = "";			FileStatus[] fList = fs.listStatus(dstpath);			for (FileStatus f : fList) {				if (null != f) {					subPath = new StringBuffer()							.append(f.getPath().getParent()).append("/")							.append(f.getPath().getName()).toString();					if (f.isDir()) {						downFromHdfsDir(subPath, localDst);					} else {						System.out.println("/t/t" + subPath);// hdfs://54.0.88.53:8020/						Path dst = new Path(subPath);						i++;						FSDataInputStream in = null;						OutputStream output = null;						try {							Path Src = http://www.mamicode.com/new Path(subPath);" download successed.");						} catch (IOException e) {							// TODO Auto-generated catch block							e.printStackTrace();							System.out.print(" download failed.");						} finally {							IOUtils.closeStream(in);							IOUtils.closeStream(output);						}					}				}			}		} catch (Exception e) {		} finally {			System.out.println("the number of files is :" + i);		}		return true;	}		//下载目录下所有文件，方法2： 按字节复制	public static boolean downFromHdfsDir2(String hdfsSrc, String localDst)			throws IOException {		Configuration conf = new Configuration();		Path dstpath = new Path(hdfsSrc);		int i = 1;		FileSystem fs = FileSystem.get(URI.create(hdfsSrc), conf);		try {			String subPath = "";			FileStatus[] fList = fs.listStatus(dstpath);			for (FileStatus f : fList) {				if (null != f) {					subPath = new StringBuffer()							.append(f.getPath().getParent()).append("/")							.append(f.getPath().getName()).toString();					if (f.isDir()) {						downFromHdfsDir(subPath, localDst);					} else {						System.out.println("/t/t" + subPath);// hdfs://54.0.88.53:8020/						Path dst = new Path(subPath);						i++;						try {							Path Src = http://www.mamicode.com/new Path(subPath);" download failed.");						} finally {						}					}				}			}		} catch (Exception e) {		} finally {			System.out.println("the number of files is :" + i);		}		return true;	}	//下载目录下所有文件，方法2： 按行复制	public static boolean downFromHdfsDir3(String hdfsSrc, String localDst)			throws IOException {		Configuration conf = new Configuration();		Path dstpath = new Path(hdfsSrc);		int i = 1;		FileSystem fs = FileSystem.get(URI.create(hdfsSrc), conf);		try {			String subPath = "";			FileStatus[] fList = fs.listStatus(dstpath);			for (FileStatus f : fList) {				if (null != f) {					subPath = new StringBuffer()							.append(f.getPath().getParent()).append("/")							.append(f.getPath().getName()).toString();					if (f.isDir()) {						downFromHdfsDir(subPath, localDst);					} else {						System.out.println("/t/t" + subPath);// hdfs://54.0.88.53:8020/						Path dst = new Path(subPath);						i++;						try {							Path Src = http://www.mamicode.com/new Path(subPath);" download failed.");						} finally {						}					}				}			}		} catch (Exception e) {		} finally {			System.out.println("the number of files is :" + i);		}		return true;	}

　　一次读取整个文件

OutputStream：(一次读入整个文件) 字节private static String readHdfsFile2(FileSystem fs, Path path, String charset)        throws IOException {    FSDataInputStream hdfsInStream = fs.open(path);    ByteArrayOutputStream bos = new ByteArrayOutputStream();    byte[] ioBuffer = new byte[1024];    int readLen = hdfsInStream.read(ioBuffer);    while (-1 != readLen) {        bos.write(ioBuffer, 0, readLen);        readLen = hdfsInStream.read(ioBuffer);    }    hdfsInStream.close();    return new String(bos.toByteArray(), charset);}

　　

Hdfs读取文件到本地总结


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