Hdfs读取文件到本地总结

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 = new Path(hdfsSrc);
			String Filename = Src.getName().toString();
			String local = localDst + Filename;
			Path Dst = new Path(local);
			FileSystem fs = FileSystem.get(URI.create(hdfsSrc), conf);
			FSDataInputStream in = fs.open(Src);
			OutputStream output = new FileOutputStream(new File(local));
			IOUtils.copyBytes(in, output, 4096, true);
			System.out.print(" 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 = new Path(subPath);
							String Filename = Src.getName().toString();
							String local = localDst + Filename;
							Path Dst = new Path(local);
							FileSystem hdfs = FileSystem.get(URI
									.create(subPath), conf);
							in = hdfs.open(Src);
							output = new FileOutputStream(new File(local));
							// true-是否关闭数据流，如果是false则在finally里关闭
							// IOUtils.copyBytes(in, output, 4096, false);
							 IOUtils.copyBytes(in, output, conf);
							 output.flush();
							System.out.print(" 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 = new Path(subPath);
							String Filename = Src.getName().toString();
							String local = localDst + Filename;
							Path Dst = new Path(local);
							FileSystem localFS = FileSystem.getLocal(conf);
							FileSystem hdfs = FileSystem.get(URI
									.create(subPath), conf);
							FSDataInputStream in = hdfs.open(Src);
							FSDataOutputStream output = localFS.create(Dst);
							byte[] buf = new byte[1024];
							int readbytes = 0;
							while ((readbytes = in.read(buf)) > 0) {
								output.write(buf, 0, readbytes);
							}
							in.close();
							output.close();
						} catch (IOException e) {
							// TODO Auto-generated catch block
							e.printStackTrace();
							System.out.print(" 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 = new Path(subPath);
							String Filename = Src.getName().toString();
							String local = localDst + Filename;
							Path Dst = new Path(local);
							FileSystem localFS = FileSystem.getLocal(conf);
							FileSystem hdfs = FileSystem.get(URI
									.create(subPath), conf);
							FSDataInputStream in = hdfs.open(Src);
							BufferedReader read = new BufferedReader(new InputStreamReader(in));
							BufferedWriter output=new BufferedWriter(new FileWriter(local));
							String line = null;
							while ((line = read.readLine()) != null) {
								output.append(line);
								output.newLine();
								output.flush();
							}
							in.close();
							read.close();
							output.close();
						} catch (IOException e) {
							// TODO Auto-generated catch block
							e.printStackTrace();
							System.out.print(" 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);
}

或者
FileStatus status = fs.getFileStatus(Src);
byte[] buffer = new byte[Integer.parseInt(String.valueOf(status.getLen()))];
in.readFully(0, buffer);
is.close();
fs.close();
System.out.println(buffer.toString());