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());