hadoop hdfs的一些用法

Example 3-1. Displaying files from a Hadoop filesystem on standard output using a 
URLStreamHandler 

//Reading Data from a Hadoop URL

public class URLCat {
    static {
        URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
    }

    public static void main(String[] args) throws Exception {
        InputStream in = null;
        try {
            in = new URL(args[0]).openStream();
            IOUtils.copyBytes(in, System.out, 4096, false);
        } finally {
            IOUtils.closeStream(in);
        }
    }
}
-----------------------------------------
result:
Here’s a sample run:
% hadoop URLCat hdfs://localhost/user/tom/quangle.txt
On the top of the Crumpetty Tree
The Quangle Wangle sat,
But his face you could not see,
On account of his Beaver Hat.

Example 3-2. Displaying files from a Hadoop filesystem on standard output by using the FileSystem 
directly 

public class FileSystemCat {
    public static void main(String[] args) throws Exception {
        String uri = args[0];
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(URI.create(uri), conf);
        InputStream in = null;
        try {
            in = fs.open(new Path(uri));
            IOUtils.copyBytes(in, System.out, 4096, false);
        } finally {
            IOUtils.closeStream(in);
        }
    }
}

------------------------------------------
The program runs as follows:
% hadoop FileSystemCat hdfs://localhost/user/tom/quangle.txt
On the top of the Crumpetty Tree
The Quangle Wangle sat,
But his face you could not see,
On account of his Beaver Hat.
The

Example 3-3 is a simple extension of Example 3-2 that writes a file to standard out 
twice: after writing it once, it seeks to the start of the file and streams through it once 
again. 

//Example 3-3. Displaying files from a Hadoop filesystem on standard output twice, by using seek

public class FileSystemDoubleCat {
    public static void main(String[] args) throws Exception {
        String uri = args[0];
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(URI.create(uri), conf); //通过get()方法获得一个FileSystem流
        FSDataInputStream in = null;
        try {
            in = fs.open(new Path(uri)); //通过open()方法打开一个FSDataInputStream流
            IOUtils.copyBytes(in, System.out, 4096, false);
            in.seek(0); // go back to the start of the file
            IOUtils.copyBytes(in, System.out, 4096, false);
        } finally {
            IOUtils.closeStream(in);
        }
    }
}
----------------------------------------------------
Here’s the result of running it on a small file:
% hadoop FileSystemDoubleCat hdfs://localhost/user/tom/quangle.txt
On the top of the Crumpetty Tree
The Quangle Wangle sat,
But his face you could not see,
On account of his Beaver Hat.
On the top of the Crumpetty Tree
The Quangle Wangle sat,
But his face you could not see,
On account of his Beaver Hat.

Example 3-4 shows how to copy a local file to a Hadoop filesystem. We illustrate progress 
by printing a period every time the progress() method is called by Hadoop, which 
is after each 64 K packet of data is written to the datanode pipeline. (Note that this 
particular behavior is not specified by the API, so it is subject to change in later versions 
of Hadoop. The API merely allows you to infer that “something is happening.”) 

//Example 3-4. Copying a local file to a Hadoop filesystem, and shows progress
public class FileCopyWithProgress {
    public static void main(String[] args) throws Exception {
        String localSrc = args[0];
        String dst = args[1];
        InputStream in = new BufferedInputStream(new FileInputStream(localSrc));
        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(URI.create(dst), conf);
        OutputStream out = fs.create(new Path(dst), new Progressable() {
            public void progress() {
                System.out.print(".");
            }
        });
        IOUtils.copyBytes(in, out, 4096, true);
    }
}

Typical usage:
% hadoop FileCopyWithProgress input/docs/1400-8.txt hdfs://localhost/user/tom/1400-8.txt
...............