InputStream in = null;
try {
    in = new URL("hdfs://host/path").openStream();
    //操作输入流in，可以读取到文件的内容
} finally {
    IOUtils.closeStream(in);
}

import java.io.InputStream;
import java.net.URL;
import org.apache.hadoop.fs.FsUrlStreamHandlerFactory;
import org.apache.hadoop.io.IOUtils;

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); 
        }
    }
}

public static FileSystem get(Configuration conf) throws IOException;
public static FileSystem get(URI uri, Configuration conf) throws IOException;
public static FileSystem get(final URI uri, final Configuration conf,  final String user) throws IOException, InterruptedException;

public static LocalFileSystem getLocal(Configuration conf)  throws IOException;

public FSDataInputStream open(Path f) throws IOException;
public abstract FSDataInputStream open(Path f, int bufferSize)  throws IOException;

import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
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);
        //System.out.println(fs.getClass().getName()); //这里可以看到得到的实例是DistributedFileSystem，因为core-site.xml里配的是hdfs
        FSDataInputStream in = null;
        try {
            in = fs.open(new Path(uri));
            IOUtils.copyBytes(in, System.out, 4096, false);
        } finally {
            IOUtils.closeStream(in);
        }
    }
}

in.seek(0);
IOUtils.copyBytes(in, System.out, 4096, false);

public int read(long position, byte[] buffer, int offset, int length) throws IOException;
public void readFully(long position, byte[] buffer, int offset, int length) throws IOException;
public void readFully(long position, byte[] buffer) throws IOException;

public FSDataOutputStream create(Path f) throws IOException;

public FSDataOutputStream create(Path f, Progressable progress) throws IOException;

public interface Progressable {
    public void progress();
}

public FSDataOutputStream append(Path f) throws IOException;

import java.io.BufferedInputStream;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URI;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
import org.apache.hadoop.util.Progressable;

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() {
            @Override
            public void progress() {
                System.out.print(".");
//             try {
//                 Thread.sleep(1000);
//             } catch (Exception e) {
//                 e.printStackTrace();
//             }
            }
        });
        IOUtils.copyBytes(in, out, 4096, true);
        System.out.println();
        System.out.println("end.");
    }
}

public long getPos() throws IOException;

import static org.junit.Assert.*;
import static org.hamcrest.CoreMatchers.*;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.OutputStream;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.hdfs.MiniDFSCluster;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;
public class ShowFileStatusTest {
    private static final String SYSPROP_KEY = "test.build.data";
    /** MiniDFSCluster类在hadoop-hdfs-2.4.1-tests.jar中，是一个专门用于测试的in-process HDFS集群 */
    private MiniDFSCluster cluster;
    private FileSystem fs;
    @Before
    public void setUp() throws IOException {
        Configuration conf = new Configuration();
        String sysprop = System.getProperty(SYSPROP_KEY);
        if (sysprop == null) {
            System.setProperty(SYSPROP_KEY, "/tmp");
        }
        cluster = new MiniDFSCluster(conf, 1, true, null);
        fs = cluster.getFileSystem();
        OutputStream out = fs.create(new Path("/dir/file"));
        out.write("content".getBytes("UTF-8"));
        out.close();
    }
    @After
    public void tearDown() throws IOException {
        if (fs != null) {
            fs.close();
        }
        if (cluster != null) {
            cluster.shutdown();
        }
    }
    @Test(expected = FileNotFoundException.class)
    public void throwsFileNotFoundForNonExistentFile() throws IOException {
        fs.getFileStatus(new Path("no-such-file"));
    }
    @Test
    public void fileStatusForFile() throws IOException {
        Path file = new Path("/dir/file");
        FileStatus stat = fs.getFileStatus(file);
       
        assertThat(stat.getPath().toUri().getPath(), is("/dir/file"));
        assertThat(stat.isDirectory(), is(false));
        assertThat(stat.getLen(), is(7L));
        assertTrue(stat.getModificationTime() <= System.currentTimeMillis());
        assertThat(stat.getReplication(), is((short)1));
        assertThat(stat.getBlockSize(), is(64 * 1024 * 1024L));
        assertThat(stat.getOwner(), is("norris"));
        assertThat(stat.getGroup(), is("supergroup"));
        assertThat(stat.getPermission().toString(), is("rw-r--r--"));
    }
    @Test
    public void fileStatusForDirectory() throws IOException {
        Path dir = new Path("/dir");
        FileStatus stat = fs.getFileStatus(dir);
        assertThat(stat.getPath().toUri().getPath(), is("/dir"));
        assertThat(stat.isDirectory(), is(true));
        assertThat(stat.getLen(), is(0L));
        assertTrue(stat.getModificationTime() <= System.currentTimeMillis());
        assertThat(stat.getReplication(), is((short)0));
        assertThat(stat.getBlockSize(), is(0L));
        assertThat(stat.getOwner(), is("norris"));
        assertThat(stat.getGroup(), is("supergroup"));
        assertThat(stat.getPermission().toString(), is("rwxr-xr-x"));
    }
}