如果你想读第一个街区，你可以得到一个 InputStream 从 FileSystem 并读取字节，直到它达到预定的数量（示例块大小64mb将是6410241024字节）。下面是一个例子（尽管64mb是大量的数据。如果您认为您需要的数据早于64mb，只需更改bytesleet）

import java.io.EOFException;
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.zookeeper.common.IOUtils;

public class TestReaderFirstBlock {

    private static final String uri = "hdfs://localhost:9000/path/to/file";
    private static int bytesLeft = 64 * 1024 * 1024;
    private static final byte[] buffer = new byte[4096];

    public static void main(String[] args) throws Exception {

        Configuration conf = new Configuration();
        FileSystem fs = FileSystem.get(URI.create(uri), conf);

        InputStream is = fs.open(new Path(uri));
        OutputStream out = System.out;

        while (bytesLeft > 0) {
            int read = is.read(buffer, 0, Math.min(bytesLeft, buffer.length));
            if (read == -1) {
                throw new EOFException("Unexpected end of data");
            }
            out.write(buffer, 0, read);
            bytesLeft -= read;
        }

        IOUtils.closeStream(is);
    }
}