hadoop提供的Java API主要用来对文件操作。最常见的也就是读、写、遍历。

总的来说，调用API的第一步获取FileSystem，可以用FileSystem fs = FileSystem.get()来获取。接下来如果是写(上传)文件，则用fs.create()，如果是读(下载)文件，则用fs.get()。然后再用FSDataInputStream、FSDataOutputStream 具体代码如下：

package hadoop;

import java.io.FileInputStream;

import java.io.IOException;

import java.io.InputStream;

import java.net.URI;

import java.net.URISyntaxException;

import org.apache.hadoop.conf.Configuration;

import org.apache.hadoop.fs.FSDataInputStream;

import org.apache.hadoop.fs.FSDataOutputStream;

import org.apache.hadoop.fs.FileStatus;

import org.apache.hadoop.fs.FileSystem;

import org.apache.hadoop.fs.Path;

import org.apache.hadoop.io.IOUtils;

public class HadoopFileSystem

{

public static final String HDFS_PATH = "hdfs://master:9000";

public static void main(String[] args)

{

//readFile();

//writeFile();

listFile("/home/hadoop");

}

static void listFile(String listPath)

{

try

{

FileSystem fs = FileSystem.get(new URI(HDFS_PATH), new Configuration());

FileStatus[] files = fs.listStatus(new Path(listPath));

for (FileStatus f : files)

{

if (f.isDir())

{

System.out.println("d " + f.getPath());

listFile(f.getPath().toString());

}

else

{

System.out.println("- " + f.getPath());

}

}

}

catch (URISyntaxException e)

{

e.printStackTrace();

}

catch (IOException e)

{

e.printStackTrace();

}

}

static void writeFile()

{

try

{

String path = "/home/hadoop/data/writefile/write.txt";

FileSystem fs = FileSystem.get(new URI(HDFS_PATH), new Configuration());

if ( fs.exists(new Path(path)) )

{

System.out.println("file already exist, delete it first...");

fs.deleteOnExit(new Path(path));

}

FSDataOutputStream out = fs.create(new Path(path));

InputStream in = new FileInputStream("C:/data.txt");

IOUtils.copyBytes(in, out, 1024, true);

System.out.println("**********write finished*******");

FSDataInputStream i = fs.open(new Path(path));

IOUtils.copyBytes(i, System.out, 1024, true);

}

catch (URISyntaxException e)

{

e.printStackTrace();

}

catch (IOException e)

{

e.printStackTrace();

}

}

static void readFile()

{

try

{

String path = HDFS_PATH + "/home/hadoop/data/input/core-site.xml";

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

FSDataInputStream in = fs.open(new Path(path));

IOUtils.copyBytes(in, System.out, 1024, true);

}

catch (IOException e)

{

e.printStackTrace();

}

}

}

其中writeFile、readFile、listFile分别代表了写、读、列举。一般操作格式就是这个样子吧，先记下来再说。。。

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