1.读出hadoop目录下的hello文件：
方案一（只能读不能写）：
import java.net.MalformedURLException;
import java.net.URL;
import java.io.*;
import org.apache.hadoop.fs.FsUrlStreamHandlerFactory;
import org.apache.hadoop.io.IOUtils;
public class App1 {
public static final String HDFS_PATH="hdfs://mlj:9000/hello";
public static void main(String[] args) throws Exception {
URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());//url解析器，url通常情况下只识别http,在这里声明是为了让它识别hdfs协议
final URL url=new URL(HDFS_PATH);
final InputStream in=url.openStream();
IOUtils.copyBytes(in, System.out, 1024, true);//输入流，输出流，缓冲区大小，是否关闭
}
}
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方案二（使用hdfs提供的filesytem类可进行所有操作）alt+shift+m alt+shift+l：
package hdfs;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
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 App2 {
/**
* @param args
*/
public static final String HDFS_PATH="hdfs://mlj:9000/hello";
public static final String DIR_PATH="/d";
public static final String FILE_PATH="/d1";
public static void main(String[] args) throws Exception {
// TODO Auto-generated method stub
final FileSystem fileSystem = FileSystem.get(new URI(HDFS_PATH), new Configuration());//获得对象
//创建文件夹
//mkdir(fileSystem);
//上传文件(欲上传，先创建)
//uploadFile(fileSystem);
//下载文件(欲下载，先打开)
//downloadData(fileSystem);
//删除文件
//deleteFile(fileSystem);
//浏览文件夹
list(fileSystem);
}
private static void list(FileSystem fileSystem) throws IOException {
final FileStatus[] listStatus = fileSystem.listStatus(new Path("/"));
for (FileStatus fileStatus : listStatus) {
String isDir = fileStatus.isDir()?"文件夹":"文件";
final String permission = fileStatus.getPermission().toString();
final short replication = fileStatus.getReplication();
final long len = fileStatus.getLen();
final String path = fileStatus.getPath().toString();
System.out.println(isDir+"\t"+permission+"\t"+replication+"\t"+len+"\t"+path);
}
}
private static void deleteFile(final FileSystem fileSystem)
throws IOException {
fileSystem.delete(new Path(FILE_PATH), true);
}
private static void downloadData(final FileSystem fileSystem)
throws IOException {
final FSDataInputStream in = fileSystem.open(new Path(FILE_PATH));
IOUtils.copyBytes(in, System.out, 1024, true);
}
private static void mkdir(final FileSystem fileSystem) throws IOException {
fileSystem.mkdirs(new Path(DIR_PATH));
}
private static void uploadFile(final FileSystem fileSystem)
throws IOException, FileNotFoundException {
final FSDataOutputStream out = fileSystem.create(new Path(FILE_PATH));//create生成一个输出流，文件目的地
final FileInputStream in = new FileInputStream("D:/b.txt");
IOUtils.copyBytes(in, out, 1024, true);
}
}