1.Java读取hdfs文件内容
1.1.在创建 /root/Downloads/ 目录下创建hello文件，并写入内容
1.2.把hello文件从linux上传到hdfs中
1.3 eclipse中创建java项目并导入jar包(jar包来自hadoop)
1.4 输入如下代码，并执行
public class TestHDFSRead {
public static final String HDFS_PATH="hdfs://192.168.80.100:9000/hadooptest/hello";
public static void main(String[] args) throws Exception {
// 将hdfs 格式的url 转换成系统能够识别的
URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());
final URL url = new URL(HDFS_PATH);
final InputStream in = url.openStream();
//copyBytes(in, out, buffSize, close)
//四个参数分别为输入流，输出流，缓冲区大小，是否关闭流
IOUtils.copyBytes(in, System.out, 1024, true);
}
}
2.java创建HDFS文件夹
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.net.URI;
import org.apache.hadoop.conf.Configuration;
public class TestHDFS {
public static final String HDFS_PATH="hdfs://192.168.80.100:9000";
//前面有斜线表示从根目录开始，没有斜线从/usr/root开始
public static final String HadoopTestPath="/hadooptest2";
public static void main(String[] args) throws Exception {
final FileSystem fileSystem = FileSystem.get(new URI(HDFS_PATH), new Configuration());
//创建文件夹
fileSystem.mkdirs(new Path(HadoopTestPath));
}
}
执行后，指令查询是否有该文件夹：
3.java上传文件到HDFS
import java.io.FileInputStream;
import java.net.URI;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IOUtils;
public class TestHDFS {
public static final String HDFS_PATH="hdfs://192.168.80.100:9000";
//前面有斜线表示从根目录开始，没有斜线从/usr/root开始
public static final String HadoopTestPath="/hadooptest2";
public static final String HadoopFilePath="/hadooptest2/hello123";//hello123为需要写入的文件
public static void main(String[] args) throws Exception {
final FileSystem fileSystem = FileSystem.get(new URI(HDFS_PATH), new Configuration());
//创建文件夹
//fileSystem.mkdirs(new Path(HadoopTestPath));
//上传文件
final FSDataOutputStream out = fileSystem.create(new Path(HadoopFilePath));
final FileInputStream in = new FileInputStream("d:/hello2.txt");//hello2.txt文件写入hello123
IOUtils.copyBytes(in,out, 1024, true);
}
}
4.java下载HDFS文件
public class TestHDFS {
public static final String HDFS_PATH="hdfs://192.168.80.100:9000";
//前面有斜线表示从根目录开始，没有斜线从/usr/root开始
public static final String HadoopTestPath="/hadooptest2";
public static final String HadoopFilePath="/hadooptest2/hello123";//hello123为需要写入的文件
public static void main(String[] args) throws Exception {
final FileSystem fileSystem = FileSystem.get(new URI(HDFS_PATH), new Configuration());
//创建文件夹
//fileSystem.mkdirs(new Path(HadoopTestPath));
//上传文件
//final FSDataOutputStream out = fileSystem.create(new Path(HadoopFilePath));
//final FileInputStream in = new FileInputStream("d:/hello2.txt");//hello2.txt文件写入hello123
//IOUtils.copyBytes(in,out, 1024, true);
//下载文件
final FSDataInputStream in = fileSystem.open(new Path(HadoopFilePath));
IOUtils.copyBytes(in,System.out, 1024, true);
}
}
5.java删除HDFS文件
public class TestHDFS {
public static final String HDFS_PATH="hdfs://192.168.80.100:9000";
//前面有斜线表示从根目录开始，没有斜线从/usr/root开始
public static final String HadoopTestPath="/hadooptest2";
public static final String HadoopFilePath="/hadooptest2/hello123";//hello123为需要写入的文件
public static void main(String[] args) throws Exception {
final FileSystem fileSystem = FileSystem.get(new URI(HDFS_PATH), new Configuration());
//创建文件夹
//fileSystem.mkdirs(new Path(HadoopTestPath));
//上传文件
//final FSDataOutputStream out = fileSystem.create(new Path(HadoopFilePath));
//final FileInputStream in = new FileInputStream("d:/hello2.txt");//hello2.txt文件写入hello123
//IOUtils.copyBytes(in,out, 1024, true);
//下载文件
//final FSDataInputStream in = fileSystem.open(new Path(HadoopFilePath));
//IOUtils.copyBytes(in,System.out, 1024, true);
//删除文件(夹)，两个参数 第一个为删除路径，第二个为递归删除
fileSystem.delete(new Path(HadoopFilePath),true);
}
}
下图第一个红框为删除前，第二个红框为删除后：