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环境：

virtualbox ubantu1604

 Linux idea社区版2023

jdk1.8

hadoop相关依赖 

使用java操作

1. 判断/user/stu/input/test.txt文件是否存在，存在则读出文件内容，打印在控制台上。反之，输出“文件不存在”。

package abc;import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.IOException;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.FSDataInputStream;
import org.apache.hadoop.fs.FSDataOutputStream;public class HDFSFlieifExit {public static void main(String[] args) {try {String filename = "input/test.txt";Configuration conf = new Configuration();conf.set("fs.defaultFS", "hdfs://localhost:9000");conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");FileSystem fs = FileSystem.get(conf);Path file = new Path(filename);if (fs.exists(file)) {FSDataInputStream getIt = fs.open(file);BufferedReader d = new BufferedReader(new InputStreamReader(getIt));String con = null;while ((con = d.readLine()) != null) {System.out.println(con);}d.close(); //关闭文件fs.close(); //关闭hdfs} else {System.out.println("文件不存在");}} catch (Exception e) {e.printStackTrace();}}
}

2. 使用JAVA编程实现
1） 在根目录下创建hdfsjava目录

package abc;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
public class createDir {public static void main(String[] args) {try {Configuration conf = new Configuration();conf.set("fs.defaultFS", "hdfs://localhost:9000");conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");FileSystem fs = FileSystem.get(conf);boolean isok = fs.mkdirs(new Path("hdfs:/hdfsjava"));if (isok) {System.out.println("成功创建目录!");} else {System.out.println("创建目录失败");}fs.close();} catch (Exception e) {e.printStackTrace();}}
}

2） 在hdfsjava目录下创建文件mobiles.txt，内容是“My telephone is HUAWEI”

package abc;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;public class Writemobile {public static void main(String[] args) {try {Configuration conf = new Configuration();conf.set("fs.defaultFS", "hdfs://localhost:9000");conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");FileSystem fs = FileSystem.get(conf);Path inFile = new Path("hdfs:/hdfsjava/mobile.txt");FSDataOutputStream outputStream = fs.create(inFile);outputStream.writeUTF("My telephone is HUAWEI");outputStream.flush();outputStream.close();fs.close();} catch (Exception e) {e.printStackTrace();}}
}

3） 将linux本地的myLocalFile.txt文件上传到hdfsjava目录下。

package abc;import com.sun.org.apache.xerces.internal.util.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;public class putfile {public static void main(String[] args) {try {Configuration conf = new Configuration();conf.set("fs.defaultFS", "hdfs://localhost:9000");conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");FileSystem fs = FileSystem.get(conf);Path src = new Path("/usr/local/hadoop/myLocalFile.txt");Path dst = new Path("/hdfsjava");fs.copyFromLocalFile(src, dst);System.out.println("上传完成...");fs.close();} catch (Exception e) {e.printStackTrace();}}
}

 

4） 列表显示hdfsjava下的所有文件，打印在控制台上。

package abc;import com.sun.org.apache.xerces.internal.util.URI;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.FileStatus;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;public class printconsole {public static void main(String[] args) {try {Configuration conf = new Configuration();conf.set("fs.defaultFS", "hdfs://localhost:9000");conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");FileSystem fs = FileSystem.get(conf);Path dst = new Path("/hdfsjava");FileStatus[] status = fs.listStatus(dst);for (int i = 0; i < status.length; i++) {System.out.println(status[i].getPath().toString());}fs.close();} catch (Exception e) {e.printStackTrace();}}
}

5） 查看hdfs上的hdfsjava目录下myLocalFile.txt文件内容

package abc;import com.sun.org.apache.xerces.internal.util.URI;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 java.io.BufferedReader;
import java.io.InputStreamReader;public class readfile {public static void main(String[] args) {try {Configuration conf = new Configuration();conf.set("fs.defaultFS", "hdfs://localhost:9000");conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");FileSystem fs = FileSystem.get(conf);Path dst = new Path("/hdfsjava/myLocalFile.txt");FSDataInputStream in = fs.open(dst);BufferedReader d = new BufferedReader(new InputStreamReader(in));String line = null;while ((line = d.readLine()) != null) {String[] stra = line.split(" ");for (int i = 0; i < stra.length; i++) {System.out.print(stra[i]);System.out.print(" ");}System.out.println(" ");}fs.close();} catch (Exception e) {e.printStackTrace();}}
}

 

 6） 将hdfs上的hdfsjava目录下mobiles.txt文件下载到本地/home/hadoop中。

 7） 删除hdfsjava目录。

package abc;import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;public class delete {public static void main(String[] args) {try {Configuration conf = new Configuration();conf.set("fs.defaultFS", "hdfs://localhost:9000");conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");FileSystem fs = FileSystem.get(conf);Path src = new Path("/hdfsjava");fs.delete(src, true);} catch (Exception e) {e.printStackTrace();}}
}