发表初衷

  有很多同学使用虚拟机无法通过 windows 和 Linux 共享复制粘贴板。实现起来可能比较麻烦，这里所给的代码是实验的测试代码。需要做改变的地方：文件包名修改成一致 类名不同也要修改，eclipse可以提示修改的。如果出现链接失败：先确定你的Hadoop hdfs要开启，其次可能需要修改访问端口，具体情况根据你的版本号而定！

第二次实验

代码提取：

package hdfs;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

public class HDFSFileIfExist {
	public static void main(String args[])
	{
		try {
			
			String fileName = "test";
			Configuration conf = new Configuration();
		    conf.set("fs.defaultFS", "hdfs://localhost:9000"); // 这里可能修改端口
		    conf.set("fs.hdfs.impl", "org.apache.hadoop.hdfs.DistributedFileSystem");
		    FileSystem fs = FileSystem.get(conf);
		    if(fs.exists(new Path(fileName))){
		    	System.out.println("文件存在");
		    	}else{
		    	System.out.println("文件不存在");
		    	}
		}
		catch(Exception e) {
			e.printStackTrace();
		}
	}

}

1.1作业1 写入文件

package hdfs;

import org.apache.hadoop.conf.Configuration; 
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.FSDataOutputStream;
import org.apache.hadoop.fs.Path;

public class Chapter3 {

	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);
			byte[] buff = "Hello world".getBytes(); // 要写入的内容
			String filename = "test"; //要写入的文件名
			FSDataOutputStream os = fs.create(new Path(filename));
			os.write(buff,0,buff.length);
			System.out.println("Create:"+ filename);
			os.close();
			fs.close();
			} catch (Exception e) { 
					e.printStackTrace(); 
			} 
	}

}

1.2 作业2 判断文件是否存在

package hdfs;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;

public class Judge_file_exist {
public static void main(String[] args) {
 try {
 String filename = "test";

 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);
 if(fs.exists(new Path(filename))){ 
	 System.out.println("文件存在");
 }else{
 System.out.println("文件不存在");
 }
 fs.close();
 } catch (Exception e) {
 e.printStackTrace();
 }
 }
 }

1.3 作业3 读取文件

package hdfs;

import java.io.BufferedReader;
import java.io.InputStreamReader;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.fs.FSDataInputStream;

public class Read_file {
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 file = new Path("test");
FSDataInputStream getIt = fs.open(file);
BufferedReader d = new BufferedReader(new InputStreamReader(getIt));
String content = d.readLine(); //读取文件一行
System.out.println(content);
d.close(); //关闭文件
fs.close(); //关闭 hdfs
} catch (Exception e) {
e.printStackTrace();
 }
}
}