hadoop與hdfs需要自己安裝，確保檔案存在於hdfs

只有一個main方法

Test.java

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

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException
 
;
import java.io.OutputStream;

public class Test {


    public static void main(String[] args) throws IOException {
        //建立configuration物件
        Configuration conf = new Configuration();
        //配置在etc/hadoop/core-site.xml   fs.defaultFS
        conf.set("fs.defaultFS","hdfs://192.168.163.132:8020"
 
);
        //建立FileSystem物件
        //檢視hdfs叢集伺服器/user/passwd.txt的內容
        FileSystem fs = FileSystem.get(conf);

        FSDataInputStream is = fs.open(new Path("hdfs://192.168.163.132:8020/user/passwd.txt"));
        File file = new File("a.txt");
        System.out.println(file.getAbsolutePath());
        OutputStream os = new FileOutputStream(file);
 

        byte[] buff = new byte[1024];
        int length = 0;
        while ((length = is.read(buff)) != -1) {
            System.out.println(new String(buff, 0, length));
            os.write(buff, 0, length);
            os.flush();
        }
        System.out.println(fs.getClass().getName());
    }
}