4.1.4、hadoop__Java連接配接操作hadoop，導包，連接配接hadoop，FileSystem靜态方法，檢視檔案listStatus資訊，讀取檔案open，寫入檔案create建立檔案寫

1、導包

<!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-hdfs -->
    <dependency>
        <groupId>org.apache.hadoop</groupId>
        <artifactId>hadoop-hdfs</artifactId>
        <version>2.7.6</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-common -->
    <dependency>
        <groupId>org.apache.hadoop</groupId>
        <artifactId>hadoop-common</artifactId>
        <version>2.7.6</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-client -->
    <dependency>
        <groupId>org.apache.hadoop</groupId>
        <artifactId>hadoop-client</artifactId>
        <version>2.7.6</version>
    </dependency>

    <!-- https://mvnrepository.com/artifact/junit/junit -->
    <dependency>
        <groupId>junit</groupId>
        <artifactId>junit</artifactId>
        <version>4.3</version>
    </dependency>
           

2、連接配接hadoop

public class hadoopconn {
    @Test
    public void getConn()throws Exception{
        Configuration configuration = new Configuration();
        //可以設定一些屬性，設定副本數
        configuration.set("dfs.replication","1");
        //uri擷取連接配接的位址
        URI uri = new URI("hdfs://master:9000");
        //使用靜态方法連接配接
        FileSystem fs = FileSystem.get(uri, configuration);
        //進行操作,建立一個目錄
        boolean b = fs.mkdirs(new Path("/test"));
        System.out.println(b);
    }
    @Test
    public void getDelete()throws Exception{
        //後面的boolean表示疊代删除,true:可以，false：不可以
        boolean b = fs.delete(new Path("/test"), true);
        System.out.println(b);
    }
}
           

3、檢視目錄下檔案詳細資訊

//檢視data檔案下目錄清單
 @Test
 public void getStatus()throws Exception{
     FileStatus[] fileStatuses = fs.listStatus(new Path("/data"));
     //擷取一個一個單個檔案
     for (FileStatus f : fileStatuses) {
         System.out.println(f.getBlockSize());   //block塊128
         System.out.println(f.getLen());         //檔案實際大小
         System.out.println(f.getGroup());       //組
         System.out.println(f.getOwner());       //所屬者
         System.out.println(f.getPath());        //路徑
    	。。。。。。
     }
 }
           

4、檢視檔案裡面的詳細資訊（存儲塊多少，哪個節點等資訊）

//檢視data檔案下目錄清單
    @Test
    public void getStatus()throws Exception{
        FileStatus[] fileStatuses = fs.listStatus(new Path("/data"));
        //擷取一個一個單個檔案
        for (FileStatus f : fileStatuses) {
            System.out.println(f.getBlockSize());   //塊128
            System.out.println(f.getLen());         //檔案大小
            System.out.println(f.getGroup());       //組
            System.out.println(f.getOwner());       //所屬者
            System.out.println(f.getPath());        //路徑
        }
    }
    //擷取檔案存儲詳細資訊
    @Test
    public void getBlock() throws Exception {
        BlockLocation[] bl = fs.getFileBlockLocations(new Path("/data/student.txt"), 0, 100000000);
        for (BlockLocation b : bl) {

        //檔案存儲的節點，由于每個塊隻能存128，所有可能有多個塊存多個節點上
            String[] hosts = b.getHosts();
            for (String host : hosts) {
                System.out.println(host);
            }
            //檔案資料的大小
            System.out.println(b.getLength());

            //還是每個節點資料的主機機器
            String[] names = b.getNames();
            for (String name : names) {
                System.out.println(name);
            }
            //存完128之後剩餘的量為偏移量
            System.out.println(b.getOffset());

            //節點
            String[] topologyPaths = b.getTopologyPaths();
            for (String s : topologyPaths) {
                System.out.println(s);
            }
        }
    }
}
           

5、讀取檔案,使用open打開檔案擷取流，讀取

@Test
public void getopen() throws Exception{
    //使用open方法打開檔案檔案
    FSDataInputStream inputStream = fs.open(new Path("/data/student.txt"));
    BufferedReader br = new BufferedReader(new InputStreamReader(inputStream));
    String line;
    while ((line=br.readLine())!=null){
        System.out.println(line);
    }
    br.close();
    inputStream.close();
}
           

6、上傳寫入檔案,hdfs上檔案不能被修改,隻能覆寫，不能追加

使用create建立檔案儲存資料
    @Test
    public void getPut()throws Exception{
        FSDataOutputStream os = fs.create(new Path("/data/test.txt"));
        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os));
        bw.write("你好");
        bw.flush();
        bw.close();
    }
}