apche hbase ResultScanner scanner 如何判断结果为空

当使用`ResultScanner`对象从HBase表中检索数据时，可以通过`next`方法从扫描器中获取下一个`Result`对象。如果表中没有更多的行可以扫描，则`next`方法将返回`null`。因此，可以通过检查`next`方法返回的结果是否为`null`来判断扫描结果是否为空。

以下是一个示例代码片段，可以演示如何使用`ResultScanner`对象并检查结果是否为空：

ResultScanner scanner = table.getScanner(scan);
Result result = scanner.next();

if (result == null) {
   System.out.println("Scan result is empty.");
} else {
   System.out.println("Scan result is not empty.");
}

在这个代码片段中，我们首先使用`getScanner`方法获取一个`ResultScanner`对象，然后使用`next`方法获取第一个`Result`对象。如果结果不为空，则输出“Scan result is not empty.”，否则输出“Scan result is empty.”。

相关问题

hbase 使用java写一个查询结果的多行数据保存在ResultScanner对象中，每行数据以Result对象 形式存储，Result中存储了多个Cell

HBase是一个基于列族的NoSQL分布式数据库，它非常适合处理大规模的数据。在HBase中，如果你想要从表中获取多行数据并将其保存到`ResultScanner`对象中，每个`Result`对象代表一行数据，并包含了该行的所有单元格(`Cells`)，这些单元格通常包含键值对。

以下是使用Java操作HBase查询并保存多行数据的基本步骤：

import org.apache.hadoop.hbase.client.Connection;
import org.apache.hadoop.hbase.client.ConnectionFactory;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.ResultScanner;
import org.apache.hadoop.hbase.client.ScannerTimeoutException;

public void fetchDataFromHBase(String tableName) {
    // 创建连接
    Connection connection = ConnectionFactory.createConnection();

    try {
        // 定义Get请求，指定需要查询的行
        Get get = new Get(Bytes.toBytes("rowKey1")); // "rowKey1"替换为你实际的行键

        // 执行查询
        ResultScanner scanner = table.getScanner(get);

        // 存储结果
        while (scanner.hasNext()) {
            Result result = scanner.next();
            List<Cell> cells = result.listCells(); // 获取当前行的所有Cell
            for (Cell cell : cells) {
                // 对每个cell进行操作，如获取其value等
                byte[] value = cell.getValueArray();
                // ...其他业务逻辑...
            }
        }

        // 关闭扫描器
        scanner.close();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        if (connection != null) {
            try {
                connection.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

使用hbase Java api完成以下操作： 1.建表userfllower 2.用户Mary有一个粉丝Alice，Alice关注列表中也存在Mary 3.用户Jack有两个粉丝Bob和Ben 4.Jack还关注了Mary 5.查看Jack被哪些人关注，Jack关注了谁 6.Bob取关了Jack 7.扫描全表数据 导入以下包完成import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.hbase.;import org.apache.hadoop.hbase.client.;import org.apache.hadoop.hbase.util.Bytes;import java.io.IOException;

以下是使用 HBase Java API 完成以上操作的代码：

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.*;
import org.apache.hadoop.hbase.client.*;
import org.apache.hadoop.hbase.util.Bytes;

import java.io.IOException;

public class HBaseExample {

    private static final String TABLE_NAME = "userfollower";
    private static final String COLUMN_FAMILY = "cf";
    private static final String USER_QUALIFIER = "user";
    private static final String FOLLOWER_QUALIFIER = "follower";

    public static void main(String[] args) throws IOException {
        Configuration config = HBaseConfiguration.create();
        Connection connection = ConnectionFactory.createConnection(config);
        Admin admin = connection.getAdmin();

        // 1.建表userfollower
        createTable(admin);

        // 2.用户Mary有一个粉丝Alice，Alice关注列表中也存在Mary
        addUserFollower(connection, "Mary", "Alice");
        addUserFollower(connection, "Alice", "Mary");

        // 3.用户Jack有两个粉丝Bob和Ben
        addUserFollower(connection, "Jack", "Bob");
        addUserFollower(connection, "Jack", "Ben");

        // 4.Jack还关注了Mary
        addUserFollower(connection, "Jack", "Mary");

        // 5.查看Jack被哪些人关注，Jack关注了谁
        scanUserFollowers(connection, "Jack");

        // 6.Bob取关了Jack
        removeUserFollower(connection, "Bob", "Jack");

        // 7.扫描全表数据
        scanTable(connection);

        admin.close();
        connection.close();
    }

    private static void createTable(Admin admin) throws IOException {
        if (!admin.tableExists(TableName.valueOf(TABLE_NAME))) {
            HTableDescriptor tableDescriptor = new HTableDescriptor(TableName.valueOf(TABLE_NAME));
            HColumnDescriptor columnDescriptor = new HColumnDescriptor(COLUMN_FAMILY);
            tableDescriptor.addFamily(columnDescriptor);
            admin.createTable(tableDescriptor);
        }
    }

    private static void addUserFollower(Connection connection, String user, String follower) throws IOException {
        Table table = connection.getTable(TableName.valueOf(TABLE_NAME));
        Put put = new Put(Bytes.toBytes(user));
        put.addColumn(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(USER_QUALIFIER), Bytes.toBytes(user));
        put.addColumn(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(FOLLOWER_QUALIFIER), Bytes.toBytes(follower));
        table.put(put);
        table.close();
    }

    private static void removeUserFollower(Connection connection, String user, String follower) throws IOException {
        Table table = connection.getTable(TableName.valueOf(TABLE_NAME));
        Delete delete = new Delete(Bytes.toBytes(user));
        delete.addColumn(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(FOLLOWER_QUALIFIER), Bytes.toBytes(follower));
        table.delete(delete);
        table.close();
    }

    private static void scanUserFollowers(Connection connection, String user) throws IOException {
        Table table = connection.getTable(TableName.valueOf(TABLE_NAME));
        Scan scan = new Scan();
        scan.addColumn(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(FOLLOWER_QUALIFIER));
        scan.setRowPrefixFilter(Bytes.toBytes(user));
        ResultScanner scanner = table.getScanner(scan);
        System.out.println(user + " 的粉丝：");
        for (Result result : scanner) {
            byte[] followerBytes = result.getValue(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(FOLLOWER_QUALIFIER));
            String follower = Bytes.toString(followerBytes);
            System.out.println(follower);
        }
        scanner.close();

        scan = new Scan();
        scan.addColumn(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(USER_QUALIFIER));
        scan.setRowPrefixFilter(Bytes.toBytes(user));
        scanner = table.getScanner(scan);
        System.out.println(user + " 关注的人：");
        for (Result result : scanner) {
            byte[] userBytes = result.getValue(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(USER_QUALIFIER));
            String followedUser = Bytes.toString(userBytes);
            System.out.println(followedUser);
        }
        scanner.close();
        table.close();
    }

    private static void scanTable(Connection connection) throws IOException {
        Table table = connection.getTable(TableName.valueOf(TABLE_NAME));
        Scan scan = new Scan();
        ResultScanner scanner = table.getScanner(scan);
        for (Result result : scanner) {
            byte[] userBytes = result.getValue(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(USER_QUALIFIER));
            String user = Bytes.toString(userBytes);
            byte[] followerBytes = result.getValue(Bytes.toBytes(COLUMN_FAMILY), Bytes.toBytes(FOLLOWER_QUALIFIER));
            String follower = Bytes.toString(followerBytes);
            System.out.println(user + " 的粉丝：" + follower);
        }
        scanner.close();
        table.close();
    }
}