hbase2.1.x 批量get数据-马育民老师

# 说明

执行 `get` 查询，可以传入 多个 `rowkey`

相当于 SQL 的：`select * from ... where id in ('1','2','3')`

### 底层实现

hbase java api，批量操作的底层，都是调用 `batch` 方法

批量 `get()` 方法在 `HTable` 类中，声明如下：
```
@Override
public Result[] get(List<Get> gets) throws IOException {
    if (gets.size() == 1) {
      return new Result[]{get(gets.get(0))};
    }
    try {
      Object[] r1 = new Object[gets.size()];
      batch((List<? extends Row>)gets, r1, readRpcTimeoutMs);
      // Translate.
      Result [] results = new Result[r1.length];
      int i = 0;
      for (Object obj: r1) {
        // Batch ensures if there is a failure we get an exception instead
        results[i++] = (Result)obj;
      }
      return results;
    } catch (InterruptedException e) {
      throw (InterruptedIOException)new InterruptedIOException().initCause(e);
    }
}
```

**解释：** 将 多个 `Get` 对象放入 `List` 中，然后将 list 传入 `get` 方法，返回 `Result[]`

# 案例

查询 `rowkey` 是 `1001`、`1002` 的数据

相当于 SQL中的: `select * from book where id in ('1001','1002')`

### 添加测试数据

清空表：

```
truncate 'student'
```

添加数据：
```
put 'book','1001','c1:title','htlm从入门到放弃'
put 'book','1001','c1:author','lucy'
put 'book','1001','c1:price','097.50'

put 'book','1002','c1:title','css从入门到放弃'
put 'book','1002','c1:author','lili'
put 'book','1002','c1:price','099.90'

put 'book','1003','c1:title','hadoop从入门到放弃'
put 'book','1003','c1:author','韩梅梅'
put 'book','1003','c1:price','190.00'
```

### 关键代码

导包：
```
import org.apache.hadoop.hbase.Cell;
import org.apache.hadoop.hbase.CellUtil;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.Get;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.Table;
import org.apache.hadoop.hbase.util.Bytes;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
```

方法：
```
public List<RowData> getBatch(String tableName, String[] rowkeys) throws IOException {
    TableName tn = TableName.valueOf(tableName);
    //admin封装对表的操作，创建表、删除表、禁用表、启用表
    Table table = conn.getTable(tn);
    List<Get> list = new ArrayList<>();
    for (String item : rowkeys) {
        Get get = new Get(Bytes.toBytes(item));
        list.add(get);
    }
    List<RowData> retList = new ArrayList<>();
    //执行get操作
    Result[] results = table.get(list);
    for (Result result : results) {
        //获取rowkey
        String rowkey = Bytes.toString(result.getRow());
        RowData rowData = new RowData(rowkey);
        List<Cell> cells = result.listCells();
        if (cells != null) {
            for (Cell item : cells) {
                String family = Bytes.toString(CellUtil.cloneFamily(item));
                String qualifier = Bytes.toString(CellUtil.cloneQualifier(item));
                String value = Bytes.toString(CellUtil.cloneValue(item));
                CellData cellData = new CellData(family, qualifier, rowkey, item.getTimestamp(), value);
                rowData.addCellData(cellData);
            }
            retList.add(rowData);
        }
    }
    table.close();
    return retList;
}

```

### 测试

```
HbaseUtils2_getBatch utils=new HbaseUtils2_getBatch();
utils.connect("hadoop1,hadoop2,hadoop3","2181");
String[] rowkeys = {"1020","1021"};
List<RowData> list = utils.getBatch("book", rowkeys);

System.out.println("-------------------------");
for (RowData rowData : list){
    List<CellData> cellDatas = rowData.getCellDatas();

for(CellData cellData :cellDatas){
        System.out.print(cellData.getFamily()+":"+cellData.getQualifier()+"="+cellData.getValue()+" | ");
    }
    System.out.println("\n-------------------------");
}
utils.close();
}
```

原文出处：http://www.malaoshi.top/show_1IX2Jspd7byw.html