One of the most popular and powerful feature in Spring Framework is the Data Access Object (or DAO) support. It makes dealing with data access technologies easy and consistent allowing easy switch or interconnection of the aforementioned persistent stores with minimal friction (no worrying about catching exceptions, writing boiler-plate code or handling resource acquisition and disposal). Rather than reiterating here the value proposal of the DAO support, we recommend the JDBC section in the Spring Framework reference documentation

SHDP provides the same functionality for Apache HBase through its org.springframework.data.hadoop.hbase package: an HbaseTemplate along with several callbacks such as TableCallback, RowMapper and ResultsExtractor that remove the low-level, tedious details for finding the HBase table, run the query, prepare the scanner, analyze the results then clean everything up, letting the developer focus on her actual job (users familiar with Spring should find the class/method names quite familiar).

At the core of the DAO support lies HbaseTemplate - a high-level abstraction for interacting with HBase. The template requires an HBase configuration, once it’s set, the template is thread-safe and can be reused across multiple instances at the same time:

// default HBase configuration
<hdp:hbase-configuration/>

// wire hbase configuration (using default name 'hbaseConfiguration') into the template
<bean id="htemplate" class="org.springframework.data.hadoop.hbase.HbaseTemplate" p:configuration-ref="hbaseConfiguration"/>

The template provides generic callbacks, for executing logic against the tables or doing result or row extraction, but also utility methods (the so-called _one-liner_s) for common operations. Below are some examples of how the template usage looks like:

// writing to 'MyTable'
template.execute("MyTable", new TableCallback<Object>() {
  @Override
  public Object doInTable(HTable table) throws Throwable {
    Put p = new Put(Bytes.toBytes("SomeRow"));
    p.add(Bytes.toBytes("SomeColumn"), Bytes.toBytes("SomeQualifier"), Bytes.toBytes("AValue"));
    table.put(p);
    return null;
  }
});

// read each row from 'MyTable'
List<String> rows = template.find("MyTable", "SomeColumn", new RowMapper<String>() {
  @Override
  public String mapRow(Result result, int rowNum) throws Exception {
    return result.toString();
  }
}));

The first snippet showcases the generic TableCallback - the most generic of the callbacks, it does the table lookup and resource cleanup so that the user code does not have to. Notice the callback signature - any exception thrown by the HBase API is automatically caught, converted to Spring’s DAO exceptions and resource clean-up applied transparently. The second example, displays the dedicated lookup methods - in this case find which, as the name implies, finds all the rows matching the given criteria and allows user code to be executed against each of them (typically for doing some sort of type conversion or mapping). If the entire result is required, then one can use ResultsExtractor instead of RowMapper.

Besides the template, the package offers support for automatically binding HBase table to the current thread through HbaseInterceptor and HbaseSynchronizationManager. That is, each class that performs DAO operations on HBase can be wrapped by HbaseInterceptor so that each table in use, once found, is bound to the thread so any subsequent call to it avoids the lookup. Once the call ends, the table is automatically closed so there is no leakage between requests. Please refer to the Javadocs for more information.