Once you have a running HBase, you probably want a way to hook your application up to it. + If your application is in Java, then you should use the Java API. Here's an example of what + a simple client might look like. This example assumes that you've created a table called + "myTable" with a column family called "myColumnFamily". +

++import java.io.IOException; +import org.apache.hadoop.hbase.client.HTable; +import org.apache.hadoop.hbase.client.Scanner; +import org.apache.hadoop.hbase.io.BatchUpdate; +import org.apache.hadoop.hbase.io.Cell; +import org.apache.hadoop.hbase.io.RowResult; +import org.apache.hadoop.hbase.util.Bytes; + +public class MyClient { + + public static void main(String args[]) throws IOException { + // You need a configuration object to tell the client where to connect. + // But don't worry, the defaults are pulled from the local config file. + HBaseConfiguration config = new HBaseConfiguration(); + + // This instantiates an HTable object that connects you to the "myTable" + // table. + HTable table = new HTable(config, "myTable"); + + // To do any sort of update on a row, you use an instance of the BatchUpdate + // class. A BatchUpdate takes a row and optionally a timestamp which your + // updates will affect. If no timestamp, the server applies current time + // to the edits. + BatchUpdate batchUpdate = new BatchUpdate("myRow"); + + // The BatchUpdate#put method takes a byte [] (or String) that designates + // what cell you want to put a value into, and a byte array that is the + // value you want to store. Note that if you want to store Strings, you + // have to getBytes() from the String for HBase to store it since HBase is + // all about byte arrays. The same goes for primitives like ints and longs + // and user-defined classes - you must find a way to reduce it to bytes. + // The Bytes class from the hbase util package has utility for going from + // String to utf-8 bytes and back again and help for other base types. + batchUpdate.put("myColumnFamily:columnQualifier1", + Bytes.toBytes("columnQualifier1 value!")); + + // Deletes are batch operations in HBase as well. + batchUpdate.delete("myColumnFamily:cellIWantDeleted"); + + // Once you've done all the puts you want, you need to commit the results. + // The HTable#commit method takes the BatchUpdate instance you've been + // building and pushes the batch of changes you made into HBase. + table.commit(batchUpdate); + + // Now, to retrieve the data we just wrote. The values that come back are + // Cell instances. A Cell is a combination of the value as a byte array and + // the timestamp the value was stored with. If you happen to know that the + // value contained is a string and want an actual string, then you must + // convert it yourself. + Cell cell = table.get("myRow", "myColumnFamily:columnQualifier1"); + // This could throw a NullPointerException if there was no value at the cell + // location. + String valueStr = Bytes.toString(cell.getValue()); + + // Sometimes, you won't know the row you're looking for. In this case, you + // use a Scanner. This will give you cursor-like interface to the contents + // of the table. + Scanner scanner = + // we want to get back only "myColumnFamily:columnQualifier1" when we iterate + table.getScanner(new String[]{"myColumnFamily:columnQualifier1"}); + + + // Scanners return RowResult instances. A RowResult is like the + // row key and the columns all wrapped up in a single Object. + // RowResult#getRow gives you the row key. RowResult also implements + // Map, so you can get to your column results easily. + + // Now, for the actual iteration. One way is to use a while loop like so: + RowResult rowResult = scanner.next(); + + while (rowResult != null) { + // print out the row we found and the columns we were looking for + System.out.println("Found row: " + Bytes.toString(rowResult.getRow()) + + " with value: " + rowResult.get(Bytes.toBytes("myColumnFamily:columnQualifier1"))); + rowResult = scanner.next(); + } + + // The other approach is to use a foreach loop. Scanners are iterable! + for (RowResult result : scanner) { + // print out the row we found and the columns we were looking for + System.out.println("Found row: " + Bytes.toString(rowResult.getRow()) + + " with value: " + rowResult.get(Bytes.toBytes("myColumnFamily:columnQualifier1"))); + } + + // Make sure you close your scanners when you are done! + // Its probably best to put the iteration into a try/finally with the below + // inside the finally clause. + scanner.close(); + } +} + +

There are many other methods for putting data into and getting data out of + HBase, but these examples should get you started. See the HTable javadoc for + more methods. Additionally, there are methods for managing tables in the + HBaseAdmin class.

If your client is NOT Java, then you should consider the Thrift or REST + libraries.

Requirements

Windows

Getting Started

Standalone Mode

Distributed Operation: Pseudo- and Fully-Distributed Modes

Distributed Operation

Fully-Distributed Operation

Example API Usage

Related Documentation