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". +
+ +
+REPLACE!!!!!!!!
+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.
+ +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.
+ +