Package org.apache.hadoop.hbase.client

import java.io.IOException;

import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.TableName;
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.Table;
import org.apache.hadoop.hbase.client.Put;
import org.apache.hadoop.hbase.client.Result;
import org.apache.hadoop.hbase.client.ResultScanner;
import org.apache.hadoop.hbase.client.Scan;
import org.apache.hadoop.hbase.util.Bytes;


// Class that has nothing but a main.
// Does a Put, Get and a Scan against an hbase table.
public class MyLittleHBaseClient {
  public static void main(String[] args) throws IOException {
    // You need a configuration object to tell the client where to connect.
    // When you create a HBaseConfiguration, it reads in whatever you've set
    // into your hbase-site.xml and in hbase-default.xml, as long as these can
    // be found on the CLASSPATH
    Configuration config = HBaseConfiguration.create();

    // Next you need a Connection to the cluster. Create one. When done with it,
    // close it (Should start a try/finally after this creation so it gets closed
    // for sure but leaving this out for readibility's sake).
    Connection connection = ConnectionFactory.createConnection(config);
    try {

      // This instantiates a Table object that connects you to
      // the "myLittleHBaseTable" table (TableName.valueOf turns String into TableName instance).
      // When done with it, close it (Should start a try/finally after this creation so it gets
      // closed for sure but leaving this out for readibility's sake).
      Table table = connection.getTable(TableName.valueOf("myLittleHBaseTable"));
      try {

        // To add to a row, use Put.  A Put constructor takes the name of the row
        // you want to insert into as a byte array.  In HBase, the Bytes class has
        // utility for converting all kinds of java types to byte arrays.  In the
        // below, we are converting the String "myLittleRow" into a byte array to
        // use as a row key for our update. Once you have a Put instance, you can
        // adorn it by setting the names of columns you want to update on the row,
        // the timestamp to use in your update, etc.If no timestamp, the server
        // applies current time to the edits.
        Put p = new Put(Bytes.toBytes("myLittleRow"));

        // To set the value you'd like to update in the row 'myLittleRow', specify
        // the column family, column qualifier, and value of the table cell you'd
        // like to update.  The column family must already exist in your table
        // schema.  The qualifier can be anything.  All must be specified as byte
        // arrays as hbase is all about byte arrays.  Lets pretend the table
        // 'myLittleHBaseTable' was created with a family 'myLittleFamily'.
        p.add(Bytes.toBytes("myLittleFamily"), Bytes.toBytes("someQualifier"),
        Bytes.toBytes("Some Value"));

        // Once you've adorned your Put instance with all the updates you want to
        // make, to commit it do the following (The HTable#put method takes the
        // Put instance you've been building and pushes the changes you made into
        // hbase)
        table.put(p);

        // Now, to retrieve the data we just wrote. The values that come back are
        // Result instances. Generally, a Result is an object that will package up
        // the hbase return into the form you find most palatable.
        Get g = new Get(Bytes.toBytes("myLittleRow"));
        Result r = table.get(g);
        byte [] value = r.getValue(Bytes.toBytes("myLittleFamily"),
          Bytes.toBytes("someQualifier"));
        // If we convert the value bytes, we should get back 'Some Value', the
        // value we inserted at this location.
        String valueStr = Bytes.toString(value);
        System.out.println("GET: " + valueStr);

        // 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.  To set up a Scanner, do like you did above making a Put
        // and a Get, create a Scan.  Adorn it with column names, etc.
        Scan s = new Scan();
        s.addColumn(Bytes.toBytes("myLittleFamily"), Bytes.toBytes("someQualifier"));
        ResultScanner scanner = table.getScanner(s);
        try {
           // Scanners return Result instances.
           // Now, for the actual iteration. One way is to use a while loop like so:
           for (Result rr = scanner.next(); rr != null; rr = scanner.next()) {
             // print out the row we found and the columns we were looking for
             System.out.println("Found row: " + rr);
           }

           // The other approach is to use a foreach loop. Scanners are iterable!
           // for (Result rr : scanner) {
           //   System.out.println("Found row: " + rr);
           // }
         } finally {
           // Make sure you close your scanners when you are done!
           // Thats why we have it inside a try/finally clause
           scanner.close();
         }

         // Close your table and cluster connection.
       } finally {
         if (table != null) table.close();
       }
     } finally {
       connection.close();
     }
  }
}