libdb/docs/programmer_reference/second.javas

/*-
 * Copyright (c) 2002,2009 Oracle.  All rights reserved.
 *
 */
package db;

import com.sleepycat.db.*;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.InputStreamReader;
import java.io.IOException;
import java.io.PrintStream;

class SecondaryExample
{
	private static final String progname = "SecondaryExample";
	private static final String DATABASE_HOME = "TESTDIR";

	public static void main(String[] args)
	{
		try {
			SecondaryExample app = new SecondaryExample();
			app.run();
		} catch(Exception e) {
			System.err.println(progname + ": " + e);
			e.printStackTrace(System.err);
			System.exit(1);
		}
	}

	void run() throws DbException, FileNotFoundException
	{
		DbEnv dbenv = new DbEnv(0);

		/* Open the environment. */
		dbenv.open(DATABASE_HOME,
		    Db.DB_CREATE | Db.DB_INIT_LOCK | Db.DB_INIT_LOG |
		    Db.DB_INIT_MPOOL | Db.DB_INIT_TXN, 0);

		try {
			run_app(dbenv);
		} finally {
			dbenv.close(0);
		}
	}

	private void run_app(DbEnv dbenv)
		throws DbException, FileNotFoundException
	{
		Db dbp, sdbp;
		Dbt key, pkey, skey, data;
		StudentRecord srec;

		/* Open/create primary */
		dbp = new Db(dbenv, 0);
		dbp.open(null, "students.db", null, Db.DB_BTREE, Db.DB_CREATE,
		    0600);

		/*
		 * Open/create secondary.  Note that it supports duplicate data
		 * items, since last names might not be unique.
		 */
		sdbp = new Db(dbenv, 0);
		sdbp.set_flags(Db.DB_DUP | Db.DB_DUPSORT);
		sdbp.open(null, "lastname.db", null, Db.DB_BTREE, Db.DB_CREATE,
		    0600);

		try {
			/* Associate the secondary with the primary. */
			dbp.associate(sdbp, new GetName(), 0);

			/* Add a new record */
			key = new Dbt();
			key.set_data("WC42".getBytes());
			key.set_size(4);
			srec = new StudentRecord();
			srec.student_id = "WC42";
			srec.last_name = "Churchill      ";
			srec.first_name = "Winston        ";
			data = new Dbt();
			srec.encode(data);

			System.out.println("Adding a record with primary key " +
			    new String(key.get_data()) + " and secondary key " +
			    srec.last_name);
			dbp.put(null, key, data, 0);

			/* Now do a lookup */
			skey = new Dbt();
			pkey = new Dbt();
			data = new Dbt();
			skey.set_data("Churchill      ".getBytes());
			skey.set_size(15);
			System.out.println("Searching with secondary key " +
			    new String(skey.get_data()));
			sdbp.pget(null, skey, pkey, data, 0);

			System.out.println("Found a record with primary key " +
			    new String(pkey.get_data()));
		} finally {
			dbp.close(0);
			sdbp.close(0);
		}
	}

	/*
	 * getname -- extracts a secondary key (the last name) from a primary
	 * 	key/data pair
	 */
	class GetName implements DbSecondaryKeyCreate {
		public int secondary_key_create(Db secondary,
		    Dbt pkey, Dbt pdata, Dbt skey) {
 			StudentRecord srec = new StudentRecord();
			srec.decode(pdata);

			// Make a fixed-length array of last_name
			byte[] last_name_data = srec.last_name.getBytes();
			byte[] last_name_raw = new byte[15];
			System.arraycopy(last_name_data, 0, last_name_raw, 0,
			    last_name_data.length);

			skey.set_data(last_name_raw);
			skey.set_size(last_name_raw.length);
			return (0);
		}
	}

	class StudentRecord
	{
		String student_id;	// assumed to be 4 bytes long
		String last_name;	// assumed to be 15 bytes long
		String first_name;	// assumed to be 15 bytes long

		void decode(Dbt dbt) {
			byte[] data = dbt.get_data();
			student_id = new String(data, 0, 4);
			last_name = new String(data, 4, 15);
			first_name = new String(data, 19, 15);
		}

		void encode(Dbt dbt) {
			byte[] data = new byte[34];
			System.arraycopy(student_id.getBytes(), 0, data, 0, 4);
			byte[] last_name_raw = last_name.getBytes();
			System.arraycopy(last_name_raw, 0, data, 4,
			    last_name_raw.length);
			byte[] first_name_raw = first_name.getBytes();
			System.arraycopy(first_name_raw, 0, data, 19,
			    first_name_raw.length);
			dbt.set_data(data);
			dbt.set_size(data.length);
		}
	}
}