dwww: tpablo.net

/*-
 * 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);
                }
        }
}

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