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HSQLDB example source code file (CompiledStatementManager.java)

This example HSQLDB source code file (CompiledStatementManager.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - HSQLDB tags/keywords

compiledstatement, compiledstatement, compiledstatementmanager, database, intkeyhashmap, intkeyintvaluehashmap, intkeyintvaluehashmap, intvaluehashmap, intvaluehashmap, iterator, session, string, string, throwable

The HSQLDB CompiledStatementManager.java source code

/* Copyright (c) 2001-2008, The HSQL Development Group
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *
 * Redistributions of source code must retain the above copyright notice, this
 * list of conditions and the following disclaimer.
 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
 * and/or other materials provided with the distribution.
 *
 * Neither the name of the HSQL Development Group nor the names of its
 * contributors may be used to endorse or promote products derived from this
 * software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED. IN NO EVENT SHALL HSQL DEVELOPMENT GROUP, HSQLDB.ORG,
 * OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
 * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
 * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.hsqldb;

import org.hsqldb.HsqlNameManager.HsqlName;
import org.hsqldb.lib.IntKeyHashMap;
import org.hsqldb.lib.IntKeyIntValueHashMap;
import org.hsqldb.lib.IntValueHashMap;
import org.hsqldb.lib.Iterator;

/**
 * This class manages the reuse of CompiledStatement objects for prepared
 * statements for a Database instance.<p>
 *
 * A compiled statement is registered by a session to be managed. Once
 * registered, it is linked with one or more sessions.<p>
 *
 * The sql statement text distinguishes different compiled statements and acts
 * as lookup key when a session initially looks for an existing instance of
 * the compiled sql statement.<p>
 *
 * Once a session is linked with a statement, it uses the uniqe compiled
 * statement id for the sql statement to access the statement.<p>
 *
 * Changes to database structure via DDL statements, will result in all
 * registered CompiledStatement objects to become invalidated. This is done by
 * setting to null all the managed CompiledStatement instances, while keeping
 * their id and sql string. When a session subsequently attempts to use an
 * invalidated (null) CompiledStatement via its id, it will reinstantiate the
 * CompiledStatement using its sql statement still held by this class.<p>
 *
 * This class keeps count of the number of different sessions that are linked
 * to each registered compiled statement, and the number of times each session
 * is linked.  It unregisters a compiled statement when no session remains
 * linked to it.<p>
 *
 * Modified by fredt@users from the original by boucherb@users to simplify,
 * support multiple identical prepared statements per session, and avoid
 * keeping references to CompiledStatement objects after DDL changes which
 * could result in memory leaks. Modified further to support schemas.<p>
 *
 * @author boucherb@users
 * @author fredt@users
 *
 * @since 1.7.2
 * @version 1.8.0
 */
final class CompiledStatementManager {

    /**
     * The Database for which this object is managing
     * CompiledStatement objects.
     */
    private Database database;

    /** Map: Schema id (int) => {Map: SQL String => Compiled Statement id (int)} */
    private IntKeyHashMap schemaMap;

    /** Map: Compiled Statement id (int) => SQL String */
    private IntKeyHashMap sqlLookup;

    /** Map: Compiled statment id (int) => CompiledStatement object. */
    private IntKeyHashMap csidMap;

    /** Map: Session id (int) => {Map: compiled statement id (int) => use count in session} */
    private IntKeyHashMap sessionUseMap;

    /** Map: Compiled statment id (int) => number of sessions that use the statement */
    private IntKeyIntValueHashMap useMap;

    /**
     * Monotonically increasing counter used to assign unique ids to compiled
     * statements.
     */
    private int next_cs_id;

    /**
     * Constructs a new instance of <code>CompiledStatementManager.
     *
     * @param database the Database instance for which this object is to
     *      manage compiled statement objects.
     */
    CompiledStatementManager(Database database) {

        this.database = database;
        schemaMap     = new IntKeyHashMap();
        sqlLookup     = new IntKeyHashMap();
        csidMap       = new IntKeyHashMap();
        sessionUseMap = new IntKeyHashMap();
        useMap        = new IntKeyIntValueHashMap();
        next_cs_id    = 0;
    }

    /**
     * Clears all internal data structures, removing any references to compiled statements.
     */
    synchronized void reset() {

        schemaMap.clear();
        sqlLookup.clear();
        csidMap.clear();
        sessionUseMap.clear();
        useMap.clear();

        next_cs_id = 0;
    }

    /**
     * Used after a DDL change that could impact the compiled statements.
     * Clears references to CompiledStatement objects while keeping the counts
     * and references to the sql strings.
     */
    synchronized void resetStatements() {

        Iterator it = csidMap.values().iterator();

        while (it.hasNext()) {
            CompiledStatement cs = (CompiledStatement) it.next();

            cs.clearVariables();
        }
    }

    /**
     * Retrieves the next compiled statement identifier in the sequence.
     *
     * @return the next compiled statement identifier in the sequence.
     */
    private int nextID() {

        next_cs_id++;

        return next_cs_id;
    }

    /**
     * Retrieves the registered compiled statement identifier associated with
     * the specified SQL String, or a value less than zero, if no such
     * statement has been registered.
     *
     * @param schema the schema id
     * @param sql the SQL String
     * @return the compiled statement identifier associated with the
     *      specified SQL String
     */
    private int getStatementID(HsqlName schema, String sql) {

        IntValueHashMap sqlMap =
            (IntValueHashMap) schemaMap.get(schema.hashCode());

        if (sqlMap == null) {
            return -1;
        }

        return sqlMap.get(sql, -1);
    }

    /**
     * Returns an existing CompiledStatement object with the given
     * statement identifier. Returns null if the CompiledStatement object
     * has been invalidated and cannot be recompiled
     *
     * @param session the session
     * @param csid the identifier of the requested CompiledStatement object
     * @return the requested CompiledStatement object
     */
    synchronized CompiledStatement getStatement(Session session, int csid) {

        CompiledStatement cs = (CompiledStatement) csidMap.get(csid);

        if (cs == null) {
            return null;
        }

        if (!cs.isValid) {
            String sql = (String) sqlLookup.get(csid);

            // revalidate with the original schema
            try {
                cs    = compileSql(session, sql, cs.schemaHsqlName.name);
                cs.id = csid;

                csidMap.put(csid, cs);
            } catch (Throwable t) {
                freeStatement(csid, session.getId(), true);

                return null;
            }
        }

        return cs;
    }

    /**
     * Links a session with a registered compiled statement.
     *
     * If this session has not already been linked with the given
     * statement, then the statement use count is incremented.
     *
     * @param csid the compiled statement identifier
     * @param sid the session identifier
     */
    private void linkSession(int csid, int sid) {

        IntKeyIntValueHashMap scsMap;

        scsMap = (IntKeyIntValueHashMap) sessionUseMap.get(sid);

        if (scsMap == null) {
            scsMap = new IntKeyIntValueHashMap();

            sessionUseMap.put(sid, scsMap);
        }

        int count = scsMap.get(csid, 0);

        scsMap.put(csid, count + 1);

        if (count == 0) {
            useMap.put(csid, useMap.get(csid, 0) + 1);
        }
    }

    /**
     * Registers a compiled statement to be managed.
     *
     * The only caller should be a Session that is attempting to prepare
     * a statement for the first time or process a statement that has been
     * invalidated due to DDL changes.
     *
     * @param csid existing id or negative if the statement is not yet managed
     * @param cs The CompiledStatement to add
     * @return The compiled statement id assigned to the CompiledStatement
     *  object
     */
    private int registerStatement(int csid, CompiledStatement cs) {

        if (csid < 0) {
            csid = nextID();

            int schemaid = cs.schemaHsqlName.hashCode();
            IntValueHashMap sqlMap =
                (IntValueHashMap) schemaMap.get(schemaid);

            if (sqlMap == null) {
                sqlMap = new IntValueHashMap();

                schemaMap.put(schemaid, sqlMap);
            }

            sqlMap.put(cs.sql, csid);
            sqlLookup.put(csid, cs.sql);
        }

        cs.id = csid;

        csidMap.put(csid, cs);

        return csid;
    }

    /**
     * Removes one (or all) of the links between a session and a compiled statement.
     *
     * If the statement is not linked with any other session, it is removed
     * from management.
     *
     * @param csid the compiled statment identifier
     * @param sid the session identifier
     * @param freeAll if true, remove all links to the session
     */
    void freeStatement(int csid, int sid, boolean freeAll) {

        if (csid == -1) {

            // statement was never added
            return;
        }

        IntKeyIntValueHashMap scsMap =
            (IntKeyIntValueHashMap) sessionUseMap.get(sid);

        if (scsMap == null) {

            // statement already removed due to invalidation
            return;
        }

        int sessionUseCount = scsMap.get(csid, 0);

        if (sessionUseCount == 0) {

            // statement already removed due to invalidation
        } else if (sessionUseCount == 1 || freeAll) {
            scsMap.remove(csid);

            int usecount = useMap.get(csid, 0);

            if (usecount == 0) {

                // statement already removed due to invalidation
            } else if (usecount == 1) {
                CompiledStatement cs =
                    (CompiledStatement) csidMap.remove(csid);

                if (cs != null) {
                    int schemaid = cs.schemaHsqlName.hashCode();
                    IntValueHashMap sqlMap =
                        (IntValueHashMap) schemaMap.get(schemaid);
                    String sql = (String) sqlLookup.remove(csid);

                    sqlMap.remove(sql);
                }

                useMap.remove(csid);
            } else {
                useMap.put(csid, usecount - 1);
            }
        } else {
            scsMap.put(csid, sessionUseCount - 1);
        }
    }

    /**
     * Releases the link betwen the session and all compiled statement objects
     * it is linked to.
     *
     * If any such statement is not linked with any other session, it is
     * removed from management.
     *
     * @param sid the session identifier
     */
    synchronized void removeSession(int sid) {

        IntKeyIntValueHashMap scsMap;
        int                   csid;
        Iterator              i;

        scsMap = (IntKeyIntValueHashMap) sessionUseMap.remove(sid);

        if (scsMap == null) {
            return;
        }

        i = scsMap.keySet().iterator();

        while (i.hasNext()) {
            csid = i.nextInt();

            int usecount = useMap.get(csid, 1) - 1;

            if (usecount == 0) {
                CompiledStatement cs =
                    (CompiledStatement) csidMap.remove(csid);

                if (cs != null) {
                    int schemaid = cs.schemaHsqlName.hashCode();
                    IntValueHashMap sqlMap =
                        (IntValueHashMap) schemaMap.get(schemaid);
                    String sql = (String) sqlLookup.remove(csid);

                    sqlMap.remove(sql);
                }

                useMap.remove(csid);
            } else {
                useMap.put(csid, usecount);
            }
        }
    }

    /**
     * Retrieves a MULTI Result describing three aspects of the
     * CompiledStatement prepared from the SQL argument for execution
     * in this session context. <p>
     *
     * <ol>
     * <li>A PREPARE_ACK mode Result describing id of the statement
     *     prepared by this request.  This is used by the JDBC implementation
     *     to later identify to the engine which prepared statement to execute.
     *
     * <li>A DATA mode result describing the statement's result set metadata.
     *     This is used to generate the JDBC ResultSetMetaData object returned
     *     by PreparedStatement.getMetaData and CallableStatement.getMetaData.
     *
     * <li>A DATA mode result describing the statement's parameter metdata.
     *     This is used to by the JDBC implementation to determine
     *     how to send parameters back to the engine when executing the
     *     statement.  It is also used to construct the JDBC ParameterMetaData
     *     object for PreparedStatements and CallableStatements.
     *
     * @param session the session
     * @param sql a string describing the desired statement object
     * @return a MULTI Result describing the compiled statement.
     */
    synchronized CompiledStatement compile(Session session,
                                           String sql) throws Throwable {

        int               csid = getStatementID(session.currentSchema, sql);
        CompiledStatement cs   = (CompiledStatement) csidMap.get(csid);

        if (cs == null ||!cs.isValid ||!session.isAdmin()) {
            cs   = compileSql(session, sql, session.currentSchema.name);
            csid = registerStatement(csid, cs);
        }

        linkSession(csid, session.getId());

        return cs;
    }

    private CompiledStatement compileSql(Session session, String sql,
                                         String schemaName) throws Throwable {

        Session sys = database.sessionManager.getSysSession(schemaName,
            session.getUser());

        return sys.sqlCompileStatement(sql);
    }
}

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