hsqldatabaseproperties.java

一个用java写的开源的数据库系统

/* Copyrights and Licenses
 *
 * This product includes Hypersonic SQL.
 * Originally developed by Thomas Mueller and the Hypersonic SQL Group. 
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 *          product includes Hypersonic SQL." 
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 * This software consists of voluntary contributions made by many individuals on behalf of the
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 * For work added by the HSQL Development Group:
 *
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 * All rights reserved.
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 * modification, are permitted provided that the following conditions are met:
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 * list of conditions and the following disclaimer, including earlier
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 *
 * Redistributions in binary form must reproduce the above copyright notice,
 * this list of conditions and the following disclaimer in the documentation
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 *
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 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */


package org.hsqldb;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.sql.SQLException;

/**
 * Manages a .properties file for a database.
 *
 * @version 1.7.0
 */
class HsqlDatabaseProperties extends org.hsqldb.HsqlProperties {

    private FileInputStream propsFileStream;    // kept open until closed

    private HsqlDatabaseProperties() {
        super();
    }

    public HsqlDatabaseProperties(String name) {

        super(name);

        // month 1-12 instead of 0-11
        setProperty("sql.month", true);

        // char trimming and padding to size and varchar trimming to size
        setProperty("sql.enforce_size", false);

        // char and varchar sorting in charset of the current jvm Locale
        setProperty("sql.compare_in_locale", false);

        // if true, requires a pre-existing unique index for foreign key
        // referenced column and returns an error if index does not exist
        // 1.61 creates a non-unique index if no index exists
        setProperty("sql.strict_fk", false);

        // has no effect if sql_strict_fk is true, otherwise if true,
        // creates a unique index for foreign keys instead of non-unique
        setProperty("sql.strong_fk", true);

        // the earliest version that can open this database
        // this is set to 1.7.0 when the db is written to
        setProperty("hsqldb.compatible_version", "1.6.0");

        // the version that created this database
        // once created, this won't change if db is used with a future version
        setProperty("hsqldb.original_version", "1.7.1");

        // data format of the cache file
        // this is set to 1.7.0 when a new *.data file is created
        setProperty("hsqldb.cache_version", "1.6.0");

        // garbage collect per Record or Cache Row objects created
        // the default, "0" means no garbage collection is forced by
        // hsqldb (the Java Runtime will do it's own garbage collection
        // in any case). Based on tests by meissnersd@users
        /*
            Setting this value can be useful when HSQLDB is used as an
            in-process part of an application. The minimum practical
            amount is probably "10000" and the maximum "1000000"

            In some versions of Java, such as 1.3.1_02 on windows,
            when the application runs out of memory it runs the gc AND
            requests more memory from the OS. Setting this property
            forces the DB to live inside its memory budget but the
            maximum amount of memory can still be set with the
            java -Xmx argument to provide the memory needed by other
            parts of the app to do graphics and networking.

            Of course there is a speed penalty for setting the value
            too low and doing garbage collection too often.
        */

        //setProperty("hsqldb.gc_interval", "0");
        // number of rows from CACHED tables kept constantly in memory
        // the number of rows in up to 3 * (2 to the power of
        // cache_scale value).
        // reduce the default 14 (3*16K rows) if memory is limited and rows
        // are large.
        // values between 8-16 are allowed
        setProperty("hsqldb.cache_scale", "14");

        // maximum size of .script file in megabytes
        setProperty("hsqldb.log_size", "200");
        setProperty("readonly", false);
        setProperty("modified", "no");

        // the property "version" is also set to the current version
    }

    public void close() throws SQLException {

        try {
            if (propsFileStream != null) {
                if (Trace.TRACE) {
                    Trace.trace();
                }

                propsFileStream.close();

                propsFileStream = null;
            }
        } catch (Exception e) {
            throw Trace.error(Trace.FILE_IO_ERROR,
                              fileName + ".properties " + e);
        }
    }

    public void load() throws SQLException {

        close();

        if (Trace.TRACE) {
            Trace.trace();
        }

        try {
            File f = new File(fileName + ".properties");

            // the file is closed only when the database is closed
            propsFileStream = new FileInputStream(f);

            stringProps.load(propsFileStream);
        } catch (Exception e) {
            throw Trace.error(Trace.FILE_IO_ERROR,
                              fileName + ".properties " + e);
        }
    }

    /**
     *  Method declaration
     *
     * @throws  SQLException
     */
    public void save() throws SQLException {

        close();

        if (Trace.TRACE) {
            Trace.trace();
        }

        try {
            super.save();

            // after saving, open the file again
            load();
        } catch (Exception e) {
            throw Trace.error(Trace.FILE_IO_ERROR,
                              fileName + ".properties " + e);
        }
    }

    /**
     *  check by trying to delete the properties file this will not work if
     *  some application has the file open this is why the properties file
     *  is kept open when running ;-) todo: check if this works in all
     *  operating systems
     *
     * @return true if file is open
     * @exception  java.sql.SQLException
     */
    protected boolean isFileOpen() throws java.sql.SQLException {

        close();

        if (Trace.TRACE) {
            Trace.trace();
        }

        if ((new File(fileName + ".properties")).delete() == false) {
            return true;
        }

        // the file was deleted, so recreate it now
        save();

        return false;
    }
}