databaseinformationmain.java

hsql是很有名的嵌入式数据库

/* Copyright (c) 2001-2005, 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
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 * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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package org.hsqldb;

import org.hsqldb.HsqlNameManager.HsqlName;
import org.hsqldb.lib.HashMap;
import org.hsqldb.lib.HashSet;
import org.hsqldb.lib.HsqlArrayList;
import org.hsqldb.lib.Iterator;
import org.hsqldb.lib.WrapperIterator;
import org.hsqldb.persist.HsqlProperties;
import org.hsqldb.store.ValuePool;

// fredt@users - 1.7.2 - structural modifications to allow inheritance
// boucherb@users - 1.7.2 - 20020225
// - factored out all reusable code into DIXXX support classes
// - completed Fred's work on allowing inheritance
// boucherb@users - 1.7.2 - 20020304 - bug fixes, refinements, better java docs
// fredt@users - 1.8.0 - updated to report latest enhancements and changes

/**
 * Produces a collection of tables that form the system data dictionary. <p>
 *
 * Implementations use a group of arrays of equal size to store various
 * attributes or cached instances of system tables.<p>
 *
 * Two fixed static lists of reserved table names are kept in String[] and
 * HsqlName[] forms. These are shared by all implementations of
 * DatabaseInformtion.<p>
 *
 * Each implementation keeps a lookup set of names for those tables whose
 * contents are never cached (nonCachedTablesSet). <p>
 *
 * An instance of this class uses three lists named sysTablexxxx for caching
 * system tables.<p>
 *
 * sysTableSessionDependent indicates which tables contain data that is
 * dependent on the user rights of the User associatiod with the Session.<p>
 *
 * sysTableSessions contains the Session with whose rights each cached table
 * was built.<p>
 *
 * sysTables contains the cached tables.<p>
 *
 * At the time of instantiation, which is part of the Database.open() method
 * invocation, an empty table is created and placed in sysTables with calls to
 * generateTable(int) for each name in sysTableNames. Some of these
 * table entries may be null if an implementation does not produce them.<p>
 *
 * Calls to getSystemTable(String, Session) return a cached table if various
 * caching rules are met (see below), or it will delete all rows of the table
 * and rebuild the contents via generateTable(int).<p>
 *
 * generateTable(int) calls the appropriate single method for each table.
 * These methods either build and return an empty table (if sysTables
 * contains null for the table slot) or populate the table with up-to-date
 * rows. <p>
 *
 * When the setDirty() call is made externally, the internal isDirty flag
 * is set. This flag is used next time a call to
 * getSystemTable(String, Session) is made. <p>
 *
 * Rules for caching are applied as follows: <p>
 *
 * When a call to getSystemTable(String, Session) is made, if the isDirty flag
 * is true, then the contents of all cached tables are cleared and the
 * sysTableUsers slot for all tables is set to null. This also has the
 * effect of clearing the isDirty and isDirtyNextIdentity flags<p>
 *
 * if the isDirtyNextIdentity flag is true at this point, then the contents
 * of all next identity value dependent cached tables are cleared and the
 * sysTableUsers slot for these tables are set to null.  Currently,
 * the only member of this set is the SYSTEM_TABLES system table.
 *
 * If a table has non-cached contents, its contents are cleared and
 * rebuilt. <p>
 *
 * For the rest of the tables, if the sysTableSessions slot is null or if the
 * Session parameter is not the same as the Session object
 * in that slot, the table contents are cleared and rebuilt. <p>
 *
 * (fredt@users) <p>
 * @author boucherb@users
 * @version 1.8.0
 * @since 1.7.2
 */
class DatabaseInformationMain extends DatabaseInformation {

    // HsqlName objects for the system tables

    /** The HsqlNames of the system tables. */
    protected static final HsqlName[] sysTableHsqlNames;

    /** Current user for each cached system table */
    protected final int[] sysTableSessions = new int[sysTableNames.length];

    /** true if the contents of a cached system table depends on the session */
    protected final boolean[] sysTableSessionDependent =
        new boolean[sysTableNames.length];

    /** cache of system tables */
    protected final Table[] sysTables = new Table[sysTableNames.length];

    /** Set: { names of system tables that are not to be cached } */
    protected static final HashSet nonCachedTablesSet;

    /**
     * Map: simple <code>Column</code> name <code>String</code> object =>
     * <code>HsqlName</code> object.
     */
    protected static final HashMap columnNameMap;

    /**
     * The <code>Session</code> object under consideration in the current
     * executution context.
     */
    protected Session session;

    /** The table types HSQLDB supports. */
    protected static final String[] tableTypes = new String[] {
        "GLOBAL TEMPORARY", "SYSTEM TABLE", "TABLE", "VIEW"
    };

    /** Provides naming support. */
    protected DINameSpace ns;

    static {
        columnNameMap      = new HashMap();
        nonCachedTablesSet = new HashSet();
        sysTableHsqlNames  = new HsqlName[sysTableNames.length];

        for (int i = 0; i < sysTableNames.length; i++) {
            sysTableHsqlNames[i] =
                HsqlNameManager.newHsqlSystemObjectName(sysTableNames[i]);
            sysTableHsqlNames[i].schema =
                SchemaManager.INFORMATION_SCHEMA_HSQLNAME;
        }

        // build the set of non-cached tables
        nonCachedTablesSet.add("SYSTEM_CACHEINFO");
        nonCachedTablesSet.add("SYSTEM_SESSIONINFO");
        nonCachedTablesSet.add("SYSTEM_SESSIONS");
        nonCachedTablesSet.add("SYSTEM_PROPERTIES");
        nonCachedTablesSet.add("SYSTEM_SEQUENCES");
    }

    /**
     * Constructs a table producer which provides system tables
     * for the specified <code>Database</code> object. <p>
     *
     * <b>Note:</b> before 1.7.2 Alpha N, it was important to observe that
     * by specifying an instance of this class or one of its descendents to
     * handle system table production, the new set of builtin permissions
     * and aliases would overwrite those of an existing database, meaning that
     * metadata reporting might have been rendered less secure if the same
     * database were then opened again using a lower numbered system table
     * producer instance (i.e. one in a 1.7.1 or earlier distribution).
     * As of 1.7.2 Alpha N, system-generated permissions and aliases are no
     * longer recorded in the checkpoint script, obseleting this issue.
     * Checkpointing of system-generated grants and aliases was removed
     * because their existence is very close to a core requirment for correct
     * operation and they are reintroduced to the system at each startup.
     * In a future release, it may even be an exception condition to attempt
     * to remove or alter system-generated grants and aliases,
     * respectvely. <p>
     *
     * @param db the <code>Database</code> object for which this object
     *      produces system tables
     * @throws HsqlException if a database access error occurs
     */
    DatabaseInformationMain(Database db) throws HsqlException {

        super(db);

        init();
    }

    /**
     * Adds a <code>Column</code> object with the specified name, data type,
     * data size and nullability to the specified <code>Table</code>
     * object. <p>
     *
     * @param t the table to which to add the specified column
     * @param name the name of the column
     * @param type the data type of the column
     * @param size the precision/length of the column
     * @param nullable <code>true</code> if the column is to allow null values,
     *      else <code>false</code>
     * @throws HsqlException if a problem occurs when adding the
     *      column (e.g. duplicate name)
     */
    protected final void addColumn(Table t, String name, int type, int size,
                                   boolean nullable) throws HsqlException {

        HsqlName cn;
        Column   c;

        cn = (HsqlName) columnNameMap.get(name);

        if (cn == null) {
            cn = database.nameManager.newHsqlName(name, false);

            columnNameMap.put(name, cn);
        }

        c = new Column(cn, nullable, type, size, 0, false, null);

        t.addColumn(c);
    }

    /**
     * Adds a <code>Column</code> object with the specified name, data type
     * and nullability to the specified <code>Table</code> object. <p>
     *
     * @param t the table to which to add the specified column
     * @param name the name of the column
     * @param type the data type of the column
     * @param nullable <code>true</code> if the column is to allow null values,
     *      else <code>false</code>
     * @throws HsqlException if a problem occurs when adding the
     *      column (e.g. duplicate name)
     */
    protected final void addColumn(Table t, String name, int type,
                                   boolean nullable) throws HsqlException {
        addColumn(t, name, type, 0, nullable);
    }

    /**
     * Adds a nullable <code>Column</code> object with the specified name and
     * data type to the specified <code>Table</code> object. <p>
     *
     * @param t the table to which to add the specified column
     * @param name the name of the column
     * @param type the data type of the column
     * @throws HsqlException if a problem occurs when adding the
     *      column (e.g. duplicate name)
     */
    protected final void addColumn(Table t, String name,
                                   int type) throws HsqlException {
        addColumn(t, name, type, true);
    }

    /**
     * Retrieves an enumeration over all of the tables in this database.
     * This means all user tables, views, system tables, system views,
     * including temporary and text tables. <p>
     *
     * @return an enumeration over all of the tables in this database
     */
    protected final Iterator allTables() {
        return new WrapperIterator(database.schemaManager.allTablesIterator(),
                                   new WrapperIterator(sysTables, true));
    }

    /**
     * Clears the contents of cached system tables and resets user slots
     * to null. <p>
     *
     * @throws HsqlException if a database access error occurs
     */
    protected final void cacheClear() throws HsqlException {

        int i = sysTables.length;

        while (i-- > 0) {
            Table t = sysTables[i];

            if (t != null) {
                t.clearAllRows(session);
            }

            sysTableSessions[i] = -1;
        }

        isDirty = false;
    }

    /**
     * Retrieves the system table corresponding to the specified
     * tableIndex value. <p>
     *
     * @param tableIndex int value identifying the system table to generate
     * @throws HsqlException if a database access error occurs
     * @return the system table corresponding to the specified tableIndex value
     */
    protected Table generateTable(int tableIndex) throws HsqlException {

        Table t = sysTables[tableIndex];

//        Please note that this class produces non-null tables for
//        just those absolutely essential to the JDBC 1 spec and the
//        HSQLDB core.  Also, all table producing methods except
//        SYSTEM_PROCEDURES() and SYSTEM_PROCEDURECOLUMNS() are declared final;
//        this class produces only an empty table for each, as per previous
//        DatabaseInformation implementations, whereas
//        DatabaseInformationFull produces comprehensive content for
//        them).
//
//        This break down of inheritance allows DatabaseInformation and
//        DatabaseInformationMain (this class) to be made as small as possible