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- /*
- Copyright (c) 2017 James Ahlborn
-
- Licensed under the Apache License, Version 2.0 (the "License");
- you may not use this file except in compliance with the License.
- You may obtain a copy of the License at
-
- http://www.apache.org/licenses/LICENSE-2.0
-
- Unless required by applicable law or agreed to in writing, software
- distributed under the License is distributed on an "AS IS" BASIS,
- WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- See the License for the specific language governing permissions and
- limitations under the License.
- */
-
- package com.healthmarketscience.jackcess.util;
-
- import java.io.Closeable;
- import java.io.IOException;
- import java.nio.channels.FileChannel;
- import java.nio.file.Files;
- import java.nio.file.Path;
- import java.nio.file.Paths;
- import java.util.Random;
-
- import com.healthmarketscience.jackcess.Database;
- import com.healthmarketscience.jackcess.Database.FileFormat;
- import com.healthmarketscience.jackcess.Table;
- import com.healthmarketscience.jackcess.impl.ByteUtil;
- import com.healthmarketscience.jackcess.impl.DatabaseImpl;
- import com.healthmarketscience.jackcess.impl.TableImpl;
-
- /**
- * Utility base implementaton of LinkResolver which facilitates loading linked
- * tables from files which are not access databases. The LinkResolver API
- * ultimately presents linked table information to the primary database using
- * the jackcess {@link Database} and {@link Table} classes. In order to
- * consume linked tables in non-mdb files, they need to somehow be coerced
- * into the appropriate form. The approach taken by this utility is to make
- * it easy to copy the external tables into a temporary mdb file for
- * consumption by the primary database.
- * <p>
- * The primary features of this utility:
- * <ul>
- * <li>Supports custom behavior for non-mdb files and default behavior for mdb
- * files, see {@link #loadCustomFile}</li>
- * <li>Temp db can be an actual file or entirely in memory</li>
- * <li>Linked tables are loaded on-demand, see {@link #loadCustomTable}</li>
- * <li>Temp db files will be automatically deleted on close</li>
- * </ul>
- *
- * @author James Ahlborn
- * @usage _intermediate_class_
- */
- public abstract class CustomLinkResolver implements LinkResolver
- {
- private static final Random DB_ID = new Random();
-
- private static final String MEM_DB_PREFIX = "memdb_";
- private static final String FILE_DB_PREFIX = "linkeddb_";
-
- /** the default file format used for temp dbs */
- public static final FileFormat DEFAULT_FORMAT = FileFormat.V2000;
- /** temp dbs default to the filesystem, not in memory */
- public static final boolean DEFAULT_IN_MEMORY = false;
- /** temp dbs end up in the system temp dir by default */
- public static final Path DEFAULT_TEMP_DIR = null;
-
- private final FileFormat _defaultFormat;
- private final boolean _defaultInMemory;
- private final Path _defaultTempDir;
-
- /**
- * Creates a CustomLinkResolver using the default behavior for creating temp
- * dbs, see {@link #DEFAULT_FORMAT}, {@link #DEFAULT_IN_MEMORY} and
- * {@link #DEFAULT_TEMP_DIR}.
- */
- protected CustomLinkResolver() {
- this(DEFAULT_FORMAT, DEFAULT_IN_MEMORY, DEFAULT_TEMP_DIR);
- }
-
- /**
- * Creates a CustomLinkResolver with the given default behavior for creating
- * temp dbs.
- *
- * @param defaultFormat the default format for the temp db
- * @param defaultInMemory whether or not the temp db should be entirely in
- * memory by default (while this will be faster, it
- * should only be used if table data is expected to
- * fit entirely in memory)
- * @param defaultTempDir the default temp dir for a file based temp db
- * ({@code null} for the system defaqult temp
- * directory)
- */
- protected CustomLinkResolver(FileFormat defaultFormat, boolean defaultInMemory,
- Path defaultTempDir)
- {
- _defaultFormat = defaultFormat;
- _defaultInMemory = defaultInMemory;
- _defaultTempDir = defaultTempDir;
- }
-
- protected FileFormat getDefaultFormat() {
- return _defaultFormat;
- }
-
- protected boolean isDefaultInMemory() {
- return _defaultInMemory;
- }
-
- protected Path getDefaultTempDirectory() {
- return _defaultTempDir;
- }
-
- /**
- * Custom implementation is:
- * <pre>
- * // attempt to load the linkeeFileName as a custom file
- * Object customFile = loadCustomFile(linkerDb, linkeeFileName);
- *
- * if(customFile != null) {
- * // this is a custom file, create and return relevant temp db
- * return createTempDb(customFile, getDefaultFormat(), isDefaultInMemory(),
- * getDefaultTempDirectory());
- * }
- *
- * // not a custmom file, load using the default behavior
- * return LinkResolver.DEFAULT.resolveLinkedDatabase(linkerDb, linkeeFileName);
- * </pre>
- *
- * @see #loadCustomFile
- * @see #createTempDb
- * @see LinkResolver#DEFAULT
- */
- @Override
- public Database resolveLinkedDatabase(Database linkerDb, String linkeeFileName)
- throws IOException
- {
- Object customFile = loadCustomFile(linkerDb, linkeeFileName);
- if(customFile != null) {
- // if linker is read-only, open linkee read-only
- boolean readOnly = ((linkerDb instanceof DatabaseImpl) ?
- ((DatabaseImpl)linkerDb).isReadOnly() : false);
- return createTempDb(customFile, getDefaultFormat(), isDefaultInMemory(),
- getDefaultTempDirectory(), readOnly);
- }
- return LinkResolver.DEFAULT.resolveLinkedDatabase(linkerDb, linkeeFileName);
- }
-
- /**
- * Creates a temporary database for holding the table data from
- * linkeeFileName.
- *
- * @param customFile custom file state returned from {@link #loadCustomFile}
- * @param format the access format for the temp db
- * @param inMemory whether or not the temp db should be entirely in memory
- * (while this will be faster, it should only be used if
- * table data is expected to fit entirely in memory)
- * @param tempDir the temp dir for a file based temp db ({@code null} for
- * the system default temp directory)
- *
- * @return the temp db for holding the linked table info
- */
- protected Database createTempDb(Object customFile, FileFormat format,
- boolean inMemory, Path tempDir,
- boolean readOnly)
- throws IOException
- {
- Path dbFile = null;
- FileChannel channel = null;
- boolean success = false;
- try {
-
- if(inMemory) {
- dbFile = Paths.get(MEM_DB_PREFIX + DB_ID.nextLong() +
- format.getFileExtension());
- channel = MemFileChannel.newChannel();
- } else {
- dbFile = ((tempDir != null) ?
- Files.createTempFile(tempDir, FILE_DB_PREFIX,
- format.getFileExtension()) :
- Files.createTempFile(FILE_DB_PREFIX,
- format.getFileExtension()));
- channel = FileChannel.open(dbFile, DatabaseImpl.RW_CHANNEL_OPTS);
- }
-
- TempDatabaseImpl.initDbChannel(channel, format);
- TempDatabaseImpl db = new TempDatabaseImpl(this, customFile, dbFile,
- channel, format, readOnly);
- success = true;
- return db;
-
- } finally {
- if(!success) {
- ByteUtil.closeQuietly(channel);
- deleteDbFile(dbFile);
- closeCustomFile(customFile);
- }
- }
- }
-
- private static void deleteDbFile(Path dbFile) {
- if((dbFile != null) &&
- dbFile.getFileName().toString().startsWith(FILE_DB_PREFIX)) {
- try {
- Files.deleteIfExists(dbFile);
- } catch(IOException ignores) {}
- }
- }
-
- private static void closeCustomFile(Object customFile) {
- if(customFile instanceof Closeable) {
- ByteUtil.closeQuietly((Closeable)customFile);
- }
- }
-
- /**
- * Called by {@link #resolveLinkedDatabase} to determine whether the
- * linkeeFileName should be treated as a custom file (thus utiliziing a temp
- * db) or a normal access db (loaded via the default behavior). Loads any
- * state necessary for subsequently loading data from linkeeFileName.
- * <p>
- * The returned custom file state object will be maintained with the temp db
- * and passed to {@link #loadCustomTable} whenever a new table needs to be
- * loaded. Also, if this object is {@link Closeable}, it will be closed
- * with the temp db.
- *
- * @param linkerDb the primary database in which the link is defined
- * @param linkeeFileName the name of the linked file
- *
- * @return non-{@code null} if linkeeFileName should be treated as a custom
- * file (using a temp db) or {@code null} if it should be treated as
- * a normal access db.
- */
- protected abstract Object loadCustomFile(
- Database linkerDb, String linkeeFileName) throws IOException;
-
- /**
- * Called by an instance of a temp db when a missing table is first requested.
- *
- * @param tempDb the temp db instance which should be populated with the
- * relevant table info for the given tableName
- * @param customFile custom file state returned from {@link #loadCustomFile}
- * @param tableName the name of the table which is requested from the linked
- * file
- *
- * @return {@code true} if the table was available in the linked file,
- * {@code false} otherwise
- */
- protected abstract boolean loadCustomTable(
- Database tempDb, Object customFile, String tableName)
- throws IOException;
-
-
- /**
- * Subclass of DatabaseImpl which allows us to load tables "on demand" as
- * well as delete the temporary db on close.
- */
- private static class TempDatabaseImpl extends DatabaseImpl
- {
- private final CustomLinkResolver _resolver;
- private final Object _customFile;
-
- protected TempDatabaseImpl(CustomLinkResolver resolver, Object customFile,
- Path file, FileChannel channel,
- FileFormat fileFormat, boolean readOnly)
- throws IOException
- {
- super(file, channel, true, false, fileFormat, null, null, null,
- readOnly, false);
- _resolver = resolver;
- _customFile = customFile;
- }
-
- @Override
- protected TableImpl getTable(String name, boolean includeSystemTables)
- throws IOException
- {
- TableImpl table = super.getTable(name, includeSystemTables);
- if((table == null) &&
- _resolver.loadCustomTable(this, _customFile, name)) {
- table = super.getTable(name, includeSystemTables);
- }
- return table;
- }
-
- @Override
- public void close() throws IOException {
- try {
- super.close();
- } finally {
- deleteDbFile(getPath());
- closeCustomFile(_customFile);
- }
- }
-
- static FileChannel initDbChannel(FileChannel channel, FileFormat format)
- throws IOException
- {
- FileFormatDetails details = getFileFormatDetails(format);
- transferDbFrom(channel, getResourceAsStream(details.getEmptyFilePath()));
- return channel;
- }
- }
-
- }
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