Package com.healthmarketscience.jackcess.util

Class CustomLinkResolver

java.lang.Object

com.healthmarketscience.jackcess.util.CustomLinkResolver

All Implemented Interfaces:

LinkResolver

public abstract class CustomLinkResolver
extends Object
implements LinkResolver

Utility base implementation 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 Database and 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.

The primary features of this utility:

• Supports custom behavior for non-mdb files, see loadCustomFile(com.healthmarketscience.jackcess.Database, java.lang.String). Mdb files fall back to the default resolver, which refuses to open them unless link resolution has been enabled, see resolveLinkedDatabase(com.healthmarketscience.jackcess.Database, java.lang.String)
• Temp db can be an actual file or entirely in memory
• Linked tables are loaded on-demand, see loadCustomTable(com.healthmarketscience.jackcess.Database, java.lang.Object, java.lang.String)
• Temp db files will be automatically deleted on close

Author:

James Ahlborn

Usage:

Intermediate: This class requires moderate API knowledge.

Field Summary

Fields

Modifier and Type	Field	Description
static Database.FileFormat	DEFAULT_FORMAT	the default file format used for temp dbs
static boolean	DEFAULT_IN_MEMORY	temp dbs default to the filesystem, not in memory
static Path	DEFAULT_TEMP_DIR	temp dbs end up in the system temp dir by default

Fields inherited from interface com.healthmarketscience.jackcess.util.LinkResolver

DEFAULT, UNRESTRICTED

Method Summary

Modifier and Type	Method	Description
Database	resolveLinkedDatabase(Database linkerDb, String linkeeFileName)	Custom implementation is:

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

DEFAULT_FORMAT

public static final Database.FileFormat DEFAULT_FORMAT

the default file format used for temp dbs

DEFAULT_IN_MEMORY

public static final boolean DEFAULT_IN_MEMORY

temp dbs default to the filesystem, not in memory

See Also:

Constant Field Values

DEFAULT_TEMP_DIR

public static final Path DEFAULT_TEMP_DIR

temp dbs end up in the system temp dir by default

Method Detail

resolveLinkedDatabase

public Database resolveLinkedDatabase(Database linkerDb,
                                      String linkeeFileName)
                               throws IOException

Custom implementation is:

   // 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 custom file, load using the default behavior
   return DatabaseImpl.getDefaultLinkResolver()
     .resolveLinkedDatabase(linkerDb, linkeeFileName);

The fallback is the resolver a Database uses when none has been configured, so it refuses to open the linked database. Override this method and delegate to LinkResolver.UNRESTRICTED only when the linked database file names can be trusted.

Specified by:

resolveLinkedDatabase in interface LinkResolver

Throws:

IOException

See Also:

loadCustomFile(com.healthmarketscience.jackcess.Database, java.lang.String), createTempDb(java.lang.Object, com.healthmarketscience.jackcess.Database.FileFormat, boolean, java.nio.file.Path, boolean), LinkResolver.DEFAULT, LinkResolver.UNRESTRICTED