# Frequently Asked Questions

# General

Does this work on Linux/Unix?

Yep, Jackcess is pure Java. It will work on any Java Virtual Machine (1.4+).

What Access formats does it support?

Jackcess currently supports only Access 2000 databases. Access 2003 is not supported.

Are password protected databases supported?

Basic password protection is merely software enforced, and Jackcess does not do any password checking at this point. So, a password protected database can be used the same as any other.

How is this different from mdbtools?

We want to give a lot of credit to mdbtools. They have been around much longer than Jackcess, and, along with POI, inspired us that a project like this could be done. mdbtools is written in C. There is a Java port of it, but if you've ever read or used a Java port of a C library, you can appreciate the difference between such a library and one written from scratch in Java.

At the time of this writing, mdbtools could only read Access databases. Jackcess can also write to them. According to their web site, "Write support is currently being worked on and the first cut is expected to be included in the 0.6 release." This status hasn't changed since we first started work on Jackcess.

mdbtools supports Access 97 databases, which Jackcess does not. The Java port of mdbtools also includes an implementation of a small subset of the JDBC APIs. Jackcess does not currently, but a pure Java JDBC driver for Access could certainly be written on top of Jackcess.

This looks like a logical addition to POI. Why not integrate with that project?

POI is released under The Apache License. Jackcess is released under The GNU Lesser General Public License. The Apache license allows closed-source and/or commercial forks. The LGPL does not. If you change or enhance Jackcess, you must contribute your changes back to the project.

I'm using the JDBC/ODBC bridge. Why should I try Jackcess?

- Portability - With Jackcess, your app has one less dependency on Windows.
- Speed - We had an app that used the ODBC bridge to write data to an Access database. When we switched it over to use Jackcess, it was 5 times faster.
- Stability - With large amounts of data, we found the ODBC brige to be pretty unreliable.
- Simplicity - With Jackcess, there is no ODBC configuration to set up.

What version of the JDK does this require?

Version 1.0 requires JDK 1.4 or higher. The version in SVN trunk and all future releases will require JDK 1.5 or higher.

However, some users have contributed patches to make later versions compatible with JDK 1.4. Please check the contributions/ directory in the source repository for any such patches. Note that any code in this directory is untested and unsupported, so please use at your own risk and do not file bugs based on that code.

Why do I get a NoClassDefFoundError?

Probably because you're missing a jar that Jackcess depends on from your classpath. Take a look at the dependencies list. The "compile" and "runtime" dependencies are necessary for using Jackcess in your application. One great place to track down these dependencies is in the Ibiblio Maven Repository.

Why is jackcess so slow for large updates?

While there is much room for improvement in update speed, one factor is whether or not all writes are automatically forced to disk. By default, "autoSync" is enabled, which keeps the database file in a more consistent state, but can be very slow for large updates. Disabling "autoSync" can dramatically increase update speed, but exceptions during update can leave the file in an unusable state. So, modifying this option essentially trades off speed for recoverability.

Why am I getting an IOException with the message "unmapped string index value"?

Update: As of the 1.1.21 release, the text index handling supports the entire Basic Multilingual Plane 0 (i.e. any unicode character 0x0000-0xFFFF). Consequently table names can (as of this release) contain any character in this character set. Therefore, the rest of this answer should no longer be an issue, but keeping it here for reference.

Jackcess cannot currently update a text column index with values which contain non-ascii characters. This situation often arises when tables are created with names which contain international characters. Access stores the table names in another table which has an index on the table name column. The index encoding is not simple to reverse engineer, so it is not likely that Jackcess will support this anytime soon.

Update: As of the 1.1.13 release, the text index handling supports the entire ISO-8859-1 character set. Consequently table names can (as of this release) contain any character in this character set.

Some suggestions (for older releases):

- Use only ascii (or ISO-8859-1 as of 1.1.13) characters in table names if at all possible
- If tables with international characters are required, create the tables using Access, then update the tables using jackcess.
- For indexes on user created tables, populate the table without indexes in jackcess, then add the index using Access.

Why am I getting an UnsupportedOperationException (or IOException) when updating an indexed table?
Previously index update support only handled tables with small numbers of rows. When the index size limit was reached an UnsupportedOperationException (or possibly an IOException) was thrown. As of the 1.1.14 release, experimental, optional large index support has been added. This support is disabled by default but can be enabled via a few different means. Please see the Database javadocs for details on enabling large index support.
Can Jackcess execute SQL queries?
As of the 1.1.19 release, Jackcess has the ability to read the Queries saved in an Access database (i.e. interpret the data stored in the system Queries table). However, Jackcess does not have the ability to execute these Queries. There have been a few attempts to use Jackcess to build JDBC drivers for Access databases, but none of the projects seem to have progressed very far before becoming inactive.
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It doesn't work!

Ok, that wasn't a question, but we'll try to respond anyway. :) Jackcess is young, and not that robust yet. As you might imagine, it's kind of hard to test, simply by its nature. There are bugs that we are aware of, and certainly many more that we are not. If you find what looks like a bug, please report it. Even better, fix it, and submit a patch.