Data Access Objects (DAO) Sample

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Overview of the sample

The DAOSample sample creates a simple database browser using DAO.

About the server

Data Access Object (DAO) is the programming interface to the Jet database engine. The Jet engine is the basis of Microsoft® Access. It also serves as the database driver for desktop ODBC data sources.

About the sample

This sample is a simple DAO browser. It only uses a very small subset of the available interface. Specifically, the sample is a database browser that permits the user to see the records in a recordset. There are only four navigation options: The sample is purposefully simple so that the interaction of Java™ and DAO can be seen more clearly.

Of special note, DAO requires a run-time license. To create a COM component with a license, use ILicenseMgr. The dao_dbengine class in this sample uses ILicenseMgr to create the DAO database engine. This class is redistributable. It can be found in the REDIST subdirectory on the CD-ROM.

About security

COM components can access any system resources. As such, they are both very powerful and potentially very dangerous. In the Java virtual machine (VM) in Microsoft Internet Explorer 3.0 only trusted class files can use COM components. Class files from digitally signed CAB files are trusted.

If the HTML file is run from Microsoft Developer Studio, the class files are also trusted. This can be very helpful during applet development. However, to deliver your applet to other users, you must put it in a signed CAB file.

When run as an application, the class file must already be on your machine. When run as an applet, the class file may be downloaded to your machine. There is a potential security threat running downloaded software. To run a Java applet that uses COM components, the applet code must be trusted. For more information on trusted class files, see the CabAndSign sample.

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How to use this sample

To run the DAOSample sample:

  1. Create a Java interface for the COM component.
    See     Creating a Java Interface for a COM component.
  2. In Developer Studio, build the applet.
  3. In Developer Studio, run the applet.
    If this is the first time you have run the applet, Developer Studio will prompt you for the name of the class. Type simpledao.
Note: This sample requires database support. Database support is a custom installation option. If you did not select database support during installation, please install again, selecting the Custom installation option so you can choose database support.

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Troubleshooting this sample

If you get the error message java.lang.VerifyError:

If you get the error message ClassNotFoundException:

If you get the error message UnsatisfiedLinkError:

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Files in this sample

This sample includes the following files.

Project files:

Support files: Return to the top of this article.