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The Qt Jambi Resource System

Qt Jambi provides a convenient way to bundle resources with you Java application - such as icons, translation files, etc. With the resource system, Jambi can search for files and directories you specify in the current classpath.

Using the Resource System

Using the resource system, you can specify resource file names relative to the classpath. This is done by prefixing the filename of the resource with "classpath:", for instance:
        QFile resourceFile = new QFile("classpath:images/star.png");
Qt Jambi then goes through the classpath entries and appends images/star.png to each entry. Notice that this makes it easy to package resources in .jar files.

For instance if you have an image, star.png, located in the root directory of the .jar file, you can simply access it by "classpath:star.png". The .jar file must be in the classpath, of course.

It is also possible to search for a file in a specific (absolute) location in the classpath, using the syntax "classpath:<absolute path>#<filename>". The absolute path can be the full path to a directory or a .jar file, while the filename is the name of the resource.

In the following code snippet, Qt Jambi will pick the classpath entry images, and search for the star.png in that directory.

        QPixmap pixmap = new QPixmap("classpath:images#/star.png");
Giving a specific location is mostly useful if you want to get an absolute path to a resource, i.e., a path to one specific file in the classpath. We give a code example below.
        QFile absoluteFilePath = new QFile("classpath:images#/star.png");
        QFile relativeFilePath = new QFile("classpath:images/star.png");
If your classpath contains resources.jar and the directory images, Qt Jambi will search for absoluteFilePath only in images, and search for relativeFilePath in images/images/ and in images inside the resources .jar file.

You can list contents of a directory in the classpath, for instance, using a QDir.

        QDir dir = new QDir("classpath:images");
        List<QFileInfo> images = dir.entryInfoList();
The resource system is read-only, so it is not possible to create new directories, write resource files, etc.

The Resource System Implementation

In Jambi it is possible to write custom file engines by extending
QAbstractFileEngine. A file engine knows how to resolve file names, read, and write files through a QIODevice. The QDir, QFile, and QFileInfo classes all make use of a file file engine. The resource system is implemented in such a custom file engine.

Note that this makes the resource system specific to Qt Jambi, so, for instance, you cannot access resources using the java.io package.

See also:
Resource System Example, and QAbstractFileEngine.


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Qt Jambi 4.5.2_01