Aspectj Cookbook

2017-07-07 02:10:07

Recipe 2.3. Compiling an Aspect and Multiple Java Files

Problem

You want to conveniently compile a selection of aspects that are to be applied to multiple Java classes.

Solution

Create an AspectJ build configuration file titled <appname>.lst containing the names of all of the class files and aspects to be included in the compilation, similar to the example .lst file in Example 2-4.

Example 2-4. The contents of an example AspectJ build configuration .lst file

// File files.lst com/oreilly/aspectjcookbook/MyClass.java com/oreilly/aspectjcookbook/MyAspect.java com/oreilly/aspectjcookbook/AnotherClass.java com/oreilly/aspectjcookbook/AnotherAspect.java

Use the following command to instruct the ajc compiler to apply the aspects to the classes:

> ajc -argfile files.lst -classpath %MY_CLASSPATH% -d %MY_DESTINATION_DIRECTORY%

Discussion

The process by which the ajc tool completes the compilation of aspects and classes is largely transparent to the developer and can be treated as a black box. You shouldn't really worry about the interim steps that may be taking place inside the AspectJ compiler, short of a desire to get into development work on ajc itself.

It is important to consider the inputs to the build process; this is handled through the creation of the .lst build configuration file. The ajc compiler does not search the source or class path for files to compile; it must be told which files are to be involved in the compilation. This means that all of your source that is to be compiled with aspects must be fed directly to the ajc compiler. There are three ways to supply the files to be compiled to the ajc compiler (two of which are semantically equivalent):

The -argfile option: You can supply all the files within a .lst file by specifying the filename on the ajc command line with this option.
The @ option: This option is equivalent to the -argfiles option.
Directly list the files: You can simply specify the files on the command line when the ajc compiler is invoked.

Recipe 2.1 shows how to prepare a simple command-line build area for development using AspectJ; the AspectJ Development Environment Guide is available at http://www.eclipse.org/aspectj and provides more details on the runtime options and flags that the ajdoc tool supports; a full description of the AspectJ compiler process is available at http://hugunin.net/papers/aosd-2004-cameraReady.pdf; Recipe 2.8 shows how the .lst file can be used to vary the aspects that are woven for a particular build configuration.