Is it possible to modify source code with ant?

Question

I would like to do conditional compilation in a program of mine. I know that if you declare a public static final boolean the compiler will ignore the branch that is not traversed. Is it possible to have an ant target change a variable before building the program?

For example if I have:

final public static boolean windows = false;

I would like two ant targets: Windows and Mac. I would like the command ant windows to change the boolean to true, while ant mac leaves the variable as is.

Thanks.

Answer 1

You can get Ant to modify a properties file, and then you can read this file in your application pretty easily:
new Properties(new FileInputStream("filename" / new File(filename))),

and read properties using:
Boolean isWindows = new Boolean(properties.getProperty("windows"))

or:
String os = properties.getProperty("os").

You can use the Ant PropertyFile task for doing this: http://ant.apache.org/manual/Tasks/propertyfile.html.

Edit: here's an alternative using another task if you absolutely must edit the source code file using Ant:

<replaceregexp file="blah.java" match="public static final boolean WINDOWS = \"(.*)\"" replace="public static final boolean WINDOWS = \"" + ${properties.windows} + "\"" />
-- replace the code as your own as required. See http://ant.apache.org/manual/Tasks/replaceregexp.html for details.

Answer 2

Skip ant and property files etc, Java already does this!

Use something like System.getProperty("os.name");

Answer 3

You should read the other answers carefully and see if there is a better solution for you. However, Ant does have a task to replace text in files. For example:

<replace file="${src}/MyFile.java" token="boolean windows=true" value="boolean windows=false"/>

Answer 4

The properties and the replace tasks should get you what you need. I concur that finding a different approach is a good idea.

However if for some reason the built in tasks will not get you what you need, it is pretty easy to write a custom task for ant. See http://ant.apache.org/manual/develop.html

Answer 5

You can also provide command-lind value as an argument while calling Java-main program from Ant.

For eg. ant -f build.xml "YouranttaskName" -Doperatingsys="windows"

Inside build.xml

<target name="YouranttaskName">
<java classname="javaclassname" fork="true" >
<arg value="${operatingsys}" />
</java>
</target> 

Inside java -main method this argument-value will be available in same order .i.e. args[0] contains "Windows".

You can write your logic by considering that what is your default OS value, as user may not provide commandline argument and then set 'boolean flag' parameter accordingly.