PreProcessor

This PreProcessor is a Gradle Plugin, that automatically preprocesses Kotlin, Java and Text Resources.

1. Build File
2. Gradle Tasks
3. Code Example
4. Keywords
5. Possible Conditions

Build File

Here’s how you can apply the plugin in a build.gradle file:

plugins {
    id('java')
    id('dev.tocraft.preprocessor') version '1.2'
}

The Kotlin implementation for a build.gradle.kts file looks similar:

plugins {
    id("org.jetbrains.kotlin.jvm") version "2.0.0"
    id("dev.tocraft.preprocessor") version "1.2"
}

Now, you’ll need to define variables so the preprocessor can evaluate the if-statements.

preprocess {
    vars.put("a", "1")
}

This sets the value of the variable a to 1. You can define any value object you want as long as the key is a String.

Gradle Tasks

By default, the plugin registers the following tasks per source set:

• preProcessJava & applyPreProcessJava, if the source set contains java sources
• preProcessKotlin & applyPreProcessKotlin, if the source set contains kotlin sources
• preProcessResources & applyPreProcessResources, if the source set contains resources

It automatically adapts the tasks compileJava, compileKotlin and processResources to use the outputs of the above tasks. The applyPreProcess*-tasks cause the plugin to update the sources and comment lines with //$$ that won’t run since their if-condition is false. This is not required for the plugin to preprocess, but for better code readability.

The plugin also registers one task simply called applyPreProcess, which automatically applies every applyPreProcess* task for every source set in this build file.

Code Example

An example Java test class looks like this;

package test;

class Test {
    public static void main(String... args) {
        //#if a
        //$$ System.out.println("Test succeeded.");
        //#else
        System.out.println("Test failed.");
        //#endif
    }
}

This will be preprocessed to the following, if a exists:

package test;

class Test {
    public static void main(String... args) {
        //#if a
        System.out.println("Test succeeded.");
        //#else
        //$$ System.out.println("Test failed.");
        //#endif
    }
}

Keywords

You’ll notice the //#if, //#$$, //#else and //#endif. There is also a //#elseif keyword. These will work as if-statements. Every if-statement must start with //#if and must end with //#endif.

You can change these keywords with the following build.gradle structure:

preprocess {
    keywords.put("json", new Keywords("//#if","//#elseif","//#endif","//\$\$"))
}

This will add custom keywords for every file ending with json.

Possible Conditions

Now, this condition is true, if a exists and is not 0 or null:

//#if a

You can also chain conditions:

//#if a && b || c

Of course you can also compare integer values with ==, !=, >=, <=, > and <.

//#if a == 1