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[[develop_binary_plugins_advanced]]
= Binary Plugin Development

When creating a plugin in Gradle, you will most likely offer tasks users can run and DSL blocks that users can use to configure your plugin.

Let's create a binary plugin that offers both.

When you write a plugin in Gradle, if you want to share it between multiple projects then the best option is to create the plugin in a separate repository.
This way, you can publish it to a private or public Maven repository, and then apply it in whatever project you need.

== Components of a Plugin

First, let's review the three components of a plugin:

image::plugin-1.png[]

[cols="1,1,2", options="header"]
|===
|Component |Role |Description

|*Plugin Class*
|Entry point
|Defines what happens when the plugin is applied. Typically, this involves registering tasks or modifying the project configuration.

|*Extension Class*
|Configuration
|Holds configuration data provided by users via the build script.

|*Task Class*
|Behavior
|Implements logic that is executed when the task is run. The plugin will typically register a task and wire it up with values from the extension.
|===

Our simple plugin compares the size of two files.
It is called `FileSizeDiff`.
Here's the suggested directory structure:

====
[.multi-language-sample]
=====
[source, kotlin]
----
.
└── plugin
    ├── settings.gradle.kts
    ├── build.gradle.kts
    └── src
       └── main
           └── java/org/example
               ├── FileSizeDiffTask.java
               ├── FileSizeDiffPlugin.java
               └── FileSizeDiffExtension.java
----
=====
[.multi-language-sample]
=====
[source, groovy]
----
.
└── plugin
    ├── settings.gradle
    ├── build.gradle
    └── src
       └── main
           └── java/org/example
               ├── FileSizeDiffTask.java
               ├── FileSizeDiffPlugin.java
               └── FileSizeDiffExtension.java
----
=====
====

This `build.gradle(.kts)` for this `filesizediff` plugin looks as follows:

====
include::sample[dir="snippets/plugins/fileSizeDiffBinaryPlugin/kotlin", files="plugin/build.gradle.kts[tags=simple]"]
include::sample[dir="snippets/plugins/fileSizeDiffBinaryPlugin/groovy", files="plugin/build.gradle[tags=simple]"]
====
<1> `java-gradle-plugin` - Sets up various configurations you need to do plugin development in Java
<2> `junit` testing framework - A popular Java testing framework
<3> Plugin configuration - Sets an id of `org.example.filesizediff` which we can use to reference the plugin

== 1. Extension

The extension defines the plugin’s configurable inputs, two file properties in this case:

.src/main/java/org/example/FileSizeDiffExtension.java
[source,java]
----
include::{snippetsPath}/plugins/fileSizeDiffBinaryPlugin/common/plugin/src/main/java/org/example/FileSizeDiffExtension.java[]
----

The two properties representing the input files are of the `RegularFileProperty` type which extends `Property` and are therefore <<lazy_eager_evaluation.adoc#lazy_evaluation,lazy>>.

== 2. Task

The task does the bulk of the work:

.src/main/java/org/example/FileSizeDiffTask.java
[source,java]
----
include::{snippetsPath}/plugins/fileSizeDiffBinaryPlugin/common/plugin/src/main/java/org/example/FileSizeDiffTask.java[]
----

The task defines two input file properties and one output file property:

* The **input files** represent the files to compare.
* The **output file** is where the plugin writes the diff result, defaulting to `build/diff-result.txt`.

The `@InputFile` and `@OutputFile` annotations tell Gradle to track these properties for **incremental builds** and **caching**, so the task will only re-run if the inputs or outputs change.

The plugin is responsible for **mapping the user-defined values** from the extension to the task’s input properties.

The task logic is implemented in a method annotated with `@TaskAction`, which:

* Compares the size of the two input files.
* Generates a descriptive text result.
* Writes that result to the output file and prints it to standard output.

== 3. Plugin

This class wires up the extension and task when the plugin is applied:

.src/main/java/org/example/FileSizeDiffPlugin.java
[source,java]
----
include::{snippetsPath}/plugins/fileSizeDiffBinaryPlugin/common/plugin/src/main/java/org/example/FileSizeDiffPlugin.java[]
----

In the plugin class, we override the `apply` method, which is invoked when the plugin is applied to a project via `build.gradle(.kts)`.

Within this method, the plugin does two things:

1. **Creates an extension named `filesizediff`:**
This allows users to configure the plugin using a `diff {}` block in their build script.
The configuration values are stored in an instance of `FileSizeDiffExtension`.

2. **Registers a task of type `FileSizeDiffTask`:**
The task is given the name `fileSizeDiff`, and its properties (`file1` and `file2`) are mapped from the corresponding properties in the `diff` extension.
This ensures the task uses the values provided by the user in their build script.

This enables the following usage in a `build.gradle(.kts)` file:

====
include::sample[dir="snippets/plugins/fileSizeDiffBinaryPlugin/kotlin", files="build.gradle.kts"]
include::sample[dir="snippets/plugins/fileSizeDiffBinaryPlugin/groovy", files="build.gradle"]
====

[.text-right]
**Next Step:** <<testing_binary_plugin_advanced.adoc#test_binary_plugins_advanced,Learn how to test Binary Plugins>> >>
