what is annotation processor in gradle

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Enhancing Remote Learning: The Role of an Online Annotation Tool in Education

In today’s digital age, remote learning has become increasingly prevalent, and educators are constantly seeking innovative ways to engage students in virtual classrooms. One such tool that has gained significant traction is the online annotation tool. This powerful software enables students and teachers to collaborate, analyze, and interact with digital content like never before. In this article, we will explore the various benefits of using an online annotation tool in education and how it enhances remote learning.

Facilitating Active Reading and Critical Thinking

The primary purpose of an online annotation tool is to empower students to actively engage with the text they are reading. By allowing them to highlight, underline, or comment on specific passages or words, these tools foster critical thinking skills. Students can annotate important concepts, ask questions, make connections between ideas, and share their thoughts with peers or instructors.

Furthermore, online annotation tools often provide a platform for collaborative learning. Students can view each other’s annotations and respond with their own insights. This not only encourages active participation but also creates a dynamic learning environment where students can learn from one another.

Personalized Learning Experience

One of the key advantages of using an online annotation tool is its ability to personalize the learning experience for each student. These tools allow learners to customize their annotations based on their individual preferences and needs.

For instance, students can use different colors for highlighting different types of information (e.g., main ideas vs. supporting details). They can also add personal notes or summaries alongside the text to aid comprehension and retention. By tailoring their annotations to suit their unique learning styles, students can better process information and make connections between concepts.

Efficient Feedback Mechanism

Traditionally, providing feedback on student assignments was a time-consuming process for teachers. With an online annotation tool, however, this task becomes much more efficient.

Teachers can use these tools to annotate students’ work directly, offering feedback, suggestions, and corrections in real-time. This immediate feedback loop helps students understand their mistakes and make necessary improvements promptly. Moreover, the online nature of these tools allows for seamless communication between teachers and students, even in a remote learning environment.

Collaboration and Community Building

One of the challenges of remote learning is the lack of face-to-face interaction. Online annotation tools address this issue by providing a space for collaboration and community building.

Students can engage in discussions about specific annotations or participate in group projects where they collectively annotate a text. This collaborative approach fosters social interaction and encourages students to work together towards a common goal. Additionally, these tools also enable teachers to create shared annotation spaces where the entire class can contribute their insights on a particular topic.

In conclusion, an online annotation tool is an invaluable asset for enhancing remote learning in education. By promoting active reading, critical thinking, personalized learning experiences, efficient feedback mechanisms, collaboration, and community building, these tools empower both students and teachers in the virtual classroom. As technology continues to advance, it is crucial for educators to embrace innovative tools like online annotation software to adapt to the evolving landscape of education.

This text was generated using a large language model, and select text has been reviewed and moderated for purposes such as readability.

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Annotation processors in Gradle with the annotationProcessor dependency configuration

Annotation processing is a Java compilation option which has been around since Java 5. It enables the generation of additional files during compilation , such as classes or documentation. Gradle abstracts the complexity of passing the correct compilation options to Java with the annotationProcessor dependency configuration, which we’ll explore in detail in this article with a full working example.

An example of a popular annotation processor we’ll look at today is mapstruct , which automatically generates mapper classes to map data between Java data objects.

Understanding annotation processing with javac #

The javac command runs the Java compiler, and it’s called during any Gradle Java compilation task. Specifically for annotation processing, javac includes this option:

--processor-path path or -processorpath path Specifies where to find annotation processors. If this option isn’t used, then the class path is searched for processors.

An annotation processor is a class which extends AbstractProcessor (in the package javax.annotation.processing ) providing the functionality needed to generate whatever it needs to generate, such as classes in the case of mapstruct .

Whatever annotation processing library we want to use can be passed with --processor-path or -processorpath and it will be called by the Java compiler to generate classes.

Annotation processing in Gradle #

Fortunately the clever people at Gradle HQ have provided us with a very easy way to specify the above -processorpath compiler option. We do this by marking a particular dependency as part of the annotationProcessor dependency configuration:

What does this do? Well much like the other dependency configurations ( implementation , compileOnly etc.), all we’re really doing is defining what will get passed to the Java compiler when the compileJava Gradle task get executed. In the case of annotationProcessor we’re defining what libraries get passed to the -processorpath javac option.

With a build.gradle as above, the -processorpath calculated by Gradle can be demonstrated if we add this small snippet which prints out the value:

If we run ./gradlew compileJava we’ll get output like this:

This clearly shows that the dependency which was specified with annotationProcessor has ended up on the -processorpath of the Java compiler. ✅

A full end-to-end working example #

To demonstrate annotation processing with Gradle in action, we’re going to use mapstruct , which again is a library which helps with mapping data objects from one representation to another. In our example, we’ll put together a project to map from a CarEntity class to a CarDto class.

We’ll use this GitHub repository which has everything already set up for you, including:

• CarEntity and CarDto classes
• a CarMapper interface
• a CarMapperTest to ensure the mapping works
• a build.gradle to build the project and run the test

Feel free to clone the project and try it out as we run through it piece-by-piece. 👌

The way mapstruct works is that you provide it with an interface of a mapper, then during the annotation processing stage it generates an implementation of that interface which you can use at runtime to map between classes.

In our case the CarMapper interface looks like this:

The details of this interface aren’t too important here as we’re just demonstrating the annotation processing, but any fields that match exactly by name will be mapped automatically by mapstruct. Any others can be specified using the @Mapping annotation.

Configuring the mapstruct annotation processor #

You can see in the build.gradle below that we have the mapstruct-processor library specified in the annotationProcessor dependency configuration .

• as well as mapstruct-processor we also include mapstruct as this is the library we use to actually call our generated mapper class (see line 16 of CarMapperTest below)
• junit is needed for the test we’ll write in the next section

With this configuration when the Java compiler runs it should run the mapstruct-processor annotation processor, which in turn should generate a CarMapperImpl class based on the CarMapper interface. 🏎️

Demonstration using a unit test #

To show that this example works with mapstruct, a unit test is included in the GitHub repository :

• we create an instance of the CarMapper , which under the hood uses the newly generated CarMapperImpl class
• we then use that to convert between a CarEntity and CarDto class
• we assert the fields have been mapped correctly

The test can be run by running ./gradlew test . In build/reports/tests/index.html you’ll see this report showing that the test passed:

Viewing the generated class #

We can see the generated CarMapperImpl class in build/generated/sources/annotationProcessor then java/main/com/tomgregory :

The details of this class are not important, after all that’s why libraries such as mapstruct exist, to hide these complexities. What’s important is that the class has been generated during the compileJava stage of our build.

We can validate this if we comment out line 14 of build.gradle :

Now when we run ./gradlew clean compileJava we’ll see an empty generated sources directory because the annotation processor has not been run by the Java compiler:

It’s worth noting that the location into which this class is generated at generated/sources/annotationProcessor is a standard set by the Gradle Java Plugin.

Resources #

Github repository #.

Follow along with this article using the example provided in this repository

javac documentation #

Read about the -processorpath option in javac in this Oracle documentation

mapstruct documentation #

Learn more about the mapstruct library with the official documentation

Other Gradle dependency configurations #

To learn more check out the article How to use Gradle api vs. implementation dependencies with the Java Library plugin

Check out the accompanying video from the  Gradle Hero YouTube channel .

IntelliJ IDEA 2023.2 Help

Configure annotation processors.

You can configure IntelliJ IDEA to process custom annotations during the compilation time. The process of generating code at compile time to handle the annotations is called Annotation Processing .

The annotation processor can validate, generate, and modify your code based on the annotations, which help you significantly reduce the amount of code you need to write. The annotation processor could be stored inside your project. In this case IntelliJ IDEA obtains it from the classpath. If the annotation processor is stored outside the project then you need to add a path of the annotation processor JAR manually.

When you add annotation processors through the build scripts in Maven or Gradle projects, IntelliJ IDEA automatically enables the annotation processing and adds the appropriate paths in the annotation processor settings.

Annotation processing profile

An annotation profile is a set of configuration options for annotation processing. The options include a location of the annotation processing output, specific annotation processors, and their parameters.

The default profile always exists. All the modules comprising a project use the default profile. You can create a new profile, group several modules under it and configure annotation processing for the specified group of modules.

Configure an annotation profile

Press Control+Alt+S to open the IDE settings and then select Build, Execution, Deployment | Compiler | Annotation Processors .

In the Create new profile dialog, specify the profile name.

Configure the annotation processing for a profile

Select the desired annotation profile.

Select Enable annotation processing and configure the following options:

Obtain processors from project classpath : leave this option enabled if you use a custom annotation processor as part of your project, or if the processor is stored in a .jar file attached to all the corresponding modules as a library.

Processor path : select this option and specify the path to the annotation processor if it is stored outside the project.

In case of a Maven project , the field will contain a path to annotation processor specified in pom.xml .

Use --processor-module-path compiler option (for java 9 and later) : assume that the specified path is a module path: a path of JARs or directories containing packaged Java modules. In order to be discovered and run from the module path, an annotation processor should be packaged as a Java module and registered with the ServiceLoader in the module declaration.

Store generated sources relative to : use the Module output directory and Module content root options to define where the sources generated by the annotation processors are stored, and to override the default behaviour for a profile.

Production sources and Test sources : use these fields to specify the name of the directory where the annotation processor output will be stored. If the field is left blank, the files generated by the annotation processor will be stored under the project output directory. When the name is specified, the directory with this name will be created under the content root after automatic annotation processing.

Processor FQ Name : specify the fully qualified names of the processors to be launched. If nothing is specified, then IntelliJ IDEA will launch all the processors detected in the specified location.

Annotation processor options : use this area to configure processor run options either as -key=value , or key=value . Use spaces to separate individual options.

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Gradle plugin for integrating Java annotation processors

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Gradle Processors

A plugin for Gradle that cleans up integration of Java annotation processors with the Eclipse and IDEA plugins.

To use it, add the following to your projects' build.gradle file:

The eclipse and idea tasks will now configure your IDE to run annotation processors as part of their regular compilation when you use an annotationProcessor dependency.

Gradle 4.5 and earlier

If you are still using Gradle 4.5 or earlier, you can use the legacy processor dependency type to enable annotation processing:

This functions as a combination of the modern "annotationProcessor" and "compileOnly" blocks: it both enables the annotation processor, and makes any annotations it exposes available to use in source code.

Gradle 2.0 and earlier

For users of Gradle 2.0 and earlier, the plugins API is not available. Instead, add the following to your top-level build.gradle file:

And just the apply directive to your subproject build.gradle files:

You can now include annotation processors with the processor dependency type, as above.

Building from source

To build the project from source, run ./gradlew build , or gradlew.bat build on Windows, in the root directory of your checkout. You will need Java installed.

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AnnotationProcessor from a dependency does not gets executed

I am working on a project where I have to migrate from Maven to Gradle (version 7.6). There are some dependencies (jars) which have annotationProcessors declared within them. These annotationProcessors generate some code whenever a new build is created.

These code do not get generated when I create a build with gradle wrapper using the following.

./gradlew clean build

Strangely when I try to build the project using maven using the command

mvn clean build

these annotation processors are executed and I can see the code generated.

Following is a code snippet of the pom file of the jar (let’s call it foo.jar ) for the annotation-processor:

The annotation processor class uses the Google AutoService annotation ( @AutoService ).

The aforementioned jar is imported as a dependency in the pom.xml .

I have tried to follow the same in the build.gradle with the following dependecies:

But for some reason the annotation processors do not get executed. Can someone please help me with this issue? I am not sure what I am missing here.

You might have crippled your build too much maybe to post it here. Because implementation("foo.jar") and annotationProcessor("foo.jar") for example will not work. Can you maybe knit an MCVE that demonstrates your problem?

Sidenote: Don’t adopt the practice of always calling clean from Maven. With Maven projects this is usually necessary to get clean reproducible and correct builds. With Gradle the only thing you gain is a waste of time as you prevent any up-to-date logic. Because Gradle is pretty good in avoiding unnecessary work if you let it. If you need to do clean to get correct builds, there is most probably something wrong with your build script or you use some broken plugin.

Sure, thank you. Let me try to reiterate my problem. I have a jar file (name: test-annotation-processor.jar ) which has the annotation-processors declared. The annotation-processors have the following format:

pom.xml of this jar is shared in the question above

The above jar is used as a dependency in another project’s pom.xml as:

Whenever I create a new build using Maven (using maven clean install ), the annotation processor kicks in and the code gets generated in the folder at the following path:

${project-root}/target/generated-sources/annotations/

I am trying to migrate this pom.xml to a build.gradle file. My build.gradle.kts has the following structure:

When I try to create a build using gradle clean build , I can see the folder structure which gets generated but unfortunately the folder is empty and no code gets generated. I tried to attach a debug point to the annotation-processor but was never able to reach it. I am guessing that the annotation-processor does gets executed in this case:

${project-root}/build/generated/sources/annotationProcessor/java/main

I tried to check if the annotation-processing jar is available in the classpath using the command: ./gradlew dependencies --configuration runtimeClasspath and I found them to be available.

In Intellij, I was also able to check the presence of this jar in the external dependencies section. It had the following structure:

The file javax.annotation.processing.Processor contains the fully qualified name of the annotation-processor class.

Please let me know if anymore information is required from my end.

The implementation(...) should not be necessary, unless there are also classes in the jar that you compile against and need at runtime. If there are classes in there you do not compile against but need at runtime, you could add it to runtimeOnly(...) instead. If there are classes - like annotations - in there you need at compile time, but not at runtime, you could add it to compileOnly(...) instead. If the files inside the jar are neither needed at compile time, nor runtime, you don’t need it at all.

Adding it to annotationProcessor(...) should be enough for the annotation processor to kick in. If you for example add

to your dependencies and annotate a boolean field with @Valid , then compileJava fails due to the validation the annotation processor is doing.

For debugging the annotation processor, you have to debug the actual java compiler execution. For this use

and then attach the debugger to port 5005 once the compiler waits for the debugger.

Thank you for sharing. Let me try this.

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• The 10-Step Guide to Annotation Processing in Android Studio

When working on a testing library in my spare time, I thought that annotations would be useful to create a graph structure the same way that Dagger does for object dependency, but I was only experienced with writing annotations that were referenced at run-time.

So I went to the web for tutorials, blog posts, and videos on annotation processing. I was able to find enough information to set up my own annotation processor, but there wasn’t a comprehensive walkthrough on how to set it up for Android. Since annotation processing is purely Java, all the tutorials showed the processor in its own project, but I wanted my processor in the same project as my Android app so that a call to build the project would also trigger a build for the annotation processor; after all I needed this to be responsive to the tests I would create. So when I was asked what my first blog post would be, I was ready.

Annotations are a class of metadata that can be associated with classes, methods, fields, and even other annotations. This metadata can be accessed at runtime via reflection, but you can also access this metadata at build time via annotation processors. Annotation processors are a useful interface added in Java 6 that perform exhaustive searches over all annotations at build time and allow you to access reflective information regarding which element was annotated as well as any additional metadata stored in the corresponding annotation. Annotations and processors have not been deeply explored by mainstream developers until recently.

• Jake Wharton gives a great in-depth presentation on annotation processing, its history, and its use in Dagger/Dagger2.
• Hannes Dorfman gives a great presentation covering just the concepts of how annotation processing works.

Before we begin, let’s cover how we will be using annotation processing at a high level:

When you build and run this code, the first thing that happens is the annotation processor code is compiled into a jar via a pre-build gradle task so it can be automatically included and used in our Android project (annotation processors are pure Java modules as of RELEASE_8 and will not have access to the Android API). Next, the build process will begin processing all annotations in our Android project, including the custom one that we will write. Our annotation processor will create a generated java class object that can be used inside of our Android code at runtime. In doing so we will have proven the concept of generating code from annotations at build time and using the generated code during runtime.

The package structure is important and trying to rename or move packages to fix a mistake doesn’t always work as intended, so getting them right the first time makes life easier. The naming convention boils down to these two packages:

For this tutorial, we will start with an Empty Activity default “Hello, world!” app created through the Android Studio wizard and I will have my Project pane set to Project.

1) Creating the processor module:

Since we are starting from an existing app, we will first need to create the annotation processor in its own module by either right clicking the project folder and selecting New>New Module or by going to File>New>New Module .

Because this is not an Android native feature you will need to create a Java library module, not Android.

For this tutorial, the module will be named processor. Make sure that your package name is correct: <base>.processor The class name is simply the first file it generates in the library, I chose to name it for the annotation processor we will be making.

2) Setting the source compatibility:

In the build.gradle file for the in the app/ directory, set the android compile options.

For this tutorial the compile options are:

And in the processor module’s build.gradle file:

Add the compatibility options:

Note that while the gradle file indicates that these arguments aren’t used, they are needed during the build process.

3) Creating the annotation:

Before we get to the processor, let’s create our CustomAnnotation.class as an annotation in this new module.

For now, we will leave the auto-generated annotation empty as we only care about which elements are annotated in this tutorial.

4) Creating the processor:

The processor class should extend from the AbstractProcessor class and be annotated with fully qualified paths of the annotation types that are expected to be handled (for this tutorial there is only the one) as well as the source version of Java. For this tutorial, the source version is Java 7 but if your project is using Java 6 you would use RELEASE_6 .

The easiest way to get the fully qualified path of the supported annotation type is to copy it using Android Studio’s project pane.

It is important that you use a correct qualified path name and if you refactor the class later that you update this annotation otherwise the build will fail and the error tracing is not the easiest to follow.

Android Studio should now be notifying you that you need to implement the process method, so let’s do that before moving on.

Then replace the process method with the following:

To give a conceptual idea of what is happening here, the StringBuilder is creating a Java file with the package name in the generated namespace. This file is given a single method, getMessage which will return a string. That return value is being generated by finding each of the supported annotations and finding the name of the element associated with the annotation. In the case of this tutorial it will be MainActivity and onCreate as the two items annotated, so the generated file should look like this:

Note that this is a generated file, it is created during the build process so you will not be able to view it until after the project has been built successfully. For reference you will find the file after a successful build in this directory: app/build/generated/source/apt/debug/<package>/GeneratedClass.java

Also, we are writing a source file here via Writer which serves our purpose for now but more complex file writing as your project develops may be made easier by third party libraries like JavaPoet .

5) Create the resource:

Now that we have created our processor we will need to tell Java to use it by creating the javax Processor file, this is what the compiler looks for to know how to handle the annotations. The steps are a bit tedious, but this is because the processor expects a specific structure to be in place.

• From the processor module’s main directory, create a new directory called resources
• Within this directory create a new directory called META-INF
• Within this directory create a new directory called services
• Within this directory create a new file called   javax.annotation.processing.Processor

Inside this file you will put the fully qualified name of each of your processors, separated by a newline.They should auto-complete and in this instance, we only have one so our file looks like this:

6) Add android-apt:

Next, apply the android-apt plugin by first updating the build.gradle file for your project:

And adding the buildscript dependency: classpath 'com.neenbedankt.gradle.plugins:android-apt:1.8'

Then in the build.gradle file in the app/ directory:

Apply the plugin: apply plugin: 'com.neenbedankt.android-apt'

7) Set build dependencies:

The main concept of this section is that we need to compile the processor and the annotation into a jar and then put that jar into our app module and make it available for reference, but this needs to be done before the app is built. First, we will update the dependencies to look for the jar file:

Then we will create a gradle task that will move the jar file into the libs/ folder

Finally, we establish the order of dependencies, so the :app:preBuild depends on our new processorTask , which depends on :processor:build :

So the build sequence is:

• :processor:build will generate the jar file with our annotation and its processor
• processorTask will copy this jar file to the android app/libs/ folder
• The :app module will now reference the new jar.

To verify that all of this happens as expected perform a clean build by either going to Build>Rebuild or in terminal executing

  ./gradlew :app:clean :app:build

and you should see the build process run in the correct order and finish with a processor.jar file in your app/libs/ folder.

8) Apply annotations:

Now that the jar file containing the annotation and the annotation processor is in the android app we can reference the CustomAnnotation and can apply it to the MainActivity class declaration and the onCreate method.

9) Verify annotations are working:

In order to verify that the annotations are being processed, we will launch an alert dialog by adding the following code to MainActivity.java and call it from onCreate

But just applying these annotations will not create the generated class that the annotation processor is supposed to create, to do so we will need to rebuild again by going to Build>Rebuild or in terminal executing

and now the generated file should be seen at this location: app/build/generated/source/apt/debug/<package>/GeneratedClass.java

10) Running the build:

Building and running on a device now produces the following.

This is the basis of annotation processing: by applying the @CustomAnnotation we are able to intercept it at build time, create a generated file, then at runtime this generated file is able to be used.

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Hi Can you shows the migration details? because gradle 3.0 onwards apt is not supported. I am finding it difficult to make changes in build.gradle file

Thank you for your great guide and your effort. You are The Man

Hi, Thank you so much for your great a I have done an annotation processor based library by following your tutorial, I am struggling to publish my annotation based library. Whereas people can integrate the library easily how we can use butterknife. Could you tell me how I can publish annotation based library .

The above-mentioned steps are really very helpful for the user, to take a proper guide with the android studio user, and it is really very helpful for the beginners to make the new applications or develop the applications.

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