Gradle android compile jar

You can find a more comprehensive glossary of dependency management terms here.

As far as configurations go, the main ones of interest are:

compileOnly — for dependencies that are necessary to compile your production code but shouldn’t be part of the runtime classpath

implementation (supersedes compile ) — used for compilation and runtime

runtimeOnly (supersedes runtime ) — only used at runtime, not for compilation

testCompileOnly — same as compileOnly except it’s for the tests

testImplementation — test equivalent of implementation

testRuntimeOnly — test equivalent of runtimeOnly

You can learn more about these and how they relate to one another in the plugin reference chapter.

Be aware that the Java Library Plugin offers two additional configurations — api and compileOnlyApi — for dependencies that are required for compiling both the module and any modules that depend on it.

The Java Library Plugin has historically used the compile configuration for dependencies that are required to both compile and run a project’s production code. It is now deprecated, and will issue warnings when used, because it doesn’t distinguish between dependencies that impact the public API of a Java library project and those that don’t. You can learn more about the importance of this distinction in Building Java libraries.

We have only scratched the surface here, so we recommend that you read the dedicated dependency management chapters once you’re comfortable with the basics of building Java projects with Gradle. Some common scenarios that require further reading include:

Defining a custom Maven- or Ivy-compatible repository

Declaring dependencies with changing (e.g. SNAPSHOT) and dynamic (range) versions

Testing your fixes to a 3rd-party dependency via composite builds (a better alternative to publishing to and consuming from Maven Local)

You’ll discover that Gradle has a rich API for working with dependencies — one that takes time to master, but is straightforward to use for common scenarios.

Compiling your code

Compiling both your production and test code can be trivially easy if you follow the conventions:

Put your production source code under the src/main/java directory

Put your test source code under src/test/java

Declare your production compile dependencies in the compileOnly or implementation configurations (see previous section)

Declare your test compile dependencies in the testCompileOnly or testImplementation configurations

Run the compileJava task for the production code and compileTestJava for the tests

Other JVM language plugins, such as the one for Groovy, follow the same pattern of conventions. We recommend that you follow these conventions wherever possible, but you don’t have to. There are several options for customization, as you’ll see next.

Customizing file and directory locations

Imagine you have a legacy project that uses an src directory for the production code and test for the test code. The conventional directory structure won’t work, so you need to tell Gradle where to find the source files. You do that via source set configuration.

Each source set defines where its source code resides, along with the resources and the output directory for the class files. You can override the convention values by using the following syntax:

Now Gradle will only search directly in src and test for the respective source code. What if you don’t want to override the convention, but simply want to add an extra source directory, perhaps one that contains some third-party source code you want to keep separate? The syntax is similar:

Crucially, we’re using the method srcDir() here to append a directory path, whereas setting the srcDirs property replaces any existing values. This is a common convention in Gradle: setting a property replaces values, while the corresponding method appends values.

You can see all the properties and methods available on source sets in the DSL reference for SourceSet and SourceDirectorySet. Note that srcDirs and srcDir() are both on SourceDirectorySet .

Changing compiler options

Most of the compiler options are accessible through the corresponding task, such as compileJava and compileTestJava . These tasks are of type JavaCompile, so read the task reference for an up-to-date and comprehensive list of the options.

For example, if you want to use a separate JVM process for the compiler and prevent compilation failures from failing the build, you can use this configuration:

That’s also how you can change the verbosity of the compiler, disable debug output in the byte code and configure where the compiler can find annotation processors.

Targeting a specific Java version

By default, Gradle will compile Java code to the language level of the JVM running Gradle. With the usage of Java toolchains, you can break that link by making sure a given Java version, defined by the build, is used for compilation, execution and documentation. It is however possible to override some compiler and execution options at the task level.

Since version 9, the Java compiler can be configured to produce bytecode for an older Java version while making sure the code does not use any APIs from a more recent version. Gradle now supports this release flag on CompileOptions directly for Java compilation. This option takes precedence over the properties described below.

Due to a bug in Java 9 that was fixed in Java 10, Gradle cannot leverage the release flag when compiling with Java 9.

Historical options for the Java compiler remain available:

Defines which language version of Java your source files should be treated as.

Defines the minimum JVM version your code should run on, i.e. it determines the version of byte code the compiler generates.

These options can be set per JavaCompile task, or on the java < >extension for all compile tasks, using properties with the same names.

Using a toolchain makes it illegal to configure the sourceCompatibility or targetCompatibility at the java < >extension level.

However, these options do not protect against the use of APIs introduced in later Java versions.

Compiling and testing Java 6/7

Gradle can only run on Java version 8 or higher. Gradle still supports compiling, testing, generating Javadoc and executing applications for Java 6 and Java 7. Java 5 and below are not supported.

If using Java 10+, leveraging the release flag might be an easier solution, see above.

To use Java 6 or Java 7, the following tasks need to be configured:

JavaCompile task to fork and use the correct Java home

Javadoc task to use the correct javadoc executable

Test and the JavaExec task to use the correct java executable.

With the usage of Java toolchains, this can be done as follows:

Example: Configure Java 7 build

The only requirement is that Java 7 is installed and has to be either in a location Gradle can detect automatically or explicitly configured.

Compiling independent sources separately

Most projects have at least two independent sets of sources: the production code and the test code. Gradle already makes this scenario part of its Java convention, but what if you have other sets of sources? One of the most common scenarios is when you have separate integration tests of some form or other. In that case, a custom source set may be just what you need.

You can see a complete example for setting up integration tests in the Java testing chapter. You can set up other source sets that fulfil different roles in the same way. The question then becomes: when should you define a custom source set?

To answer that question, consider whether the sources:

Need to be compiled with a unique classpath

Generate classes that are handled differently from the main and test ones

Form a natural part of the project

If your answer to both 3 and either one of the others is yes, then a custom source set is probably the right approach. For example, integration tests are typically part of the project because they test the code in main . In addition, they often have either their own dependencies independent of the test source set or they need to be run with a custom Test task.

Other common scenarios are less clear cut and may have better solutions. For example:

Separate API and implementation JARs — it may make sense to have these as separate projects, particularly if you already have a multi-project build

Generated sources — if the resulting sources should be compiled with the production code, add their path(s) to the main source set and make sure that the compileJava task depends on the task that generates the sources

If you’re unsure whether to create a custom source set or not, then go ahead and do so. It should be straightforward and if it’s not, then it’s probably not the right tool for the job.

Managing resources

Many Java projects make use of resources beyond source files, such as images, configuration files and localization data. Sometimes these files simply need to be packaged unchanged and sometimes they need to be processed as template files or in some other way. Either way, the Java Library Plugin adds a specific Copy task for each source set that handles the processing of its associated resources.

The task’s name follows the convention of processSourceSetResources — or processResources for the main source set — and it will automatically copy any files in src/[sourceSet]/resources to a directory that will be included in the production JAR. This target directory will also be included in the runtime classpath of the tests.

Since processResources is an instance of the Copy task, you can perform any of the processing described in the Working With Files chapter.

Java properties files and reproducible builds

You can easily create Java properties files via the WriteProperties task, which fixes a well-known problem with Properties.store() that can reduce the usefulness of incremental builds.

The standard Java API for writing properties files produces a unique file every time, even when the same properties and values are used, because it includes a timestamp in the comments. Gradle’s WriteProperties task generates exactly the same output byte-for-byte if none of the properties have changed. This is achieved by a few tweaks to how a properties file is generated:

no timestamp comment is added to the output

the line separator is system independent, but can be configured explicitly (it defaults to ‘\n’ )

the properties are sorted alphabetically

Sometimes it can be desirable to recreate archives in a byte for byte way on different machines. You want to be sure that building an artifact from source code produces the same result, byte for byte, no matter when and where it is built. This is necessary for projects like reproducible-builds.org.

These tweaks not only lead to better incremental build integration, but they also help with reproducible builds. In essence, reproducible builds guarantee that you will see the same results from a build execution — including test results and production binaries — no matter when or on what system you run it.

Running tests

Alongside providing automatic compilation of unit tests in src/test/java, the Java Library Plugin has native support for running tests that use JUnit 3, 4 & 5 (JUnit 5 support came in Gradle 4.6) and TestNG. You get:

An automatic test task of type Test, using the test source set

An HTML test report that includes the results from all Test tasks that run

Easy filtering of which tests to run

Fine-grained control over how the tests are run

The opportunity to create your own test execution and test reporting tasks

You do not get a Test task for every source set you declare, since not every source set represents tests! That’s why you typically need to create your own Test tasks for things like integration and acceptance tests if they can’t be included with the test source set.

As there is a lot to cover when it comes to testing, the topic has its own chapter in which we look at:

How tests are run

How to run a subset of tests via filtering

How Gradle discovers tests

How to configure test reporting and add your own reporting tasks

How to make use of specific JUnit and TestNG features

You can also learn more about configuring tests in the DSL reference for Test.

Packaging and publishing

How you package and potentially publish your Java project depends on what type of project it is. Libraries, applications, web applications and enterprise applications all have differing requirements. In this section, we will focus on the bare bones provided by the Java Library Plugin.

By default, the Java Library Plugin provides the jar task that packages all the compiled production classes and resources into a single JAR. This JAR is also automatically built by the assemble task. Furthermore, the plugin can be configured to provide the javadocJar and sourcesJar tasks to package Javadoc and source code if so desired. If a publishing plugin is used, these tasks will automatically run during publishing or can be called directly.

If you want to create an ‘uber’ (AKA ‘fat’) JAR, then you can use a task definition like this:

See Jar for more details on the configuration options available to you. And note that you need to use archiveClassifier rather than archiveAppendix here for correct publication of the JAR.

You can use one of the publishing plugins to publish the JARs created by a Java project:

Modifying the JAR manifest

Each instance of the Jar , War and Ear tasks has a manifest property that allows you to customize the MANIFEST.MF file that goes into the corresponding archive. The following example demonstrates how to set attributes in the JAR’s manifest:

See Manifest for the configuration options it provides.

You can also create standalone instances of Manifest . One reason for doing so is to share manifest information between JARs. The following example demonstrates how to share common attributes between JARs:

Another option available to you is to merge manifests into a single Manifest object. Those source manifests can take the form of a text for or another Manifest object. In the following example, the source manifests are all text files except for sharedManifest , which is the Manifest object from the previous example:

Manifests are merged in the order they are declared in the from statement. If the base manifest and the merged manifest both define values for the same key, the merged manifest wins by default. You can fully customize the merge behavior by adding eachEntry actions in which you have access to a ManifestMergeDetails instance for each entry of the resulting manifest. Note that the merge is done lazily, either when generating the JAR or when Manifest.writeTo() or Manifest.getEffectiveManifest() are called.

Speaking of writeTo() , you can use that to easily write a manifest to disk at any time, like so:

Generating API documentation

The Java Library Plugin provides a javadoc task of type Javadoc, that will generate standard Javadocs for all your production code, i.e. whatever source is in the main source set. The task supports the core Javadoc and standard doclet options described in the Javadoc reference documentation. See CoreJavadocOptions and StandardJavadocDocletOptions for a complete list of those options.

As an example of what you can do, imagine you want to use Asciidoc syntax in your Javadoc comments. To do this, you need to add Asciidoclet to Javadoc’s doclet path. Here’s an example that does just that:

You don’t have to create a configuration for this, but it’s an elegant way to handle dependencies that are required for a unique purpose.

You might also want to create your own Javadoc tasks, for example to generate API docs for the tests:

These are just two non-trivial but common customizations that you might come across.

Cleaning the build

The Java Library Plugin adds a clean task to your project by virtue of applying the Base Plugin. This task simply deletes everything in the $buildDir directory, hence why you should always put files generated by the build in there. The task is an instance of Delete and you can change what directory it deletes by setting its dir property.

Building JVM components

All of the specific JVM plugins are built on top of the Java Plugin. The examples above only illustrated concepts provided by this base plugin and shared with all JVM plugins.

Read on to understand which plugins fits which project type, as it is recommended to pick a specific plugin instead of applying the Java Plugin directly.

Building Java libraries

The unique aspect of library projects is that they are used (or «consumed») by other Java projects. That means the dependency metadata published with the JAR file — usually in the form of a Maven POM — is crucial. In particular, consumers of your library should be able to distinguish between two different types of dependencies: those that are only required to compile your library and those that are also required to compile the consumer.

Gradle manages this distinction via the Java Library Plugin, which introduces an api configuration in addition to the implementation one covered in this chapter. If the types from a dependency appear in public fields or methods of your library’s public classes, then that dependency is exposed via your library’s public API and should therefore be added to the api configuration. Otherwise, the dependency is an internal implementation detail and should be added to implementation.

If you’re unsure of the difference between an API and implementation dependency, the Java Library Plugin chapter has a detailed explanation. In addition, you can explore a basic, practical sample of building a Java library.

Building Java applications

Java applications packaged as a JAR aren’t set up for easy launching from the command line or a desktop environment. The Application Plugin solves the command line aspect by creating a distribution that includes the production JAR, its dependencies and launch scripts Unix-like and Windows systems.

See the plugin’s chapter for more details, but here’s a quick summary of what you get:

assemble creates ZIP and TAR distributions of the application containing everything needed to run it

A run task that starts the application from the build (for easy testing)

Shell and Windows Batch scripts to start the application

You can see a basic example of building a Java application in the corresponding sample.

Building Java web applications

Java web applications can be packaged and deployed in a number of ways depending on the technology you use. For example, you might use Spring Boot with a fat JAR or a Reactive-based system running on Netty. Whatever technology you use, Gradle and its large community of plugins will satisfy your needs. Core Gradle, though, only directly supports traditional Servlet-based web applications deployed as WAR files.

That support comes via the War Plugin, which automatically applies the Java Plugin and adds an extra packaging step that does the following:

Copies static resources from src/main/webapp into the root of the WAR

Copies the compiled production classes into a WEB-INF/classes subdirectory of the WAR

Copies the library dependencies into a WEB-INF/lib subdirectory of the WAR

This is done by the war task, which effectively replaces the jar task — although that task remains — and is attached to the assemble lifecycle task. See the plugin’s chapter for more details and configuration options.

There is no core support for running your web application directly from the build, but we do recommend that you try the Gretty community plugin, which provides an embedded Servlet container.

Building Java EE applications

Java enterprise systems have changed a lot over the years, but if you’re still deploying to JEE application servers, you can make use of the Ear Plugin. This adds conventions and a task for building EAR files. The plugin’s chapter has more details.

Building Java Platforms

A Java platform represents a set of dependency declarations and constraints that form a cohesive unit to be applied on consuming projects. The platform has no source and no artifact of its own. It maps in the Maven world to a BOM.

The support comes via the Java Platform plugin, which sets up the different configurations and publication components.

This plugin is the exception as it does not apply the Java Plugin.

Enabling Java preview features

Using a Java preview feature is very likely to make your code incompatible with that compiled without a feature preview. As a consequence, we strongly recommend you not to publish libraries compiled with preview features and restrict the use of feature previews to toy projects.

To enable Java preview features for compilation, test execution and runtime, you can use the following DSL snippet:

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