Table of Contents
The Java plugin adds Java compilation along with testing and bundling capabilities to a project. It serves as the basis for many of the other Gradle plugins.
To use the Java plugin, include the following in your build script:
The Java plugin assumes the project layout shown below. None of these directories need to exist or have anything in them. The Java plugin will compile whatever it finds, and handles anything which is missing.
Java plugin - default project layout
| Directory | Meaning | |
|
Production Java source |
|
|
Production resources |
|
|
Test Java source |
|
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Test resources |
|
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Java source for the given source set |
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Resources for the given source set |
You configure the project layout by configuring the appropriate source set. This is discussed in more detail in the following sections. Here is a brief example which changes the main Java and resource source directories.
Example: Custom Java source layout
build.gradle
sourceSets {
main {
java {
srcDirs = ['src/java']
}
resources {
srcDirs = ['src/resources']
}
}
}
The plugin adds the following source sets:
mainContains the production source code of the project, which is compiled and assembled into a JAR.
testContains your test source code, which is compiled and executed using JUnit or TestNG. These are typically unit tests, but you can include any test in this source set as long as they all share the same compilation and runtime classpaths.
The following table lists some of the important properties of a source set. You can find more details in the API documentation for SourceSet.
(read-only) String nameThe name of the source set, used to identify it. Default value: Not null
(read-only)SourceSetOutputoutputThe output files of the source set, containing its compiled classes and resources. Default value: Not null
FileCollectionoutput.classesDirsThe directories to generate the classes of this source set into. Default value: Not null
File output.resourcesDirThe directory to generate the resources of this source set into. Default value:
buildDir/resources/nameFileCollectioncompileClasspathThe classpath to use when compiling the source files of this source set. Default value:
sourceSetCompileClasspathconfiguration.FileCollectionannotationProcessorPathThe processor path to use when compiling the source files of this source set. Default value:
sourceSetAnnotationProcessorconfiguration.FileCollectionruntimeClasspathThe classpath to use when executing the classes of this source set. Default value:
output+sourceSetRuntimeClasspathconfiguration.(read-only)SourceDirectorySetjavaThe Java source files of this source set. Contains only
.javafiles found in the Java source directories, and excludes all other files. Default value: Not nullSet<File> java.srcDirsThe source directories containing the Java source files of this source set. Default value:
[projectDir/src/name/java]. Can set using anything described in the section called “Understanding implicit conversion to file collections”.File java.outputDirThe directory to generate compiled Java sources into. Default value:
buildDir/classes/java/sourceSetName. Can set using anything described in the section called “File paths in depth”.(read-only)SourceDirectorySetresourcesThe resources of this source set. Contains only resources, and excludes any
.javafiles found in the resource source directories. Other plugins, such as the Groovy plugin, exclude additional types of files from this collection. Default value: Not nullSet<File> resources.srcDirsThe source directories containing the resources of this source set. Default value:
[projectDir/src/name/resources]. Can set using anything described in the section called “Understanding implicit conversion to file collections”.(read-only)SourceDirectorySetallJavaAll
.javafiles of this source set. Some plugins, such as the Groovy plugin, add additional Java source files to this collection. Default value:java(read-only)SourceDirectorySetallSourceAll source files of this source set. This include all resource files and all Java source files. Some plugins, such as the Groovy plugin, add additional source files to this collection. Default value:
resources + java
See the integration test example in the Testing in Java & JVM projects chapter.
Adding a JAR containing the classes of a source set:
Example: Assembling a JAR for a source set
build.gradle
task intTestJar(type: Jar) {
from sourceSets.intTest.output
}
Generating Javadoc for a source set:
Example: Generating the Javadoc for a source set
build.gradle
task intTestJavadoc(type: Javadoc) {
source sourceSets.intTest.allJava
}
Adding a test suite to run the tests in a source set:
Example: Running tests in a source set
build.gradle
task intTest(type: Test) {
testClassesDirs = sourceSets.intTest.output.classesDirs
classpath = sourceSets.intTest.runtimeClasspath
}
The Java plugin adds a number of tasks to your project, as shown below.
compileJava(type:JavaCompile)Compiles production Java source files using javac. Depends on all tasks which produce the compile classpath. This includes the
jartask for project dependencies included in thecompileconfiguration.processResources(type:Copy)Copies production resources into the production resources directory.
classes(type:Task)Assembles the production classes and resources directories.
compileTestJava(type:JavaCompile)Compiles test Java source files using javac. Depends on
compile, plus all tasks which produce the test compile classpath.processTestResources(type:Copy)Copies test resources into the test resources directory.
testClasses(type:Task)Assembles the test classes and resources directories. Depends on
compileTestJavatask andprocessTestResourcestask. Some plugins add additional test compilation tasks.jar(type:Jar)Assembles the JAR file. Depends on
compile.javadoc(type:Javadoc)Generates API documentation for the production Java source, using Javadoc. Depends on
compile.test(type:Test)Runs the unit tests using JUnit or TestNG. Depends on
compile,compileTest, plus all tasks which produce the test runtime classpath.uploadArchives(type:Upload)Uploads artifacts in the
archivesconfiguration, including the JAR file. Depends on the tasks which produce the artifacts in thearchivesconfiguration, includingjar.clean(type:Delete)Deletes the project build directory.
cleanTaskName(type:Delete)Deletes files created by specified task.
cleanJarwill delete the JAR file created by thejartask, andcleanTestwill delete the test results created by thetesttask.
For each source set you add to the project, the Java plugin adds the following compilation tasks:
compileSourceSetJava(type:JavaCompile)Compiles the given source set’s Java source files using javac. Depends on all tasks which produce the source set’s compile classpath.
processSourceSetResources(type:Copy)Copies the given source set’s resources into the resources directory.
sourceSetClasses(type:Task)Assembles the given source set’s classes and resources directories. Depends on the
compileSourceSetJavatask and theprocessSourceSetResourcestask. Some plugins add additional compilation tasks for the source set.
The Java plugin also adds a number of tasks which form a lifecycle for the project:
assemble(type:Task)Assembles all the archives in the project. Depends on all archive tasks in the project, including
jar. Some plugins add additional archive tasks to the project.check(type:Task)Performs all verification tasks in the project. Depends on all verification tasks in the project, including
test. Some plugins add additional verification tasks to the project.build(type:Task)Performs a full build of the project. Depends on
checkandassemble.buildNeeded(type:Task)Performs a full build of the project and all projects it depends on. Depends on
buildandbuildNeededtasks in all project lib dependencies of thetestRuntimeconfiguration.buildDependents(type:Task)Performs a full build of the project and all projects which depend on it. Depends on
buildandbuildDependentstasks in all projects with a project lib dependency on this project in atestRuntimeconfiguration.buildConfigName(type:Task)Assembles the artifacts in the specified configuration. The task is added by the Base plugin which is implicitly applied by the Java plugin. Depends on the tasks which produce the artifacts in configuration ConfigName.
uploadConfigName(type:Upload)Assembles and uploads the artifacts in the specified configuration. The task is added by the Base plugin which is implicitly applied by the Java plugin. Depends on the tasks which uploads the artifacts in configuration ConfigName.
The following diagram shows the relationships between these tasks.
The Java plugin adds a number of dependency configurations to your project, as shown below. It assigns those configurations to tasks such as compileJava and test.
To find information on the api configuration, please consult the Java Library Plugin reference documentation and the Dependency Management Tutorial.
compile(Deprecated)Compile time dependencies. Superseded by
implementation.implementationextendscompileImplementation only dependencies.
compileOnlyCompile time only dependencies, not used at runtime.
compileClasspathextendscompile, compileOnly, implementationCompile classpath, used when compiling source. Used by task
compileJava.annotationProcessorAnnotation processors used during compilation.
runtime(Deprecated) extendscompileRuntime dependencies. Superseded by
runtimeOnly.runtimeOnlyRuntime only dependencies.
runtimeClasspathextendsruntimeOnly, runtime, implementationRuntime classpath contains elements of the implementation, as well as runtime only elements.
testCompile(Deprecated) extendscompileAdditional dependencies for compiling tests. Superseded by
testImplementation.testImplementationextendstestCompile, implementationImplementation only dependencies for tests.
testCompileOnlyAdditional dependencies only for compiling tests, not used at runtime.
testCompileClasspathextendstestCompile, testCompileOnly, testImplementationTest compile classpath, used when compiling test sources. Used by task
compileTestJava.testRuntime(Deprecated) extendsruntime, testCompileAdditional dependencies for running tests only. Used by task
test. Superseded bytestRuntimeOnly.testRuntimeOnlyextendsruntimeOnlyRuntime only dependencies for running tests. Used by task
test.testRuntimeClasspathextendstestRuntimeOnly, testRuntime, testImplementationRuntime classpath for running tests.
archivesArtifacts (e.g. jars) produced by this project. Used by tasks
uploadArchives.defaultextendsruntimeThe default configuration used by a project dependency on this project. Contains the artifacts and dependencies required by this project at runtime.
For each source set you add to the project, the Java plugins adds the following dependency configurations:
sourceSetCompile(Deprecated)Compile time dependencies for the given source set. Superseded by
sourceSetImplementation.sourceSetImplementationextendssourceSetCompileCompile time dependencies for the given source set. Used by
sourceSetCompileClasspath, sourceSetRuntimeClasspath.sourceSetCompileOnlyCompile time only dependencies for the given source set, not used at runtime.
sourceSetCompileClasspathextendscompileSourceSetJavaCompile classpath, used when compiling source. Used by
sourceSetCompile, sourceSetCompileOnly, sourceSetImplementation.sourceSetAnnotationProcessorAnnotation processors used during compilation of this source set.
sourceSetRuntime(Deprecated)Runtime dependencies for the given source set. Used by
sourceSetCompile. Superseded bysourceSetRuntimeOnly.sourceSetRuntimeOnlyRuntime only dependencies for the given source set.
sourceSetRuntimeClasspathextendssourceSetRuntimeOnly, sourceSetRuntime, sourceSetImplementationRuntime classpath contains elements of the implementation, as well as runtime only elements.
The Java plugin adds a number of convention properties to the project, shown below. You can use these properties in your build script as though they were properties of the project object.
String reporting.baseDirThe name of the directory to generate reports into, relative to the build directory. Default value:
reports(read-only) File reportsDirThe directory to generate reports into. Default value:
buildDir/reporting.baseDirString testResultsDirNameThe name of the directory to generate test result .xml files into, relative to the build directory. Default value:
test-results(read-only) File testResultsDirThe directory to generate test result .xml files into. Default value:
buildDir/testResultsDirNameString testReportDirNameThe name of the directory to generate the test report into, relative to the reports directory. Default value:
tests(read-only) File testReportDirThe directory to generate the test report into. Default value:
reportsDir/testReportDirNameString libsDirNameThe name of the directory to generate libraries into, relative to the build directory. Default value:
libs(read-only) File libsDirThe directory to generate libraries into. Default value:
buildDir/libsDirNameString distsDirNameThe name of the directory to generate distributions into, relative to the build directory. Default value:
distributions(read-only) File distsDirThe directory to generate distributions into. Default value:
buildDir/distsDirName
String docsDirName:
:_The name of the directory to generate documentation into, relative to the build directory._ Default value: docs
(read-only) File docsDirThe directory to generate documentation into. Default value:
buildDir/docsDirNameString dependencyCacheDirNameThe name of the directory to use to cache source dependency information, relative to the build directory. Default value:
dependency-cache
(read-only)SourceSetContainersourceSetsContains the project’s source sets. Default value: Not null
SourceSetContainerJavaVersionsourceCompatibilityJava version compatibility to use when compiling Java source. Default value: version of the current JVM in use
JavaVersion. Can also set using a String or a Number, e.g.'1.5'or1.5.JavaVersiontargetCompatibilityJava version to generate classes for. Default value:
sourceCompatibility. Can also set using a String or Number, e.g.'1.5'or1.5.String archivesBaseNameThe basename to use for archives, such as JAR or ZIP files. Default value:
projectNameManifestmanifestThe manifest to include in all JAR files. Default value: an empty manifest.
These properties are provided by convention objects of type JavaPluginConvention, and BasePluginConvention.
The javadoc task is an instance of Javadoc. It supports the core Javadoc options and the options of the standard doclet described in the reference documentation of the Javadoc executable. For a complete list of supported Javadoc options consult the API documentation of the following classes: CoreJavadocOptions and StandardJavadocDocletOptions.
FileCollectionclasspathDefault value:
sourceSets.main.output+sourceSets.main.compileClasspathFileTreesourceDefault value:
sourceSets.main.allJava. Can set using anything described in the section called “Understanding implicit conversion to file collections”.File destinationDirDefault value:
docsDir/javadocString titleDefault value: The name and version of the project
The clean task is an instance of Delete. It simply removes the directory denoted by its dir property.
The Java plugin uses the Copy task for resource handling. It adds an instance for each source set in the project. You can find out more about the copy task in the section called “File copying in depth”.
Object srcDirsDefault value:
sourceSet.resources. Can set using anything described in the section called “Understanding implicit conversion to file collections”.File destinationDirDefault value:
sourceSet.output.resourcesDir. Can set using anything described in the section called “File paths in depth”.
The Java plugin adds a JavaCompile instance for each source set in the project. Some of the most common configuration options are shown below.
FileCollectionclasspathDefault value:
sourceSet.compileClasspathFileTreesourceDefault value:
sourceSet.java. Can set using anything described in the section called “Understanding implicit conversion to file collections”.File destinationDirDefault value:
sourceSet.java.outputDir
By default, the Java compiler runs in the Gradle process. Setting options.fork to true causes compilation to occur in a separate process. In the case of the Ant javac task, this means that a new process will be forked for each compile task, which can slow down compilation. Conversely, Gradle’s direct compiler integration (see above) will reuse the same compiler process as much as possible. In both cases, all fork options specified with options.forkOptions will be honored.
Starting with Gradle 2.1, it is possible to compile Java incrementally. See the JavaCompile task for information on how to enable it.
Main goals for incremental compilations are:
Avoid wasting time compiling source classes that don’t have to be compiled. This means faster builds, especially when a change to a source class or a jar does not incur recompilation of many source classes that depend on the changed input.
Change as few output classes as possible. Classes that don’t need to be recompiled remain unchanged in the output directory. An example scenario when this is really useful is using JRebel - the fewer output classes are changed the quicker the JVM can use refreshed classes.
The incremental compilation at a high level:
The stale class detection favors reliability over speed. The algorithm uses bytecode analysis and deals gracefully with compiler optimizations (inlining of non-private constants), transitive class dependencies, etc. Example: When a class with a public constant changes, we eagerly compile classes that use the same constants to avoid problems with constants inlined by the compiler.
To make incremental compilation fast, we cache class analysis results and jar snapshots. The initial incremental compilation can be slower due to the cold caches.
If a compile task fails due to a compile error, it will do a full compilation again the next time it is invoked.
Because of type erasure, the incremental compiler is not able to recognize when a type is only used in a type parameter, and never actually used in the code. For example, imagine that you have the following code:
List<? extends A> list = Lists.newArrayList();but that no member ofAis in practice used in the code, then changes toAwill not trigger recompilation of the class. In practice, this should very rarely be an issue.
Starting with Gradle 4.7, the incremental compiler also supports incremental annotation processing. Annotation processors need to opt in to this feature, otherwise they will trigger a full recompilation.
As a user you can see which annotation processors are triggering full recompilations in the --info log.
Incremental annotation processing will be deactivated if a custom executable or javaHome is configured on the compile task.
Gradle supports incremental compilation for two common categories of annotation processors: "Isolating" and "Aggregating". As a processor author, please consult the information below to decide which category fits your processor. You can then register it for incremental compilation in its META-INF folder. The format is one line per processor, with the qualified name of the processor and its category separated by a comma.
Example: Registering incremental annotation processors
processor/src/main/resources/META-INF/gradle/incremental.annotation.processors
EntityProcessor,isolating ServiceRegistryProcessor,aggregating
Processors that don’t fit these categories will result in full recompilation.
This includes processors that use java.io instead of the Filer API and processors that need to read or write resource files.
These look at each annotated element in isolation, creating generated files or validation messages for it.
For instance an EntityProcessor could create a <TypeName>Repository for each type annotated with @Entity.
Example: An isolated annotation processor
processor/src/main/java/EntityProcessor.java
Set<? extends Element> entities = roundEnv.getElementsAnnotatedWith(entityAnnotation); for (Element entity : entities) { createRepository((TypeElement) entity); }
Isolating processors have the following limitations:
Can’t read resources
Can’t write resources
Can’t have any side effects except for using the
FilerandMessagerAPIsCan’t depend on compiler-specific APIs like
com.sun.source.util.TreesMust provide exactly one originating element for each file generated with the
FilerAPIMust make all decisions about an element based on information reachable from its AST. For instance it can query the super class, method return types etc, but can’t look at other, unrelated elements.
Gradle will recompile the generated file whenever the source file is affected. If the source file is deleted, the generated file is deleted.
These aggregate several source files into one ore more output files or validation messages.
For instance, a ServiceRegistryProcessor could create a single ServiceRegistry with one method for each type annotated with @Service
Example: An aggregating annotation processor
processor/src/main/java/ServiceRegistryProcessor.java
JavaFileObject serviceRegistry = filer.createSourceFile("ServiceRegistry"); Writer writer = serviceRegistry.openWriter(); writer.write("public class ServiceRegistry {"); for (Element service : roundEnv.getElementsAnnotatedWith(serviceAnnotation)) { addServiceCreationMethod(writer, (TypeElement) service); } writer.write("}"); writer.close();
Aggregating processors have the following limitations:
Its annotations need to have
CLASSorRUNTIMEretentionCan’t read resources (this may change in the future)
Can’t write resources (this may change in the future)
Can’t have any side effects except for using the
FilerandMessagerAPIsCan’t depend on compiler-specific APIs like
com.sun.source.util.TreesCan’t depend on information only available from source files (See comment on parameter names below)
Gradle will always reprocess (but not recompile) all annotated files that the processor was registered for.
If your aggregating processor requires access to parameter names, you need to instruct users to add the -parameters compiler argument.
Gradle will always recompile any files the processor generates.
If a dependent project has changed in an ABI-compatible way (only its private API has changed), then Java compilation tasks will be up-to-date. This means that if project A depends on project B and a class in B is changed in an ABI-compatible way (typically, changing only the body of a method), then Gradle won’t recompile A.
Some of the types of changes that do not affect the public API and are ignored:
Changing a method body
Changing a comment
Adding, removing or changing private methods, fields, or inner classes
Adding, removing or changing a resource
Changing the name of jars or directories in the classpath
Renaming a parameter
Compile-avoidance is deactivated if annotation processors are found on the compile classpath, because for annotation processors the implementation details matter. Annotation processors should be declared on the annotation processor path instead. Gradle 5.0 will ignore processors on the compile classpath.
Example: Declaring annotation processors
build.gradle
dependencies {
// The dagger compiler and its transitive dependencies will only be found on annotation processing classpath
annotationProcessor 'com.google.dagger:dagger-compiler:2.8'
// And we still need the Dagger library on the compile classpath itself
implementation 'com.google.dagger:dagger:2.8'
}
The test task is an instance of Test. It automatically detects and executes all unit tests in the test source set. It also generates a report once test execution is complete. JUnit and TestNG are both supported. Have a look at Test for the complete API.
See the Testing in Java & JVM projects chapter for more details.
The jar task creates a JAR file containing the class files and resources of the project. The JAR file is declared as an artifact in the archives dependency configuration. This means that the JAR is available in the classpath of a dependent project. If you upload your project into a repository, this JAR is declared as part of the dependency descriptor. You can learn more about how to work with archives in the section called “Archive creation in depth” and artifact configurations in Publishing artifacts.
Each jar or war object has a manifest property with a separate instance of Manifest. When the archive is generated, a corresponding MANIFEST.MF file is written into the archive.
Example: Customization of MANIFEST.MF
build.gradle
jar {
manifest {
attributes("Implementation-Title": "Gradle",
"Implementation-Version": version)
}
}
You can create stand-alone instances of a Manifest. You can use that for example, to share manifest information between jars.
Example: Creating a manifest object.
build.gradle
ext.sharedManifest = manifest {
attributes("Implementation-Title": "Gradle",
"Implementation-Version": version)
}
task fooJar(type: Jar) {
manifest = project.manifest {
from sharedManifest
}
}
You can merge other manifests into any Manifest object. The other manifests might be either described by a file path or, like in the example above, by a reference to another Manifest object.
Example: Separate MANIFEST.MF for a particular archive
build.gradle
task barJar(type: Jar) {
manifest {
attributes key1: 'value1'
from sharedManifest, 'src/config/basemanifest.txt'
from('src/config/javabasemanifest.txt',
'src/config/libbasemanifest.txt') {
eachEntry { details ->
if (details.baseValue != details.mergeValue) {
details.value = baseValue
}
if (details.key == 'foo') {
details.exclude()
}
}
}
}
}
Manifests are merged in the order they are declared by 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. The merge is not immediately triggered by the from statement. It is done lazily, either when generating the jar, or by calling writeTo or effectiveManifest
You can easily write a manifest to disk.

