The powerful support for multi-project builds is one of Gradle's unique selling points. This topic is also the most intellectually challenging.
Let's start with a very simple multi-project build. After all Gradle is a general purpose build tool at its core, so the projects don't have to be java projects. Our first examples are about marine life.
We have the following project tree. This is a multi-project build with a root project
water and a subproject bluewhale.
Example 42.1. Multi-project tree - water & bluewhale projects
Build layout
water/ build.gradle settings.gradle bluewhale/
Note: The code for this example can be found at samples/userguide/multiproject/firstExample/water which is in both the binary and source distributions of Gradle.
settings.gradle
include 'bluewhale'And where is the build script for the bluewhale project? In Gradle build scripts are optional.
Obviously for a single project build, a project without a build script doesn't make much sense. For
multiproject builds the situation is different. Let's look at the build script for the water project and
execute it:
Example 42.2. Build script of water (parent) project
build.gradle
Closure cl = { task -> println "I'm $task.project.name" }
task hello << cl
project(':bluewhale') {
task hello << cl
}Output of gradle -q hello
> gradle -q hello I'm water I'm bluewhale
Gradle allows you to access any project of the multi-project build from any build script. The Project
API provides a method called project(), which takes a path as an argument and returns
the Project object for this path. The capability to configure a project build from any build script we
call cross project configuration. Gradle implements this via
configuration injection.
We are not that happy with the build script of the water project. It is inconvenient to add the task
explicitly for every project. We can do better. Let's first add another project called
krill to our multi-project build.
Example 42.3. Multi-project tree - water, bluewhale & krill projects
Build layout
water/ build.gradle settings.gradle bluewhale/ krill/
Note: The code for this example can be found at samples/userguide/multiproject/addKrill/water which is in both the binary and source distributions of Gradle.
settings.gradle
include 'bluewhale', 'krill'
Now we rewrite the water build script and boil it down to a single line.
Example 42.4. Water project build script
build.gradle
allprojects {
task hello << { task -> println "I'm $task.project.name" }
}Output of gradle -q hello
> gradle -q hello I'm water I'm bluewhale I'm krill
Is this cool or is this cool? And how does this work? The Project API provides a property
allprojects
which returns a list with the current project and all its subprojects underneath it. If you call
allprojects
with a closure, the statements of the closure are delegated to the projects associated with
allprojects. You could also do an iteration via allprojects.each, but
that would be more verbose.
Other build systems use inheritance as the primary means for defining common behavior. We also offer inheritance for projects as you will see later. But Gradle uses configuration injection as the usual way of defining common behavior. We think it provides a very powerful and flexible way of configuring multiproject builds.
The Project API also provides a property for accessing the subprojects only.
Example 42.5. Defining common behaviour of all projects and subprojects
build.gradle
allprojects {
task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
hello << {println "- I depend on water"}
}Output of gradle -q hello
> gradle -q hello I'm water I'm bluewhale - I depend on water I'm krill - I depend on water
You can add specific behavior on top of the common behavior. Usually we put the project specific
behavior in the build script of the project where we want to apply this specific behavior. But as we
have already seen, we don't have to do it this way. We could add project specific behavior for the
bluewhale project like this:
Example 42.6. Defining specific behaviour for particular project
build.gradle
allprojects {
task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
hello << {println "- I depend on water"}
}
project(':bluewhale').hello << {
println "- I'm the largest animal that has ever lived on this planet."
}Output of gradle -q hello
> gradle -q hello I'm water I'm bluewhale - I depend on water - I'm the largest animal that has ever lived on this planet. I'm krill - I depend on water
As we have said, we usually prefer to put project specific behavior into the build script of this
project. Let's refactor and also add some project specific behavior to the krill
project.
Example 42.7. Defining specific behaviour for project krill
Build layout
water/
build.gradle
settings.gradle
bluewhale/
build.gradle
krill/
build.gradleNote: The code for this example can be found at samples/userguide/multiproject/spreadSpecifics/water which is in both the binary and source distributions of Gradle.
settings.gradle
include 'bluewhale', 'krill'
bluewhale/build.gradle
hello.doLast { println "- I'm the largest animal that has ever lived on this planet." }krill/build.gradle
hello.doLast {
println "- The weight of my species in summer is twice as heavy as all human beings."
}build.gradle
allprojects {
task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
hello << {println "- I depend on water"}
}Output of gradle -q hello
> gradle -q hello I'm water I'm bluewhale - I depend on water - I'm the largest animal that has ever lived on this planet. I'm krill - I depend on water - The weight of my species in summer is twice as heavy as all human beings.
To show more of the power of configuration injection, let's add another project
called tropicalFish and add more behavior to the build via the build script of the
water project.
Example 42.8. Adding custom behaviour to some projects (filtered by project name)
Build layout
water/
build.gradle
settings.gradle
bluewhale/
build.gradle
krill/
build.gradle
tropicalFish/Note: The code for this example can be found at samples/userguide/multiproject/addTropical/water which is in both the binary and source distributions of Gradle.
settings.gradle
include 'bluewhale', 'krill', 'tropicalFish'
build.gradle
allprojects {
task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
hello << {println "- I depend on water"}
}
configure(subprojects.findAll {it.name != 'tropicalFish'}) {
hello << {println '- I love to spend time in the arctic waters.'}
}Output of gradle -q hello
> gradle -q hello I'm water I'm bluewhale - I depend on water - I love to spend time in the arctic waters. - I'm the largest animal that has ever lived on this planet. I'm krill - I depend on water - I love to spend time in the arctic waters. - The weight of my species in summer is twice as heavy as all human beings. I'm tropicalFish - I depend on water
The configure() method takes a list as an argument and applies the
configuration to the projects in this list.
Using the project name for filtering is one option. Using dynamic project properties is another.
Example 42.9. Adding custom behaviour to some projects (filtered by project properties)
Build layout
water/
build.gradle
settings.gradle
bluewhale/
build.gradle
krill/
build.gradle
tropicalFish/
build.gradleNote: The code for this example can be found at samples/userguide/multiproject/tropicalWithProperties/water which is in both the binary and source distributions of Gradle.
settings.gradle
include 'bluewhale', 'krill', 'tropicalFish'
bluewhale/build.gradle
arctic = true
hello.doLast { println "- I'm the largest animal that has ever lived on this planet." }krill/build.gradle
arctic = true
hello.doLast {
println "- The weight of my species in summer is twice as heavy as all human beings."
}tropicalFish/build.gradle
arctic = false
build.gradle
allprojects {
task hello << {task -> println "I'm $task.project.name" }
}
subprojects {
hello {
doLast {println "- I depend on water"}
afterEvaluate { Project project ->
if (project.arctic) { doLast {
println '- I love to spend time in the arctic waters.' }
}
}
}
}Output of gradle -q hello
> gradle -q hello I'm water I'm bluewhale - I depend on water - I'm the largest animal that has ever lived on this planet. - I love to spend time in the arctic waters. I'm krill - I depend on water - The weight of my species in summer is twice as heavy as all human beings. - I love to spend time in the arctic waters. I'm tropicalFish - I depend on water
In the build file of the water project we use an afterEvaluate
notification. This means that the closure we are passing gets evaluated after
the build scripts of the subproject are evaluated. As the property arctic
is set in those build scripts, we have to do it this way. You will find more on this topic in
Section 42.6, “Dependencies - Which dependencies?”
When we have executed the hello task from the root project dir things behaved in an
intuitive way. All the hello tasks of the different projects were executed. Let's switch
to the bluewhale dir and see what happens if we execute Gradle from there.
Example 42.10. Running build from subproject
Output of gradle -q hello
> gradle -q hello I'm bluewhale - I depend on water - I'm the largest animal that has ever lived on this planet. - I love to spend time in the arctic waters.
The basic rule behind Gradle's behavior is simple. Gradle looks down the hierarchy, starting with the
current dir, for tasks with the name
hello
an executes them. One thing is very important to note. Gradle
always
evaluates
every
project of the multi-project build and creates all existing task objects. Then, according to the task name
arguments and the current dir, Gradle filters the tasks which should be executed. Because of Gradle's
cross project configuration every project has to be evaluated before any
task gets executed. We will have a closer look at this in the next section. Let's now have our last marine
example. Let's add a task to bluewhale and krill.
Example 42.11. Evaluation and execution of projects
bluewhale/build.gradle
arctic = true
hello << { println "- I'm the largest animal that has ever lived on this planet." }
task distanceToIceberg << {
println '20 nautical miles'
}krill/build.gradle
arctic = true
hello << { println "- The weight of my species in summer is twice as heavy as all human beings." }
task distanceToIceberg << {
println '5 nautical miles'
}Output of gradle -q distanceToIceberg
> gradle -q distanceToIceberg 20 nautical miles 5 nautical miles
Here the output without the -q option:
Example 42.12. Evaluation and execution of projects
Output of gradle distanceToIceberg
> gradle distanceToIceberg :bluewhale:distanceToIceberg 20 nautical miles :krill:distanceToIceberg 5 nautical miles BUILD SUCCESSFUL Total time: 1 secs
The build is executed from the water project. Neither water nor
tropicalFish have a task with the name distanceToIceberg. Gradle does
not care. The simple rule mentioned already above is: Execute all tasks down the hierarchy which have this
name. Only complain if there is no such task!
As we have seen, you can run a multi-project build by entering any subproject dir and execute the build from there. All matching task names of the project hierarchy starting with the current dir are executed. But Gradle also offers to execute tasks by their absolute path (see also Section 42.5, “Project and task paths”):
Example 42.13. Running tasks by their absolute path
Output of gradle -q :hello :krill:hello hello
> gradle -q :hello :krill:hello hello I'm water I'm krill - I depend on water - The weight of my species in summer is twice as heavy as all human beings. - I love to spend time in the arctic waters. I'm tropicalFish - I depend on water
The build is executed from the tropicalFish project. We execute the hello
tasks of the water, the krill and the tropicalFish
project. The first two tasks are specified by there absolute path, the last task is executed on the name
matching mechanism described above.
A project path has the following pattern: It starts always with a colon, which denotes the root project.
The root project is the only project in a path that is not specified by its name. The path
:bluewhale
corresponds to the file system path
water/bluewhale
in the case of the example above.
The path of a task is simply its project path plus the task name. For example
:bluewhale:hello. Within a project you can address a task of the same project just by its name.
This is interpreted as a relative path.
Originally Gradle has used the
'/'
character as a natural path separator. With the introduction of directory tasks (see Section 12.1, “Directory creation”) this was no longer possible, as the name of the directory task
contains the
'/'
character.
The examples from the last section were special, as the projects had no Execution Dependencies. They had only Configuration Dependencies. Here is an example where this is different:
Example 42.14. Dependencies and execution order
Build layout
messages/
settings.gradle
consumer/
build.gradle
producer/
build.gradleNote: The code for this example can be found at samples/userguide/multiproject/dependencies/firstMessages/messages which is in both the binary and source distributions of Gradle.
settings.gradle
include 'consumer', 'producer'
consumer/build.gradle
task action << {
println("Consuming message: " +
(rootProject.hasProperty('producerMessage') ? rootProject.producerMessage : 'null'))
}producer/build.gradle
task action << {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}Output of gradle -q action
> gradle -q action Consuming message: null Producing message:
This did not work out. If nothing else is defined, Gradle executes the task in alphanumeric order.
Therefore
:consumer:action
is executed before :producer:action. Let's try to solve this with a hack and
rename the producer project to aProducer.
Example 42.15. Dependencies and execution order
Build layout
messages/
settings.gradle
aProducer/
build.gradle
consumer/
build.gradlesettings.gradle
include 'consumer', 'aProducer'
aProducer/build.gradle
task action << {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}consumer/build.gradle
task action << {
println("Consuming message: " +
(rootProject.hasProperty('producerMessage') ? rootProject.producerMessage : 'null'))
}Output of gradle -q action
> gradle -q action Producing message: Consuming message: Watch the order of execution.
Now we take the air out of this hack. We simply switch to the consumer dir and
execute the build.
Example 42.16. Dependencies and execution order
Output of gradle -q action
> gradle -q action Consuming message: null
For Gradle the two
action
tasks are just not related. If you execute the build from the
messages
project Gradle executes them both because they have the same name and they are down the hierarchy.
In the last example only one
action
was down the hierarchy and therefore it was the only task that got executed. We need something
better than this hack.
Example 42.17. Declaring dependencies
Build layout
messages/
settings.gradle
consumer/
build.gradle
producer/
build.gradleNote: The code for this example can be found at samples/userguide/multiproject/dependencies/messagesWithDependencies/messages which is in both the binary and source distributions of Gradle.
settings.gradle
include 'consumer', 'producer'
consumer/build.gradle
dependsOn(':producer') task action << { println("Consuming message: " + (rootProject.hasProperty('producerMessage') ? rootProject.producerMessage : 'null')) }
producer/build.gradle
task action << {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}Output of gradle -q action
> gradle -q action Producing message: Consuming message: Watch the order of execution.
Running this from the consumer directory gives:
Example 42.18. Declaring dependencies
Output of gradle -q action
> gradle -q action Producing message: Consuming message: Watch the order of execution.
We have now declared that the
consumer
project has an
execution dependency
on the
producer
project. For Gradle declaring
execution dependencies
between
projects
is syntactic sugar. Under the hood Gradle creates task dependencies out of them. You can also create
cross project tasks dependencies manually by using the absolute path of the tasks.
Let's change the naming of our tasks and execute the build.
Example 42.19. Project execution dependencies
consumer/build.gradle
dependsOn(':producer') task consume << { println("Consuming message: " + (rootProject.hasProperty('producerMessage') ? rootProject.producerMessage : 'null')) }
producer/build.gradle
task produce << {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}Output of gradle -q consume
> gradle -q consume Consuming message: null
Oops. Why does this not work? The
dependsOn
command is created for projects with a common lifecycle. Provided you have two Java projects where
one depends on the other. If you trigger a compile for the dependent project you don't want that
all
tasks of the other project get executed. Therefore a
dependsOn
creates dependencies between tasks with equal names. To deal with the scenario above you would do
the following:
Example 42.20. Cross project task dependencies
consumer/build.gradle
task consume(dependsOn: ':producer:produce') << { println("Consuming message: " + (rootProject.hasProperty('producerMessage') ? rootProject.producerMessage : 'null')) }
producer/build.gradle
task produce << {
println "Producing message:"
rootProject.producerMessage = 'Watch the order of execution.'
}Output of gradle -q consume
> gradle -q consume Producing message: Consuming message: Watch the order of execution.
Let's have one more example with our producer-consumer build before we enter Java land. We add a property to the producer project and create now a configuration time dependency from consumer on producer.
Example 42.21. Configuration time dependencies
consumer/build.gradle
message = rootProject.hasProperty('producerMessage') ? rootProject.producerMessage : 'null' task consume << { println("Consuming message: " + message) }
producer/build.gradle
rootProject.producerMessage = 'Watch the order of evaluation.'Output of gradle -q consume
> gradle -q consume Consuming message: null
The default
evaluation
order of the projects is alphanumeric (for the same nesting level). Therefore the
consumer
project is evaluated before the
producer
project and the
key
value of the
producer
is set
after
it is read by the
consumer
project. Gradle offers a solution for this.
Example 42.22. Configuration time dependencies - evaluationDependsOn
consumer/build.gradle
evaluationDependsOn(':producer') message = rootProject.hasProperty('producerMessage') ? rootProject.producerMessage : 'null' task consume << { println("Consuming message: " + message) }
Output of gradle -q consume
> gradle -q consume Consuming message: Watch the order of evaluation.
The command
evaluationDependsOn
triggers the evaluation of
producer
before
consumer
is evaluated. The example is a bit contrived for the sake of showing the mechanism. In
this
case there would be an easier solution by reading the key property at execution time.
Example 42.23. Configuration time dependencies
consumer/build.gradle
task consume << {
println("Consuming message: " +
(rootProject.hasProperty('producerMessage') ? rootProject.producerMessage : 'null'))
}Output of gradle -q consume
> gradle -q consume Consuming message: Watch the order of evaluation.
Configuration dependencies are very different to execution dependencies. Configuration dependencies are between projects whereas execution dependencies are always resolved to task dependencies. Another difference is that always all projects are configured, even when you start the build from a subproject. The default configuration order is top down, which is usually what is needed.
On the same nesting level the configuration order depends on the alphanumeric position. The most
common use case is to have multi-project builds that share a common lifecycle (e.g. all projects use the
Java plugin). If you declare with
dependsOn
a
execution dependency
between different projects, the default behavior of this method is to create also a
configuration
dependency between the two projects. Therefore it is likely that you don't have to define configuration
dependencies explicitly.
Gradle's multi-project features are driven by real life use cases. The first example for describing such a use case, consists of two webapplication projects and a parent project that creates a distribution out of them. [19] For the example we use only one build script and do cross project configuration.
Example 42.24. Dependencies - real life example - crossproject configuration
Build layout
webDist/
settings.gradle
build.gradle
date/
src/main/java/
org/gradle/sample/
DateServlet.java
hello/
src/main/java/
org/gradle/sample/
HelloServlet.javaNote: The code for this example can be found at samples/userguide/multiproject/dependencies/webDist which is in both the binary and source distributions of Gradle.
settings.gradle
include 'date', 'hello'
build.gradle
dependsOnChildren()
allprojects {
apply plugin: 'java'
group = 'org.gradle.sample'
version = '1.0'
}
subprojects {
apply plugin: 'war'
repositories {
mavenCentral()
}
dependencies {
compile "javax.servlet:servlet-api:2.5"
}
}
task explodedDist(dependsOn: assemble) << {
File explodedDist = mkdir(buildDir, 'explodedDist')
subprojects.each {project ->
project.tasks.withType(Jar).each {archiveTask ->
copy {
from archiveTask.archivePath
into explodedDist
}
}
}
}We have an interesting set of dependencies. Obviously the
date
and
hello
projects have a
configuration
dependency on webDist, as all the build logic for the webapp projects is injected by
webDist. The
execution
dependency is in the other direction, as
webDist
depends on the build artifacts of
date
and hello. There is even a third dependency.
webDist
has a
configuration
dependency on
date
and
hello
because it needs to know the archivePath. But it asks for this information at
execution time. Therefore we have no circular dependency.
Such and other dependency patterns are daily bread in the problem space of multi-project builds. If a build system does not support such patterns, you either can't solve your problem or you need to do ugly hacks which are hard to maintain and massively afflict your productivity as a build master.
There is one more thing to note from the current example. We have used the command
dependsOnChildren(). It is a convenience method and calls the
dependsOn
method of the parent project for every child project (not every sub project). It declares a
execution
dependency of
webDist
on
date
and hello.
Another use case would be a situation where the subprojects have a configuration
and
execution dependency on the parent project. This is the case when the parent project does configuration
injection into its subprojects, and additionally produces something at execution time that is needed by
its child projects (e.g. code generation). In this case the parent project would call the
childrenDependOnMe
method to create an execution dependency for the child projects. We might add an example for this in a
future version of the user guide.
What if one projects needs the jar produced by another project in its compile path? And not just the jar but also the transitive dependencies of this jar? Obviously this is a very common use case for Java multi-project builds. As already mentioned in Section 36.4.3, “Project dependencies”, Gradle offers project lib dependencies for this.
Example 42.25. Project lib dependencies
Build layout
java/
settings.gradle
build.gradle
api/
src/main/java/
org/gradle/sample/
api/
Person.java
apiImpl/
PersonImpl.java
services/personService/
src/
main/java/
org/gradle/sample/services/
PersonService.java
test/java/
org/gradle/sample/services/
PersonServiceTest.java
shared/
src/main/java/
org/gradle/sample/shared/
Helper.javaNote: The code for this example can be found at samples/userguide/multiproject/dependencies/java which is in both the binary and source distributions of Gradle.
We have the projects shared, api andpersonService.
personService has a lib dependency on the other two projects. api
has a lib dependency on shared.
[20]
Example 42.26. Project lib dependencies
settings.gradle
include 'api', 'shared', 'services:personService'
build.gradle
subprojects {
apply plugin: 'java'
group = 'org.gradle.sample'
version = '1.0'
repositories {
mavenCentral()
}
dependencies {
testCompile "junit:junit:4.8.2"
}
}
project(':api') {
dependencies {
compile project(':shared')
}
}
project(':services:personService') {
dependencies {
compile project(':shared'), project(':api')
}
}
dependsOnChildren()All the build logic is in the
build.gradle of the root project.
[21]
A lib
dependency is a special form of an execution dependency. It causes the other project to be built first and
adds the jar with the classes of the other project to the classpath. It also adds the dependencies of the
other project to the classpath. So you can enter the
api
directory and trigger a gradle compile. First
shared
is built and then
api
is built. Project dependencies enable partial multi-project builds.
If you come from Maven land you might be perfectly happy with this. If you come from Ivy land, you might expect some more fine grained control. Gradle offers this to you:
Example 42.27. Fine grained control over dependencies
build.gradle
subprojects {
apply plugin: 'java'
group = 'org.gradle.sample'
version = '1.0'
}
project(':api') {
configurations {
spi
}
dependencies {
compile project(':shared')
}
task spiJar(type: Jar) {
baseName = 'api-spi'
dependsOn classes
from sourceSets.main.output
include('org/gradle/sample/api/**')
}
artifacts {
spi spiJar
}
}
project(':services:personService') {
dependencies {
compile project(':shared')
compile project(path: ':api', configuration: 'spi')
testCompile "junit:junit:4.8.2", project(':api')
}
}The Java plugin adds per default a jar to your project libraries which contains all the classes. In this
example we create an
additional
library containing only the interfaces of the
api
project. We assign this library to a new dependency configuration. For the person
service we declare that the project should be compiled only against the
api
interfaces but tested with all classes from api.
The build task of the Java plugin is typically used to compile, test, and perform
code style checks (if the CodeQuality plugin is used) of a single project. In multi-project builds
you may often want to do all of these tasks across a range of projects. The buildNeeded
and buildDependents tasks can help with this.
Let's use the project structure shown in Example 42.26, “Project lib dependencies”. In this example :services:personservice depends on both :api and :shared. The :api project also depends on :shared.
Assume you are working on a single project, the :api project. You have been making changes, but
have not built the entire project since performing a clean. You want to build any necessary supporting
jars, but only perform code quality and unit tests on the project you have changed.
The build task does this.
Example 42.28. Build and Test Single Project
Output of gradle :api:build
> gradle :api:build :shared:compileJava :shared:processResources :shared:classes :shared:jar :api:compileJava :api:processResources :api:classes :api:jar :api:assemble :api:compileTestJava :api:processTestResources :api:testClasses :api:test :api:check :api:build BUILD SUCCESSFUL Total time: 1 secs
While you are working in a typical development cycle repeatedly building and testing changes to
the :api project (knowing that you are only changing files in this one project), you may not want to
even suffer the expense of :shared:compile checking to see what has changed in the :shared project.
Adding the -a option will cause gradle to use cached jars to resolve any project lib
dependencies and not try to re-build the depended on projects.
Example 42.29. Partial Build and Test Single Project
Output of gradle -a :api:build
> gradle -a :api:build :api:compileJava :api:processResources :api:classes :api:jar :api:assemble :api:compileTestJava :api:processTestResources :api:testClasses :api:test :api:check :api:build BUILD SUCCESSFUL Total time: 1 secs
If you have just gotten the latest version of source from your version control system which included changes
in other projects that :api depends on, you might want to not only build all the projects you depend on,
but test them as well. The buildNeeded task also tests all the projects from the
project lib dependencies of the testRuntime configuration.
Example 42.30. Build and Test Depended On Projects
Output of gradle :api:buildNeeded
> gradle :api:buildNeeded :shared:compileJava :shared:processResources :shared:classes :shared:jar :api:compileJava :api:processResources :api:classes :api:jar :api:assemble :api:compileTestJava :api:processTestResources :api:testClasses :api:test :api:check :api:build :shared:assemble :shared:compileTestJava :shared:processTestResources :shared:testClasses :shared:test :shared:check :shared:build :shared:buildNeeded :api:buildNeeded BUILD SUCCESSFUL Total time: 1 secs
You also might want to refactor some part of the :api project that is used in other projects.
If you make these types of changes, it is not sufficient to test just the :api
project, you also need to test all projects that depend on the :api project.
The buildDependents task also tests all the projects that have a project lib dependency
(in the testRuntime configuration) on the specified project.
Example 42.31. Build and Test Dependent Projects
Output of gradle :api:buildDependents
> gradle :api:buildDependents :shared:compileJava :shared:processResources :shared:classes :shared:jar :api:compileJava :api:processResources :api:classes :api:jar :api:assemble :api:compileTestJava :api:processTestResources :api:testClasses :api:test :api:check :api:build :services:personService:compileJava :services:personService:processResources :services:personService:classes :services:personService:jar :services:personService:assemble :services:personService:compileTestJava :services:personService:processTestResources :services:personService:testClasses :services:personService:test :services:personService:check :services:personService:build :services:personService:buildDependents :api:buildDependents BUILD SUCCESSFUL Total time: 1 secs
Finally, you may want to build and test everything in all projects. If the root project has declared
dependsOnChildren() (as this one does), then any task you run against the root project
will cause that same named task to be run on all the children. So you can just run
gradle build to build and test all projects.
Properties and methods declared in a project are inherited to all its subprojects. This is an alternative to configuration injection. But we think that the model of inheritance does not reflect the problem space of multi-project builds very well. In a future edition of this user guide we might write more about this.
Method inheritance might be interesting to use as Gradle's Configuration Injection does not support methods yet (but will in a future release).
You might be wondering why we have implemented a feature we obviously don't like that much. One reason is that it is offered by other tools and we want to have the check mark in a feature comparison :). And we like to offer our users a choice.
Writing this chapter was pretty exhausting and reading it might have a similar effect. Our final message
for this chapter is that multi-project builds with Gradle are usually
not
difficult. There are six elements you need to remember: allprojects,
subprojects, dependsOn, childrenDependOnMe,
dependsOnChildren
and project lib dependencies.
[22]
With those elements, and keeping in mind that Gradle has a distinct configuration and execution phase, you
have already a lot of flexibility. But when you enter steep territory Gradle does not become an obstacle and
usually accompanies and carries you to the top of the mountain.
[19] The real use case we had, was using http://lucene.apache.org/solr, where you need a separate war for each index your are accessing. That was one reason why we have created a distribution of webapps. The Resin servlet container allows us, to let such a distribution point to a base installation of the servlet container.
[20]
services
is also a project, but we use it just as a container. It has no build script and gets nothing
injected by another build script.
[21] We do this here, as it makes the layout a bit easier. We usually put the project specific stuff into the build script of the respective projects.
[22] So we are well in the range of the 7 plus 2 Rule :)