DPE University Training

Gradle Incremental Builds and Local Build Caching Exercise

This is a hands-on exercise to go along with the Incremental Builds and Build Caching training module. In this exercise you will go over the following:

Recap of Incremental Builds
Enable and use Local Cache
Order of lookup for cached outputs

Prerequisites

Finished going through the relevant sections in the training course
JDK 1.8+ and recent version of Gradle build tool installed
- https://gradle.org/install/
Gradle Build Tool experience
- Knowledge of core concepts
- Authoring build files
- Kotlin experience a plus but not required
Basic experience with Java software development

Recap of Incremental Cache and Limitations

Open the Gradle project in this repository in an editor of your choice
Inspect the build and source files, there is only one subproject called app
Run tests on the project. Notice the task outcome labels indicate that most tasks' actions were executed.

$ ./gradlew :app:test
- Task :app:compileJava
# Task :app:processResources NO-SOURCE
- Task :app:classes
- Task :app:compileTestJava
# Task :app:processTestResources NO-SOURCE
- Task :app:testClasses
- Task :app:test

Run the tests again. Notice that the outcome labels indicate that most tasks' actions were not executed. The output from the previous execution in the build directory was used.

$ ./gradlew :app:test
> Task :app:compileJava UP-TO-DATE
# Task :app:processResources NO-SOURCE
> Task :app:classes UP-TO-DATE
> Task :app:compileTestJava UP-TO-DATE
# Task :app:processTestResources NO-SOURCE
> Task :app:testClasses UP-TO-DATE
> Task :app:test UP-TO-DATE

Make a change to the app/src/main/java/com/gradle/lab/App.java file, add 2 more exclamation marks to the Hello World! string:

public String getGreeting() {
    return "Hello World!!!";
}

Run the tests again. Notice that the actions of compileJava and test were executed since changes were made to the inputs for those tasks.

$ ./gradlew :app:test
- Task :app:compileJava
# Task :app:processResources NO-SOURCE
- Task :app:classes
> Task :app:compileTestJava UP-TO-DATE
# Task :app:processTestResources NO-SOURCE
> Task :app:testClasses UP-TO-DATE
- Task :app:test

Revert the changes made to app/src/main/java/com/gradle/lab/App.java and run the tests again. Notice that the actions of compileJava and test were executed since the most recent build had different inputs for those tasks.

$ ./gradlew :app:test
- Task :app:compileJava
# Task :app:processResources NO-SOURCE
- Task :app:classes
> Task :app:compileTestJava UP-TO-DATE
# Task :app:processTestResources NO-SOURCE
> Task :app:testClasses UP-TO-DATE
- Task :app:test

Enable and Use Local Cache

Edit the gradle.properties file and add org.gradle.caching=true to it. The contents of the file now look like:

org.gradle.console=verbose
org.gradle.caching=true

Run the clean task and then the tests, this will populate the cache.

$ ./gradlew :app:clean :app:test
# Task :app:clean
- Task :app:compileJava
# Task :app:processResources NO-SOURCE
- Task :app:classes
- Task :app:compileTestJava
# Task :app:processTestResources NO-SOURCE
- Task :app:testClasses
- Task :app:test

Change the string in app/src/main/java/com/gradle/lab/App.java to have 2 extra exclamations again. Run the tests, notice that the task actions were executed. The inputs and outputs for these changes are not in the cache.

$ ./gradlew :app:test
- Task :app:compileJava
# Task :app:processResources NO-SOURCE
- Task :app:classes
> Task :app:compileTestJava UP-TO-DATE
# Task :app:processTestResources NO-SOURCE
> Task :app:testClasses UP-TO-DATE
- Task :app:test

Revert the changes to app/src/main/java/com/gradle/lab/App.java and run the tests again. Notice that some task actions were skipped and the outputs from the cache were used. It is important to understand that the outputs from the cache are put into the build directory and that's how the outputs are available to the tasks.

$ ./gradlew :app:test
! Task :app:compileJava FROM-CACHE
# Task :app:processResources NO-SOURCE
> Task :app:classes UP-TO-DATE
> Task :app:compileTestJava UP-TO-DATE
# Task :app:processTestResources NO-SOURCE
> Task :app:testClasses UP-TO-DATE
! Task :app:test FROM-CACHE

If you run the tests again, you will notice that the outcome label indicates the output from the previous execution in the build directory was used. This shows the order in which Gradle will look for the cached outputs, first in the build directory, then in the cache.

$ ./gradlew :app:test
> Task :app:compileJava UP-TO-DATE
# Task :app:processResources NO-SOURCE
> Task :app:classes UP-TO-DATE
> Task :app:compileTestJava UP-TO-DATE
# Task :app:processTestResources NO-SOURCE
> Task :app:testClasses UP-TO-DATE
> Task :app:test UP-TO-DATE

If you use the -i flag you can see the cache key used for each task input. Run a clean followed by the tests to see this.

$ ./gradlew :app:clean :app:test -i
...
...
...
> Task :app:test FROM-CACHE
Build cache key for task ':app:test' is 5eea5b00209094c7c5d641d592af0a2b
Task ':app:test' is not up-to-date because:
  Output property 'binaryResultsDirectory' file /Users/adayal/trainings/dpeuni-gradle-incremental-and-caching-local/app/build/test-results/test/binary has been removed.
  Output property 'binaryResultsDirectory' file /Users/adayal/trainings/dpeuni-gradle-incremental-and-caching-local/app/build/test-results/test/binary/output.bin has been removed.
  Output property 'binaryResultsDirectory' file /Users/adayal/trainings/dpeuni-gradle-incremental-and-caching-local/app/build/test-results/test/binary/output.bin.idx has been removed.
  Output property 'binaryResultsDirectory' file /Users/adayal/trainings/dpeuni-gradle-incremental-and-caching-local/app/build/test-results/test/binary/results.bin has been removed.
  Output property 'reports.enabledReports.html.outputLocation' file /Users/adayal/trainings/dpeuni-gradle-incremental-and-caching-local/app/build/reports/tests/test has been removed.
Loaded cache entry for task ':app:test' with cache key 5eea5b00209094c7c5d641d592af0a2b

You can also use the -Dorg.gradle.caching.debug=true flag to view more details.

$ ./gradlew :app:clean :app:test -Dorg.gradle.caching.debug=true

You can see the cache entries by looking in the cache directory:

$ ls -ltr ~/.gradle/caches/build-cache-1/

Local Cache Configuration

By default items will expire from the local cache after 7 days. Let's modify the configuration to keep items for 30 days. Edit the ~/.gradle/init.gradle.kts file and put the following configuration:

gradle.settingsEvaluated {
     buildCache {
        local {
            removeUnusedEntriesAfterDays = 30
        }
    }
}

Run a clean then the tests to make sure there was no mistake in the configuration:

$ ./gradlew :app:clean :app:test
# Task :app:clean
! Task :app:compileJava FROM-CACHE
# Task :app:processResources NO-SOURCE
> Task :app:classes UP-TO-DATE
! Task :app:compileTestJava FROM-CACHE
# Task :app:processTestResources NO-SOURCE
> Task :app:testClasses UP-TO-DATE
! Task :app:test FROM-CACHE

Solution Reference

If you get stuck you can refer to the solution branch of this repository.

gradle / dpeuni-gradle-incremental-and-caching-local