Gradle Dependencies and Dependency Configurations
External
- https://docs.gradle.org/current/userguide/core_dependency_management.html
- https://docs.gradle.org/current/userguide/dependency_management_for_java_projects.html
Internal
TO DEPLETE
Overview
The vast majority of Java projects rely on external libraries so managing a project's dependencies is an important part of building a Java project.
Specifying a dependency for a Java project requires just three pieces of information:
- Which dependency - specified by the library name and version. This is specified in the dependencies {} block.
- What is needed for - compilation or running. This is specified in the dependencies {} block.
- Where to look for it. This is specified in the repositories {...} block.
Dependencies for a project can be managed with Project.dependencies(Closure), Project.getDependencies() and the "dependencies" build.gradle DSL element:
dependencies {
// configuration closure
}
Configurations for a project can be managed with Project.configurations(Closure), Project.getConfigurations() and the "configurations" build.gradle DSL element:
configurations {
// configuration closure
}
Concepts
Dependency
Configuration
A configuration represents a named collection of artifacts and their dependencies, grouped together for a specific goal such as compiling and running the code from a source set.
Configuration, in this context, does not refer to a configuration file of any sort, as in a settings configuration settings.gradle or a build configuration build.gradle. It refers to named set of artifacts, and it can probably thought of as being a concept similar to a Maven scope.
Each source set points to several configurations required to compile and run the code included in the source set. Also see:
build.gradle Syntax
dependencies {
implementation 'io.someproject:someartifact:0.1.0'
}
The Dependency Cache
Once a dependency is resolved as result of the dependency resolution, Gradle stores the associated artifacts in a local cache, known as the dependency cache. One of the goals of storing artifacts locally in the cache is to minimize the number of remote requests made during the dependency resolution process.
The dependency cache is located under $GRADLE_USER_HOME/caches (typically ~/.gradle/caches). The directory contains two storage types: file-based storage for downloaded artifacts and raw metadata files, and a binary store of resolved module meta-data. This cache is also known as the metadata cache. The metadata cache contains, among other things, the result of resolving dynamic versions to concrete versions, the resolved module metadata, including module artifacts and module dependencies, the resolved artifact metadata, including a pointer to the downloaded file in the file-based storage, the absence of a particular module or artifact, eliminating repeated attempts to access a resource that does not exist.
For a specific dependency version, the files are maintained under .gradle/caches/modules-2/files-* and the corresponding binary metadata is maintained in .gradle/caches/modules-2/metadata-*. For example, the binary artifacts for SLF4J API 1.7.25, where "org.slf4j" is the group ID and "slf4j-api" is the artifact ID, are stored as follows:
.gradle/caches/modules-2/files-2.1/org.slf4j/slf4j-api/1.7.25
|
+ df51c4a85dd6acf8b6cdc9323596766b3d577c28/slf4j-api-1.7.25.pom
|
+ da76ca59f6a57ee3102f8f9bd9cee742973efa8a/slf4j-api-1.7.25.jar
|
+ 962153db4a9ea71b79d047dfd1b2a0d80d8f4739/slf4j-api-1.7.25-sources.jar
The corresponding binary metadata is stored as:
.gradle/caches/modules-2/metadata-2.58/descriptors/org.slf4j/slf4j-api/1.7.25
|
+ 1dd858de07b774d6be9d3e38c5646087/descriptor.bin
|
+ 33ddd5448b9e1258ce46034f20c899a8/descriptor.bin
|
+ f8e6315c37eb56998f7a5ba08e30db71/descriptor.bin
Dependency resolution will fail if the required artifacts are not available in any repository specified in the build, even if the local cache has a copy of the artifact that was retrieved from a different repository.
Before downloading an artifact from a repository, Gradle tries to get its checksum first by attempting to download the SHA file associated with the artifact. If the checksum can be retrieved, and Gradle determines that a file with the same id and checksum exists in the cache. If the checksum cannot be retrieved, the artifact will be downloaded (and ignored if it matches an existing artifact).
The cache is periodically scanned (at most every 24 hours) for artifacts that have not been used for more than 30 days and obsolete artifacts are deleted, to ensure the cache does not grow indefinitely.
Forced Cache Update
Gradle can be told to ignore all cached entries for resolved modules and artifacts with the --refresh-dependencies command line option. When used, a fresh resolve will be performed against all configured repositories, with dynamic versions recalculated, modules refreshed, and artifacts downloaded. However, where possible Gradle will check if the previously downloaded artifacts are valid before downloading again. This is done by comparing published SHA1 values in the repository with the SHA1 values for existing downloaded artifacts. A new snapshot repository will produce the following log:
gradle clean build --refresh-dependencies ... Download s3://my-repo/snapshots/com/example/my-artifact/1.0.0-SNAPSHOT/maven-metadata.xml ... Download s3://my-repo/snapshots/com/example/my-artifact/1.0.0-SNAPSHOT/my-artifact-1.0.0-20181008.231746-18.jar
Low-Level Cache Manipulation
It is sometimes necessary to remove individual dependency from cache. TODO.