We can use the --offline command-line option to skip any network requests. So, with this option, Gradle never tries to access remote repositories and all information is fetched from the Gradle dependency caches. If the information in the caches is not sufficient for a build, then the build fails.

With the --refresh-dependencies option, we can refresh the metadata caches. If, for some reason, we expect the metadata to be no longer correct, we can use this option. Gradle will then refresh all information in the metadata caches for each repository. Artifacts are only downloaded when the SHA1 checksum is different than the checksum for artifacts in the artifacts cache.

A dependency with a static version can be easily cached. The contents of the artifact has a checksum, and this can be used to either use the cache or download the artifact (and place it in the artifact cache). A dependency with a dynamic version or changing module can have a changing artifact, so we need to be able to customize the cache settings. We can change the expiration time for cached dependencies with a dynamic version and changing modules. The default expiration time is 24 hours. After the expiration time, Gradle will invalidate the cache and determine whether an artifact needs to be downloaded again.

We change the expiration time for dependencies with a dynamic version using the cacheDynamicVersionsFor method of the resolutionStrategy configuration closure. The method accepts a number and time unit to set the value for the cache expiration. The time unit can be either of the java.util.concurrent.TimeUnit type or a string that is converted to TimeUnit.

To change modules, we use the cacheChangingModulesFor method to change the expiration time. This method also accepts a number and time unit just as the cacheDynamicVersionsFor method does.

In the next example build file, we change the cache expiration for both dynamic versions and changing modules for runtime configurations. We can also set it for all configurations with the all method and configuration block. The following code shows this:

// Import needed for cache methods time unit.
import java.util.concurrent.TimeUnit

apply plugin: 'java'

repositories.jcenter()

configurations {
  runtime {
    resolutionStrategy {
      // Change expiration time for caching
      // dynamic version to 30 minutes.
      cacheDynamicVersionsFor 30, 'minutes'

      // Alternative syntax is using TimeUnit:
      // cacheDynamicVersionsFor 1, TimeUnit.HOURS

      // Change expiration time for cached
      // changing modules to 5 minutes using
      // java.util.concurrent.TimeUnit.
      cacheChangingModulesFor 5, TimeUnit.MINUTES

      // Or we could use string notation.
      // cacheChangingModulesFor 1, 'minutes'
    }
  }

  // Alternatively we could apply
  // this to all configurations:
  // all {
  //     resolutionStrategy {
  //         cacheDynamicVersionsFor 4, 'hours'
  //         cacheChangingModulesFor 10, 'minutes'
  //     }
  // }
}

dependencies {
  compile 'org.slf4j:slf4j-api:1.7.7'

  runtime 'ch.qos.logback:logback-classic:1.1.2'
}

Gradle knows about artifacts that are stored in a Maven repository, and that if the version attribute ends with -SNAPSHOT, the module is a changing module. We can also define in our build script whether a dependency is a changing module, for example, if this cannot be derived from the version attribute. We must set the changing property to the value true in the configuration closure for a dependency.

In the following example build file, we have the com.vehicles:cars dependency, which is a changing module, but we use the static version 1.0:

apply plugin: 'java'

repositories {
  maven {
    url 'http://ourcompany.com/maven'
  }
}

dependencies {
  compile('com.vehicles:cars:1.0') {
    // Instruct Gradle this a changing
    // module, although it cannot
    // be derived from the version attribute.
    changing = true
  }

  // Other syntax using the map notation:
  // compile group: 'com.vehicles', name: 'cars',
  //         version: '1.0', changing: true
}