Relocating Packages

Shadow is capable of scanning a project's classes and relocating specific dependencies to a new location. This is often required when one of the dependencies is susceptible to breaking changes in versions or to classpath pollution in a downstream project.

Google's Guava and the ASM library are typical cases where package relocation can come in handy.

Shadow uses the ASM library to modify class byte code to replace the package name and any import statements for a class. Any non-class files that are stored within a package structure are also relocated to the new location.

// Relocating a Package
shadowJar {
   relocate 'junit.framework', 'shadow.junit'
}

The code snippet will rewrite the location for any class in the junit.framework to be shadow.junit. For example, the class junit.textui.TestRunner becomes shadow.junit.TestRunner. In the resulting JAR, the class file is relocated from junit/textui/TestRunner.class to shadow/junit/TestRunner.class.

Relocation operates at a package level. It is not necessary to specify any patterns for matching, it will operate simply on the prefix provided.

Relocation will be applied globally to all instance of the matched prefix. That is, it does not scope to only the dependencies being shadowed. Be specific as possible when configuring relocation as to avoid unintended relocations.

Filtering Relocation

Specific classes or files can be included/excluded from the relocation operation if necessary.

// Configuring Filtering for Relocation
shadowJar {
   relocate('junit.textui', 'a') {
       exclude 'junit.textui.TestRunner'
   }
   relocate('junit.framework', 'b') {
       include 'junit.framework.Test*'
   }
}

Automatically Relocating Dependencies

Shadow ships with a task that can be used to automatically configure all packages from all dependencies to be relocated. This feature was formally shipped into a 2nd plugin (com.github.johnrengelman.plugin-shadow) but has been removed for clarity reasons in version 4.0.0.

To configure automatic dependency relocation, declare a task of type ConfigureShadowRelocation and configure the target parameter to be the ShadowJar task you wish to auto configure. You will also need to declared a task dependency so the tasks execute in the correct order.

// Configure Auto Relocation
import com.github.jengelman.gradle.plugins.shadow.tasks.ConfigureShadowRelocation

task relocateShadowJar(type: ConfigureShadowRelocation) {
    target = tasks.shadowJar
    prefix = "myapp" // Default value is "shadow"

}

tasks.shadowJar.dependsOn tasks.relocateShadowJar

Configuring package auto relocation can add significant time to the shadow process as it will process all dependencies in the configurations declared to be shadowed. By default, this is the runtime or runtimeClasspath configurations. Be mindful that some Gradle plugins (such as java-gradle-plugin will automatically add dependencies to your class path (e.g. java-gradle-plugin automatically adds the full Gradle API to your compile configuratinon. You may need to remove these dependencies if you do not intend to shadow them into your library.