# 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 instances 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. Use
Ant Path Matcher
syntax to specify matching path for your files and directories.
// Configuring Filtering for Relocation
shadowJar {
relocate('junit.textui', 'a') {
exclude 'junit.textui.TestRunner'
}
relocate('junit.framework', 'b') {
include 'junit.framework.Test*'
}
}
For a more advanced path matching you might want to use Regular Expressions instead. Wrap the expresion in %regex[]
before
passing it to include
/exclude
.
// Configuring Filtering for Relocation with Regex
shadowJar {
relocate('org.foo', 'a') {
include '%regex[org/foo/.*Factory[0-9].*]'
}
}
# Automatically Relocating Dependencies
Shadow is shipped 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 declare a task
dependency so the tasks execute in the correct order.
// Configure Auto Relocation
import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar
tasks.named('shadowJar', ShadowJar) {
enableRelocation true
relocationPrefix "myapp"
}
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
orruntimeClasspath
configurations. Be mindful that some Gradle plugins will automatically add dependencies to your class path. You may need to remove these dependencies if you do not intend to shadow them into your library. Thejava-gradle-plugin
would normally cause such problems if it were not for the special handling that Shadow provides as described in Special Handling of the Java Gradle Plugin Development Plugin.