shadow_jars.md

Problem statement

we are need quickbooks library 6.3.0 and the joda-time library is 2.1 is added as transitive dependency. https://mvnrepository.com/artifact/com.intuit.quickbooks-online/ipp-v3-java-data/6.3.0

In our project, we need joda time library is 2.12.7. https://mvnrepository.com/artifact/joda-time/joda-time/2.12.7

Now, we are facing class path conflict in joda libary.

Solution

The solution is to change the base package of joda-time library and it's usage in Quickbooks library.

The Shadow Jar plugin helps us acheive this.

Shadow Jar

Shadow is a Gradle plugin for combining a project's dependency classes and resources into a single output Jar. The combined Jar is often referred to a fat-jar or uber-jar. Shadow utilizes JarInputStream and JarOutputStream to efficiently process dependent libraries into the output jar without incurring the I/O overhead of expanding the jars to disk

Plugin

Gradle Shadow Plugin

Benefits of Shadow

Shadowing a project output has 2 major use cases:

• Creating an executable JAR distribution
• Bundling and relocating (changing package names) common dependencies in libraries to avoid classpath conflicts

Steps

1. Create new module (shadow-module) in your Java/Kotlin project
2. Create build.gradle.kt in shadow-module with the following content

import com.github.jengelman.gradle.plugins.shadow.tasks.ShadowJar

plugins {
    id("java")
    id("com.github.johnrengelman.shadow") version "7.0.0"
}

group = "com.example"
version = "0.0.1"

repositories {
    mavenCentral()
}

dependencies {
    testImplementation(platform("org.junit:junit-bom:5.10.0"))
    testImplementation("org.junit.jupiter:junit-jupiter")
    implementation("com.intuit.quickbooks-online:ipp-v3-java-data:6.1.2")
}

tasks.test {
    useJUnitPlatform()
}

tasks.withType<ShadowJar>() {
    relocate("org.joda.time", "com.super.shaded.org.joda.time")
}

3. Include the module in your project

// https://mvnrepository.com/artifact/joda-time/joda-time
implementation("joda-time:joda-time:2.12.7")

implementation(project("path" to "shadow-module", "configuration" to "shadow"))

Now, the joda-time 2.17.7 lib is accessible under the original package org.joda.time.

import org.joda.time.Instant

In the quickbooks lib, all the joda-time lib usage is changed to com.super.shaded.org.joda.time. Also, we can use older version of joda using the shaded package name.

import com.super.shaded.org.joda.time.Instant like this