12.2.1.2 Java Gradle Build

A focused guide to Java Gradle Build, connecting core concepts with practical Docker and container operations.

A Java Gradle build within Docker uses Gradle's build system to compile, test, and package a Java application, following a similar multi-stage pattern to a Maven-based build but accounting for Gradle's specific dependency caching and wrapper conventions.

The Basic Gradle Build Stage

A build stage uses an image with Gradle and an appropriate JDK pre-installed, or relies on the project's own Gradle wrapper.

FROM gradle:8-jdk21 AS build
WORKDIR /app
COPY build.gradle settings.gradle ./
COPY src ./src
RUN gradle build --no-daemon

Using the Gradle Wrapper for Build Consistency

Many projects rely on the Gradle wrapper, ensuring the exact same Gradle version is used regardless of what might otherwise be available in a given build image.

FROM eclipse-temurin:21-jdk AS build
WORKDIR /app
COPY gradlew .
COPY gradle ./gradle
COPY build.gradle settings.gradle ./
RUN ./gradlew dependencies --no-daemon
COPY src ./src
RUN ./gradlew build --no-daemon

This approach copies the wrapper itself, ensuring build reproducibility independent of whatever Gradle version a generic gradle base image might otherwise provide.

Leveraging Dependency Caching Through Layer Ordering

Similar to the Maven pattern, copying build configuration files before source code allows Docker to cache dependency resolution separately from compilation.

COPY build.gradle settings.gradle ./
RUN ./gradlew dependencies --no-daemon
COPY src ./src
RUN ./gradlew build --no-daemon

Disabling the Gradle Daemon for Container Builds

The --no-daemon flag is commonly used within a container build, since Gradle's persistent daemon process, useful for speeding up repeated local builds, provides little benefit within a single, ephemeral container build context.

./gradlew build --no-daemon

Why Java Gradle Build Matters

Properly structuring a Gradle-based build stage, accounting for the wrapper convention and Gradle's specific caching behavior, produces efficient, reproducible Java image builds analogous to the Maven-based pattern, appropriate for projects using Gradle as their build system.