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Java

The Java buildpack will automatically detect the type of project and artifacts. However, you can override the default settings through the many build arguments available.

System Requirements​

To ensure your Spring Boot application starts up quickly and runs well, we recommend at least 0.75 GB and 0.75 vCPU of Compute.

caution

Spring Boot applications may not have sufficient resources to run on the FL0 Free Tier. We recommend upgrading to the Pro plan to run Spring Boot.

Features​

Build from Source​

The Java buildpack is comprised of several child buildpacks that assist with building for specific tools and frameworks. These include:

  • Maven
  • Gradle
  • Lein
  • Scala (SBT)

The correct build tool to use will be detected based on the contents of the application directory. Your build needs to produce a supported artifact format.

Once the source code is built into an artifact, the build will continue as per the Building from a Compiled Artifact section.

Select a Module or Artifact​

You can select a module or artifact using the BP_<TOOL>_BUILT_MODULE and BP_<TOOL>_BUILT_ARTIFACT build arguments.

Specify the Build Command​

See the BP_<TOOL>_BUILD_ARGUMENTS build argument for more details.

Building from a Compiled Artifact​

FL0 will automatically detect the type of artifact in your repository. If a WAR is detected, Apache Tomcat will be installed as well.

Installing a Specific JVM Version​

Configure the JVM at Runtime​

There are several additional build arguments that can be used to adjust the JAVA_TOOL_OPTIONS environment variable. See the Bellsoft Liberica Buildpack documentation for a full list.

Supported Artifacts​

FL0 supports the following archive formats:

  • Executable JAR
  • WAR
  • Distribution ZIP

The buildpack will do the following:

  • Requests that a JDK be installed
  • Links the ~/.gradle to a layer for caching
  • If <APPLICATION_ROOT>/gradlew exists
    • Runs <APPLICATION_ROOT>/gradlew --no-daemon assemble to build the application
  • If <APPLICATION_ROOT>/gradlew does not exist
    • Contributes Gradle to a layer with all commands on $PATH
    • Runs <GRADLE_ROOT>/bin/gradle --no-daemon assemble to build the application
  • Removes the source code in <APPLICATION_ROOT>, following include/exclude rules

Build Arguments​

Build Arguments let you configure how your application is built. There are many options depending on the language-specific buildpack. See the documentation page for more details on how to use Build Arguments.

For any Build Arguments containing <TOOL>, replace <TOOL> with one of MAVEN, GRADLE, LEIN or SBT.

BP_JVM_VERSION​

Use this build argument to specify a different JVM version. The default is the latest 17.x version at the time of release.

Example: BP_JVM_VERSION=8 or BP_JVM_VERSION=8.*

BP_JVM_TYPE​

This build argument configures whether a JDK or JRE is installed at runtime. Defaults to JRE.

Example: BP_JVM_TYPE=JDK

BP_<TOOL>_BUILT_MODULE​

Defaults to the root module.

Example: BP_MAVEN_BUILT_MODULE=api - will look for the artifact with the file pattern target/api/*.[jw]ar

BP_<TOOL>_BUILT_ARTIFACT​

Defaults to a tool-specific pattern (e.g. target/*.[jw]ar for Maven, build/libs/*.[jw]ar for gradle).

Example: BP_MAVEN_BUILT_ARTIFACT=out/api-*.jar - FL0 will select a file with name name out/api-1.0.0.jar

BP_<TOOL>_BUILD_ARGUMENTS​

Maven builds can also use two additional build arguments, BP_MAVEN_ADDITIONAL_BUILD_ARGUMENTS and BP_MAVEN_ACTIVE_PROFILES

Gradle builds can also use the BP_GRADLE_ADDITIONAL_BUILD_ARGUMENTS build argument.

BP_MAVEN_ADDITIONAL_BUILD_ARGUMENTS​

Configures additional arguments to pass to the maven build tool; it defaults to empty string and can be handy when you want to keep the default BP_MAVEN_BUILD_ARGUMENTS but just need one additional argument.

Example: BP_MAVEN_ADDITIONAL_BUILD_ARGUMENTS=-DskipTool

BP_MAVEN_ACTIVE_PROFILES​

Configures active profiles to pass to the maven build tool; it defaults to empty string and can be handy when you want to keep the default BP_MAVEN_BUILD_ARGUMENTS but just need several profiles activated/deactivated.

Example: BP_MAVEN_ACTIVE_PROFILES=p1,!p2,?p3 - activate the p1 profile, deactivate the p2 profile, and optionally activate the p3 profile, without changing BP_MAVEN_BUILD_ARGUMENTS

BP_GRADLE_ADDITIONAL_BUILD_ARGUMENTS​

Configures additional arguments to pass to the gradle build tool; it defaults to empty string and can be handy when you want to keep the default BP_GRADLE_BUILD_ARGUMENTS but just need one additional argument.

Example: BP_GRADLE_ADDITIONAL_BUILD_ARGUMENTS=--no-build-cache - disable build cache without changing BP_GRADLE_BUILD_ARGUMENTS

BP_JAVA_INSTALL_NODE​

When building from source with the Maven or Gradle buildpacks, you can enable installation of Node and/or Yarn using this build argument. When set to true, FL0 will check for either yarn.lock or package.json to determine the package manager to use.

Example: BP_JAVA_INSTALL_NODE=true

BP_NODE_PROJECT_PATH​

When using BP_JAVA_INSTALL_NODE, the yarn.lock and package.json files are expected to be in the root of the project. Use this build argument to override this behavior and set a custom path.

Example: BP_NODE_PROJECT_PATH=path/to/project

BP_JAVA_APP_SERVER​

Defaults to Apache Tomcat. To override this, specify one of the following:

Example: BP_JAVA_APP_SERVER=tomee

Example Template​

An example of the Java Spring Boot with Maven Application can be found in the FL0 templates repository: fl0zone/template-java-maven.