Building a Java application

Specify a Java version

By default, the latest version of Java 11 is used. If your application requires a specific version, you can use the GOOGLE_RUNTIME_VERSION environment variable to specify a JDK version:

  pack 
  
 build 
  
 sample 
 - 
 java 
  
 -- 
 builder 
 = 
 gcr 
 . 
 io 
 / 
 buildpacks 
 / 
 builder 
  
 \ 
  
 -- 
 env 
  
 GOOGLE_RUNTIME_VERSION 
 = 
 17 
 

You can also use a project.toml project descriptor to encode the environment variable alongside your project files. See instructions on building the application with environment variables .

Manage dependencies

Dependency configuration is supported for projects that use Maven or Gradle.

Configure Maven

Maven configurations can be applied using the MAVEN_OPTS environment variable. See documentation for additional instructions.

Examples:

• MAVEN_OPTS=-Xms256m -Xmx512m passes these flags to the JVM running Maven.
• MAVEN_OPTS=--add-opens java.base/java.lang=ALL-UNNAMED to suppress "illegal reflective access" warnings from Maven.

To manage your project's dependency on Maven itself, you can use the Maven Wrapper . If you do not use the Maven Wrapper, buildpacks defaults to using a recent version of Maven when running pack build .

Configure Gradle

Gradle configurations can be applied using the GRADLE_OPTS environment variable. See documentation for additional instructions.

Example:

GRADLE_OPTS=-Xms256m -Xmx512m passes these flags to the JVM running Gradle.

Google Cloud hosted Maven Central mirror

You can use the hosted mirror of Maven Central by specifying the available URLs .

Mirror repositories in Maven

To configure a mirror, follow the Using Mirrors for Repositories instructions in the Maven project documentation.

Create a copy of the settings.xml from the default location of ~/.m2/settings.xml to inside your application source directory and specify GOOGLE_BUILD_ARGS=--settings <path/to/settings> .

Note: is relative to the source directory.

Example settings.xml file:

 <settings>  
<mirrors>  
<mirror>  
<id>google-maven-central</id>  
<name>Cloud  
Storage  
Maven  
Central  
mirror</name>  
<url>https://maven-central.storage-download.googleapis.com/maven2/</url>  
<mirrorOf>central</mirrorOf>  
</mirror>  
</mirrors>
</settings> 

Mirror repositories in Gradle

To configure a mirror, follow the Declaring Repositories instructions in the Gradle project documentation.

Example build.gradle entry:

   
 reposi 
 t 
 ories 
  
 { 
  
 mave 
 n 
  
 { 
  
 url 
  
 "https://maven-central.storage-download.googleapis.com/maven2/" 
  
 } 
  
 }