For general information on extending the buildpack, refer to Configuration and Extension.
To add a component, its class name must be added added to config/components.yml. It is recommended, but not required, that the class' file be placed in a directory that matches its type.
| Component Type | Location |
|---|---|
| Container | lib/java_buildpack/container |
| Framework | lib/java_buildpack/framework |
| JRE | lib/java_buildpack/jre |
Each component class must satisfy a contract defined by the following methods:
# If the component should be used when staging an application
#
# @return [Array<String>, String, nil] If the component should be used when staging the application, a +String+ or
# an +Array<String>+ that uniquely identifies the component (e.g.
# +open_jdk-1.7.0_40+). Otherwise, +nil+.
def detect
# Modifies the application's file system. The component is expected to transform the application's file system in
# whatever way is necessary (e.g. downloading files or creating symbolic links) to support the function of the
# component. Status output written to +STDOUT+ is expected as part of this invocation.
#
# @return [Void]
def compile
# Modifies the application's runtime configuration. The component is expected to transform members of the +droplet+
# (e.g. +java_home+, +java_opts+, etc.) in whatever way is necessary to support the function of the component.
#
# Container components are also expected to create the command required to run the application. These components
# are expected to read the +droplet+ values and take them into account when creating the command.
#
# @return [void, String] components other than containers are not expected to return any value. Container
# compoonents are expected to return the command required to run the application.
def releaseEach component class must have an initialize method that takes a Hash containing helper types for the application. These helper types are the way that components to communicate with one another. The context contains the following entries:
| Name | Type | Description |
|---|---|---|
application |
JavaBuildpack::Component::Application |
A read-only abstraction around the application |
configuration |
Hash |
The component configuration provided by the user via config/<component-name>.yml |
droplet |
JavaBuildpack::Component::Droplet |
A read-write abstraction around the droplet |
The buildpack provides a collection of base classes that may help you implement a component.
This base class is recommended for use by all components. It ensures that each component has a name, and that the contents of the context are exposed as instance variables (e.g. context[:application] is available as @application). In addition it provides two helper methods for downloading files as part of the component's operation.
This base class is recommended for use by any component that is sufficiently complex to need modularization. It enables a component to be composed of multiple "sub-components" and coordinates the component lifecycle across all of them.
This base class is recommended for use by any component that uses the buildpack repository support to download a dependency. It ensures that each component has a @version and @uri that were resolved from the repository specified in the component's configuration. It also implements the detect method with a standard implementation.
The following example components are relatively simple and good for copying as the basis for a new component.
The Java Main Class Container (lib/java_buildpack/container/java_main.rb) extends the JavaBuildpack::Component::BaseComponent base class described above.
The Tomcat Container (lib/java_buildpack/container/tomcat.rb) extends the JavaBuildpack::Component::ModularComponent base class described above.
The Spring Boot CLI Container (lib/java_buildpack/container/spring_boot_cli.rb) extends the JavaBuildpack::Component::VersionedDependencyComponent base class described above.