METAINFservice

METAINFservice is a Java specification that defines a mechanism for discovering and loading service providers. It is part of the Java SE Platform. The core idea is to allow libraries and frameworks to expose functionality that can be extended or implemented by other modules without requiring explicit configuration in the application's code.

The METAINFservice mechanism relies on the presence of specific files within the META-INF directory of a JAR file. For each service, a configuration file is created. This file's name is the fully qualified name of the service interface or abstract class. Inside this file, each line specifies the fully qualified name of a concrete implementation class that provides the service.

When an application needs to use a service, it can use the ServiceLoader class to find all available implementations. The ServiceLoader iterates through all JAR files on the classpath, looking for the service configuration files in their META-INF directories. It then instantiates the listed provider classes, making them available for use. This decoupled approach promotes modularity and extensibility in Java applications. Common uses include loading drivers, logging implementations, or custom plugins.