Java ServiceLoader loadInstalled() Method

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Description

The Java ServiceLoader loadInstalled(Class<S> service) method creates a new service loader for the given service type, using the extension class loader. This method is intended for use when only installed providers are desired. The resulting service will only find and load providers that have been installed into the current Java virtual machine; providers on the application's class path will be ignored.

Declaration

Following is the declaration for java.util.ServiceLoader.loadInstalled() method

public static <S> ServiceLoader<S> loadInstalled(Class<S> service)

Parameters

service − The interface or abstract class representing the service

Return Value

This method returns a new service loader

Exception

NA

Loading a ServiceLoader Instance using Extension Implementation Class Example

This example requires the service to be installed in our Java Virtual Machine

Our service code is the following −

package com.tutorialspoint;

public class ServiceImplementation extends ServiceProvider {
   public String getMessage() {
      return "Hello World";
   }
}

The following code loads the service that is registered and uses it to get the message from the service. We've created a method getDefault() which returns a ServiceProvider. This method gets a serviceLoader object using ServiceLoader.loadInstalled(Class<S> service). Then serviceLoader is iterated and first provider is returned. In the end we're throwing error if provider is not returned. Then using getDefault() we've retrieved the serviceProvider and printed the message using this object.

package com.tutorialspoint;

import java.util.ServiceLoader;

public abstract class ServiceProvider {
   public static ServiceProvider getDefault() {

      // load our plugin provided it is installed in our Java Virtual Machine
      ServiceLoader<ServiceProvider> serviceLoader =
      ServiceLoader.loadInstalled(ServiceProvider.class);

      //checking if load was successful
      for (ServiceProvider provider : serviceLoader) {
         return provider;
      }
      throw new Error("Something is wrong with registering the addon");
   }

   public abstract String getMessage();

   public static void main(String[] ignored) {
   
      // create a new provider and call getMessage()
      ServiceProvider provider = ServiceProvider.getDefault();
      System.out.println(provider.getMessage());
   }
}

Output

Let us compile and run the above program, this will produce the following result −

Hello World