Java ServiceLoader reload() Method

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Description

The Java ServiceLoader reload() method clears this loader's provider cache so that all providers will be reloaded.

After invoking this method, subsequent invocations of the iterator method will lazily look up and instantiate providers from scratch, just as is done by a newly-created loader.

This method is intended for use in situations in which new providers can be installed into a running Java virtual machine.

Declaration

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

public void reload()

Parameters

NA

Return Value

This method does not return a value

Exception

NA

Reloading a ServiceLoader Instance Example

In order the service to be registered, we need a META-INF/services folder in our classpath. In this particular folder, we need a text file with the name of the interface we implementing containing a single line listing the concrete class name of the implementation. In our case the name of the file is com.tutorialspoint.ServiceProvider and contains this line −

com.tutorialspoint.ServiceImplementation

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.load(). Using serviceLoader.reload() method, we've reloaded the service loader. 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
      ServiceLoader<ServiceProvider> serviceLoader =
         ServiceLoader.load(ServiceProvider.class);

      // reload the service
      System.out.println("Reloading...");
      serviceLoader.reload();
      System.out.println("Reloaded.");

      // 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 −

Reloading...
Reloaded.
Hello World