Package ratpack.core.service

Interface Service

All Known Subinterfaces:

SessionStore

All Known Implementing Classes:

HikariService

public interface Service

A service participates in the application lifecycle.

When the application starts, all services in the server registry will be notified. Similarly when the application stops.

 import ratpack.core.server.RatpackServer;
 import ratpack.core.server.ServerConfig;
 import ratpack.core.service.Service;
 import ratpack.core.service.StartEvent;
 import ratpack.core.service.StopEvent;

 import java.util.List;
 import java.util.LinkedList;
 import static org.junit.jupiter.api.Assertions.*;

 public class Example {

   static class RecordingService implements Service {
     public final List<String> events = new LinkedList<>();

     public void onStart(StartEvent event) {
       events.add("start");
     }

     public void onStop(StopEvent event) {
       events.add("stop");
     }
   }

   public static void main(String... args) throws Exception {
     RecordingService service = new RecordingService();

     RatpackServer server = RatpackServer.of(s -> s
       .serverConfig(ServerConfig.embedded())
       .registryOf(r -> r.add(service))
       .handler(r -> ctx -> ctx.render("ok"))
     );

     assertEquals("[]", service.events.toString());
     server.start();
     assertEquals("[start]", service.events.toString());
     server.reload();
     assertEquals("[start, stop, start]", service.events.toString());
     server.stop();
     assertEquals("[start, stop, start, stop]", service.events.toString());
   }
 }
 

Ordering

Services can be ordered by the DependsOn and ServiceDependencies mechanisms.

Async services

The onStart(ratpack.core.service.StartEvent) and onStop(ratpack.core.service.StopEvent) methods are always executed within a distinct Execution, for each service. This means that implementations of these methods are free to perform async ops (e.g. use the HTTP client, or block).

 import ratpack.core.server.RatpackServer;
 import ratpack.core.server.ServerConfig;
 import ratpack.core.service.Service;
 import ratpack.core.service.StartEvent;
 import ratpack.core.service.StopEvent;
 import ratpack.exec.Promise;

 import java.util.List;
 import java.util.LinkedList;
 import static org.junit.jupiter.api.Assertions.*;

 public class Example {

   static class RecordingService implements Service {
     public final List<String> events = new LinkedList<>();

     public void onStart(StartEvent event) {
       Promise.value("start").map(String::toUpperCase).then(events::add);
     }

     public void onStop(StopEvent event) {
       Promise.value("stop").map(String::toUpperCase).then(events::add);
     }
   }

   public static void main(String... args) throws Exception {
     RecordingService service = new RecordingService();

     RatpackServer server = RatpackServer.of(s -> s
       .serverConfig(ServerConfig.embedded())
       .registryOf(r -> r.add(service))
       .handler(r -> ctx -> ctx.render("ok"))
     );

     server.start();
     assertEquals("[START]", service.events.toString());
     server.stop();
     assertEquals("[START, STOP]", service.events.toString());
   }
 }
 

There is no need to catch promise errors. An error handler for the execution is installed that effectively treats any exceptions as if they were thrown by the method.

Relationship with “business-logic”

This interface does need to be used for business-logic type services, unless such services need to participate in the application lifecycle. Even in such a case, it is generally better to decouple the business-logic type service from Ratpack (i.e. this interface) and have a Service implementation that drives the business-logic service.

Accessing the server registry

The event objects given to the start/stop methods provide access to the server registry. This can be used, for example, to get hold of a database connection that was added to the server registry as part of the server definition.

Alternatively, when using the Guice support the service can be injected by Guice.

 import ratpack.core.server.RatpackServer;
 import ratpack.core.server.ServerConfig;
 import ratpack.core.service.Service;
 import ratpack.core.service.StartEvent;
 import ratpack.core.service.StopEvent;
 import ratpack.guice.Guice;
 import ratpack.func.Types;
 import javax.inject.Inject;

 import java.util.List;
 import java.util.LinkedList;
 import static org.junit.jupiter.api.Assertions.*;

 public class Example {

   static class RecordingService implements Service {
     public final List<String> events;

     @Inject
     public RecordingService(List<String> events) {
       this.events = events;
     }

     public void onStart(StartEvent event) {
       events.add("start");
     }

     public void onStop(StopEvent event) {
       events.add("stop");
     }
   }

   public static void main(String... args) throws Exception {
     List<String> list = new LinkedList<>();

     RatpackServer server = RatpackServer.of(s -> s
       .serverConfig(ServerConfig.embedded())
       .registry(Guice.registry(b -> b
         .bindInstance(Types.listOf(String.class), list)
         .bind(RecordingService.class)
       ))
       .handler(r -> ctx -> ctx.render("ok"))
     );

     server.start();
     assertEquals("[start]", list.toString());
     server.stop();
     assertEquals("[start, stop]", list.toString());
   }
 }
 

Errors

If an onStart method errors, it will prevent the “application” from launching. In development mode, the application will start and display the error page for all requests with the error. When not in development mode, the exception will be thrown from the RatpackServer.start() method. If starting the app in a “main method”, this will prevent the JVM from starting.

If an onStop method errors, the error will be logged and then the next service invoked. That is, a failed onStop method is not considered fatal.

When a startup failure occurs, the server effectively shuts down which includes executing all the onStop methods.

Since:

1.3

Method Summary

Modifier and Type	Method	Description
default String	getName()	The name of this service, used for display purposes.
default void	onStart(StartEvent event)	Server startup event.
default void	onStop(StopEvent event)	Server stop event.
static Service	shutdown(String name, Action<? super StopEvent> action)	Creates a service that executes the given action as the onStop(StopEvent) implementation.
static Service	startup(String name, Action<? super StartEvent> action)	Creates a service that executes the given action as the onStart(StartEvent) implementation.

Method Detail

getName

default String getName()

The name of this service, used for display purposes.

The default implementation is to return getClass().getName().

Returns:

the name of this service, used for display purposes

onStart

@NonBlocking
default void onStart(StartEvent event)
              throws Exception

Server startup event. Executed after the root registry and server instance are constructed and before the server begins accepting requests.

Parameters:

event - meta information about the startup event

Throws:

Exception - any

onStop

@NonBlocking
default void onStop(StopEvent event)
             throws Exception

Server stop event. Executed after the root handler stops accepting requests and before the server closes the channel and thread pool.

Parameters:

event - meta information about the stop event

Throws:

Exception - any

startup

static Service startup(String name,
                       Action<? super StartEvent> action)

Creates a service that executes the given action as the onStart(StartEvent) implementation.

This can be used to create a service implementation from a lambda expression, instead of creating an anonymous impl of Service.

Parameters:

name - the name of the service

action - the action to execute on start

Returns:

the service implementation

Since:

1.4

shutdown

static Service shutdown(String name,
                        Action<? super StopEvent> action)

Creates a service that executes the given action as the onStop(StopEvent) implementation.

This can be used to of a service implementation from a lambda expression, instead of creating an anonymous impl of Service.

Parameters:

name - the name of the service

action - the action to execute on stop

Returns:

the service implementation

Since:

1.4