Guice-bootstrap

Guice-bootstrap is an extension of Guice that adds support for JSR 250 Life Cycle annotations.

@PostConstruct annotation is used on methods that need to get executed after dependency injection is done to perform any initialization.

@PreDestroy annotation is used on methods that are called before the application shuts down.

PostConstruct

Methods with @PostConstruct annotation are called after all depedency injection is done.

import javax.annotation.PostConstruct;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

class MyService implements Runnable
{
    private final ExecutorService executor = Executors.newSingleThreadExecutor();

    @PostConstruct
    public void start() {
        executor.submit(() -> { ... });
    }
}

PreDestroy

Methods with @PreDestroy annotation are called after the application shuts down.

import javax.annotation.PreDestroy;
import java.io.File;
import java.util.ArrayList;
import java.util.List;

class MyService implements Runnable
{
    private final List<File> files = new ArrayList<>();

    @PreDestroy
    public void cleanup() {
        files.stream().forEach(file -> file.delete());
    }
}

Bootstrap

Bootstrap is the main class to use guice-bootstrap.

Injector injector = new Bootstrap()
    .addModules(new MyGuiceModule1(), new MyGuiceModule2(), ...)
    .addModules(new MyGuiceModule3(), new MyGuiceModule4(), ...)
    .initialize();

Overriding bindings

Bootstrap.overrideModulesWith method allows you to override bindings. This is useful to customize bindings defined by a base class.

// The base class
public class MyService {
    public Bootstrap bootstrap()
    {
        return new Bootstrap()
            .addModules(new MyGuiceModule1(), new MyGuiceModule2(), ...)
            .addModules(new MyGuiceModule3(), new MyGuiceModule4(), ...)
            ;
    }

    public void start()
    {
        Injector injector = bootstrap().initialize();
        ...
    }
}

// Extending class that overrides some bindings
public class MyExtendedService extend MyService {
    @Override
    public Bootstrap bootstrap()
    {
        return super()
            .overrideModulesWith(new MyGuiceModule4(), ...)
            ;
    }
}

CloseableInjector

Bootstrap.initialize() sets up a shutdown hook to the Java VM (@Runtime.addShutdownHook`). It ensures that PostDestroy methods are called when Java VM exits even if it’s killed by a SIGTERM or Ctrl-C.

But if you want to control the exact timing of shutdown, you can use Bootstrap.initializeCloseable() instead. It returns CloseableInjector which implements Injector and Closeable interfaces.

Bootstrap bootstrap = new Bootstrap()
    .addModules(...);

try (CloseableInjector injector = bootstrap.initializeCloseable()) {
    ...
}