Dagger for a Servlet Example

BaseServlet.java

import dagger.ObjectGraph;

public abstract class BaseServlet extends HttpServlet {
	private ObjectGraph graph;
	
	/**
	 * inits the Servlet with the object graph from Dagger
	 * if you override this, be sure your implementation calls that of this super class
	 * 
	 * @param config
	 */
	public void init(ServletConfig config) {
		this.graph = (ObjectGraph) config.getServletContext().getAttribute(DIListener.ATTR_OBJECT_GRAPH);
	}
	
	/**
	 * used to get injected instances
	 * 
	 * @param arg
	 * @return
	 */
	public <T> T get(Class<T> arg) {
		return this.getObjectGraph().get(arg);
	}
}

DIListener.java

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;

import dagger.ObjectGraph;

/**
 * DaggerListener - inits objectgraph and sets it in ServletContext, so it can be accessed in servlet's init() method
 * 
 * @author Erik Schultink <erik@engetc.com>
 */
public class DIListener implements ServletContextListener {
	
	static final public String ATTR_OBJECT_GRAPH = "ObjectGraph";		
	
	ObjectGraph objectGraph;
	
	/***
	 * called when servlet initialized
	 * 
	 * @see javax.servlet.ServletContextListener#contextInitialized(javax.servlet.ServletContextEvent)
	 */
	@Override
	public void contextInitialized(ServletContextEvent sce) {
	  
	  //your object graph is initialized here, from your Dagger Module(s)
		this.objectGraph = ObjectGraph.create(new ProductionModule());
		
		sce.getServletContext().setAttribute(ATTR_OBJECT_GRAPH, this.objectGraph);
	}

	/**
	 * no-op
	 * 
	 * @see javax.servlet.ServletContextListener#contextDestroyed(javax.servlet.ServletContextEvent)
	 */
	@Override
	public void contextDestroyed(ServletContextEvent sce) {
		//do nothing
	}
}

ExampleServlet.java

public class ExampleServlet extends BaseServlet {
  
  //some dependency that the servlet needs
  private Dependency dependency;
  
  public void init(ServletConfig config) {
    super.init(config);
    
    this.dependency = this.get(Dependency.class);
  }
  
  //you're now free to implement doGet()/etc as you wish
  //dependency should be defined, with the binding provided by the Dagger Module
  ...
}