Java on Guice - Developer Day Slides.pdf

Java on Guice Dependency Injection the Java Way Bob Lee Copyright 2007 Google Inc.3 What can dependency injection do for me? ? Easier testing ? More decoupling ? Less boilerplate ? Better maintainability A Simple Example Copyright 2007 Google Inc.5 High Level Design ClientClientTest Service ServiceImpl Copyright 2007 Google Inc.6 We’ll examine 3 approaches... 1. The Factory Pattern 2. Dependency Injection by Hand 3. Dependency Injection with Guice Copyright 2007 Google Inc.7 One Variable ? From approach to approach, how does Client get a Service? Client Service Copyright 2007 Google Inc.8 A Few Constants public interface Service { void go(); } public class ServiceImpl implements Service { public void go() { // Some expensive stuff. ... } } Service ServiceImpl ? Regardless of the approach, Service stays the same: Copyright 2007 Google Inc.9 Mock Service public class MockService implements Service { private boolean gone = false; public void go() { gone = true; } public boolean isGone() { return gone; } } Service MockService ? We also need a mock implementation of Service which we can use to test clients: Approach #1: The Factory Pattern Copyright 2007 Google Inc.11 The Factory Client public class Client { public void go() { Service service = ServiceFactory.getInstance(); service.go(); } } Copyright 2007 Google Inc.12 Service Factory public class ServiceFactory { private ServiceFactory() {} private static Service instance = new ServiceImpl(); public static Service getInstance() { return instance; } public static void setInstance(Service service) { instance = service; } } Copyright 2007 Google Inc.13 A Unit Test public void testClient() { Service previous = ServiceFactory.getInstance(); try { final MockService mock = new MockService(); ServiceFactory.setInstance(mock); Client client = new Client(); client.go(); assertTrue(mock.isGone()); } finally { ServiceFacto