Dependency Injection & Inversion of Control

The presentation demystifies the concept of dependency injection and inversion of control using a sample java application using Spring.

Transcript

1. Which is which?
   @charlesmuchene
   IoC DI
   !
   

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2. Agenda
   • Dependency Injection
   • Inversion of Control
   

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3. Dependency Injection
   “A 25-dollar term for a 5-cent concept”
   

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4. Dependency Injection
   “A 25-dollar term for a 5-cent concept”
   a pattern (or process) of providing the
   dependencies to a component
   

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5. Task
   

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6. Task
   public class User {
   private String name;
   private int age;
   public User(String name, int age) {
   this.name = name;
   this.age = age;
   }
   

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7. Task
   User Service
   User Data Access Object
   

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8. User Service
   public interface UserService {
   void save(User user);
   User findOne(long id);
   }
   

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9. User DAO
   public interface UserDao {
   void save(User user);
   User findOne(long id);
   }
   

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10. Main
    User user = new User("Charles", 24);
    System.out.println("******************************");
    User fetchedUser = userService.findOne(-1);
    System.out.println(fetchedUser);
    UserService userService = new UserServiceImpl();
    userService.save(user);
    

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11. User Service Impl
    public class UserServiceImpl implements UserService {
    @Override
    public void save(User user) {
    userDao.save(user);
    }
    ...
    }
    Dependency
    private UserDao userDao = new UserDaoImpl();
    

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12. User Service Impl
    public class UserServiceImpl implements UserService {
    private UserDao userDao;
    public UserServiceImpl(UserDao userDao) {
    this.userDao = userDao;
    }
    @Override
    public void save(User user) {
    userDao.save(user);
    }
    ...
    }
    

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13. Main
    User user = new User("Charles", 24);
    System.out.println("******************************");
    User fetchedUser = userService.findOne(-1);
    System.out.println(fetchedUser);
    UserDao userDao = new UserDaoImpl();
    UserService userService = new UserServiceImpl(userDao);
    userService.save(user);
    

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14. User Service Impl
    public class UserServiceImpl implements UserService {
    private UserDao userDao;
    public UserServiceImpl(UserDao userDao) {
    this.userDao = userDao;
    }
    @Override
    public void save(User user) {
    userDao.save(user);
    }
    ...
    }
    

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15. User Service Impl
    @Service
    public class UserServiceImpl implements UserService {
    @Autowired
    private UserDao userDao;
    @Override
    public void save(User user) {
    userDao.save(user);
    }
    ...
    }
    

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16. Main
    User user = new User("Charles", 24);
    System.out.println("******************************");
    User fetchedUser = userService.findOne(-1);
    System.out.println(fetchedUser);
    UserService userService = new UserServiceImpl();
    userService.save(user);
    

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17. Main: Spring
    User user = new User("Charles", 24);
    System.out.println("******************************");
    User fetchedUser = userService.findOne(-1);
    System.out.println(fetchedUser);
    String contextLocation = "context/applicationContext.xml";
    ApplicationContext context = new
    ClassPathXmlApplicationContext(contextLocation);
    UserService userService = context.getBean(UserService.class);
    userService.save(user);
    

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18. IoC Container
    // Load up config
    String contextLocation = "context/applicationContext.xml";
    ApplicationContext context = new
    ClassPathXmlApplicationContext(contextLocation);
    // Ask IoC for instance (bean)
    UserService userService = context.getBean(UserService.class);
    // Use the (wired-up) instance
    userService.save(user);
    

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19. IoC Container
    • Creates
    • Wires together
    • Manages (creation -> destruction)
    

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20. Inversion of Control
    Programming principle
    principle of delegating the creation,
    configuration and lifecycle management
    of objects to another component or
    framework
    

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21. In Spring, Inversion of Control is
    achieved through Dependency Injection.
    

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22. IoC DI
    !
    
    

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23. Resources
    • https://github.com/charlesmuchene/di-spring
    

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24. charlesmuchene
    

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