Learning IoC

Inversion of Control

1. Hollywood's principle: Don't call me, I'll call you
2. Instead of lookup the resource we want. we leave it to the framework

 

Traditional 'pull approach'

Context ctx = new InitialContext();
AccountEJB accountEJB = (AccountEJB) ctx.lookup("java:comp/env/ejb/AccountEJB");

Drawback:
1. client codes tied to a specific implementation
2. codes are difficult to test (must be tested within the container)

 

IoC Approach:

private Account accountManager;
public void setAccountManager(Account account) {
      this.accountManager = account;
}

Addvantage:
1. client code does not need to deal with component discovery
2. client code isn't tied to any specific implementations
3. codes can Unit Testing?individually with mock object

 

3 Types:

Type 1: interface injection?

dependency satisfied by interfaces it implemented

Type 2: setter injection

dependency satisfied by JavaBean properties and its setter exposed by a component

 Type 3: constructor injection

dependedcy satisfied by the component's constructor