========
实例工厂
========

既然可以通过FactoryBean创建复杂对象，为什么还需要实例工厂？
- 我们的代码必须实现FactoryBean接口，这实际上一种来自Spring框架侵入
- 在现有的遗留系统中已有这样的类
  public class ConnectionFactory {
    public Connection getObject() {
        ...
        return conn;
    }
  }
  但它并不是FactoryBean接口的实现类，且存在于以.class文件而非.java文件中

/src/main/java/cn/tedu/injection/ConnectionFactory.java：

public class ConnectionFactory {
    public Connection getConnection() {
        Connection conn = null;

        try {
            Class.forName("com.mysql.jdbc.Driver");
            conn = DriverManager.getConnection(
                "jdbc:mysql://localhost:3306/springdb?useSSL=false",
                "root", "123456");
        }
        catch (ClassNotFoundException | SQLException e) {
            e.printStackTrace();
        }

        return conn;
    }
}

/src/main/resources/applicationContext.xml：

<bean id="connFactory" class="cn.tedu.injection.ConnectionFactory"/>
<bean id="conn" factory-bean="connFactory" factory-method="getConnection"/>

                _________________________________________
               |                                         v
<bean id="connFactory" class="cn.tedu.injection.ConnectionFactory"/>
               ^___________________                      |_______
                                   |                             v
<bean id="conn" factory-bean="connFactory" factory-method="getConnection"/>
           ^|______________________^                             |
 __________|    _________________________________________________|
|              v
| Connection conn = applicationContext.getBean(
|     "conn", Connection.class);
|________|

例程：Injection