通过调用静态工厂方法创建Bean

• 调用静态工厂方法创建Bean是将对象创建的过程封装到静态方法中，当客户端需要对象时，只需要简单的调用静态方法，而不关心创建对象的细节。
• 要声明通过静态方法创建Bean，需要在Bean的class属性里指定拥有改工厂的方法的类，同时在factory-method属性里指定工厂方法的名称，最后使用元素为该方法传递方法参数

// src/beans.xml
<beans>
    <bean id="car1" class="com.lijunyang.model.StaticCarFactory"
        factory-method="getCar">
        <constructor-arg value="audi" />
    </bean>
    <!-- 配置工厂实例 -->
    <bean id="carFactory" class="com.lijunyang.model.InstanceCarFactory" />
    <!-- 通过实例工厂获取Bean -->
    <bean id="car2" factory-bean="carFactory" factory-method="getCar">
        <constructor-arg value="ford" />
    </bean>
</beans>

// src/com/lijunyang/model/StaticCarFactory.java
public class StaticCarFactory {
    private static Map<String, Car> cars = new HashMap<String, Car>();
  static {
      cars.put("audi", new Car("audi", 300000));
      cars.put("ford", new Car("audi", 400000));
  }
  public static Car getCar(String name) {
      return cars.get(name);
  }
}
// src/com/lijunyang/model/InstanceCarFactory.java
public class InstanceCarFactory {
    private Map<String, Car> cars = null;
  public InstanceCarFactory() {
      cars = new HashMap<String, Car>();
    cars.put("audi", new Car("audi", 300000));
      cars.put("ford", new Car("audi", 400000));
  }
  public Car getCar(String name) {
      return cars.get(name);
  }
}
// src/com/lijunyang/test/Main.java
public class Main {
    public static main(String args[]) {
      ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml")
      Car car1 = (Car) ctx.getBean("car1");
    System.out.println(car1);
    Car car2 = (Car) ctx.getBean("car2");
    System.out.println(car2);
  }
}

FactoryBean

// org.springframework.beans.factory.FactoryBean.java具有3个方法
public interface FactoryBean<T> {
    T getObject() throws Exception;
    Class<?> getObjectType();
    boolean isSingleton();
}

// src/beans.xml
<beans>
    <!-- 通过FactoryBean 来配置Bean的实例
         class:指向FactoryBean的全类名
        property: 配置FactoryBean的属性
        但实际返回的实例确实 FactoryBean的getObject()方法返回的实例!
    -->
    <bean id="car" class="com.lijunyang.model.CarFactoryBean">
        <property name="brand" value="BMW" />
    </bean>
</beans>

// src/com/lijunyang/model/CarFactoryBean.java
import org.springframework.beans.factory.FactoryBean;
public class CarFactoryBean implements FactoryBean {
    private String brand;
    public setBrand(String brand) {
        this.brand = brand;
    }
    // 返回Bean对象
    @Override
    public Car getObject() throws Exception {
        return new Car(brand, 500000);
    }
    // 返回Bean的类型
    @Override 
    public Class<?> getObjectType() {
        return Car.class;
    }
    @Override
    public boolean isSingleton() {
        return true;
    }
}
// src/com/lijunyang/test/Main.java
public class Main {
    public static main(String args[]) {
      ApplicationContext ctx = new ClassPathXmlApplicationContext("beans.xml")
      Car car1 = (Car) ctx.getBean("car");
    System.out.println(car1);
  }
}