Spring(十三):使用工廠方法來配置Bean的兩種方式(靜態工廠方法&實例工廠方法)
通過調用靜態工廠方法創建Bean
1)調用靜態工廠方法創建Bean是將對象創建的過程封裝到靜態方法中。當客戶端需要對象時,只需要簡單地調用靜態方法,而不需要關心創建對象的具體細節。
2)要聲明通過靜態方法創建的Bean,需要在Bean的class屬性中指定擁有該工廠的方法的類,同時需要在bean的factory-method屬性裏指定工廠方法的名稱。最後,使用<constructor-arg>元素為該方法傳遞方法參數。
示例:
第一步:創建一個java project,導入包:
第二步:創建com.dx.spring.beans.factory.Car.java,com.dx.spring.beans.factory.StaticCarFactory.java,bean-factory.xml:
Car.java
package com.dx.spring.beans.factory; public class Car { private String brand; private double price; public Car() { } public Car(String brand, double price) { super(); this.brand = brand; this.price = price; }View Codepublic String getBrand() { return brand; } public void setBrand(String brand) { this.brand = brand; } public double getPrice() { return price; } public void setPrice(double price) { this.price = price; } @Overridepublic String toString() { return "Car [brand=" + brand + ", price=" + price + "]"; } }
StaticCarFactory.java
package com.dx.spring.beans.factory; import java.util.HashMap; import java.util.Map; public class StaticCarFactory { private static Map<String, Car> cars = null; static { cars = new HashMap<>(); cars.put("audi", new Car("AUDI", 350000)); cars.put("ford", new Car("FORD", 200000)); } public static Car getCar(String key) { return cars.get(key); } }
bean-factory.xml
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"> <bean id="car1" class="com.dx.spring.beans.factory.StaticCarFactory" factory-method="getCar"> <constructor-arg name="key" value="audi"></constructor-arg> </bean> </beans>
第三步:添加Client.java測試類,並執行測試:
package com.dx.spring.beans.factory; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Client { public static void main(String[] args) { ApplicationContext ctx = new ClassPathXmlApplicationContext("bean-factory.xml"); Car car1 = (Car) ctx.getBean("car1"); System.out.println(car1); } }
發現執行結果成功返回car1:
Car [brand=AUDI, price=350000.0]
通過調用實例工廠方法創建Bean
1)實例工行方法:將對象的創建過程封裝到另外一個對象實例的方法裏,當客戶端需要請求對象時,只需要簡單的調用該實例方法而不需要關心對象的創建細節。
2)需要聲明通過實例工廠方法創建的Bean:
---- 在bean的factory-bean屬性裏指定擁有該工廠方法的Bean;
---- 在factory-method屬性裏指定該工廠方法的名稱;
---- 使用<constructor-arg>元素為工廠方法傳遞方法參數。
示例:(備註:基於上邊的示例修改)
第一步:創建com.dx.spring.beans.factory.InstanceCarFactory.java
package com.dx.spring.beans.factory; import java.util.HashMap; import java.util.Map; public class InstanceCarFactory { private Map<String, Car> cars = null; public InstanceCarFactory() { cars = new HashMap<>(); cars.put("audi", new Car("audi", 350000)); cars.put("ford", new Car("ford", 200000)); } public Car getCar(String key) { return cars.get(key); } }
第二步:在bean-factory.xml(spring bean配置文件)中添加如下配置:
<bean id="instanceCarFactory" class="com.dx.spring.beans.factory.InstanceCarFactory"></bean> <bean id="car2" factory-bean="instanceCarFactory" factory-method="getCar"> <constructor-arg name="key" value="ford"></constructor-arg> </bean>
第三步:修改Client.java,添加car2測試:
package com.dx.spring.beans.factory; import org.springframework.context.ApplicationContext; import org.springframework.context.support.ClassPathXmlApplicationContext; public class Client { public static void main(String[] args) { ApplicationContext ctx = new ClassPathXmlApplicationContext("bean-factory.xml"); Car car1 = (Car) ctx.getBean("car1"); System.out.println(car1); Car car2 = (Car) ctx.getBean("car2"); System.out.println(car2); } }
測試結果為:
Car [brand=AUDI, price=350000.0]
Car [brand=ford, price=200000.0]
Spring(十三):使用工廠方法來配置Bean的兩種方式(靜態工廠方法&實例工廠方法)