Spring Bean之間的關係
一、繼承(指的是配置上的繼承)
假設有一個Address類
package com.at.beans.relation;
public class Address {
private String city;
private String street;
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getStreet() {
return street;
}
public void setStreet(String street) {
this.street = street;
}
@Override
public String toString() {
return "Address [city=" + city + ", street=" + street + "]";
}
}
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 抽象bean:bean的abstract屬性爲true的Bean,這樣的bean不能被ioc容器實例化,只能被繼承配置
若某一個bean的class屬性沒有指定,則這個bean必須是抽象bean -->
<bean id="address" class="com.at.beans.relation.Address"
p:city="Beijing@@" p:street="WuDaoKou"></bean>
<bean id="address2" class="com.at.beans.relation.Address"
p:city="Beijing" p:street="SiDaoKou"></bean>
</beans>
測試代碼
package com.at.beans.relation;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class TestAddress {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-relation.xml");
Address address = (Address) ctx.getBean("address");
System.out.println(address);
Address address2 = (Address) ctx.getBean("address2");
System.out.println(address2);
}
}
五月 22, 2017 7:33:40 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@323f348a: startup date [Mon May 22 19:33:40 CST 2017]; root of context hierarchy
五月 22, 2017 7:33:40 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-relation.xml]
Address [city=Beijing@@, street=WuDaoKou]
Address [city=Beijing, street=SiDaoKou]
上面的程序雖然準確的輸出了,但是我們發現在bean配置文件中,兩個bean有相同的地方,所以我們可以通過如下繼承的配置文件來優化:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 抽象bean:bean的abstract屬性爲true的Bean,這樣的bean不能被ioc容器實例化,只能被繼承配置
若某一個bean的class屬性沒有指定,則這個bean必須是抽象 -->
<bean id="address" class="com.at.beans.relation.Address"
p:city="Beijing@@" p:street="WuDaoKou"></bean>
<bean id="address2" p:city="Beijing" p:street="SiDaoKou" parent="address"></bean>
</beans>
(1)Spring 允許繼承 bean 的配置, 被繼承的 bean 稱爲父 bean. 繼承這個父 Bean 的 Bean 稱爲子 Bean.
(2)子 Bean 從父 Bean 中繼承配置, 包括 Bean 的屬性配置。
(3)子 Bean 也可以覆蓋從父 Bean 繼承過來的配置。
(4)父 Bean 可以作爲配置模板, 也可以作爲 Bean 實例. 若只想把父 Bean 作爲模板, 可以設置 <bean> 的abstract 屬性爲 true, 這樣 Spring 將不會實例化這個 Bean。
(5)並不是 <bean> 元素裏的所有屬性都會被繼承. 比如: autowire, abstract 等。
(6)也可以忽略父 Bean 的 class 屬性, 讓子 Bean 指定自己的類, 而共享相同的屬性配置. 但此時 abstract 必須設爲 true 。
二、依賴
使用上文中繼承的Address類,除了這個類,還有Person類和Car類
Person類
package com.at.beans.relation;
public class Person {
private String name;
private Address address;
private Car car;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Address getAddress() {
return address;
}
public void setAddress(Address address) {
this.address = address;
}
public Car getCar() {
return car;
}
public void setCar(Car car) {
this.car = car;
}
public String toString() {
return "Person [name=" + name + ", address=" + address + ", car=" + car
+ "]";
}
}
package com.at.beans.relation;
public class Car {
private String brand;
private double price;
public 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;
}
@Override
public String toString() {
return "Car [brand=" + brand + ", price=" + price + "]";
}
}
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
<!-- 抽象bean:bean的abstract屬性爲true的Bean,這樣的bean不能被ioc容器實例化,只能被繼承配置
若某一個bean的class屬性沒有指定,則這個bean必須是抽象 -->
<bean id="address" class="com.at.beans.relation.Address"
p:city="Beijing@@" p:street="WuDaoKou"></bean>
<bean id="car" class="com.at.beans.relation.Car"
p:brand="Audi" p:price="400000"></bean>
<!-- 我們要求在配置bean時候,每一個person必須有一個關聯的car,也即是說person這個bean依賴於car這個bean,這個car的bean會在本bean實例化之前創建好 -->
<bean id="person" class="com.at.beans.relation.Person"
p:name="luoyepiaoxue2014" p:address-ref="address" depends-on="car">
<property name="car" ref="car"></property>
</bean>
</beans>
測試函數如下
package com.at.beans.relation;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class TestAddress {
public static void main(String[] args) {
ApplicationContext ctx = new ClassPathXmlApplicationContext("beans-relation.xml");
Address address = (Address) ctx.getBean("address");
System.out.println(address);
Car car = (Car) ctx.getBean("car");
System.out.println(car);
Person person = (Person) ctx.getBean("person");
System.out.println(person);
}
}
運行結果如下
五月 22, 2017 8:06:33 下午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
信息: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@725b1426: startup date [Mon May 22 20:06:33 CST 2017]; root of context hierarchy
五月 22, 2017 8:06:33 下午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
信息: Loading XML bean definitions from class path resource [beans-relation.xml]
Address [city=Beijing@@, street=WuDaoKou]
Car [brand=Audi, price=400000.0]
Person [name=luoyepiaoxue2014, address=Address [city=Beijing@@, street=WuDaoKou], car=Car [brand=Audi, price=400000.0]]
(1)Spring 允許用戶通過 depends-on 屬性設定 bean前置依賴的bean,前置依賴的 bean會在本 bean實例化之前創建好。
(2)如果前置依賴於多個 bean,則可以通過逗號,空格或的方式配置 bean的名稱。
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