Spring学习--Bean 之间的关系

Bean 之间的关系：继承、依赖。

Bean 继承：

• Spring 允许继承 bean 的配置 , 被继承的 bean 称为父 bean , 继承这个父 bean 的 bean 称为子 bean。
• 子 bean 从父 bean 中继承配置 , 包括 bean 的属性配置。
• 子 bean 也可以覆盖从父 bean 继承过来的配置。
• 父 bean 可以作为配置模板 , 也可以作为 bean 实例。若只想把父 bean 作为模板 , 可以设置 <bean> 的 abstract 属性为 true , 这样 IOC容器将不会实例这个 bean。
• 并不是 <bean> 元素里的所有属性都会被继承。比如： autowire , abstract 等。
• 父 bean 的 class 属性可以忽略 , 让子 bean 指定自己的类 , 而共享相同的属性配置。但此时 abstract 必须设为 true。

<?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">

    <bean id="address" class="com.itdoc.spring.extendsinfo.Address" p:city="DaLian" p:street="ShaHeKou"/>

    <bean id="address1" class="com.itdoc.spring.extendsinfo.Address" p:street="GanJingZi" parent="address"/>

</beans>

package com.itdoc.spring.extendsinfo;

/**
 * http://www.cnblogs.com/goodcheap
 *
 * @author: Wáng Chéng Dá
 * @create: 2017-03-01 20:48
 */
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 + '\'' +
                '}';
    }
}

package com.itdoc.spring.extendsinfo;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * http://www.cnblogs.com/goodcheap
 *
 * @author: Wáng Chéng Dá
 * @create: 2017-03-01 20:55
 */
public class Main {

    public static void main(String[] args) {
        ApplicationContext app = new ClassPathXmlApplicationContext("beans_extends.xml");
        Address address = (Address) app.getBean("address");
        System.out.println(address);

        System.out.println("-------------------");
        address = (Address) app.getBean("address1");
        System.out.println(address);
        
    }
}

 

控制台输出：

Address{city='DaLian', street='ShaHeKou'}
-------------------
Address{city='DaLian', street='GanJingZi'}

<?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">

    <bean id="address" class="com.itdoc.spring.extendsinfo.Address" p:city="DaLian" p:street="ShaHeKou" abstract="true"/>

    <bean id="address1" class="com.itdoc.spring.extendsinfo.Address" p:street="GanJingZi" parent="address"/>

</beans>

 

控制台输出：

Exception in thread "main" org.springframework.beans.factory.BeanIsAbstractException: Error creating bean with name 'address': Bean definition is abstract
at org.springframework.beans.factory.support.AbstractBeanFactory.checkMergedBeanDefinition(AbstractBeanFactory.java:1321)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:285)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1081)
at com.itdoc.spring.extendsinfo.Main.main(Main.java:16)

原因：address 成为了模板 bean , 不可以实例化。

<?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">

    <bean id="address" p:city="DaLian" p:street="ShaHeKou"/>

    <bean id="address1" class="com.itdoc.spring.extendsinfo.Address" p:street="GanJingZi" parent="address"/>

</beans>

package com.itdoc.spring.extendsinfo;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * http://www.cnblogs.com/goodcheap
 *
 * @author: Wáng Chéng Dá
 * @create: 2017-03-01 20:55
 */
public class Main {

    public static void main(String[] args) {
        ApplicationContext app = new ClassPathXmlApplicationContext("beans_extends.xml");
        Address address = (Address) app.getBean("address1");
        System.out.println(address);

    }
}

 

控制台输出：

警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'address' defined in class path resource [beans_extends.xml]: Instantiation of bean failed; nested exception is java.lang.IllegalStateException: No bean class specified on bean definition
Exception in thread "main" org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'address' defined in class path resource [beans_extends.xml]: Instantiation of bean failed; nested exception is java.lang.IllegalStateException: No bean class specified on bean definition
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1155)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1099)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:513)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:483)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:306)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:302)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:197)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:761)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:866)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:542)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:139)
at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:83)
at com.itdoc.spring.extendsinfo.Main.main(Main.java:15)
Caused by: java.lang.IllegalStateException: No bean class specified on bean definition
at org.springframework.beans.factory.support.AbstractBeanDefinition.getBeanClass(AbstractBeanDefinition.java:372)
at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:66)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1147)
... 13 more

原因：父 bean 中的 class 属性忽略 , 该 bean 必须是 abstract="true" 的。

 

Bean 依赖：

• Spring 允许用户通过 depends-on 属性设定 bean 前置依赖的 bean , 前置依赖的 bean 会在本 bean 实例化前创建好。
• 如果前置依赖于多个 bean , 则可以通过逗号或空格的方式配置 bean 的名称。

<?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">

    <bean id="person" class="com.itdoc.spring.extendsinfo.Person" p:name="华崽儿" p:car-ref="car" p:address-ref="address"/>
    <bean id="address" class="com.itdoc.spring.extendsinfo.Address" p:city="DaLian" p:street="ShaHeKou"/>
    <bean id="car" class="com.itdoc.spring.beans.Car" p:brand="8手奥拓" p:price="3000" p:maxSpeed="120"/>

</beans>

package com.itdoc.spring.extendsinfo;

import com.itdoc.spring.beans.Car;

/**
 * http://www.cnblogs.com/goodcheap
 *
 * @author: Wáng Chéng Dá
 * @create: 2017-03-01 20:47
 */
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 Person() {
        System.out.println("I am Person Constructor...");
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", address=" + address +
                ", car=" + car +
                '}';
    }
}

package com.itdoc.spring.extendsinfo;

/**
 * http://www.cnblogs.com/goodcheap
 *
 * @author: Wáng Chéng Dá
 * @create: 2017-03-01 20:48
 */
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;
    }

    public Address() {
        System.out.println("I am Address Constructor...");
    }

    @Override
    public String toString() {
        return "Address{" +
                "city='" + city + '\'' +
                ", street='" + street + '\'' +
                '}';
    }
}

package com.itdoc.spring.beans;

/**
 * 集合中的对象
 * http://www.cnblogs.com/goodcheap
 *
 * @author: Wáng Chéng Dá
 * @create: 2017-02-28 19:56
 */
public class Car {

    private String brand;

    private double price;

    private int maxSpeed;

    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;
    }

    public int getMaxSpeed() {
        return maxSpeed;
    }

    public void setMaxSpeed(int maxSpeed) {
        this.maxSpeed = maxSpeed;
    }

    public Car() {
        System.out.println("I am Car Constructor...");
    }

    @Override
    public String toString() {
        return "Car{" +
                "brand='" + brand + '\'' +
                ", price=" + price +
                ", maxSpeed=" + maxSpeed +
                '}';
    }
}

package com.itdoc.spring.extendsinfo;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

/**
 * http://www.cnblogs.com/goodcheap
 *
 * @author: Wáng Chéng Dá
 * @create: 2017-03-01 20:55
 */
public class Main {

    public static void main(String[] args) {
        ApplicationContext app = new ClassPathXmlApplicationContext("beans_extends.xml");
        Person person = (Person) app.getBean("person");
        System.out.println(person);

    }
}

 

控制台输出：

I am Person Constructor...
I am Address Constructor...
I am Car Constructor...
Person{name='华崽儿', address=Address{city='DaLian', street='ShaHeKou'}, car=Car{brand='8手奥拓', price=3000.0, maxSpeed=120}}

<?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">

    <bean id="person" class="com.itdoc.spring.extendsinfo.Person" p:name="华崽儿" p:car-ref="car" p:address-ref="address" depends-on="car, address"/>

    <bean id="address" class="com.itdoc.spring.extendsinfo.Address" p:city="DaLian" p:street="ShaHeKou"/>

    <bean id="car" class="com.itdoc.spring.beans.Car" p:brand="8手奥拓" p:price="3000" p:maxSpeed="120"/>

</beans>

 

控制台输出：

I am Car Constructor...
I am Address Constructor...
I am Person Constructor...
Person{name='华崽儿', address=Address{city='DaLian', street='ShaHeKou'}, car=Car{brand='8手奥拓', price=3000.0, maxSpeed=120}}

根据控制台输出我们不难看出 bean 的初始化顺序发生了改变 , 前置依赖的 bean 会在本 bean 实例化前创建好。