XML配置里的Bean自动装配

Spring IOC容器可以自动装配Bean,需要做的仅仅是在<bean>的autowire属性里指定自动装配的模式,模式包含:byType,byName,constructor

举例:

常规用法:

Member.java

package com.dx.spring.bean.autowire;

public class Member {
private String name;
private int age;
private Address address;
private Work work; public String getName() {
return name;
} public void setName(String name) {
this.name = name;
} public int getAge() {
return age;
} public void setAge(int age) {
this.age = age;
} public Address getAddress() {
return address;
} public void setAddress(Address address) {
this.address = address;
} public Work getWork() {
return work;
} public void setWork(Work work) {
this.work = work;
} @Override
public String toString() {
return "Member [name=" + name + ", age=" + age + ", address=" + address + ", work=" + work + "]";
} }

Address.java

package com.dx.spring.bean.autowire;

public class Address {
private String city;
private String area; public String getCity() {
return city;
} public void setCity(String city) {
this.city = city;
} public String getArea() {
return area;
} public void setArea(String area) {
this.area = area;
} @Override
public String toString() {
return "Address [city=" + city + ", area=" + area + "]";
} }

Work.java

package com.dx.spring.bean.autowire;

public class Work {
private String company;
private int money; public String getCompany() {
return company;
} public void setCompany(String company) {
this.company = company;
} public int getMoney() {
return money;
} public void setMoney(int money) {
this.money = money;
} @Override
public String toString() {
return "Work [company=" + company + ", money=" + money + "]";
} }

bean-autowire.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" 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.dx.spring.bean.autowire.Address">
<property name="city" value="beijing"></property>
<property name="area" value="huilongguan"></property>
</bean> <bean id="work" class="com.dx.spring.bean.autowire.Work">
<property name="company" value="baidu"></property>
<property name="money" value="80000"></property>
</bean> <bean id="member" class="com.dx.spring.bean.autowire.Member"
p:name="Rose" p:age="27" p:address-ref="address" p:work-ref="work"></bean> </beans>

Main.java

package com.dx.spring.bean.autowire;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext; public class Main {
public static void main(String[] args) {
ApplicationContext cxt = new ClassPathXmlApplicationContext("bean-autowire.xml");
Member member = (Member) cxt.getBean("member");
System.out.println(member);
}
}

测试打印结果:

Member [name=Rose, age=27, address=Address [city=beijing, area=huilongguan], work=Work [company=baidu, money=80000]]

1)byName(根据名称自动装配):

必须将目标Bean的名称和属性名设置的完成相同。

修改常规用法中的bean-autowire.xml:

    <bean id="member" class="com.dx.spring.bean.autowire.Member"
p:name="Rose" p:age="27" autowire="byName"></bean>

此时,如果修改work bean的名字为work2

    <bean id="work2" class="com.dx.spring.bean.autowire.Work">
<property name="company" value="baidu"></property>
<property name="money" value="80000"></property>
</bean>

则Main.java调用时,无法匹配上work属性:

Member [name=Rose, age=27, address=Address [city=beijing, area=huilongguan], work=null]

2)byType(根据类型自动装配):

若IOC容器中有多个与目标Bean类型一致的Bean,在这种情况下,Spring将无法判定哪个Bean最合适该属性,所以不能执行自动装配。

    <bean id="member" class="com.dx.spring.bean.autowire.Member"
p:name="Rose" p:age="27" autowire="byType"></bean>

此时如果在bean-autowire.xml中包含多个Work的bean时:

<?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.dx.spring.bean.autowire.Address">
<property name="city" value="beijing"></property>
<property name="area" value="huilongguan"></property>
</bean> <bean id="work" class="com.dx.spring.bean.autowire.Work">
<property name="company" value="baidu"></property>
<property name="money" value="80000"></property>
</bean>
<bean id="work3" class="com.dx.spring.bean.autowire.Work">
<property name="company" value="jd"></property>
<property name="money" value="90000"></property>
</bean> <bean id="member" class="com.dx.spring.bean.autowire.Member"
p:name="Rose" p:age="27" autowire="byType"></bean> </beans>

此时运行时,将会抛出异常:

Exception in thread "main" org.springframework.beans.factory.UnsatisfiedDependencyException: 
Error creating bean with name 'member' defined in class path resource [bean-autowire.xml]:
Unsatisfied dependency expressed through bean property 'work';
nested exception is org.springframework.beans.factory.NoUniqueBeanDefinitionException:
No qualifying bean of type 'com.dx.spring.bean.autowire.Work' available: expected single matching bean but found 2: work,work3

3)constructor(通过构造器自动装配):

当Bean中存在多个构造器时,此种自动装配方式将会很复杂,不推荐使用。

XML配置里的Bean自动装配缺点

1)在bean配置文件里设置autowire属性进行自动装配将会装配bean所有属性。然而,若只希望装配个别属性是,autowire属性就不够灵活了。

2)autowire属性要么根据类型自动装配,要么根据名称自动装配,不能两者兼而有之。

3)一般情况下,在实际项目中很少使用自动装配功能,因为和自动装配功能所带来的好处比起来,明确清晰的配置文档更有说服力。

bean之间的关系:继承;依赖。

bean之间的关系:继承

1)Spring允许继承bean的配置,被集成的bean称为父bean。继承这个父bean的bean称为子bean。

2)子bean从父bean中继承配置,包括bean的属性配置

3)父bean可以作为配置模版,也可以作为bean实例。若只想把父bean作为模版,可以设置<bean>的abstract属性为true,这样Spring将不会实例化这个bean。

4)并不是<bean>元素里的所有属性都会被继承。比如:autowire,abstract等。

5)也可以忽略父bean的class属性,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。

常规示例:有两个address bean,此时用法如下:

bean-relation-dependence.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" 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.dx.spring.beans.relation_dependence.Address"
p:city="Beijing" p:street="HuiLongGuan">
</bean>
<bean id="address2" class="com.dx.spring.beans.relation_dependence.Address"
p:city="Beijing" p:street="ZhongGuanCun">
</bean>
</beans>

Adress.java

package com.dx.spring.beans.relation_dependence;

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 + "]";
} }

Client.java

package com.dx.spring.beans.relation_dependence;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext; public class Client {
public static void main(String[] args) {
ApplicationContext cxt = new ClassPathXmlApplicationContext("bean-relation-dependence.xml");
Address address = (Address) cxt.getBean("address");
System.out.println(address); Address address2 = (Address) cxt.getBean("address2");
System.out.println(address2);
}
}

a)实际上address2是可以通过继承address bean的,修改bean-relation-dependence.xml为如下:

<?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.dx.spring.beans.relation_dependence.Address"
p:city="Beijing" p:street="HuiLongGuan">
</bean> <bean id="address2" p:street="ZhongGuanCun" parent="address">
</bean> </beans>

b)可以把父类bean配置为一个模版(抽象)bean:

<?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="Beijing" p:street="HuiLongGuan" class="com.dx.spring.beans.relation_dependence.Address" abstract="true">
</bean> <bean id="address2" p:street="ZhongGuanCun"
class="com.dx.spring.beans.relation_dependence.Address" parent="address">
</bean> </beans>

此时address这个bean是不能够被实例化的,否则会抛出异常。

package com.dx.spring.beans.relation_dependence;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext; public class Client {
public static void main(String[] args) {
ApplicationContext cxt = new ClassPathXmlApplicationContext("bean-relation-dependence.xml");
// 当把address bean的属性设置abstract="true"时,该bean不能被实例化,否则会抛出异常。
// Address address = (Address) cxt.getBean("address");
// System.out.println(address); Address address2 = (Address) cxt.getBean("address2");
System.out.println(address2);
}
}

c)也可以把父类bean配置为一个无class属性的模版(抽象)bean:

<?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="Beijing" p:street="HuiLongGuan" abstract="true">
</bean>
<bean id="address2" p:street="ZhongGuanCun"
class="com.dx.spring.beans.relation_dependence.Address" parent="address">
</bean>
</beans>

备注:如果一个bean的class属性没有被指定,则该bean必须为一个抽象bean。

bean之间的关系:依赖

1)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实例化之前创建好。

2)如果前置依赖于多个bean,则可以通过逗号、空格的方式配置bean的名称

bean-relation-dependence.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" 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="Beijing" p:street="HuiLongGuan"
abstract="true">
</bean> <bean id="address2" p:street="ZhongGuanCun"
class="com.dx.spring.beans.relation_dependence.Address" parent="address">
</bean> <bean id="car" class="com.dx.spring.beans.relation_dependence.Car"
p:brand="Audi" p:corp="Shanghai" p:price="400000" p:maxSpeed="260"></bean> <bean id="person" class="com.dx.spring.beans.relation_dependence.Person"
p:name="RoseGun" p:age="35" p:address-ref="address2" depends-on="car"></bean>
</beans>

此时,如果depends-on的car不存在,则会抛出异常。

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