spring<bean>标签 IOC:控制反转

使用Bean创建对象：

在applicationContext.xml中

<?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="people" class="com.spring.pojo.People"/>
</beans>

测试：（读取applicationContext.xml时就已经创建类）

public class Test {
    public static void main(String[] args) {
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("applicationContext.xml");
        People people = applicationContext.getBean("people",People.class);
        System.out.println(people);
    }
}

有参构造：

    <bean id="people" class="com.spring.pojo.People">
        <constructor-arg name="id" index="0" value="1"></constructor-arg>
        <constructor-arg name="name" index="1" value="spring"></constructor-arg>
    </bean>

使用工厂设计模式创建对象：

1.静态工厂：（不需要new一个工厂对象）

工厂类：

public class PeopleFactory {
    public static People instancePeople() {
        return new People();
    }
}

配置bean:

<!-- 静态工厂 -->
    <bean id="people3" class="com.spring.pojo.PeopleFactory" factory-method="instancePeople"></bean>

1.实例工厂：（需要new一个工厂对象）

工厂类：

public class PeopleFactory {
    public People instancePeople() {
        return new People();
    }
}

配置bean:

<!-- 实例工厂 -->
    <bean id="peopleFactory" class="com.spring.pojo.PeopleFactory"></bean>
    <bean id="people2" factory-bean="peopleFactory" factory-method="instancePeople"></bean>

 在配置文件中给Bean对象的属性赋值：

    <bean id="people1" class="com.spring.pojo.People">
        <property name="id">
            <value>123</value>
        </property>
        <property name="name">
            <value>springName</value>
        </property>
    </bean>

等价写法：

    <bean id="people1" class="com.spring.pojo.People">
        <property name="id" value="123"></property>
        <property name="name" value="spring"></property>
    </bean>

spring内部使用了类的无参构造器和setXxx方法

<property>内各种标签示例：set,array,map,props(java.util.properties)....

<property name="sets">
            <set> 
                <value>1</value>
                <value>2</value>
                <value>3</value>
            </set>
        </property>
        <property name="strs">
            <array>
                <value>1</value>
                <value>2</value>
                <value>3</value>
            </array>
        </property>
        <property name="map">
            <map>
                <entry key="a" value="1"></entry>
                <entry key="b" value="2"></entry>
                <entry key="c" value="3"></entry>
            </map>
        </property>
        <property name="desk">
            <ref bean="desk" />
        </property>
        <property name="pros">
            <props>
                <prop key="a">1</prop>
            </props>
        </property>

DI ( 依赖注入，一个对象中包含另一个对象):在property中使用ref

<property name="desk">
            <ref bean="desk" />
</property>    


-------------------------------------------------
<bean id="desk" class="com.spring.pojo.Desk">
        <property name="id">
            <value>1</value>
        </property>
        <property name="name">
            <value>desk</value>
        </property>
</bean>