[spring]Bean注入——在XML中配置

Bean注入的方式有两种：

一、在XML中配置

• 属性注入
• 构造函数注入
• 工厂方法注入

二、使用注解的方式注入@Autowired,@Resource,@Required

本文首先讲解在XML中配置的注入方式

1.属性注入 

属性注入即通过setXxx()方法注入Bean的属性值或依赖对象，由于属性注入方式具有可选择性和灵活性高的优点，因此属性注入是实际应用中最常采用的注入方式。 

属性注入要求Bean提供一个默认的构造函数，并为需要注入的属性提供对应的Setter方法。Spring先调用Bean的默认构造函数实例化Bean对象，然后通过反射的方式调用Setter方法注入属性值。 

java代码：

public class LogonService implements BeanNameAware{
    private UserDao userDao;
    
    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    public UserDao getUserDao() {
        return userDao;
    }    
}

bean.xml配置：

<?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:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans 
         http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
         http://www.springframework.org/schema/context
         http://www.springframework.org/schema/context/spring-context-3.0.xsd"
       default-autowire="byName"
         >
   <bean id="userDao" class="com.baobaotao.anno.UserDao"/>
   <bean id="propertyId" class="com.baobaotao.anno.LogonService">
       //ref中的"userDao"为前一行的bean id
       <property name="userDao" ref="userDao"></property>
   </bean>
</beans>

2.构造方法注入（使用构造函数注入的前提是Bean必须提供带参数的构造函数）

java代码：

public class LogonService implements BeanNameAware{

    public LogonService(){}
    //使用构造函数注入的前提是Bean必须提供带参数的构造函数
    public LogonService(LogDao logDao, UserDao userDao) {
        this.logDao = logDao;
        this.userDao = userDao;
    }

    private LogDao logDao;

    private UserDao userDao;

    public void setUserDao(UserDao userDao) {
        this.userDao = userDao;
    }

    public void setLogDao(LogDao logDao) {
        this.logDao = logDao;
    }
    
    public LogDao getLogDao() {
        return logDao;
    }
    public UserDao getUserDao() {
        return userDao;
    }
    
}

bean.xml配置：

<?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:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/beans 
         http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
         http://www.springframework.org/schema/context
         http://www.springframework.org/schema/context/spring-context-3.0.xsd"
       default-autowire="byName">

    <bean id="logDao" class="com.baobaotao.anno.LogDao"/>
    <bean id="userDao" class="com.baobaotao.anno.UserDao"/>
   <bean class="com.baobaotao.anno.LogonService">
      <constructor-arg  ref="logDao"></constructor-arg>
      <constructor-arg ref="userDao"></constructor-arg>
   </bean>

</beans>

3.工厂方法注入

factory-bean：用于实例化工厂类；

factory-method：用于调用工厂类方法；

java代码：

public class CarFactory {
   //非静态方法
   public Car createCar(){
       Car car = new Car();
       car.setBrand("BMW");
       return car;
   }
   
   //静态方法
   public static Car createStaticCar(){
       Car car = new Car();
       return car;
   }
}

bean.xml配置：

对于非静态方法createCar(必须实例化工厂类（factory-bean）后才能调用工厂方法)的注入方式：

<?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-3.0.xsd">

    <!-- 工厂方法-->
    <bean id="carFactory" class="com.baobaotao.ditype.CarFactory" />
    <bean id="car5" factory-bean="carFactory" factory-method="createCar">
    </bean>


</beans>

对于静态方法createStaticCar（无须创建工厂类实例的情况下就可以调用工厂类方法）的注入方式：

<?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-3.0.xsd">

    <bean id="car6" class="com.baobaotao.ditype.CarFactory"
        factory-method="createStaticCar"></bean>

</beans>