Spring的初体验-2

一. Spring 自动装配（AutoWire）

实体bean

public class People {
  private int id;
  private String name;
  private int age;
  private Dog dog;
  ......
    public People(Dog dog) {
    this.dog = dog;
  }
  ......
}      

1. 通过配置 default-autowire 属性，Spring IoC 容器可以自动为程序注入 bean。默认是 no，不启用自动装配机制。

<?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"
        default-autowire="byName">      

1. default-autowire 的类型

• byName：通过名称进行自动匹配；

<?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"
        default-autowire="byName">

    根据bean中的属性名（dog）来自动装配
    <bean id="dog" class="com.bee.entity.Dog">
        <property name="name" value="Jack"></property>
    </bean>
    
    bean中的属性名（dog）不匹配，不自动装配之。
    <bean id="dog2" class="com.bee.entity.Dog">
        <property name="name" value="Tom"></property>
    </bean>
    
    <bean id="people" class="com.bee.entity.People">
        <property name="id" value="1"></property>
        <property name="name" value="张麻子"></property>
        <property name="age" value="11"></property>
    </bean>
    
</beans>      

• byType：根据类型进行自动匹配；

<?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"
        default-autowire="byType">

    根据bean中的属性类型（Dog）来自动装配
    <bean id="dog" class="com.bee.entity.Dog">
        <property name="name" value="Jack"></property>
    </bean>
    
    如果保留下边的配置，那么bean中的属性类型（Dog）在本配置文件中就有多个匹配，Spring将报错。
    <!--
    <bean id="dog2" class="com.bee.entity.Dog">
        <property name="name" value="Tom"></property>
    </bean>
    -->
    
    <bean id="people" class="com.bee.entity.People">
        <property name="id" value="1"></property>
        <property name="name" value="张麻子"></property>
        <property name="age" value="11"></property>
    </bean>
    
</beans>      

• constructor：和 byType 类似，只不过它是根据构造方法注入而言的，根据类型，自动注入；

<?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"
        default-autowire="constructor">

    根据bean中的与属性相关的构造方法（public People(Dog dog) {}）来自动装配（还需参考参数类型）
    <bean id="dog" class="com.bee.entity.Dog">
        <property name="name" value="Jack"></property>
    </bean>

    <bean id="people" class="com.bee.entity.People">
        <property name="id" value="1"></property>
        <property name="name" value="张麻子"></property>
        <property name="age" value="11"></property>
    </bean>
    
</beans>      

1. 建议：自动装配机制慎用，它屏蔽了装配细节，容易产生潜在的错误。

二. 方法注入

Spring bean 作用域默认是单例 singleton，可以通过配置prototype实现多实例。

方法注入需使用关键字lookup-method。

<?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="dog" class="com.bee.entity.Dog" scope="prototype">
        <property name="name" value="Jack"></property>
    </bean>
    
    <bean id="people1" class="com.bee.entity.People">
        <property name="id" value="1"></property>
        <property name="name" value="张麻子"></property>
        <property name="age" value="18"></property>
        <lookup-method name="getDog" bean="dog"/>
    </bean>
    
</beans>      

实体bean

public abstract class People {

  private int id;
  private String name;
  private int age;
  private Dog dog;
  ......
  public abstract Dog getDog();
  ......
}      

三. 方法替换

public class People {
  private int id;
  private String name;
  private int age;
  private Dog dog;
  ......
  public Dog getDog() {
    Dog dog=new Dog();
    dog.setName("Jack");
    return dog;
  }

}

public class People2 implements MethodReplacer {
  @Override
  public Object reimplement(Object arg0, Method arg1, Object[] arg2)
      throws Throwable {
    Dog dog=new Dog();
    dog.setName("Tom");
    return dog;
  }
}      

<?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.bee.entity.People">
        <property name="id" value="1"></property>
        <property name="name" value="张麻子"></property>
        <property name="age" value="28"></property>
        <replaced-method name="getDog" replacer="people2"></replaced-method>
    </bean>
    
    <bean id="people2" class="com.bee.entity.People2"></bean>
</beans>      

四. bean 之间的关系

<?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="weapon" class="com.bee.entity.Weapon">
        <property name="name" value="血滴子"></property>
    </bean>
        
    <bean id="spider" class="com.bee.entity.Spider" abstract="true">
        <property name="ablility" value="蛛丝"></property>
        <property name="energy" value="90"></property>
    </bean>
    
                   继承——parent    依赖——depends-on
    <bean id="spiderMan" parent="spider" depends-on="autority">
        <property name="id" value="1"></property>
        <property name="name" value="张麻子"></property>
    </bean>
    
    <bean id="spiderGirl" parent="spider">
        <property name="id" value="2"></property>
        <property name="name" value="王二丫"></property>
        <property name="energy" value="100"></property>  重写属性
        <property name="weapon" ref="weapon"></property> 引用——ref
    </bean>
    
    <bean id="autority" class="com.bee.service.Authority"></bean>
</beans>      

五. bean 作用范围

1. singleton Spring IoC 容器中仅有一个 Bean 实例，Bean 以单例的方式存在。
2. prototype 每次从容器中调用 Bean 时，都返回一个新的实例。
3. request 每次 HTTP 请求都会创建一个新的 Bean。
4. session 同一个 HTTP Session 共享一个 Bean。
5. global session 同一个全局 Session 共享一个 Bean，一般用于 Portlet 应用环境。
6. application 同一个 Application 共享一个 Bean。