Spring的初體驗-2

一. Spring 自動裝配（AutoWire）

實體bean

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

1. 通過配置 default-autowire 屬性，Spring IoC 容器可以自動為程式注入 bean。預設是 no，不啟用自動裝配機制。

<?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 的類型

• byName：通過名稱進行自動比對；

<?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">

    根據bean中的屬性名（dog）來自動裝配
    <bean id="dog" class="com.bee.entity.Dog">
        <property name="name" value="Jack"></property>
    </bean>
    
    bean中的屬性名（dog）不比對，不自動裝配之。
    <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="張麻子"></property>
        <property name="age" value="11"></property>
    </bean>
    
</beans>      

• byType：根據類型進行自動比對；

<?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">

    根據bean中的屬性類型（Dog）來自動裝配
    <bean id="dog" class="com.bee.entity.Dog">
        <property name="name" value="Jack"></property>
    </bean>
    
    如果保留下邊的配置，那麼bean中的屬性類型（Dog）在本配置檔案中就有多個比對，Spring将報錯。
    <!--
    <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="張麻子"></property>
        <property name="age" value="11"></property>
    </bean>
    
</beans>      

• constructor：和 byType 類似，隻不過它是根據構造方法注入而言的，根據類型，自動注入；

<?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">

    根據bean中的與屬性相關的構造方法（public People(Dog dog) {}）來自動裝配（還需參考參數類型）
    <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="張麻子"></property>
        <property name="age" value="11"></property>
    </bean>
    
</beans>      

1. 建議：自動裝配機制慎用，它屏蔽了裝配細節，容易産生潛在的錯誤。

二. 方法注入

Spring bean 作用域預設是單例 singleton，可以通過配置prototype實作多執行個體。

方法注入需使用關鍵字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="張麻子"></property>
        <property name="age" value="18"></property>
        <lookup-method name="getDog" bean="dog"/>
    </bean>
    
</beans>      

實體bean

public abstract class People {

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

三. 方法替換

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="張麻子"></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 之間的關系

<?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="蛛絲"></property>
        <property name="energy" value="90"></property>
    </bean>
    
                   繼承——parent    依賴——depends-on
    <bean id="spiderMan" parent="spider" depends-on="autority">
        <property name="id" value="1"></property>
        <property name="name" value="張麻子"></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>  重寫屬性
        <property name="weapon" ref="weapon"></property> 引用——ref
    </bean>
    
    <bean id="autority" class="com.bee.service.Authority"></bean>
</beans>      

五. bean 作用範圍

1. singleton Spring IoC 容器中僅有一個 Bean 執行個體，Bean 以單例的方式存在。
2. prototype 每次從容器中調用 Bean 時，都傳回一個新的執行個體。
3. request 每次 HTTP 請求都會建立一個新的 Bean。
4. session 同一個 HTTP Session 共享一個 Bean。
5. global session 同一個全局 Session 共享一個 Bean，一般用于 Portlet 應用環境。
6. application 同一個 Application 共享一個 Bean。