Spring学习--依赖注入的方式

Spring 依赖注入

1. 属性注入(最常使用)
2. 构造函数注入
3. 工厂方法注入(很少使用，不推荐)

属性注入

通过 setter 方法注入 Bean 的属性值或依赖的对象 , 使用<property> 元素 , 使用 name 属性指定 Bean 的属性名称 , value 属性或 <value> 子节点指定属性值。

 <?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="person" class="com.itdjx.spring.dependency.injection.Person">
         <property name="name" value="张三" />
         <property name="age" value="23" />
         <property name="sex" value="男" />
     </bean>

 </beans>

 package com.itdjx.spring.dependency.injection;

 /**
  * 属性注入
  *
  * @author Wáng Chéng Dá
  * @create 2017-02-28 15:14
  */
 public class Person {

     private String name;

     private String sex;

     private int age;

     public String getName() {
         return name;
     }

     public void setName(String name) {
         this.name = name;
     }

     public String getSex() {
         return sex;
     }

     public void setSex(String sex) {
         this.sex = sex;
     }

     public int getAge() {
         return age;
     }

     public void setAge(int age) {
         this.age = age;
     }

     @Override
     public String toString() {
         return "Person{" +
                 "name='" + name + '\'' +
                 ", sex='" + sex + '\'' +
                 ", age=" + age +
                 '}';
     }
 }

 package com.itdjx.spring.dependency.injection;

 import org.springframework.context.ApplicationContext;
 import org.springframework.context.support.ClassPathXmlApplicationContext;

 /**
  * 依赖注入main
  *
  * @author Wáng Chéng Dá
  * @create 2017-02-28 15:16
  */
 public class MainIOC {

     public static void main(String[] args) {
         ApplicationContext app = new ClassPathXmlApplicationContext("applicationConfig.xml");
         Person person = (Person) app.getBean("person");
         System.out.println(person);
     }
 }

控制台输出：

Person{name='张三', sex='男', age=23}

构造函数注入

通过构造函数注入 Bean 的属性值或依赖的对象 , 它保证了 Bean 实例在实例化后就可以使用。构造函数注入在 <constructor-arg> 元素里声明属性 , 没有 name 属性。

 <?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="person" class="com.itdjx.spring.dependency.injection.Person">
         <property name="name" value="张三" />
         <property name="age" value="23" />
         <property name="sex" value="男" />
     </bean>

     <bean id="car" class="com.itdjx.spring.dependency.injection.Car">
         <constructor-arg value="BaoMa"/>
         <constructor-arg value="HuaChen"/>
         <constructor-arg value="230000"/>
     </bean>

 </beans>

 package com.itdjx.spring.dependency.injection;

 /**
  * 构造器注入
  *
  * @author Wáng Chéng Dá
  * @create 2017-02-28 15:32
  */
 public class Car {

     private String brand;

     private String address;

     private double price;

     private int maxSpeed;

     public Car(String brand, String address, double price) {
         this.brand = brand;
         this.address = address;
         this.price = price;
     }

     public Car(String brand, String address, int maxSpeed) {
         this.brand = brand;
         this.address = address;
         this.maxSpeed = maxSpeed;
     }

     public Car(String brand, double price, int maxSpeed) {
         this.brand = brand;
         this.price = price;
         this.maxSpeed = maxSpeed;
     }

     public Car() {
     }

     @Override
     public String toString() {
         return "Car{" +
                 "brand='" + brand + '\'' +
                 ", address='" + address + '\'' +
                 ", price=" + price +
                 ", maxSpeed=" + maxSpeed +
                 '}';
     }
 }

 package com.itdjx.spring.dependency.injection;

 import org.springframework.context.ApplicationContext;
 import org.springframework.context.support.ClassPathXmlApplicationContext;

 /**
  * 依赖注入main
  *
  * @author Wáng Chéng Dá
  * @create 2017-02-28 15:16
  */
 public class MainIOC {

     public static void main(String[] args) {
         ApplicationContext app = new ClassPathXmlApplicationContext("applicationConfig.xml");
         Person person = (Person) app.getBean("person");
         System.out.println(person);

         Car car = (Car) app.getBean("car");
         System.out.println(car);
     }
 }

控制台输出:

Person{name='张三', sex='男', age=23}
Car{brand='BaoMa', address='HuaChen', price=0.0, maxSpeed=230000}

通过控制台输出我们看到 IOC 容器初始化调用的构造函数出现的匹配问题，匹配不到咱们想要调用的构造函数。这时候我们就得继续给 <constructor-arg> 中添加新的属性。分为：按索引匹配入参(index)，按类型匹配入参(type) , 可混合使用，也可同时使用。

 <?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="person" class="com.itdjx.spring.dependency.injection.Person">
         <property name="name" value="张三" />
         <property name="age" value="23" />
         <property name="sex" value="男" />
     </bean>

     <bean id="car" class="com.itdjx.spring.dependency.injection.Car">
         <constructor-arg value="BaoMa"/>
         <constructor-arg value="HuaChen"/>
         <constructor-arg value="230000"/>
     </bean>

     <bean id="car2" class="com.itdjx.spring.dependency.injection.Car">
         <constructor-arg value="BaoMa" index="0"/>
         <constructor-arg value="HuaChen" index="1"/>
         <constructor-arg value="230000" index="2"/>
     </bean>

     <bean id="car3" class="com.itdjx.spring.dependency.injection.Car">
         <constructor-arg value="BaoMa" index="0"/>
         <constructor-arg value="HuaChen" index="1"/>
         <constructor-arg value="230000" index="2" type="double"/>
     </bean>

     <bean id="car4" class="com.itdjx.spring.dependency.injection.Car">
         <constructor-arg value="BaoMa" index="0"/>
         <constructor-arg value="HuaChen" index="1"/>
         <constructor-arg value="230" type="int"/>
     </bean>

 </beans>

 package com.itdjx.spring.dependency.injection;

 import org.springframework.context.ApplicationContext;
 import org.springframework.context.support.ClassPathXmlApplicationContext;

 /**
  * 依赖注入main
  *
  * @author Wáng Chéng Dá
  * @create 2017-02-28 15:16
  */
 public class MainIOC {

     public static void main(String[] args) {
         ApplicationContext app = new ClassPathXmlApplicationContext("applicationConfig.xml");
         Person person = (Person) app.getBean("person");
         System.out.println(person);
         System.out.println("----------------------");

         Car car = (Car) app.getBean("car");
         System.out.println(car);
         System.out.println("----------------------");

         car = (Car) app.getBean("car2");
         System.out.println(car);
         System.out.println("----------------------");

         car = (Car) app.getBean("car3");
         System.out.println(car);
         System.out.println("----------------------");

         car = (Car) app.getBean("car4");
         System.out.println(car);
         System.out.println("----------------------");
     }
 }

控制台输出：

Person{name='张三', sex='男', age=23}
----------------------
Car{brand='BaoMa', address='HuaChen', price=0.0, maxSpeed=230000}
----------------------
Car{brand='BaoMa', address='HuaChen', price=0.0, maxSpeed=230000}
----------------------
Car{brand='BaoMa', address='HuaChen', price=230000.0, maxSpeed=0}
----------------------
Car{brand='BaoMa', address='HuaChen', price=0.0, maxSpeed=230}
----------------------