依赖注入（ID）是Spring协调不同Bean实例之间的合作而提供的一种工作机制，在确保Bean实例之间合作的同时，并能保持每个Bean的相对独立性。在Spring框架下，当Bean实例 A运行过程中需要引用另外一个Bean实例B时，Spring框架会创建Bean的实例B，并将实例B通过实例A的构造函数、set方法、自动装配和注解方式注入到实例A，这种注入实例Bean到另外一个实例Bean的过程称为依赖注入(DI)。

基于构造函数的依赖注入
基于设置函数的依赖注入(Setter方法)
工厂方式的依赖注入
基于自动装配的依赖注入
基于注解的依赖注入

Setter 注入

基本类型值注入(value)

（1）Student类

public class Student {
    private String name;
    private int age;
    public void setName(String name) {
        this.name = name;
    }
    public void setAge(int age) {
        this.age = age;
    }
    @Override
    public String toString() {
        return "Student{" +
                "name='" + name + '\'' +
                ", age=" + age +
                '}';
    }
}

（2）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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="student" class="com.haan.di.Student">
        <property name="name" value="libai"/>
        <property name="age" value="22"/>
    </bean>
</beans>

（3）测试

public class Main {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
        Student student = context.getBean(Student.class);
        System.out.println(  student.toString());
    }
}
//Student{name='libai', age=22}

引用类型值注入(ref)

（1）class
AddressInfo.class

public class AddressInfo {
    private String tel;        //基本类型
    private String city;
    public void setTel(String tel) {
        this.tel = tel;
    }
    public void setCity(String city) {
        this.city = city;
    }
    @Override
    public String toString() {
        return "AddressInfo{" +
                "tel='" + tel + '\'' +
                ", city='" + city + '\'' +
                '}';
    }
}

Student2.class

public class Student2 {
    private String name;            //基本类型
    private int age;                //基本类型
    private AddressInfo addressInfo; //引用类型
    public void setName(String name) {
        this.name = name;
    }
    public void setAge(int age) {
        this.age = age;
    }
    public void setAddressInfo(AddressInfo addressInfo) {
        this.addressInfo = addressInfo;
    }
    @Override
    public String toString() {
        return "Student2{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", addressInfo=" + addressInfo +
                '}';
    }
}

（2）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"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="student2" name="student2" class="com.haan.di.Student2">
        <property name="name" value="libai" />
        <property name="age" value="22"/>
        <property name="addressInfo" ref="addressInfo"/>
    </bean>
    <bean id="addressInfo" class="com.haan.di.AddressInfo">
        <property name="tel" value="1008611"/>
        <property name="city" value="上海" />
    </bean>
</beans>

（3）main函数测试

public class Main {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
        Student2 student2 = context.getBean(Student2.class);
        System.out.println(  student2.toString());
    }
}

使用 p-namespace 实现 XML 配置

构造函数注入

当容器调用带有一组参数的类构造函数时，基于构造函数的 DI 就完成了，其中每个参数代表一个对其他类的依赖。

单个有参构造方法注入

    <bean id="person1" class="com.haan.di.Person">
        <constructor-arg name="name" value="libai"/>
    </bean>

type属性

Index属性

public class Main {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
        Person person1 = (Person) context.getBean("person1");
        System.out.println("person1"+person1.toString());
        Person person2 = (Person) context.getBean("person2");
        System.out.println("person2"+person2.toString());
        Person person3 = (Person) context.getBean("person3");
        System.out.println("person3"+person3.toString());
    }
}

<?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="person1" class="com.haan.di.Person">
        <constructor-arg name="name" value="libai"/>
    </bean>
    <bean id="person2" class="com.haan.di.Person">
        <constructor-arg type="java.lang.String" value="zhangfei"/>
        <constructor-arg type="java.lang.Integer" value="22"/>
    </bean>
    <bean id="person3" class="com.haan.di.Person">
        <constructor-arg index="0" value="zhangfei"/>
        <constructor-arg index="1" value="22"/>
        <constructor-arg index="2" value="1008611"/>
    </bean>
    <bean id="test1" class="com.haan.test.Test1" />
    <bean id="test2" class="com.haan.test.Test2" />
</beans>

public class Person {
    private String name;
    private Integer age;
    private String tel;
    public Person(){}
    public Person(String name){
        this.name = name;
    }
    public Person(String name, Integer age) {
        this.name = name;
        this.age = age;
    }
    public Person(String name, Integer age, String tel) {
        this.name = name;
        this.age = age;
        this.tel = tel;
    }
    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", tel='" + tel + '\'' +
                '}';
    }
}

public class Main {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml");
        Person person1 = (Person) context.getBean("person1");
        System.out.println("person1"+person1.toString());
        Person person2 = (Person) context.getBean("person2");
        System.out.println("person2"+person2.toString());
        Person person3 = (Person) context.getBean("person3");
        System.out.println("person3"+person3.toString());
    }
    //person1Person{name='libai', age=null, tel='null'}
    //person2Person{name='zhangfei', age=22, tel='null'}
    //person3Person{name='zhangfei', age=22, tel='1008611'}    
}

Java 学习笔记 - Javaer 成长之路

Spring 依赖注入