Spring多种方式实现依赖注入

平常的Java开发中，程序员在某个类中需要依赖其它类的方法。

通常是new一个依赖类再调用类实例的方法，这种开发存在的问题是new的类实例不好统一管理。

Spring提出了依赖注入的思想，即依赖类不由程序员实例化，而是通过Spring容器帮我们new指定实例并且将实例注入到需要该对象的类中。

依赖注入的另一种说法是"控制反转"。通俗的理解是：平常我们new一个实例，这个实例的控制权是我们程序员。

而控制反转是指new实例工作不由我们程序员来做而是交给Spring容器来做。

1.Set注入

构建一个Student对象

package cn.happy.entity;

/**
 * Created by CKW on 2017/3/19.
 */
public class Student {
    private String sname;
    private Integer sage;

    public Integer getSage() {
        return sage;
    }

    public void setSage(Integer sage) {
        this.sage = sage;
    }

    public String getSname() {
        return sname;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }

}

在配置applicationContext.xml中：

    <!--set 注入  prototype  原型   singletion  单例-->
    <bean id="stu" class="cn.happy.entity.Student" scope="prototype">
        <property name="sname" value="张三"></property>
        <property name="sage" value=""></property>
    </bean>

测试类中：

    //被Spring管理的bean默认都是单例的
    @Test
    public void myTest1(){
        //ac  就是Spring容器
        ApplicationContext ac=new ClassPathXmlApplicationContext("applicationContext.xml");
        Student stu=(Student) ac.getBean("stu");
        Student stu1=(Student) ac.getBean("stu");
        System.out.println(stu+"\n"+stu1);
    }

2.构造器注入

在对象中添加构造

配置中：

    <!--构造注入-->
    <bean id="car1" class="cn.happy.entity.Car">
        <property name="cname" value="图驴子"></property>
    </bean>
    <bean id="stu1" class="cn.happy.entity.Student">
        <!--()创建构造器注入,如果主类有带参的构造方法则需添加此配置-->
        <constructor-arg index="" value="哇哈哈"></constructor-arg>
        <constructor-arg index="" value=""></constructor-arg>
        <constructor-arg index="" ref="car1"></constructor-arg>
    </bean>

测试类：

    //构造注入
    @Test
    public void myTest2(){
        ApplicationContext ac=new ClassPathXmlApplicationContext("applicationContext.xml");
        Student stu1=(Student) ac.getBean("stu1");
        Student stu2=(Student) ac.getBean("stu2");
        System.out.println("构造："+stu1);

    }

3.空间命名注入

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop.xsd
">

    <!--命名空间P注入-->
    <bean id="car2" class="cn.happy.entity.Car">
        <property name="cname" value="毛驴"></property>
    </bean>
    <bean id="stu2" class="cn.happy.entity.Student" p:sname="李四" p:sage="" p:car-ref="car2"></bean>

    //构造注入   命名空间注入
    @Test
    public void myTest2(){
        ApplicationContext ac=new ClassPathXmlApplicationContext("applicationContext.xml");
        Student stu1=(Student) ac.getBean("stu1");
        Student stu2=(Student) ac.getBean("stu2");
        System.out.println("构造："+stu1+"\n命名空间："+stu2);

    }

4.集合注入

    <!--list集合属性注入-->
    <bean id="collection1" class="cn.happy.entity.MyCollection">
        <property name="list">
            <list>
                <value>哈哈</value>
                <value>呵呵</value>
                <value>嘿嘿</value>
            </list>
        </property>
    </bean>

    <!--set集合属性注入-->
    <bean id="collection2" class="cn.happy.entity.MyCollection">
        <property name="set">
            <set>
                <value>哈哈</value>
                <value>呵呵</value>
                <value>嘿嘿</value>
            </set>
        </property>
    </bean>

    <!--Map集合属性注入-->
    <bean id="collection3" class="cn.happy.entity.MyCollection">
        <property name="map">
            <map>
                <entry key="">
                    <value>呵呵</value>
                </entry>
                <entry key="">
                    <value>哈哈</value>
                </entry>
                <entry key="">
                    <value>嘿嘿</value>
                </entry>
            </map>
        </property>
    </bean>

5.注解注入

package cn.happy.entity;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Controller;
import org.springframework.stereotype.Repository;
import org.springframework.stereotype.Service;

/**
 * Created by CKW on 2017/3/22.
 */
@Component("car") //不分层
/*@Repository  //dao层*/
/*@Service  //biz层*/
/*@Controller  //action层*/
public class Car {
    @Value("特斯拉")
    private String cname;

    @Override
    public String toString() {
        return getCname();
    }

    public Car() {
    }

    public Car(String cname) {
        this.cname = cname;
    }

    public String getCname() {
        return cname;
    }

    public void setCname(String cname) {
        this.cname = cname;
    }
}

package cn.happy.entity;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;

import javax.annotation.Resource;

/**
 * Created by CKW on 2017/3/22.
 */

@Component("student")
public class Student {
    @Value("撒打发")
    private String sname;
    @Value("")
    private Integer sage;
    //jdk注解
//    @Resource
    @Autowired
    @Qualifier("car")
    private Car car;

    @Override
    public String toString() {
        return "name="+getSname()+",age="+getSage()+",car="+getCar();
    }

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }

    public Student() {

    }

    public String getSname() {
        return sname;
    }

    public Student(String sname, Integer sage, Car car) {
        this.sname = sname;
        this.sage = sage;
        this.car = car;
    }

    public void setSname(String sname) {
        this.sname = sname;
    }

    public Integer getSage() {
        return sage;
    }

    public void setSage(Integer sage) {
        this.sage = sage;
    }
}

在配置applicationContext.xml中：

<?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:aop="http://www.springframework.org/schema/aop"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/aop
        http://www.springframework.org/schema/aop/spring-aop.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd
">

  <!--注解-->
    <!--配置包扫描器-->
    <context:component-scan base-package="cn.happy.entity"></context:component-scan>

测试类：

    //注解
    @Test
    public void myTest4(){
        ApplicationContext ac=new ClassPathXmlApplicationContext("applicationContext.xml");
        Student stu=(Student)ac.getBean("student");
        System.out.println(stu.getCar().getCname());
    }