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;

    }

}