简单解释一下注入：就是给对象赋值（直接给出代码，解释全部在代码里面 ）

前提是你已经配置好了spring的环境，如果还不会配置可以去看我的入门spring配置


1、所用到的实体类

    1-1 car类

package spring.bean;

public class Car {
	private String color;
	private String name;
	public String getColor() {
		return color;
	}
	public void setColor(String color) {
		this.color = color;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@Override
	public String toString() {
		return "Car [color=" + color + ", name=" + name + "]";
	}
	
}

    1-2 User类

package spring.bean;

public class User {
	private String name;
	private int age;
	private Car car;
	
	
	public User() {
		super();
	}
	public User(String name, Car car) {
		
		this.name = name;
		this.car = car;
	}
	
	public Car getCar() {
		return car;
	}
	public void setCar(Car car) {
		this.car = car;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	@Override
	public String toString() {
		return "User [name=" + name + ", age=" + age + ", car=" + car + "]";
	}	
}


2、applicationContext.xml  （核心)    

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
		xmlns="http://www.springframework.org/schema/beans" 
		xmlns:p="http://www.springframework.org/schema/p"  
		xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.2.xsd ">
	 <!--beans 第三行是如果要使用p名称空间才需要加上  -->
	
	<!-- 如果看不到bena中的基本配置，可以去看我的spring入门配置，里面有详解 -->
	
	
	<!-- set方式注入 -->
	<bean name="user" class="spring.bean.User">
		<!-- 值类型注入 ： 为user对象中名为name的属性注入tom作为值 -->
		<property name="name" value="tom"></property>
		<property name="age" value="19"></property>
		<!-- 引用类型注入 ：  为car属性注入下面的car对象 -->
		<property name="car" ref="car"></property>
	</bean>
	
	<!-- 将car对象配置到容器中 -->
	<bean name="car" class="spring.bean.Car">
		<property name="name" value="大众"></property>
		<property name="color" value="黄色"></property>
	</bean>
	
<!-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->
<!-- 构造函数注入  (必须提供相对应的构造方法) -->
	<bean name="user2" class="spring.bean.User">
		<!-- 
			name属性：构造函数的参数名
			index属性：构造函数的参数索引
			type属性：构造函数的参数类型
			
			index:主要是解决这样的情况
			public User(String name, Car car) {
		
				this.name = name;
				this.car = car;
			}
			public User(Car car, String name) {
		
				this.name = name;
				this.car = car;
			}
			type:主要是解决这样的情况
			public User(String name, Car car) {
		
				this.name = name;
				this.car = car;
			}
			
			public User(Integer name, Car car) {
		
				
				this.car = car;
			}
			
		 -->
		<constructor-arg name="name" value="jerry" index="" type=""></constructor-arg>
		<constructor-arg name="car" ref="car" index=""></constructor-arg>
	
	</bean>



<!-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->
	<!-- 
		p名称空间注入
		值类型：p ： 属性名 = "值"
		对象类型： p : 属性名-ref="bean名称"	
	 -->
	<bean name="user3" class="spring.bean.User" p:name="jack" p:age="18" p:car-ref="car"></bean>


<!-- !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! -->
	<!-- 
		spel注入： spring Expression Language     spring表达式语言
		
	 -->
		
		<bean name="user4" class="spring.bean.User" >
				
			<property name="name" value="#{user.name}"></property>
			<property name="age" value="#{user3.age}"></property>
			<property name="car" ref="car"></property>
		</bean>
		
</beans>


3、Demo测试

package spring.injection;

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

import spring.bean.User;

public class Demo {
	
	@Test
	public void fun1(){
		
		ApplicationContext ac = new ClassPathXmlApplicationContext("spring/injection/applicationContext.xml");
		User u = (User) ac.getBean("user");		
		System.out.println(u);
		
	}
	
	//构造函数注入
	@Test
	public void fun2(){
		
		ApplicationContext ac = new ClassPathXmlApplicationContext("spring/injection/applicationContext.xml");
		User u = (User) ac.getBean("user2");		
		System.out.println(u);
		
	}
	
	
	//p名称空间注入 
	@Test
	public void fun3(){
		
		ApplicationContext ac = new ClassPathXmlApplicationContext("spring/injection/applicationContext.xml");	
		User u = (User) ac.getBean("user3");	
		System.out.println(u);		
	}
	
	//spel注入
	@Test
	public void fun4(){
				
		ApplicationContext ac = new ClassPathXmlApplicationContext("spring/injection/applicationContext.xml");		
		User u = (User) ac.getBean("user4");
		System.out.println(u);
		
	}
	
}

代码亲测有效