Spring依赖注入的两种常用方式：属性注入与构造器注入

set方法注入

applicationContext.xml

Main.java

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

public class Main {
	public static void main(String[] args) {
		// 1.创建Spring的IOC容器对象
		// ApplicationContext代表的是IOC容器
		// ClassPathXmlApplicationContext：是 ApplicationContext接口的实现类。该实现类从类路径下加载配置文件
		ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
		// 2.从IOC容器中获取Bean示例
		// getBean方法是在BeanFactory中定义的，有两种常用的getBean方法
		// 方法一：getBean(xml中bean的id名称);通过id获取
		HelloWorld helloWorld = (HelloWorld)ctx.getBean("helloWorld2");
		// 方法二：getBean(Class)；通过类型获取
		// 缺点：当IOC容器中配置了两个bean时，此方法不知道返回哪一个，会报错
		HelloWorld helloWorld = ctx.getBean(HelloWorld.class);
		// 3.调用hello方法
		helloWorld.hello();
		
	}
}

HelloWorld.java

package com.atguigu.spring.beans;

public class HelloWorld {
	private String name;
	// setName2与applicationContext.xml中的property中的name的值对应。即set方法注入
	public void setName2(String name) {
		this.name = name;
	}
	
	public void hello() {
		System.out.println("hello: " + name);
	}
}

构造方法注入

Car.java

package com.atguigu.spring.beans;

public class Car {
	private String brand;
	private String corp;
	private double price;
	private int maxSpeed;
	public Car(String brand, String corp, double price) {
		super();
		this.brand = brand;
		this.corp = corp;
		this.price = price;
	}
	@Override
	public String toString() {
		return "Car [brand=" + brand + ", corp=" + corp + ", price=" + price + ", maxSpeed=" + maxSpeed + "]";
	}	
}

ApplicationContext.xml

Main.java

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
public class Main {
	public static void main(String[] args) {
		// 1.创建Spring的IOC容器对象
		// ApplicationContext代表的是IOC容器
		ApplicationContext ctx = new ClassPathXmlApplicationContext("applicationContext.xml");
		// 2.从IOC容器中获取Bean示例
		Car car = ctx.getBean(Car.class);
		System.out.println(car);		
	}
}