---
title: '01-Spring Boot Ioc and DI'
disqus: hackmd
---
###### tags: `SpringCore`
Spring Boot bean 的注入方式@Autowired
===

[TOC]

## IoC 和 DI的關係

控制反轉是一種設計原則、一種概念，而依賴注入則是實現這種概念的方式
，依賴注入只是其中一種實踐他的方法

## 英文解釋

IOC(Inversion of Control) is a concept that means: Instead of creating objects with the new operator,let the container do it for you.

DI(Dependency injection) is way to inject the dependency of a framework component by the following ways of spring:

## Types of dependency injections

Constructor Injection
Setter Injection
Field Injection(很少用暫且忽略)

## 沒有依賴注入的例子

package com.allproducts.ai_center.springcore;

class Address {

	private String street;
	private String city;

	public String getStreet() {
		return street;
	}

	public void setStreet(String street) {
		this.street = street;
	}

	public String getCity() {
		return city;
	}

	public void setCity(String city) {
		this.city = city;
	}
	
	/**
	 * @param street
	 * @param city
	 */
	 Address(String street, String city) {
		this.street = street;
		this.city = city;
	}
	
}

package com.allproducts.ai_center.springcore;

class Employee {

	
	private Address address;

	Employee() {
		address = new Address("Astreet","taipei");
	}
	
	public void printEmployaddress() {

		System.out.println(address.getCity());

	}

	public static void main(String[] args) {

		Employee myEmployee = new Employee();
		myEmployee.printEmployaddress();
	}

}

## 沒有依賴注入，而且新增了欄位 country

package com.allproducts.ai_center.springcore;

class Address {

	private String street;
	private String city;
	private String country;
	
	public String getStreet() {
		return street;
	}

	public void setStreet(String street) {
		this.street = street;
	}

	public String getCity() {
		return city;
	}

	public void setCity(String city) {
		this.city = city;
	}
	
	/**
	 * @param street
	 * @param city
	 */
	 Address(String street, String city,String country) {
		this.street = street;
		this.city = city;
		this.country=country;
	}
	
}

package com.allproducts.ai_center.springcore;

class Employee {

	
	private Address address;
	Employee() {
		address = new Address("Astreet","taipei","taiwan");
	}
	public void printEmployaddress() {

		System.out.println(address.getCity());

	}

	public static void main(String[] args) {

		Employee myEmployee = new Employee();
		myEmployee.printEmployaddress();
	}

}

> 除了必須要更改Address的constructur以外，Employee也要更著改

## 使用了dependency injection後

package com.allproducts.ai_center.springcore;

class Employee {

	
	private Address address;
	/**
	 * @param address
	 */
	public Employee(Address address) {
		super();
		this.address = address;
	}

	public void printEmployaddress() {

		System.out.println(address.getCity());

	}

	public static void main(String[] args) {

		Address myAddress=new Address("B street", "taipei", "taiwan");
		Employee myEmployeewithDI = new Employee( myAddress);
		
		myEmployeewithDI.printEmployaddress();
	}

}

## 參考連結

[What is the advantage of autowiring in spring](https://stackoverflow.com/questions/16344062/what-is-the-advantage-of-autowiring-in-spring)

[Spring Framework](https://spring.io/projects/spring-framework)

[Spring 使用@Autowired依賴注入物件](https://matthung0807.blogspot.com/2018/08/spring-autowired.html)

[Spring Dependency Injection with Example](https://www.geeksforgeeks.org/spring-dependency-injection-with-example/)

[Inversion of Control and Dependency Injection](https://medium.com/geekculture/inversion-of-control-and-dependency-injection-58240337ef1a)

[必看What is Dependency Injection and Inversion of Control in Spring Framework?](https://stackoverflow.com/questions/9403155/what-is-dependency-injection-and-inversion-of-control-in-spring-framework)

[Spring Dependency Injection – Field vs Setter vs Constructor Injection](http://www.amitph.com/spring-field-setter-constructor-injection/)