面試官：為什么要用 Spring？它到底解決了什么問題？

為什么要用 Spring？它到底解決了什么問題？

目的：對比傳統(tǒng)方式和 Spring注入方式創(chuàng)建對象以達(dá)到解耦的目的，以Service層調(diào)用 Dao層為例。

方式一：傳統(tǒng)方式

1.Service層

/**
?*?@author ：Prannt
?*?@description ：Service層
?*?@program?:?Test
?*/
public?class?UserService?{
????public?void?add(){
????????System.out.println("service?add...");
????????UserDao?dao?=?new?UserDaoImpl();
????????dao.query();
????}
}

2.UserDao接口

/**
?*?@description ：接口中只有一個(gè)抽象方法
?*/
public?interface?UserDao?{
????void?query();
}

3.UserDao接口的實(shí)現(xiàn)類

/**
?*?@description ：接口的實(shí)現(xiàn)類，重寫 query方法
?*/
public?class?UserDaoImpl?implements?UserDao{
????@Override
????public?void?query()?{
????????System.out.println("dao?query...");
????}
}
//測試
public?class?test?{
????@Test
????public?void?test1(){
????????UserService?service?=?new?UserService();
????????service.add();
????}
}

Spring Boot 基礎(chǔ)就不介紹了，推薦下這個(gè)實(shí)戰(zhàn)教程：https://github.com/javastacks/spring-boot-best-practice

測試結(jié)果：

結(jié)論一：由以上過程可以看出，在UserService類中直接調(diào)用實(shí)現(xiàn)類的query方法，一旦實(shí)現(xiàn)類出問題，UserService立即報(bào)錯(cuò)，具有高度的耦合性

方式二：Spring注入對象

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">1.xml文件配置bean

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">"1.0"?encoding="UTF-8"?>
"http://www.springframework.org/schema/beans"
???????xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
???????xsi:schemaLocation="http://www.springframework.org/schema/beans?http://www.springframework.org/schema/beans/spring-beans.xsd">

????"userService"?class="Service.UserService">
????????
????????"dao"?ref="Dao">
????

????"Dao"?class="Dao.UserDaoImpl">

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">2.Service層

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">import?Dao.UserDao;
/**
?*?@author ：Prannt
?*?@description ：
?*?@program?:?Demo01
?*/
public?class?UserService?{
????public?void?add(){
????????System.out.println("service?add......");
????????dao.update();
????}

????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法
????private?UserDao?dao;

????public?void?setDao(UserDao?dao)?{
????????this.dao?=?dao;
????}
}

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">3.UserDao接口

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????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">public?interface?UserDao?{
????void?update();
}

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">4.接口的實(shí)現(xiàn)類

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">public?class?UserDaoImpl?implements?UserDao{
????@Override
????public?void?update()?{
????????System.out.println("Dao?update......");
????}
}

推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">測試

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" data-linktype="2">import?Service.UserService;
import?org.junit.Test;
import?org.springframework.context.ApplicationContext;
import?org.springframework.context.support.ClassPathXmlApplicationContext;

public?class?TestBean?{
????@Test
????public?void?testBean(){
????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");
????????UserService?userService?=?context.getBean("userService",UserService.class);
????????userService.add();
????}
}

????????????????????????????2.Service層import?Dao.UserDao;/**?*?@author ：Prannt?*?@description ：?*?@program?:?Demo01?*/public?class?UserService?{????public?void?add(){????????System.out.println("service?add......");????????dao.update();????}????//創(chuàng)建dao類型的屬性，生成對應(yīng)的set方法????private?UserDao?dao;????public?void?setDao(UserDao?dao)?{????????this.dao?=?dao;????}}3.UserDao接口public?interface?UserDao?{????void?update();}4.接口的實(shí)現(xiàn)類public?class?UserDaoImpl?implements?UserDao{????@Override????public?void?update()?{????????System.out.println("Dao?update......");????}}推薦一個(gè) Spring Boot 基礎(chǔ)教程及實(shí)戰(zhàn)示例：https://github.com/javastacks/spring-boot-best-practice測試import?Service.UserService;import?org.junit.Test;import?org.springframework.context.ApplicationContext;import?org.springframework.context.support.ClassPathXmlApplicationContext;public?class?TestBean?{????@Test????public?void?testBean(){????????ApplicationContext?context?=?new?ClassPathXmlApplicationContext("bean2.xml");????????UserService?userService?=?context.getBean("userService",UserService.class);????????userService.add();????}}測試結(jié)果" linktype="text" imgurl="" imgdata="null" data-itemshowtype="0" tab="innerlink" style="color: rgb(58, 58, 58);" data-linktype="2">測試結(jié)果

結(jié)論二：觀察以上過程，在UserService類中，沒有直接new實(shí)現(xiàn)類，而是通過將Dao注入外部配置文件中的方式，使用“第三方文件”來達(dá)到解耦的目的。

總結(jié)

第一種傳統(tǒng)方式創(chuàng)建對象，就像圖一中的齒輪組。如果有一個(gè)齒輪出了問題，就可能會影響到整個(gè)齒輪組的正常運(yùn)轉(zhuǎn)。

而用Spring注入對象猶如圖二的齒輪，利用第三方xml文件使任意兩個(gè)齒輪之間無必然聯(lián)系，B齒輪壞了也影響不到A、C、D齒輪。齒輪組相互之間的依賴關(guān)系降到最低。

原文鏈接：https://blog.csdn.net/qq_38050259/article/details/113414419

版權(quán)聲明：本文為CSDN博主「Prannt」的原創(chuàng)文章，遵循CC 4.0 BY-SA版權(quán)協(xié)議，轉(zhuǎn)載請附上原文出處鏈接及本聲明。

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