Spring学习之—

一、Spring的概述

(一)什么是Spring?

Spring是针对bean对象的生命周期进行管理的轻量级容器。提供了功能强大IOC、AOP及Web MVC等功能。Spring框架主要由七部分组成：分别是 Spring Core、 Spring AOP、 Spring ORM、 Spring DAO、Spring Context、 Spring Web和 Spring Web MVC。

官网：https://spring.io/

(二)Spring核心功能

Spring框架可以和任意框架进行整合。

IOC——控制反转

DI——依赖注入

AOP——面向切面

(三)Spring的好处

高内聚低耦合

高内聚：让方法责任更加单一，更加纯粹，最大程度的保证内聚以及责任单一

低耦合：减少代码之间的关联，即一个类对另外一个类的依赖程度，极可能让类与类之间的关联降到最低

原则：

责任单一原则：需要用整个编程生涯来贯彻

最少知道原则：禁止跨级调用；让一个类认识/调用最少的类

简化事务：仅仅使用一个注解，就能让事务生效

集成了Junit，方便测试

简化了开发

方便集成各种框架：使用Spring去管理所有的框架

二、IOC(控制反转)

(一)IOC的概念

控制权从应用程序代码转移到外部容器，由容器负责管理对象的创建和依赖关系。

(二)创建Spring项目

添加依赖

<dependencies><dependency><groupId>org.springframework</groupId><artifactId>spring-context</artifactId><version>5.1.9.RELEASE</version></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.18.30</version><scope>provided</scope></dependency></dependencies>

创建spring配置文件：spring1.xml

编辑spring.xml来管理bean

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"><!--当前的Student类交给了Spring容器去创建--><bean id="stu" class="com.javatest.demo.Student"/>
</beans>

创建Student类

@Getter
@Setter
public class Student {private Integer id;private String name;private Integer age;
}

测试类

private static void test1() {// 从类加载路径中,加载配置文件spring1.xml// 读取配置文件中的内容// 解析xml标签// 创建一个bean的集合,new一个对象,存入bean的集合等待调用// applicationContext 实际上就是Spring容器对象// 不论是否调用bean对象,在Spring容器初始化的时候,都会创建bean对象ClassPathXmlApplicationContext applicationContext =new ClassPathXmlApplicationContext("spring1.xml");// 从Spring容器中,寻找id=stu的bean对象Student stu= (Student) applicationContext.getBean("stu");// 赋值stu.setId(100);stu.setName("张三");stu.setAge(11);System.out.println(stu);
}

运行结果：

----------Student创建了-------------
Student(id=100, name=张三, age=11)

(三)Spring的启动原理

程序启动 → 读取xml文件 → 解析xml配置文件 → 读取了bean标签的内容 → 通过反射,初始化bean对象(new对象) → bean对象存入Spring容器，等待调用。

代码实现：

public static void main(String[] args) throws Exception {test4();
}
private static void test4() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {Student student = (Student) test3("stu");student.setId(10);student.setName("张三");student.setAge(30);System.out.println(student);// Student(id=10, name=张三, age=30)
}
private static Object test3(String id) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {Map<String, Object> map = test2();Object o = map.get(id);return o;
}
private static Map<String, Object> test2() throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, InstantiationException, IllegalAccessException {String id = "stu";String className = "com.javatest.demo.Student";Class<?> aClass = Class.forName(className);Object o = aClass.getConstructor().newInstance();Map<String, Object> springApplication = new ConcurrentHashMap<>();springApplication.put(id, o);return springApplication;
}

运行结果：

---------------Student对象被创建了---------------
Student(id=10, name=张三, age=30)

(四)Spring中获取bean的三种方式

Studen类：

@Getter
@Setter
//@ToString
public class Student {private Integer id;private String name;private Integer age;public Student(){System.out.println("---------------Student对象被创建了---------------");}
}

spring1.xml配置文件：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"><!--当前的Student类交给了Spring容器去创建--><bean id="stu" class="com.javasm.demo.Student"/>
</beans>

Spring获取bean的三种方式：

public class Test2 {static ClassPathXmlApplicationContext applicationContext =new ClassPathXmlApplicationContext("spring1.xml");public static void main(String[] args) throws Exception {test1();}/*** 获取bean的方式*/private static void test1() {// 根据id获取Student student = (Student) applicationContext.getBean("stu");System.out.println(student);// 根据类型获取Student student1 = applicationContext.getBean(Student.class);System.out.println(student1);// 根据id+类型获取Student student2 = applicationContext.getBean("stu", Student.class);System.out.println(student2);}
}

运行结果：

----------Student创建了-------------
com.javatest.demo.Student@6989da5e
com.javatest.demo.Student@6989da5e
com.javatest.demo.Student@6989da5e

(五)bean别名

<!--别名,不常用-->
<alias name="stu" alias="s"/>

Student s = context.getBean("s", Student.class);

(六)Spring创建bean的几种方式

1.无参构造(最常用)

<bean id="stu" class="com.javatest.demo.Student"/>

2.静态工厂创建bean对象

<bean id="xiaoming" class="com.javatest.demo.StudentStaticFactory" factory-method="getStudent"/>

public class StudentStaticFactory {public static Student getStudent() {Student student = new Student();student.setName("小明");return student;}
}

private static void test3() {Object xiaoming = applicationContext.getBean("xiaoming");System.out.println(xiaoming);// Student(id=null, name=小明, age=null)
}

3.实例工厂创建bean对象

<bean id="stuFactory" class="com.javatest.demo.StudentFactory"/>
<bean id="xiaohong" factory-bean="stuFactory" factory-method="getStudent"/>

public class StudentFactory {public Student getStudent() {Student student = new Student();student.setName("小红");return student;}
}

private static void test4() {Object xiaohong = applicationContext.getBean("xiaohong");System.out.println(xiaohong);// Student(id=null, name=小红, age=null)
}

4.Spring工厂创建bean对象

<bean id="huowang" class="com.javatest.demo.StudentSpringFactory"/>

public class StudentSpringFactory implements FactoryBean<Student> {@Overridepublic Student getObject() throws Exception {//返回的对象是什么，Spring容器中存什么Student student = new Student();student.setName("李火旺");return student;}@Overridepublic Class<?> getObjectType() {return Student.class;}@Overridepublic boolean isSingleton() {//是否是单例//true:单例//false:多例//默认是truereturn true;}
}

private static void test5() {Object huowang = applicationContext.getBean("huowang");System.out.println(huowang);Object huowang1 = applicationContext.getBean("huowang");System.out.println(huowang1);// com.javatest.demo.Student@489115ef// com.javatest.demo.Student@489115ef
}

(七)单例

Spring的bean对象，在默认情况下，都是单例的

<bean id="teacher" class="com.javasm.demo.Teacher" scope="prototype"/>

单例：Spring启动 → 加载解析XML文件 → 创建Bean对象 →bean保存到容器 →随着容器关闭销毁

多例：Spring启动→加载解析XML文件→先把解析的内容记录下来→调用的时候创建bean

(八)懒加载

不使用不创建对象

仅仅对单例生效：

<bean id="teacher1" class="com.javasm.demo.Teacher" lazy-init="true"/>

全局配置：

<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"default-lazy-init="true"
>

(九)初始化&销毁

@Getter
@Setter
public class Teacher {private Integer id;private String name;public Teacher(Integer id, String name) {this.id = id;this.name = name;}public Teacher() {System.out.println("------------Teacher---------");}public void test1() {System.out.println("我是Test1-----------初始化");}public void test2() {System.out.println("我是Test2=============销毁");}
}

<bean id="teacher2" class="com.javatest.demo.Teacher" init-method="test1" destroy-method="test2"/>

private static void test7() {Object teacher2 = applicationContext.getBean("teacher2");System.out.println(teacher2);applicationContext.close();
}

执行顺序：

构造方法
初始化方法
正常调用方法
---销毁
关闭容器

三、DI(依赖注入)

(一)DI的概念

通过外部容器将依赖的对象传递给类，而不是让类自己创建或查找依赖，从而实现松耦合。

(二)代码实现

1.实体类

@Data
@NoArgsConstructor
@AllArgsConstructor
public class Game {private Integer id;private String name;private Double price;//公司private Company company;//英雄列表private String[] heros;//关卡private List<String> levels;//背包private Map<Integer, String> items;//成就private Set<String> achievements;//游戏配置private Properties gameConfig;//玩家列表private List<Player> playerList;
}

@Data
public class Company {private String name;private String address;
}

@Data
public class Player {private Integer id;private String nickname;
}

2.spring2.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="game" class="com.javatest.demo2.Game"><property name="id" value="1000"/><property name="name" value="黑神话·悟空"/><property name="price" value="648.88"/><!--公司--><property name="company" ref="company"/><!--英雄列表--><property name="heros"><array><value>孙悟空</value><value>杨戬</value><value>哪吒</value></array></property><!--关卡列表--><property name="levels"><list><value>黑风寨</value><value>黄风岭</value><value>小西天</value></list></property><!--背包列表--><property name="items"><map><entry key="1001" value="金箍棒"/><entry key="1002" value="三尖两刃刀"/><entry key="1003" value="定风珠"/></map></property><!--成就列表--><property name="achievements"><set><value>借刀杀人</value><value>顺手牵羊</value><value>万箭齐发</value></set></property><!--游戏配置列表--><property name="gameConfig"><props><prop key="maxPlayer">100</prop><prop key="maxLevel">120</prop></props></property><!--玩家列表--><property name="playerList"><list><bean class="com.javatest.demo2.Player"><property name="id" value="1001"/><property name="nickname" value="玩家1"/></bean><ref bean="player2"/></list></property></bean><bean id="company" class="com.javatest.demo2.Company"><property name="name" value="游戏科学"/><property name="address" value="杭州"/></bean><bean id="player2" class="com.javatest.demo2.Player"><property name="id" value="1002"/><property name="nickname" value="玩家2"/></bean>
</beans>

3.测试类

public class Test {static ClassPathXmlApplicationContext applicationContext =new ClassPathXmlApplicationContext("spring2.xml");public static void main(String[] args) {test1();}private static void test1() {Game game = applicationContext.getBean("game", Game.class);System.out.println(game);}
}

4.运行结果

Game(id=1000, name=黑神话·悟空, price=648.88, 
company=Company(name=游戏科学, address=杭州), 
heros=[孙悟空, 杨戬, 哪吒], 
levels=[黑风寨, 黄风岭, 小西天], 
items={1001=金箍棒, 1002=三尖两刃刀, 1003=定风珠}, 
achievements=[借刀杀人, 顺手牵羊, 万箭齐发], 
gameConfig={maxLevel=120, maxPlayer=100}, 
playerList=[Player(id=1001, nickname=玩家1), Player(id=1002, nickname=玩家2)])

(三)自动装配

<!--autowire 自动装配：byType 根据属性的类型，去Spring容器中寻找对应的bean对象，如果找到了，自动赋值给对应的属性-->
<bean id="g2" class="com.javatest.demo2.Game" autowire="byType"/>
<!--autowire 自动装配：byName 根据属性的名字，去寻找id和属性名一样的bean-->
<bean id="g3" class="com.javatest.demo2.Game" autowire="byName"/>

全局配置：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"default-autowire="byName"
>

(四)构造方法的注入

Music类：

@Data
public class Music {private Integer id;private String name;private String time;private Company company;public Music(Integer id, String name, String time, Company company) {this.id = id;this.name = name;this.time = time;this.company = company;}
}

spring3.xml：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"><bean id="company" class="com.javatest.demo2.Company"><property name="name" value="酷狗音乐"/><property name="address" value="北京"/></bean><!--index:构造方法第几个参数name: 构造方法的参数名称推荐使用index配置参数--><bean id="music" class="com.javatest.demo3.Music"><constructor-arg name="id" value="100" type="java.lang.Integer"/><constructor-arg index="1" value="云顶天宫"/><constructor-arg index="2" value="10mins"/><constructor-arg index="3" ref="company"/></bean>
</beans>

四、Spring中常见异常

1.bean的id写错了，没有找到名字是stu1的bean对象

2.根据类型，从Spring容器中获取bean对象，但是容器中有两个bean对象，是相同类型的，所以报错
因为要找1个bean，但是发现了2个

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsd"><!--当前的Student类交给了Spring容器去创建--><bean id="stu" class="com.javatest.demo.Student"/><bean id="stu1" class="com.javatest.demo.Student"/>
</beans>

---------------Student对象被创建了---------------
---------------Student对象被创建了---------------
com.javatest.demo.Student@6989da5e
Exception in thread "main" org.springframework.beans.factory.NoUniqueBeanDefinitionException: 
No qualifying bean of type 'com.javatest.demo.Student' available: 
expected single matching bean but found 2: stu,stu1at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveNamedBean(DefaultListableBeanFactory.java:1144)at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveBean(DefaultListableBeanFactory.java:411)at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:344)at org.springframework.beans.factory.support.DefaultListableBeanFactory.getBean(DefaultListableBeanFactory.java:337)at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1123)at com.javatest.demo.Test2.test1(Test2.java:29)at com.javatest.demo.Test2.main(Test2.java:18)

3.类中没有无参构造，报错
要养成一个习惯，只要写有参构造，不论是否需要无参构造，都要写一个

12月 20, 2024 9:50:48 下午 org.springframework.context.support.AbstractApplicationContext refresh
警告: Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'teacher' defined in class path resource [spring1.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.javatest.demo.Teacher]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.javatest.demo.Teacher.<init>()
Exception in thread "main" java.lang.ExceptionInInitializerError
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'teacher' defined in class path resource [spring1.xml]: Instantiation of bean failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.javatest.demo.Teacher]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.javatest.demo.Teacher.<init>()at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1303)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1197)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:555)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515)at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320)at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318)at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:845)at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877)at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549)at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:144)at org.springframework.context.support.ClassPathXmlApplicationContext.<init>(ClassPathXmlApplicationContext.java:85)at com.javatest.demo.Test2.<clinit>(Test2.java:14)
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [com.javatest.demo.Teacher]: No default constructor found; nested exception is java.lang.NoSuchMethodException: com.javatest.demo.Teacher.<init>()at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:83)at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateBean(AbstractAutowireCapableBeanFactory.java:1295)... 13 more
Caused by: java.lang.NoSuchMethodException: com.javatest.demo.Teacher.<init>()at java.base/java.lang.Class.getConstructor0(Class.java:3349)at java.base/java.lang.Class.getDeclaredConstructor(Class.java:2553)at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:78)... 14 moreProcess finished with exit code 1