Spring学习(一)——Sping-XML
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/beans
http://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/beans
http://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> {
@Override
public 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;
}
@Override
public Class<?> getObjectType() {
return Student.class;
}
@Override
public boolean isSingleton() {
//是否是单例
//true:单例
//false:多例
//默认是true
return 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/beans
http://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/beans
http://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/beans
http://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/beans
http://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/beans
http://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,stu1
at 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 more
Process finished with exit code 1