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。
(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
原文地址：https://blog.csdn.net/Helen_1997_1997/article/details/144616348
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