Spring基础知识点

Spring框架文档
https://docs.spring.io/spring-framework/docs/current/spring-framework-reference/

一.IOC实例化对象的三种方式：

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
    <!--构造函数实例化-->
    <!-- 1.调用无参构造函数 -->
    <bean id="person1" class="com.imooc.spring.instance.Person"></bean>

    <!-- 2.调用有参构造函数 -->
    <bean id="person2" class="com.imooc.spring.instance.Person">
        <constructor-arg name="name" value="哈哈(构造函数)"/>
        <constructor-arg name="age" value="18"/>
    </bean>


    <!-- 通过静态工厂创建对象-->
    <bean id="person3" class="com.imooc.spring.instance.PersonStaticFactory" factory-method="createPerson">
        <constructor-arg name="name" value="呵呵(静态工厂)"/>
        <constructor-arg name="age" value="20"/>
    </bean>

    <!-- 通过实例工厂创建对象-->
    <bean id="instanceFactory" class="com.imooc.spring.instance.PersonFactory"></bean>

    <bean id="person4" factory-bean="instanceFactory" factory-method="createPerson">
        <constructor-arg name="name" value="嘻嘻(实例工厂)"/>
        <constructor-arg name="age" value="22"/>
    </bean>

</beans>

二.DI四种注入方式

 1.setter注入
 2.构造器注入
 3.注解注入
 4.JavaConfig

UserService

package com.imooc.spring.injection;

import org.springframework.stereotype.Service;

import javax.annotation.Resource;

//@Service("userService")
public class UserService {
//    @Resource(name="userDAO")
    private UserDAO userDAO;

    public UserService() {
        System.out.println(this + "已创建");
    }

    //通过构造函数注入
    public UserService(UserDAO userDAO) {
        this.userDAO = userDAO;
        System.out.println(this + ":正在调用构造函数注入，UserService(" + userDAO + ")");
    }

    //通过Setter方法注入
    public void setUserDAO(UserDAO userDAO) {
        this.userDAO = userDAO;
        System.out.println(this + ":正在调用Setter方法注入，setUserDAO(" + userDAO + ")");
    }

    public void createUser(){
        System.out.println(this + ":正在调用UserService.createUser()");
        userDAO.insert();
    }
}

UserDAO

package com.imooc.spring.injection;

public interface UserDAO {
    public void insert();
}

UserDAOImpl

package com.imooc.spring.injection;

import org.springframework.stereotype.Repository;

//@Repository("userDAO")
public class UserDAOImpl implements UserDAO{
    public UserDAOImpl(){
        System.out.println(this + "已创建");
    }
    public void insert() {
        System.out.println(this + ":正在调用UserDAOImpl.insert()");
    }
}

AppConfig

package com.imooc.spring.injection;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class AppConfig {
    @Bean(name="userDAO")
    public UserDAO userDAO(){
        return new UserDAOImpl();
    }

    @Bean(name="userService")
    public UserService userService(){
        UserService userService = new UserService();
        userService.setUserDAO(this.userDAO());
        return userService;
    }
}

InjectionRunner

package com.imooc.spring.injection;

import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;

public class InjectionRunner {
    public static void main(String[] args) {
        ApplicationContext ctx = new ClassPathXmlApplicationContext("classpath:injection.xml");
        UserService userService = (UserService)ctx.getBean("userService");
        userService.createUser();
    }
}

injection.xml

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context.xsd">
    <context:component-scan base-package="com.imooc.spring"/>
    <!--<bean id="userDAO" class="com.imooc.spring.injection.UserDAOImpl"/>
    <bean id="userService" class="com.imooc.spring.injection.UserService">
        &lt;!&ndash;<property name="userDAO" ref="userDAO"/>&ndash;&gt;
        <constructor-arg name="userDAO" ref="userDAO"/>
    </bean>-->
</beans>

三.自动装配、spring注解开发、xml与注解

1.自动装配

<bean id="cat" class="Cat"/>
<bean id="dog" class="Dog"/>

<bean id="people" class="People" autowire="byName">
    <property name="name" value="red"/>
</bean>

ByName 会自动在容器上下文中查找，和自己对象set方法后面的值对应的beanid
ByType 会自动在容器上下文中查找，和自己对象属性类型相同的bean

注解实现自动装配 <context:annotation-config/> 注解驱动

@Autowired和@Resource的区别

都是用来自动装配的，都可以放在属性字段上
@Autowired 通过byType 的方式实现，而且必须要求这个对象存在
@Resource 默认通过ByName 的方式实现，如果找不到名字，则通过ByType实现，如果俩个都找不到就报错

2.spring注解开发

 在spring4之后，要使用注解，必须要保证aop包的引入了
 使用注解导入context约束，增加注解的支持


@Nullable 这个字段可以为空了
@Component组件  等价于<bean id="" class=""/> 名字默认类名的小写
@Value 等价于<property name="" value=""/>

衍生的注解  mvc三层架构分层 (@Resposity,@Service,@Controller)  把类放到容器中

@Scope(scopeName="singleton")  作用域

3.xml与注解
xml更加万能，适用于任何场合，维护简单方便
注解不是自己的类用不了，维护相对复杂

最佳实践
xml用来管理bean
注解完成属性的注入

Spring基础知识点

一.IOC实例化对象的三种方式：

二.DI四种注入方式

三.自动装配 、spring注解开发、xml与注解

三.自动装配、spring注解开发、xml与注解