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Spring IoC注解式开发

为什么使用注解

注解的存在主要是为了简化XML的配置，注解的开发能大大提高我们的开发效率的，但它在一定程度上违背了OCP原则。

Spring注解的使用

如何使用以上的注解呢？

第一步：加入aop的依赖

加入spring-context依赖之后，会关联加入aop的依赖，不用做

第二步：在配置文件中指定扫描的包，Alt+enter添加context命名空间 annotate.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"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 https://www.springframework.org/schema/context/spring-context.xsd"><context:component-scan base-package="com.w.spring6.annotate"/>
</beans>

第三步：在Bean类上使用注解

package com.w.spring6.annotate;import org.springframework.stereotype.Component;@Component(value = "userBean")
public class User {
}

编写测试程序：
AnnotationTest.java

package com.w.spring.test;import com.w.spring6.annotate.User;
import org.junit.Test;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;public class AnnotationTest {@Testpublic void testBean(){ApplicationContext applicationContext = new ClassPathXmlApplicationContext("annotate.xml");User userBean = applicationContext.getBean("userBean", User.class);System.out.println(userBean);}
}

运行结果：

@Value注解

当属性的类型是简单类型时，可以使用@Value注解进行注入。

例：
User.java

package com.w.spring6.annotate;import org.springframework.beans.factory.annotation.Value;
import org.springframework.stereotype.Component;@Component(value = "userBean")
public class User {@Value(value = "zhangsan")private String name;@Value("20")private int age;@Overridepublic String toString() {return "User{" +"name='" + name + '\'' +", age=" + age +'}';}
}

annotate.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"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 https://www.springframework.org/schema/context/spring-context.xsd"><context:component-scan base-package="com.w.spring6.annotate"/></beans>

测试程序：

    @Testpublic void testValue(){ApplicationContext applicationContext = new ClassPathXmlApplicationContext("annotate.xml");Object user = applicationContext.getBean("userBean");System.out.println(user);}

运行结果：

@Autowired注解

@Autowired注解可以用来注入非简单类型
单独使用@Autowired注解，默认根据类型装配。

例：
UserDao接口

package com.w.spring6.dao;public interface UserDao {void insert();
}

UserDaoForMySQL.java

package com.w.spring6.dao;import org.springframework.stereotype.Component;@Component //纳入bean管理
public class UserDaoForMySQL implements UserDao{@Overridepublic void insert() {System.out.println("正在向mysql数据库插入User数据");}
}

UserService.java

package com.w.spring6.service;import com.w.spring6.dao.UserDao;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;@Component // 纳入bean管理
public class UserService {@Autowired // 在属性上注入private UserDao userDao;// 没有提供构造方法和setter方法。public void save(){userDao.insert();}
}

annotate.xml

<context:component-scan base-package="com.w.spring6.dao,com.w.spring6.service"/>

测试程序：

@Test
public void testAutowired(){ApplicationContext applicationContext = new ClassPathXmlApplicationContext("annotate.xml");UserService userService = applicationContext.getBean("userService", UserService.class);userService.save();
}

运行结果：

全注解式开发

所谓的全注解开发就是不再使用spring配置文件了。写一个配置类来代替配置文件。

配置类代替spring配置文件
Spring6Configuration.java

package com.w.spring6.config;import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;@Configuration
@ComponentScan({"com.w.spring6.dao", "com.w.spring6.service"})
public class Spring6Configuration {
}

编写测试程序：不再new ClassPathXmlApplicationContext()对象了。

@Test
public void testNoXml(){ApplicationContext applicationContext = new AnnotationConfigApplicationContext(Spring6Configuration.class);UserService userService = applicationContext.getBean("userService", UserService.class);userService.save();
}

运行结果：