<dependencies>
<dependency>
<groupId>org.springframeworkgroupId>
<artifactId>spring-contextartifactId>
<version>6.0.3version>
dependency>
<dependency>
<groupId>org.junit.jupitergroupId>
<artifactId>junit-jupiter-apiartifactId>
dependency>
<dependency>
<groupId>org.apache.logging.log4jgroupId>
<artifactId>log4j-coreartifactId>
<version>2.19.0version>
dependency>
<dependency>
<groupId>org.apache.logging.log4jgroupId>
<artifactId>log4j-slf4j2-implartifactId>
<version>2.19.0version>
dependency>
dependencies>
Spring 默认不使用注解装配 Bean,因此我们需要在 Spring 的 XML 配置中,通过 context:component-scan 元素开启 Spring Beans的自动扫描功能。开启此功能后,Spring 会自动从扫描指定的包(base-package 属性设置)及其子包下的所有类,如果类上使用了 @Component 注解,就将该类装配到容器中。
<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-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="org.kkk.spring6">context:component-scan>
beans>
注意:在使用 context:component-scan 元素开启自动扫描功能前,首先需要在 XML 配置的一级标签 中添加 context 相关的约束。使用方式如下:
方式一:最基本的扫描方式
<context:component-scan base-package="org.kkk.spring6"> context:component-scan>
方式二:指定要排除的组件
<context:component-scan base-package="org.kkk.spring6">
<context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
context:component-scan>
方式三:仅扫描指定组件
<context:component-scan base-package="org.kkk" use-default-filters="false">
<context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
context:component-scan>
Spring 提供了以下多个注解,这些注解可以直接标注在 Java 类上,将它们定义成 Spring Bean。
注解 | 说明 |
---|---|
@Component | 该注解用于描述 Spring 中的 Bean,它是一个泛化的概念,仅仅表示容器中的一个组件(Bean),并且可以作用在应用的任何层次,例如 Service 层、Dao 层等。 使用时只需将该注解标注在相应类上即可。 |
@Repository | 该注解用于将数据访问层(Dao 层)的类标识为 Spring 中的 Bean,其功能与 @Component 相同。 |
@Service | 该注解通常作用在业务层(Service 层),用于将业务层的类标识为 Spring 中的 Bean,其功能与 @Component 相同。 |
@Controller | 该注解通常作用在控制层(如SpringMVC 的 Controller),用于将控制层的类标识为 Spring 中的 Bean,其功能与 @Component 相同。 |
单独使用@Autowired注解,默认根据类型装配。在需要注入的属性上添加注解@Autowired即可,spring会自动根据类型进行注入。
例如:
创建UserServiceImpl实现类,且给这个实现类添加注解service,将其交给容器管理。
package org.kkk.spring6.service.impl;
import org.kkk.spring6.dao.UserDao;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
@Autowired
private UserDao userDao;
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
在UserController类中,在属性userService上添加注解autowired,那么spring就可以进行属性注入。
package org.kkk.spring6.controller;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
@Autowired
private UserService userService;
public void out() {
userService.out();
System.out.println("Controller层执行结束。");
}
}
与3.1不同,在3.1中,注解autowired是添加在属性上,而set注入是将注解autowired添加到该属性的set方法上。举例如下:
修改UserServiceImpl类
package org.kkk.spring6.service.impl;
import org.kkk.spring6.dao.UserDao;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
private UserDao userDao;
@Autowired
public void setUserDao(UserDao userDao) {
this.userDao = userDao;
}
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
修改UserController类,注意注解@Autowired的位置
package org.kkk.spring6.controller;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
private UserService userService;
@Autowired
public void setUserService(UserService userService) {
this.userService = userService;
}
public void out() {
userService.out();
System.out.println("Controller层执行结束。");
}
}
这种方式是将注解@autowired加在有参构造函数上。举例如下:
修改UserServiceImpl类
package org.kkk.spring6.service.impl;
import org.kkk.spring6.dao.UserDao;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
private UserDao userDao;
@Autowired
public UserServiceImpl(UserDao userDao) {
this.userDao = userDao;
}
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
修改UserController类
package org.kkk.spring6.controller;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
private UserService userService;
@Autowired
public UserController(UserService userService) {
this.userService = userService;
}
public void out() {
userService.out();
System.out.println("Controller层执行结束。");
}
}
这种方式与3.3类似,也需要有参构造函数。与3.3不同的是,这种方式需要将注解加在形参前面。举例如下:
修改UserServiceImpl类
package org.kkk.spring6.service.impl;
import org.kkk.spring6.dao.UserDao;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
private UserDao userDao;
public UserServiceImpl(@Autowired UserDao userDao) {
this.userDao = userDao;
}
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
修改UserController类
package org.kkk.spring6.controller;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
@Controller
public class UserController {
private UserService userService;
public UserController(@Autowired UserService userService) {
this.userService = userService;
}
public void out() {
userService.out();
System.out.println("Controller层执行结束。");
}
}
当构造方法只有一个,且该构造方法是有参构造时,@Autowired注解可以省略。 举例如下:
修改UserServiceImpl类
package org.kkk.spring6.service.impl;
import org.kkk.spring6.dao.UserDao;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
private UserDao userDao;
public UserServiceImpl(UserDao userDao) {
this.userDao = userDao;
}
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
如果一个类型的Bean数量超过一个时,那么根据这个类型去进行属性注入会出现错误。这种情况下,如果要正确的进行属性注入,那就需要用到注解Qualifier根据名称进行装配。
举例如下:
添加dao层实现,此时接口UserDao的实现类有两个,因此无法只根据类型进行装配。
package org.kkk.spring6.dao.impl;
import org.kkk.spring6.dao.UserDao;
import org.springframework.stereotype.Repository;
@Repository
public class UserDaoRedisImpl implements UserDao {
@Override
public void print() {
System.out.println("Redis Dao层执行结束");
}
}
修改UserServiceImpl类,使用注解Qualifier根据名称进行装配。
package org.kkk.spring6.service.impl;
import org.kkk.spring6.dao.UserDao;
import org.kkk.spring6.service.UserService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
@Autowired
@Qualifier("userDaoImpl") // 指定bean的名字
private UserDao userDao;
@Override
public void out() {
userDao.print();
System.out.println("Service层执行结束");
}
}
@Resource注解也可以完成属性注入。它和@Autowired注解区别如下:
@Resource注解属于JDK扩展包,所以不在JDK当中,需要额外引入以下依赖:【如果是JDK8的话不需要额外引入依赖。高于JDK11或低于JDK8需要引入以下依赖。】
<dependency>
<groupId>jakarta.annotationgroupId>
<artifactId>jakarta.annotation-apiartifactId>
<version>2.1.1version>
dependency>
修改UserDaoImpl类
package org.kkk.spring6.dao.impl;
import org.kkk.spring6.dao.UserDao;
import org.springframework.stereotype.Repository;
@Repository("myUserDao")
public class UserDaoImpl implements UserDao {
@Override
public void print() {
System.out.println("Dao层执行结束");
}
}
修改UserServiceImpl类
package org.kkk.spring6.service.impl;
import org.kkk.spring6.dao.UserDao;
import org.kkk.spring6.service.UserService;
import jakarta.annotation.Resource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
@Resource(name = "myUserDao")
private UserDao myUserDao;
@Override
public void out() {
myUserDao.print();
System.out.println("Service层执行结束");
}
}
当@Resource注解使用时没有指定name的时候,还是根据name进行查找,这个name是属性名。
修改UserDaoImpl类
package org.kkk.spring6.dao.impl;
import org.kkk.spring6.dao.UserDao;
import org.springframework.stereotype.Repository;
@Repository("myUserDao")
public class UserDaoImpl implements UserDao {
@Override
public void print() {
System.out.println("Dao层执行结束");
}
}
修改UserServiceImpl类
package org.kkk.spring6.service.impl;
import org.kkk.spring6.dao.UserDao;
import org.kkk.spring6.service.UserService;
import jakarta.annotation.Resource;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;
@Service
public class UserServiceImpl implements UserService {
@Resource
private UserDao myUserDao;
@Override
public void out() {
myUserDao.print();
System.out.println("Service层执行结束");
}
}
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。
package org.kkk.spring6.config;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan("org.kkk.spring6")
public class Spring6Config {
}
加载方法与XML相同
@Test
public void testAllAnnotation(){
ApplicationContext context = new AnnotationConfigApplicationContext(Spring6Config.class);
UserController userController = context.getBean("userController", UserController.class);
userController.out();
logger.info("执行成功");
}