1. 什么是注解
(1)注解是代码中的特殊标记,格式为:@注解名称(属性名称=属性值, 属性名称=属性值, …)
(2)注解可以作用在类、方法、属性上面
(3)使用注解的目的:简化xml配置
2. 使用注解管理Bean
2.1 基于注解方式创建对象
2.1.1 注解说明
- @Component
- @Service
- @Controller
- @Repository
上面四个注解功能是一样的,都可以用来创建bean实例,为了区分不同层级的功能,因此建议不同的层级用不同注解进行表示
2.1.2 代码实现
-
引入依赖
需要引入apo依赖
-
开启组件扫描
<?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 http://www.springframework.org/schema/context/spring-context.xsd">
<context:component-scan base-package="com.study.spring5.demo10"></context:component-scan>
</beans>
-
创建UserService类,在类上面添加创建对象的注解
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Service;
@Service
public class UserService {
public void add() {
System.out.println("service add");
}
}
-
创建主方法
public class Main {
public static void main(String[] args) {
ApplicationContext applicationContext =
new ClassPathXmlApplicationContext("bean10.xml");
UserService userService = applicationContext.getBean("userService", UserService.class);
userService.add();
}
}
2.2 组件扫描配置
UserService类
import org.springframework.stereotype.Component;
import org.springframework.stereotype.Controller;
import org.springframework.stereotype.Service;
@Controller
public class UserService {
public void add() {
System.out.println("service add");
}
}
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"
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.study.spring5.demo11" use-default-filters="false">
<context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
</context:component-scan>
<context:component-scan base-package="com.study.spring5.demo11">
<context:exclude-filter type="annotation" expression="org.springframework.stereotype.Component"/>
</context:component-scan>
</beans>
主方法
public class Main {
public static void main(String[] args) {
ApplicationContext applicationContext =
new ClassPathXmlApplicationContext("bean11.xml");
UserService userService = applicationContext.getBean("userService", UserService.class);
userService.add();
}
}
2.3 基于注解方式实现属性注入
2.3.1 注解说明
-
@Autowired
根据属性类型进行自动注入
-
@Qualifier
根据属性名称进行注入
-
@Resource
可以根据类型注入,也可以根据名称注入
-
@Value
注入普通类型属性
2.3.2 代码实现
-
@Autowired
第一步:创建service和dao对象,在service和dao类添加创建对象的注解
UserService类
@Service
public class UserService {
public void add() {
System.out.println("UserService::add");
}
}
UserDao接口
public interface UserDao {
void add();
}
UserDao接口实现类UserDaoImpl
@Repository
public class UserDaoImpl implements UserDao {
@Override
public void add() {
System.out.println("UserDaoImpl::add");
}
}
第二步:在service注入dao对象,在UserServiceImpl类添加UserDao类型属性
将UserService改为以下内容
@Service
public class UserService {
@Autowired
private UserDao userDao;
public void add() {
System.out.println("UserService::add");
userDao.add();
}
}
主方法
public class Main {
public static void main(String[] args) {
ApplicationContext applicationContext =
new ClassPathXmlApplicationContext("bean12.xml");
UserService userService = applicationContext.getBean("userService", UserService.class);
userService.add();
}
}
-
@Qualifier
需要和@Autowired一起使用
用于当一个接口有多个实现类时候,按照名称注入指定的实现类
UserDaoImpl改为
@Repository(value = "userDaoImpl")
public class UserDaoImpl implements UserDao {
@Override
public void add() {
System.out.println("UserDaoImpl::add");
}
}
UserService改为
@Service
public class UserService {
@Autowired
@Qualifier(value = "userDaoImpl")
private UserDao userDao;
public void add() {
System.out.println("UserService::add");
userDao.add();
}
}
-
@Resource(spring不建议使用)
JDK11版本及以上需要引用javax.annotation-api才可使用@Resource注解
将UserService改为
@Service
public class UserService {
@Resource(name = "userDaoImpl")
private UserDao userDao;
public void add() {
System.out.println("UserService::add");
userDao.add();
}
}
-
@Value
UserService改写为
@Service
public class UserService {
@Resource(name = "userDaoImpl")
private UserDao userDao;
@Value(value = "注入的名称")
private String name;
public void add() {
System.out.println("UserService::add");
userDao.add();
System.out.println("注入的name值:" + name);
}
}
2.4 完全注解开发
-
创建配置类,替代xml配置文件
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
@Configuration
@ComponentScan(basePackages = {"com.study.spring5.demo13"})
public class SpringConfig {
}
-
编写UserDao接口
public interface UserDao {
void add();
}
-
编写UserDaoImpl实现类
@Repository
public class UserDaoImpl implements UserDao {
@Override
public void add() {
System.out.println("UserDaoImpl::add");
}
}
-
编写主方法
public class Main {
public static void main(String[] args) {
ApplicationContext applicationContext =
new AnnotationConfigApplicationContext(SpringConfig.class);
UserService userService = applicationContext.getBean("userService", UserService.class);
userService.add();
}
}
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