常用注解

1、用于创建bean对象的注解

1.1、@Component

package com.ly.spring;
import org.springframework.stereotype.Component;
//@Component：不配置value属性时通过类名小写获取person
//@Component(value = "pers"):只能通过配置的value属性值获取
//@Component("pers"):可省略value属性直接写value属性值
@Component("pers")
public class Person {
}

1.2、由@Component衍生出的注解

@Controller：一般用于创建表现层bean对象

@Service：一般用于创建业务层bean对象

@Repository：一般用于创建持久层bean对象

2、自动按照类型注入属性@Autowired

spring容器中一个该类型的bean也没找到时会报错

spring容器中只找到一个该类型的bean时会注入成功

spring容器中若找到多个该类型的bean时，会继续根据属性名去匹配容器中bean的id，若匹配上了唯一的一个则会注入成功，若还是没匹配到则会报错

package com.ly.spring.service.impl;

import com.ly.spring.dao.IAccountDao;
import com.ly.spring.service.IAccountService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

@Service
public class AccountServiceImpl implements IAccountService {
    @Autowired
    //accountDao为属性名，若找到多个该类型的bean则会继续根据此属性名去匹配
    private IAccountDao accountDao;
    @Override
    public void save() {
        System.out.println("AccountServiceImpl --- save");
        accountDao.save();
    }
}

3、用于注入数据的注解

3.1、@Qualifier注解，用于注入类的属性时不可以单独使用，需配合@Autowired注解

若spring容器中一个该类型的bean都没找到时会报错

若spring容器中只找到一个该类型的bean，则继续用@Qualifier注解的value属性值与找到的bean的id去匹配，若匹配到则注入成功，若没匹配到则报错

若spring容器中找到多个该类型的bean时，继续用@Qualifier注解的value属性值与找到的bean的id去匹配，若匹配到则注入成功，若没匹配到则报错

package com.ly.spring.service.impl;

import com.ly.spring.dao.IAccountDao;
import com.ly.spring.service.IAccountService;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Qualifier;
import org.springframework.stereotype.Service;

@Service
public class AccountServiceImpl implements IAccountService {
    @Autowired
    @Qualifier(value = "accountDao2")
    private IAccountDao accountDao1;
    @Override
    public void save() {
        System.out.println("AccountServiceImpl --- save");
        accountDao1.save();
    }
}

3.2、@Resource注解根据bean的id注入

需要引入javax.annotation.Resource

<dependency>
    <groupId>javax.annotation</groupId>
    <artifactId>javax.annotation-api</artifactId>
    <version>1.2</version>
</dependency>

package com.ly.spring.service.impl;
import com.ly.spring.dao.IAccountDao;
import com.ly.spring.service.IAccountService;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
@Service
public class AccountServiceImpl implements IAccountService {
    //name属性指定spring容器中bean的id
    @Resource(name = "accountDao1")
    private IAccountDao accountDao;
    public void save() {
        System.out.println("AccountServiceImpl --- save");
        accountDao.save();
    }
}

4、改变bean作用范围的注解@Scope

package com.ly.spring.service.impl;
import com.ly.spring.dao.IAccountDao;
import com.ly.spring.service.IAccountService;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
import java.util.List;

@Service
//@Scope(value = "prototype") 
//@Scope(value = "singleton") 单例，默认值
@Scope(value = "singleton")
public class AccountServiceImpl implements IAccountService {
    @Resource(name = "accountDao1")
    private IAccountDao accountDao;
    public void save() {
        System.out.println("AccountServiceImpl --- save");
        accountDao.save();
    }
}