我遇到的关于spring注解的问题

一、关于bean对象的参数为空的问题

我最开始通过@Repository来创建Mapper实现类的bean，结果报错了

nested exception is java.lang.IllegalArgumentException: Property
 ‘sqlSessionFactory’ or ‘sqlSessionTemplate’ are required

报错原因：是我Mapper实现类是继承了SqlSessionDaoSupport，其中有个参数SqlSessionFactoryTemplate没有注入，所以就报错了。

所以建议在通过继承SqlSessionDaoSupport来写mapper的实现类时，用xml文件来管理bean。

二、关于bean对象名字匹配问题

@Component
@Controller【Controller层】
@Service 【Service层】
@Repository 【Dao层】
四个注册bean对象的注解，其不带参数值的会，bean的id默认为以开头为小写的类的驼峰式命名，举个栗子：
UserServiceImpl，使用注解注册bean时，其bean的id时“userServiceImpl”。
好了，所到这里也没什么重要的，但是我们通常在获取bean对象的时候，我们一般是获取该bean的接口名，而不是实体类的名字，也就是"userService",所以这是就会出现如下错误

org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named ‘studentService’ available

其实遇到这种情况一般都是注册bean失败或者注册的和注入的bean名字不相同导致的

三、关于Controller层注入Service失败

这个问题在我打算第一次整合ssm框架，写个项目时出现的，困扰我了几日天，然后在网上查找很久才解决了，所以我打算在这提一下，免得记性不好的我又遇见这种折磨我的错误。OK，我们进入正题，直接上代码
Service层

@Service
public class StudentServiceImpl implements StudentService{
    private StudentMapper studentMapper;
    private RecordMapper recordMapper;
    private BookMapper bookMapper;
    @Override
    public Student login(Map<String, Object> map) {
        System.out.println("studentMapper:"+studentMapper);
        return studentMapper.loginQuery(map);
    }

    @Override
    public int updatePwd(Map<String, Object> map) {
        return studentMapper.updatePwd(map);
    }

    @Override
    public int updateInfo(Student student) {
        return studentMapper.update(student);
    }

    @Override
    public List<Map<String,Object>> borrowBook(Map<String, Object> map) {
        //添加借书记录
        map.put("rTime", TimeUtil.getCurrentDateAndTime());
        map.put("rState","未还");
        Record record = MapToClass.toRecord(map);
        recordMapper.add(record);
        //图书数量减一
        map.put("bAvailable",(Integer) map.get("bAvailable")-1);
        Book book = MapToClass.toBook(map);
        bookMapper.update(book);
        //返回结果
        return recordMapper.query(map);
    }

    @Override
    public List<Map<String, Object>> returnBook(Map<String, Object> map) {
        //归还图书状态
        map.put("rTime",TimeUtil.getCurrentDateAndTime());
        map.put("rState","已还");
        recordMapper.update(map);
        //图书数量加一
        map.put("bAvailable",(Integer) map.get("bAvailable")+1);
        Book book = MapToClass.toBook(map);
        bookMapper.update(book);
        //返回结果
        return recordMapper.query(map);
    }
    //set注入
    @Autowired
    public void setStudentMapper(StudentMapper studentMapper) {
        this.studentMapper = studentMapper;
    }
    @Autowired
    public void setRecordMapper(RecordMapper recordMapper) {
        this.recordMapper = recordMapper;
    }
    @Autowired
    public void setBookMapper(BookMapper bookMapper) {
        this.bookMapper = bookMapper;
    }

Controller层

@RestController
public class StudentController {
    private StudentService studentService;
    //学生登录
    @RequestMapping("/student/login")
    public String login(@RequestParam String sId,@RequestParam String sPwd){
        Map<String,Object> map = new HashMap<>();
        map.put("sId",Integer.valueOf(sId));
        map.put("sPwd",sPwd);
        Student student = studentService.login(map);
        ObjectMapper mapper = new ObjectMapper();
        String sInfo = null;
        try {
            sInfo = mapper.writeValueAsString(student);
        }catch (JsonProcessingException e){
            e.printStackTrace();
        }
        System.out.println(student);
        return sInfo;
    }
    @Autowired
    public void setStudentService(StudentService studentService) {
        this.studentService = studentService;
    }
}

咋一看，该注入的都注入，该注册的都注册了，结果一启动Tomcat
直接报了一个很长的错误

Unsatisfied dependency expressed through method ‘setStudentService’ parameter 0; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type ‘com.hoary.service.StudentService’ available: expected at least 1 bean which qualifies as autowire candidate. Dependency annotations: {}

这个问题困扰了我很久，直到我到网上去查，才知道，原来是web.xml文件中加载的spring容器压根就没有service bean。
web.xml

<servlet>
    <servlet-name>springmvc</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:springmvc-servlet.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>springmvc</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

然后我将springmvc-servlet.xml改成aplicaitonContext.xml就行了，其实问题很简单，但是简单的Bug也架不住学艺不精的我呀！

最后希望各位同僚大佬能看得起鄙人，有bug可以私信我，我可以来学习学习。嘻嘻🤭