kotlin+Autowired报错lateinit property has not been initialized？

Question

初学springboot，被mybatis-plus难住了。

我用Kotlin写的springboot项目，用mybatis-plus操作数据库，用@Autowired注入BaseMapper，但是在运行的时候却提示lateinit property registerUserDao has not been initialized，注入的对象没有被初始化。请问问题可能会出现在哪里呢？

项目结构

启动类：

@SpringBootApplication
@ComponentScan(value = ["com.jingyin.imusic_server_dao", "com.jingyin.imusic_server_api"])       // 扫描子模块中的RestController
@MapperScan(basePackages = ["com.jingyin.imusic_server_dao"])
class ImusicServerApplication

fun main(args: Array<String>) {
    runApplication<ImusicServerApplication>(*args)
    println("启动成功！")
}

数据库entity：

@TableName(value = "user_auth")
class DbUserAuth {

    @TableId(type = IdType.AUTO)
    var id: Long? = null
    var phone: String? = null
    var password: String? = null
    var token: String? = null

    @TableLogic
    var deleted: Int? = null

    companion object {
        fun new(
            id: Long?,
            phone: String?,
            password: String?,
            token: String?,
        ): DbUserAuth = DbUserAuth().apply {
            this.id = id
            this.phone = phone
            this.password = password
            this.token = token
            this.deleted = 0
        }
    }
}

dao调用数据库：

@Repository
public open interface RegisterUserMapper: BaseMapper<DbUserAuth> {

    fun queryByPhone(@Param("phone") phone: String): DbUserAuth? =
        selectOne(QueryWrapper<DbUserAuth>().eq("phone", phone))
}

service调用dao实现业务：

@Component
class RegisterUserService {
    这里报错：未被初始化
    这里报错：未被初始化
    这里报错：未被初始化
    @Autowired
    private lateinit var registerUserDao: RegisterUserMapper



    /**
     * @description: 查看是[phone]否有对应的用户
     * @author: lizhenxin
     * @date: 2022/10/13 下午5:04
     * @param phone 手机号码
     * @return 如果有注册用户，则返回该用户；否则返回空
     **/
    open fun checkLogin(phone: String): DbUserAuth? =
        registerUserDao.queryByPhone(phone)


    open fun insertRegisterUser(user: DbUserAuth) {
        registerUserDao.let {
            it.insert(user).run { println("insertRegisterUser result: $this") }
        }
    }
}

调用service的地方：

@RestController
@RequestMapping(value = ["/auth"])
class AuthApi {

    private val userService: RegisterUserService by lazy { RegisterUserService() }

    /**
     * @description: 用户登录
     * @author: lizhenxin
     * @date: 2022/10/13 下午5:57
     * @param
     * @return
     **/
    @PostMapping(value = ["/login"])
    fun login(@RequestBody request: String): String {
        val user = request.asJson<LoginInfo>()
        println("request: ${request}")
        println("login info: ${user}")
        return userService.checkLogin(user.phone)
            ?.let { "登录成功" }
            ?: let {
                userService.insertRegisterUser(createNewUser(user))
                "注册为新用户"
            }
    }

    private fun createNewUser(loginInfo: LoginInfo): DbUserAuth = DbUserAuth.new(
        id = 0,
        phone = loginInfo.phone,
        password = loginInfo.password,
        token = "sfdsdfsdf",
    )
}

报错：

kotlin.UninitializedPropertyAccessException: lateinit property registerUserDao has not been initialized
    at com.jingyin.imusic_server_service.authentication.RegisterUserService.checkLogin(RegisterUserService.kt:36) ~[main/:na]
    at com.jingyin.imusic_server_api.authentication.AuthApi.login(AuthApi.kt:39) ~[main/:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:na]
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na]
    at java.base/java.lang.reflect.Method.invoke(Method.java:566) ~[na:na]
    at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1071) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:964) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:681) ~[tomcat-embed-core-9.0.65.jar:4.0.FR]
    at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883) ~[spring-webmvc-5.3.23.jar:5.3.23]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:764) ~[tomcat-embed-core-9.0.65.jar:4.0.FR]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-5.3.23.jar:5.3.23]
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117) ~[spring-web-5.3.23.jar:5.3.23]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:197) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:97) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:541) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:135) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:78) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:360) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:399) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:65) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:890) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1789) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-9.0.65.jar:9.0.65]
    at java.base/java.lang.Thread.run(Thread.java:839) ~[na:na]

求大神指点我一下应该怎么排查这个错误，刚学springboot实在是无力啊

Answer 1

API里的service不是bean，不受spring管理，里面的dao也就没有注入
spring是可以注入kotlin的构造方法的，于是 RegisterUserService(val registerUserDao: RegisterUserMapper) 就可以了

---

建议要么学kotlin要么学spring，这俩一起来学不明白太正常了
另外kotlin长期看服务端应用有限，学了也用不上……除非做安卓