얼거스 개발 일지

MyBatis를 공부하던 중에

xml mapper를 익혀보려고

Dto 클래스 두 개를 만들어서

다른 하나에 조인을 걸어 출력해 보는 실습을 해보고 있었는데,

계속 오류가 났다.

오류 메시지

2023-05-30T01:05:29.362+09:00 ERROR 12160 --- [nio-8080-exec-6] o.a.c.c.C.[.[.[/].[dispatcherServlet]    : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed: org.mybatis.spring.MyBatisSystemException] with root cause  java.lang.ClassCastException: Cannot cast java.lang.String to kim.zhyn.mybatis.dto.TestDto 	at java.base/java.lang.Class.cast(Class.java:3946) ~[na:na] 	at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:67) ~[na:na] 	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:500) ~[na:na] 	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:484) ~[na:na] 	at org.apache.ibatis.reflection.factory.DefaultObjectFactory.instantiateClass(DefaultObjectFactory.java:77) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.reflection.factory.DefaultObjectFactory.create(DefaultObjectFactory.java:53) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.applyConstructorAutomapping(DefaultResultSetHandler.java:774) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.createByConstructorSignature(DefaultResultSetHandler.java:721) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.createResultObject(DefaultResultSetHandler.java:685) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.createResultObject(DefaultResultSetHandler.java:655) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.getRowValue(DefaultResultSetHandler.java:436) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValuesForNestedResultMap(DefaultResultSetHandler.java:1020) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleRowValues(DefaultResultSetHandler.java:331) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSet(DefaultResultSetHandler.java:306) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.resultset.DefaultResultSetHandler.handleResultSets(DefaultResultSetHandler.java:202) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.statement.PreparedStatementHandler.query(PreparedStatementHandler.java:66) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.statement.RoutingStatementHandler.query(RoutingStatementHandler.java:80) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.SimpleExecutor.doQuery(SimpleExecutor.java:65) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.BaseExecutor.queryFromDatabase(BaseExecutor.java:333) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:158) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:110) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.executor.CachingExecutor.query(CachingExecutor.java:90) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:154) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:147) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:142) ~[mybatis-3.5.13.jar:3.5.13] 	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104) ~[na:na] 	at java.base/java.lang.reflect.Method.invoke(Method.java:578) ~[na:na] 	at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:425) ~[mybatis-spring-3.0.2.jar:3.0.2] 	at jdk.proxy2/jdk.proxy2.$Proxy60.selectList(Unknown Source) ~[na:na] 	at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:224) ~[mybatis-spring-3.0.2.jar:3.0.2] 	at org.apache.ibatis.binding.MapperMethod.executeForMany(MapperMethod.java:147) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.binding.MapperMethod.execute(MapperMethod.java:80) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.binding.MapperProxy$PlainMethodInvoker.invoke(MapperProxy.java:142) ~[mybatis-3.5.13.jar:3.5.13] 	at org.apache.ibatis.binding.MapperProxy.invoke(MapperProxy.java:86) ~[mybatis-3.5.13.jar:3.5.13] 	at jdk.proxy2/jdk.proxy2.$Proxy64.findAllJoinId(Unknown Source) ~[na:na] 	at kim.zhyn.mybatis.service.TestXmlServiceimpl.findAllJoinId(TestXmlServiceimpl.java:28) ~[classes/:na] 	at kim.zhyn.mybatis.controller.TestController.get4(TestController.java:42) ~[classes/:na] 	at java.base/jdk.internal.reflect.DirectMethodHandleAccessor.invoke(DirectMethodHandleAccessor.java:104) ~[na:na] 	at java.base/java.lang.reflect.Method.invoke(Method.java:578) ~[na:na] 	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:207) ~[spring-web-6.0.9.jar:6.0.9] 	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:152) ~[spring-web-6.0.9.jar:6.0.9] 	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:118) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:884) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:797) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1081) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:974) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1011) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:903) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:564) ~[tomcat-embed-core-10.1.8.jar:6.0] 	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:885) ~[spring-webmvc-6.0.9.jar:6.0.9] 	at jakarta.servlet.http.HttpServlet.service(HttpServlet.java:658) ~[tomcat-embed-core-10.1.8.jar:6.0] 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:205) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:51) ~[tomcat-embed-websocket-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100) ~[spring-web-6.0.9.jar:6.0.9] 	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.0.9.jar:6.0.9] 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93) ~[spring-web-6.0.9.jar:6.0.9] 	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.0.9.jar:6.0.9] 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:201) ~[spring-web-6.0.9.jar:6.0.9] 	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:116) ~[spring-web-6.0.9.jar:6.0.9] 	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:174) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:149) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:166) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:90) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:482) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:115) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:93) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:341) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:390) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:63) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:894) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1741) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:52) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.tomcat.util.threads.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1191) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.tomcat.util.threads.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:659) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) ~[tomcat-embed-core-10.1.8.jar:10.1.8] 	at java.base/java.lang.Thread.run(Thread.java:1589) ~[na:na]

핵심은 java.lang.ClassCastException: Cannot cast java.lang.String to kim.zhyn.mybatis.dto.TestDto

이 문장인데,

TestDto를 UserDto에 조인해서 UserDto로 출력하려고 시도했다가 발생한 오류이다.

나는 Dto 클래스에 어노테이션을

@ToString
@Getter
@Setter
@Builder

이 4개를 붙여주어서 다음 형태를 갖추고 있었는데

@Getter
@Setter
@ToString
@Builder
public class TestDto {
 
    int idx;
    String description;
 
}
 
@Getter
@Setter
@ToString
@Builder
public class UserDto {
 
    int idx;
    String name;
 
    // xml mapper에서 사용
    private TestDto testDto;
 
}

해결 방법은

@ToString
@Getter
@Setter

이 3개의 어노테이션을 사용하는 거였다.

문제를 일으킨 어노테이션은 @Builder 어노테이션이었다.

@Builder 어노테이션을 제거해 주니 정상적으로 동작하였다.

왤까 🥸