MyBatis The expression 'list' evaluated to a null value
阿新 • • 發佈：2018-11-12
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完整錯誤資訊：
嚴重: Servlet.service() for servlet [springmvc] in context with path [/xinghe-platform-web] threw exception [Request processing failed; nested exception is org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.builder.BuilderException: The expression 'list' evaluated to a null value.] with root causeorg.apache.ibatis.builder.BuilderException: The expression 'list' evaluated to a null value. at org.apache.ibatis.scripting.xmltags.ExpressionEvaluator.evaluateIterable(ExpressionEvaluator.java:40) at org.apache.ibatis.scripting.xmltags.ForEachSqlNode.apply(ForEachSqlNode.java:54) at org.apache.ibatis.scripting.xmltags.MixedSqlNode.apply(MixedSqlNode.java:32) at org.apache.ibatis.scripting.xmltags.DynamicSqlSource.getBoundSql(DynamicSqlSource.java:40) at org.apache.ibatis.mapping.MappedStatement.getBoundSql(MappedStatement.java:278) at org.apache.ibatis.executor.BaseExecutor.query(BaseExecutor.java:118) at sun.reflect.GeneratedMethodAccessor67.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49) at com.xinghe.frame.mybatis.FlushCacheInterceptor.intercept(FlushCacheInterceptor.java:61) at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:60) at com.sun.proxy.$Proxy24.query(Unknown Source) at sun.reflect.GeneratedMethodAccessor67.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.apache.ibatis.plugin.Invocation.proceed(Invocation.java:49) at com.xinghe.frame.mybatis.OffsetLimitInterceptor.intercept(OffsetLimitInterceptor.java:55) at org.apache.ibatis.plugin.Plugin.invoke(Plugin.java:60) at com.sun.proxy.$Proxy24.query(Unknown Source) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:108) at org.apache.ibatis.session.defaults.DefaultSqlSession.selectList(DefaultSqlSession.java:102) at sun.reflect.GeneratedMethodAccessor71.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.mybatis.spring.SqlSessionTemplate$SqlSessionInterceptor.invoke(SqlSessionTemplate.java:358) at com.sun.proxy.$Proxy17.selectList(Unknown Source) at org.mybatis.spring.SqlSessionTemplate.selectList(SqlSessionTemplate.java:198) at com.xinghe.platform.dao.ResScoreDao.getByResourceLocalId(ResScoreDao.java:43) at com.xinghe.platform.service.ResScoreManager.getByResourceLocalId(ResScoreManager.java:41) at com.xinghe.platform.service.ResScoreManager$$FastClassBySpringCGLIB$$68ba2513.invoke(<generated>) at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:204) at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:717) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:157) at org.springframework.transaction.interceptor.TransactionInterceptor$1.proceedWithInvocation(TransactionInterceptor.java:99) at org.springframework.transaction.interceptor.TransactionAspectSupport.invokeWithinTransaction(TransactionAspectSupport.java:281) at org.springframework.transaction.interceptor.TransactionInterceptor.invoke(TransactionInterceptor.java:96) at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:179) at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:653) at com.xinghe.platform.service.ResScoreManager$$EnhancerBySpringCGLIB$$9b94cd4.getByResourceLocalId(<generated>) at com.xinghe.platform.action.ResResourcePublic.getScore(ResResourcePublic.java:433) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source) at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source) at java.lang.reflect.Method.invoke(Unknown Source) at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:177) at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:446) at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:434) at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:943) at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:877) at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:966) at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:857) at javax.servlet.http.HttpServlet.service(HttpServlet.java:622) at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:842) at javax.servlet.http.HttpServlet.service(HttpServlet.java:729) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:291) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at com.auth.filter.AuthorizationFilter.doFilterInternal(AuthorizationFilter.java:77) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344) at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at com.auth.filter.AuthenticationFilter.doFilterInternal(AuthenticationFilter.java:115) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344) at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at com.xinghe.activate.filter.ActivateFilter.doFilterInternal(ActivateFilter.java:52) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.springframework.web.filter.DelegatingFilterProxy.invokeDelegate(DelegatingFilterProxy.java:344) at org.springframework.web.filter.DelegatingFilterProxy.doFilter(DelegatingFilterProxy.java:261) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88) at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:239) at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206) at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:219) at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:106) at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502) at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:142) at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79) at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:617) at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:88) at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:518) at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1091) at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:668) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1521) at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.run(NioEndpoint.java:1478) at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) at java.lang.Thread.run(Unknown Source)
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**環境：**Java專案，SpringMVC+MyBatis框架，
此錯誤的原始碼位置：
看到 MyBatisSystemException ，首先想到的是錯誤可能發生在ResScoreMapper.xml 檔案中，但Dao層直接與Mapper.xml檔案相關聯，檢視錯誤資訊可以看到以下資訊：
com.xinghe.platform.dao.ResScoreDao.getByResourceLocalId(ResScoreDao.java:43)
我遇到的這個錯誤就發生在這裡！
錯誤原因：
說起錯誤原因，這裡犯了一個小兒科的錯誤，從別的Dao檔案中複製過來的程式碼，方法名改了，selectOne 中呼叫的Mapper中的命令空間及方法名忘記改了，所以導致此錯誤；
修正後如下：
由於 selectOne SQL返回多條記錄時會出異常，所以這裡改用：selectList 。
2018-10-30更新
有小夥伴反應沒看懂，我這裡再詳細說一下。
1、注意 selectOne 和 selectList，一個返回一條，一個返回多條。
2、mapper.xml裡面是否存在對應的SQL定義。看圖：
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