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CONCAT函数使用中出现空指针异常问题分析

news 2025/11/5 9:37:49

文章目录

前言
为什么？
如何解决？
总结

前言

在项目中，遇到一个场景，使用mysql的CONCAT函数实现字段值拼接，出现如下报错：
总的来说：空指针异常。

原始sql:

<select id="findFailedTaskNames" resultType="java.lang.String">SELECTCONCAT(software_name, '_', software_version, '_', developer) as taskNameFROMxxxWHEREid IN<foreach collection="list" item="item" open="(" close=")" separator=",">#{item}</foreach>
</select>

报错：

2025-11-03 11:10:16.596 [jyh-detect-whl] traceId[] [http-nio-10002-exec-3] ERROR c.q.w.t.c.s.h.ControllerExceptionAdvice - [handleRuntimeException,83] - 请求地址'/detect/task/storage/delete/tasks',发生未知异常.
java.lang.NullPointerException: nullat cn.qbs.wa.teach.course.standard.service.impl.CodeCheckTaskServiceImpl.lambda$deleteFailedTasks$5(CodeCheckTaskServiceImpl.java:417)at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:195)at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1655)at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:484)at java.base/java.util.stream.AbstractPipeline.wrapAndCopyInto(AbstractPipeline.java:474)at java.base/java.util.stream.ReduceOps$ReduceOp.evaluateSequential(ReduceOps.java:913)at java.base/java.util.stream.AbstractPipeline.evaluate(AbstractPipeline.java:234)at java.base/java.util.stream.ReferencePipeline.collect(ReferencePipeline.java:578)at cn.qbs.wa.teach.course.standard.service.impl.CodeCheckTaskServiceImpl.deleteFailedTasks(CodeCheckTaskServiceImpl.java:418)at cn.qbs.wa.teach.course.standard.service.impl.CodeCheckTaskServiceImpl$$FastClassBySpringCGLIB$$372942fe.invoke(<generated>)at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218)at org.springframework.aop.framework.CglibAopProxy.invokeMethod(CglibAopProxy.java:386)at org.springframework.aop.framework.CglibAopProxy.access$000(CglibAopProxy.java:85)at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:704)at cn.qbs.wa.teach.course.standard.service.impl.CodeCheckTaskServiceImpl$$EnhancerBySpringCGLIB$$e6d08e42.deleteFailedTasks(<generated>)at cn.qbs.wa.teach.course.standard.controller.web.TrustApplyController.deleteFailedTasks(TrustApplyController.java:152)at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)at java.base/java.lang.reflect.Method.invoke(Method.java:566)at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:205)at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:150)at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:117)at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895)at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:808)at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87)at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1067)at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:963)at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:1006)at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:909)at javax.servlet.http.HttpServlet.service(HttpServlet.java:681)at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:883)at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:227)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:100)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:93)at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:117)at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:189)at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:162)

为什么？

这是因为，部分字段的值为null，在大多数数据库中（MySQL、PostgreSQL等），CONCAT 函数中任何参数为 NULL 都会导致整个结果为 NULL。

如何解决？

使用 CONCAT_WS,CONCAT_WS 会忽略 NULL 值，只连接非 NULL 的部分。
使用数据库特定的函数：
- MySQL: IFNULL(字段名, ‘’) 或 COALESCE(字段名, ‘’)
- PostgreSQL: COALESCE(字段名, ‘’)
使用 CASE WHEN
- CASE WHEN 字段名 IS NULL THEN '' ELSE 字段名 END