CONCAT函数使用中出现空指针异常问题分析

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">
      SELECT
          CONCAT(software_name, '_', software_version, '_', developer) as taskName
      FROM
          xxx
      WHERE
          id 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: null
  at cn.qbs.wa.teach.course.standard.service.impl.CodeCheckTaskServiceImpl.lambdadeleteFailedTasks5(CodeCheckTaskServiceImpl.java:417)
  at java.base/java.util.stream.ReferencePipeline31.accept(ReferencePipeline.java:195)
  at java.base/java.util.ArrayListArrayListSpliterator.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.ReduceOpsReduceOp.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.access000(CglibAopProxy.java:85) at org.springframework.aop.framework.CglibAopProxyDynamicAdvisedInterceptor.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

总结

以上为个人学习分享，如有问题，欢迎指出：）