解决MapStruct映射处理器报错：java: Internal error in the mapping processor: java.lang.NullPointerException

引言

MapStruct是一个强大的Java映射框架，它能够在编译时生成映射代码，提高了映射的性能。然而，有时候在使用MapStruct时可能会遇到一些问题，其中之一就是java: Internal error in the mapping processor: java.lang.NullPointerException错误。

错误原因

这个错误通常是由于MapStruct在处理映射时出现了空指针异常引起的。可能的原因是：
版本兼容性问题： 使用不兼容的MapStruct版本可能导致内部处理器错误。

 
 <dependency>
      <groupId>org.mapstructgroupId>
      <artifactId>mapstructartifactId>
      <version>1.3.1.Finalversion>
  dependency>
  
  <dependency>
      <groupId>org.mapstructgroupId>
      <artifactId>mapstruct-processorartifactId>
      <version>1.3.1.Finalversion>
  dependency>

java: Internal error in the mapping processor: java.lang.NullPointerException  	at org.mapstruct.ap.internal.processor.DefaultVersionInformation.createManifestUrl(DefaultVersionInformation.java:182)  	at org.mapstruct.ap.internal.processor.DefaultVersionInformation.openManifest(DefaultVersionInformation.java:153)  	at org.mapstruct.ap.internal.processor.DefaultVersionInformation.getLibraryName(DefaultVersionInformation.java:129)  	at org.mapstruct.ap.internal.processor.DefaultVersionInformation.getCompiler(DefaultVersionInformation.java:122)  	at org.mapstruct.ap.internal.processor.DefaultVersionInformation.fromProcessingEnvironment(DefaultVersionInformation.java:95)  	at org.mapstruct.ap.internal.processor.DefaultModelElementProcessorContext.<init>(DefaultModelElementProcessorContext.java:50)  	at org.mapstruct.ap.MappingProcessor.processMapperElements(MappingProcessor.java:218)  	at org.mapstruct.ap.MappingProcessor.process(MappingProcessor.java:156)  	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)  	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)  	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)  	at java.lang.reflect.Method.invoke(Method.java:498)  	at org.jetbrains.jps.javac.APIWrappers$1.invoke(APIWrappers.java:248)  	at org.mapstruct.ap.MappingProcessor.process(Unknown Source)  	at com.sun.tools.javac.processing.JavacProcessingEnvironment.callProcessor(JavacProcessingEnvironment.java:794)  	at com.sun.tools.javac.processing.JavacProcessingEnvironment.discoverAndRunProcs(JavacProcessingEnvironment.java:705)  	at com.sun.tools.javac.processing.JavacProcessingEnvironment.access$1800(JavacProcessingEnvironment.java:91)  	at com.sun.tools.javac.processing.JavacProcessingEnvironment$Round.run(JavacProcessingEnvironment.java:1035)  	at com.sun.tools.javac.processing.JavacProcessingEnvironment.doProcessing(JavacProcessingEnvironment.java:1176)  	at com.sun.tools.javac.main.JavaCompiler.processAnnotations(JavaCompiler.java:1170)  	at com.sun.tools.javac.main.JavaCompiler.compile(JavaCompiler.java:856)  	at com.sun.tools.javac.main.Main.compile(Main.java:523)  	at com.sun.tools.javac.api.JavacTaskImpl.doCall(JavacTaskImpl.java:129)  	at com.sun.tools.javac.api.JavacTaskImpl.call(JavacTaskImpl.java:138)  	at org.jetbrains.jps.javac.JavacMain.compile(JavacMain.java:231)  	at org.jetbrains.jps.incremental.java.JavaBuilder.compileJava(JavaBuilder.java:501)  	at org.jetbrains.jps.incremental.java.JavaBuilder.compile(JavaBuilder.java:353)  	at org.jetbrains.jps.incremental.java.JavaBuilder.doBuild(JavaBuilder.java:277)  	at org.jetbrains.jps.incremental.java.JavaBuilder.build(JavaBuilder.java:231)  	at org.jetbrains.jps.incremental.IncProjectBuilder.runModuleLevelBuilders(IncProjectBuilder.java:1441)  	at org.jetbrains.jps.incremental.IncProjectBuilder.runBuildersForChunk(IncProjectBuilder.java:1100)  	at org.jetbrains.jps.incremental.IncProjectBuilder.buildTargetsChunk(IncProjectBuilder.java:1224)  	at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunkIfAffected(IncProjectBuilder.java:1066)  	at org.jetbrains.jps.incremental.IncProjectBuilder.buildChunks(IncProjectBuilder.java:832)  	at org.jetbrains.jps.incremental.IncProjectBuilder.runBuild(IncProjectBuilder.java:419)  	at org.jetbrains.jps.incremental.IncProjectBuilder.build(IncProjectBuilder.java:183)  	at org.jetbrains.jps.cmdline.BuildRunner.runBuild(BuildRunner.java:132)  	at org.jetbrains.jps.cmdline.BuildSession.runBuild(BuildSession.java:302)  	at org.jetbrains.jps.cmdline.BuildSession.run(BuildSession.java:132)  	at org.jetbrains.jps.cmdline.BuildMain$MyMessageHandler.lambda$channelRead0$0(BuildMain.java:219)  	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)  	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)  	at java.lang.Thread.run(Thread.java:748)  

解决方案

将 MapStruct 更新到 1.4.1.Final 或更高版本

<dependency>
      <groupId>org.mapstructgroupId>
      <artifactId>mapstructartifactId>
      <version>1.4.1.Finalversion>
  dependency>
  
  <dependency>
      <groupId>org.mapstructgroupId>
      <artifactId>mapstruct-processorartifactId>
      <version>1.4.1.Finalversion>
  dependency>

如果还出现以下错误

java:No property named "xxx" exists in source parameter(s). Did you mean "null"?

引入依赖解决

<dependency>
      <groupId>org.projectlombok</groupId>
      <artifactId>lombok-mapstruct-binding</artifactId>
      <version>0.2.0</version>
</dependency>