调用maven-war-plugin时的NPE

Question

在多模块构建期间，eclipse中会出现如下错误：

Execution default of goal org.apache.maven.plugins:maven-war-plugin:3.3.1:exploded failed. (org.apache.maven.plugins:maven-war-plugin:3.3.1:exploded:default:process-resources)

此错误的堆栈跟踪为

org.apache.maven.plugin.PluginExecutionException: Execution default of goal org.apache.maven.plugins:maven-war-plugin:3.3.1:exploded failed.
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:148)
at org.eclipse.m2e.core.internal.embedder.MavenImpl.execute(MavenImpl.java:332)
at org.eclipse.m2e.core.internal.embedder.MavenImpl.lambda$8(MavenImpl.java:1380)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:179)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:114)
at org.eclipse.m2e.core.internal.embedder.MavenImpl.execute(MavenImpl.java:1379)
at org.eclipse.m2e.core.project.configurator.MojoExecutionBuildParticipant.build(MojoExecutionBuildParticipant.java:54)
at org.eclipse.m2e.core.internal.builder.MavenBuilderImpl.build(MavenBuilderImpl.java:135)
at org.eclipse.m2e.core.internal.builder.MavenBuilder$1.method(MavenBuilder.java:169)
at org.eclipse.m2e.core.internal.builder.MavenBuilder$1.method(MavenBuilder.java:1)
at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.lambda$1(MavenBuilder.java:114)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:179)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:114)
at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.lambda$0(MavenBuilder.java:105)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:179)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:153)
at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:101)
at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.execute(MavenBuilder.java:88)
at org.eclipse.m2e.core.internal.builder.MavenBuilder.build(MavenBuilder.java:197)
at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:832)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:220)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:263)
at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:316)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:45)
at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:319)
at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:371)
at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:392)
at org.eclipse.core.internal.resources.Workspace.buildInternal(Workspace.java:515)
at org.eclipse.core.internal.resources.Workspace.build(Workspace.java:405)
at org.eclipse.ui.actions.GlobalBuildAction$1.run(GlobalBuildAction.java:180)
at org.eclipse.core.internal.jobs.Worker.run(Worker.java:63)
Caused by: java.lang.NullPointerException
at org.apache.maven.plugins.war.AbstractWarMojo$DefaultWarPackagingContext$1.visitFile(AbstractWarMojo.java:661)
at org.apache.maven.plugins.war.AbstractWarMojo$DefaultWarPackagingContext$1.visitFile(AbstractWarMojo.java:656)
at java.base/java.nio.file.Files.walkFileTree(Files.java:2804)
at java.base/java.nio.file.Files.walkFileTree(Files.java:2876)
at org.apache.maven.plugins.war.AbstractWarMojo$DefaultWarPackagingContext.<init>(AbstractWarMojo.java:655)
at org.apache.maven.plugins.war.AbstractWarMojo.buildWebapp(AbstractWarMojo.java:520)
at org.apache.maven.plugins.war.AbstractWarMojo.buildExplodedWebapp(AbstractWarMojo.java:453)
at org.apache.maven.plugins.war.WarExplodedMojo.execute(WarExplodedMojo.java:43)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:137)
... 31 more
pom.xml /my-legacy-app line 1753 Maven Build Problem

我已经调试过AbstractWarMojo.visitFile了，session.getStartTime()是空的，所以对getTime()的调用抛出了一个NPE。试图追踪开始时间为空的原因将我带到了MavenImpl，在这一点上，我在试图进一步追踪这个问题时遇到了一些困难。我认为它指向了MavenExecutionContext中的某些东西，但我不能完全确定。

我该如何着手解决这个问题？

Eclipse版本:20200910-1200.

m2e版本: 1.16.1.20200710-1008

Answer 1

这是由于在maven-war-plugin版本3.3.1中引入的代码，使用3.3.0解决了这个问题。