pom报错

pom文件一直报如下的错误：

Failure to transfer commons-digester:commons-digester:jar:1.8 from 
https://repository.apache.org/content/repositories/snapshots was cached in the local repository,
 resolution will not be reattempted until the update interval of apache.snapshots.https has elapsed or updates are forced. 
Original error: Could not transfer artifact commons-digester:commons-digester:jar:1.8 from/to apache.snapshots.
https (https://repository.apache.org/content/repositories/snapshots): The operation was cancelled.

org.eclipse.aether.transfer.ArtifactTransferException: Failure to transfer commons-digester:commons-digester:jar:1.8 from https://repository.apache.org/content/repositories/snapshots was cached in the local repository, resolution will not be reattempted until the update interval of apache.snapshots.https has elapsed or updates are forced. Original error: Could not transfer artifact commons-digester:commons-digester:jar:1.8 from/to apache.snapshots.https (https://repository.apache.org/content/repositories/snapshots): The operation was cancelled.
    at org.eclipse.aether.internal.impl.DefaultUpdateCheckManager.newException(DefaultUpdateCheckManager.java:238)
    at org.eclipse.aether.internal.impl.DefaultUpdateCheckManager.checkArtifact(DefaultUpdateCheckManager.java:206)
    at org.eclipse.aether.internal.impl.DefaultArtifactResolver.gatherDownloads(DefaultArtifactResolver.java:585)
    at org.eclipse.aether.internal.impl.DefaultArtifactResolver.performDownloads(DefaultArtifactResolver.java:503)
    at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:421)
    at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifacts(DefaultArtifactResolver.java:246)
    at org.eclipse.aether.internal.impl.DefaultRepositorySystem.resolveDependencies(DefaultRepositorySystem.java:367)
    at org.apache.maven.project.DefaultProjectDependenciesResolver.resolve(DefaultProjectDependenciesResolver.java:205)
    at org.apache.maven.project.DefaultProjectBuilder.resolveDependencies(DefaultProjectBuilder.java:215)
    at org.apache.maven.project.DefaultProjectBuilder.build(DefaultProjectBuilder.java:188)
    at org.apache.maven.project.DefaultProjectBuilder.build(DefaultProjectBuilder.java:119)
    at org.eclipse.m2e.core.internal.embedder.MavenImpl.readMavenProject(MavenImpl.java:636)
    at org.eclipse.m2e.core.internal.project.registry.DefaultMavenDependencyResolver.resolveProjectDependencies(DefaultMavenDependencyResolver.java:63)
    at org.eclipse.m2e.core.internal.project.registry.ProjectRegistryManager.refreshPhase2(ProjectRegistryManager.java:530)
    at org.eclipse.m2e.core.internal.project.registry.ProjectRegistryManager$3.call(ProjectRegistryManager.java:492)
    at org.eclipse.m2e.core.internal.project.registry.ProjectRegistryManager$3.call(ProjectRegistryManager.java:1)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:177)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:151)
    at org.eclipse.m2e.core.internal.project.registry.ProjectRegistryManager.refresh(ProjectRegistryManager.java:496)
    at org.eclipse.m2e.core.internal.project.registry.ProjectRegistryManager.refresh(ProjectRegistryManager.java:351)
    at org.eclipse.m2e.core.internal.project.registry.ProjectRegistryManager.refresh(ProjectRegistryManager.java:298)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.getProjectFacade(MavenBuilder.java:154)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod$1.call(MavenBuilder.java:89)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.executeBare(MavenExecutionContext.java:177)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:151)
    at org.eclipse.m2e.core.internal.embedder.MavenExecutionContext.execute(MavenExecutionContext.java:99)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder$BuildMethod.execute(MavenBuilder.java:86)
    at org.eclipse.m2e.core.internal.builder.MavenBuilder.build(MavenBuilder.java:200)
    at org.eclipse.core.internal.events.BuildManager$2.run(BuildManager.java:735)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:206)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:246)
    at org.eclipse.core.internal.events.BuildManager$1.run(BuildManager.java:301)
    at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
    at org.eclipse.core.internal.events.BuildManager.basicBuild(BuildManager.java:304)
    at org.eclipse.core.internal.events.BuildManager.basicBuildLoop(BuildManager.java:360)
    at org.eclipse.core.internal.events.BuildManager.build(BuildManager.java:383)
    at org.eclipse.core.internal.events.AutoBuildJob.doBuild(AutoBuildJob.java:142)
    at org.eclipse.core.internal.events.AutoBuildJob.run(AutoBuildJob.java:232)
    at org.eclipse.core.internal.jobs.Worker.run(Worker.java:56)

看到第二行resolution will not be reattempted until the update interval of apache.snapshots有这么一句话，于是打算更新项目，右击项目，选择强制更新


但是报错还是没有消除，于是我右击项目，如下图



在pom中引入tools.jar

        
            jdk.tools
            jdk.tools
            1.8
            system
            ${JAVA_HOME}/lib/tools.jar
        

保存之后问题解决。