java - 当这个异常发生时，我的maven-3.1.1和nexus-2.6.4-02出了什么问题？

Question

我在计算机上运行带有 nexus 的 Maven，但是当我运行命令 mvn help:system 时，出现此异常:

[ERROR] Failed to execute goal org.apache.maven.plugins:maven-help-plugin:2.2:system (default-cli) on project standalone-pom: Execution default-cli of goal org.apache.maven.plugins:maven-help-plugin:2.2:system failed: Plugin org.apache.maven.plugins:maven-help-plugin:2.2 or one of its dependencies could not be resolved: Failed to collect dependencies at org.apache.maven.plugins:maven-help-plugin:jar:2.2 -> org.apache.maven.plugin-tools:maven-plugin-tools-api:jar:2.4.3: Failed to read artifact descriptor for org.apache.maven.plugin-tools:maven-plugin-tools-api:jar:2.4.3: Failure to find org.apache.maven:maven-parent:pom:8 in `http://127.0.0.1:8081/nexus/content/groups/public` was cached in the local repository, resolution will not be reattempted until the update interval of roger-nexus has elapsed or updates are forced -> [Help 1]org.apache.maven.lifecycle.LifecycleExecutionException: Failed to execute goal org.apache.maven.plugins:maven-help-plugin:2.2:system (default-cli) on project standalone-pom: Execution default-cli of goal org.apache.maven.plugins:maven-help-plugin:2.2:system failed: Plugin org.apache.maven.plugins:maven-help-plugin:2.2 or one of its dependencies could not be resolved: Failed to collect dependencies at org.apache.maven.plugins:maven-help-plugin:jar:2.2 -> org.apache.maven.plugin-tools:maven-plugin-tools-api:jar:2.4.3
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:224)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
        at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
        at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
        at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
        at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:317)
        at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:152)
        at org.apache.maven.cli.MavenCli.execute(MavenCli.java:555)
        at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:214)
        at org.apache.maven.cli.MavenCli.main(MavenCli.java:158)
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
        at java.lang.reflect.Method.invoke(Method.java:606)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
        at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
        at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
        at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: org.apache.maven.plugin.PluginExecutionException: Execution default-cli of goal org.apache.maven.plugins:maven-help-plugin:2.2:system failed: Pluginorg.apache.maven.plugins:maven-help-plugin:2.2 or one of its dependencies couldnot be resolved: Failed to collect dependencies at org.apache.maven.plugins:maven-help-plugin:jar:2.2 -> org.apache.maven.plugin-tools:maven-plugin-tools-api:jar:2.4.3
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:87)
        at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:208)
        ... 19 more
Caused by: org.apache.maven.plugin.PluginResolutionException: Plugin org.apache.maven.plugins:maven-help-plugin:2.2 or one of its dependencies could not be resolved: Failed to collect dependencies at org.apache.maven.plugins:maven-help-plugin:jar:2.2 -> org.apache.maven.plugin-tools:maven-plugin-tools-api:jar:2.4.3
        at org.apache.maven.plugin.internal.DefaultPluginDependenciesResolver.resolve(DefaultPluginDependenciesResolver.java:204)
        at org.apache.maven.plugin.internal.DefaultMavenPluginManager.createPluginRealm(DefaultMavenPluginManager.java:357)
        at org.apache.maven.plugin.internal.DefaultMavenPluginManager.setupPluginRealm(DefaultMavenPluginManager.java:325)
        at org.apache.maven.plugin.DefaultBuildPluginManager.getPluginRealm(DefaultBuildPluginManager.java:180)
        at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:83)
        ... 20 more
Caused by: org.eclipse.aether.collection.DependencyCollectionException: Failed to collect dependencies at org.apache.maven.plugins:maven-help-plugin:jar:2.2 ->org.apache.maven.plugin-tools:maven-plugin-tools-api:jar:2.4.3
        at org.eclipse.aether.internal.impl.DefaultDependencyCollector.collectDependencies(DefaultDependencyCollector.java:292)
        at org.eclipse.aether.internal.impl.DefaultRepositorySystem.collectDependencies(DefaultRepositorySystem.java:317)
        at org.apache.maven.plugin.internal.DefaultPluginDependenciesResolver.resolve(DefaultPluginDependenciesResolver.java:192)
        ... 24 more
Caused by: org.eclipse.aether.resolution.ArtifactDescriptorException: Failed toread artifact descriptor for org.apache.maven.plugin-tools:maven-plugin-tools-ap
i:jar:2.4.3
        at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:370)
        at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.readArtifactDescriptor(DefaultArtifactDescriptorReader.java:217)
        at org.eclipse.aether.internal.impl.DefaultDependencyCollector.process(DefaultDependencyCollector.java:461)
        at org.eclipse.aether.internal.impl.DefaultDependencyCollector.collectDependencies(DefaultDependencyCollector.java:261)
        ... 26 more
Caused by: org.apache.maven.model.resolution.UnresolvableModelException: Failure to find org.apache.maven:maven-parent:pom:8 in `http://127.0.0.1:8081/nexus/content/groups/public` was cached in the local repository, resolution will not be reattempted until the update interval of roger-nexus has elapsed or updates are for
ced
        at org.apache.maven.repository.internal.DefaultModelResolver.resolveModel(DefaultModelResolver.java:126)
        at org.apache.maven.model.building.DefaultModelBuilder.readParentExternally(DefaultModelBuilder.java:817)
        at org.apache.maven.model.building.DefaultModelBuilder.readParent(DefaultModelBuilder.java:669)
        at org.apache.maven.model.building.DefaultModelBuilder.build(DefaultModelBuilder.java:307)
        at org.apache.maven.repository.internal.DefaultArtifactDescriptorReader.loadPom(DefaultArtifactDescriptorReader.java:361)
        ... 29 more
Caused by: org.eclipse.aether.resolution.ArtifactResolutionException: Failure to find org.apache.maven:maven-parent:pom:8 in `http://127.0.0.1:8081/nexus/content/groups/public` was cached in the local repository, resolution will not be reattempted until the update interval of roger-nexus has elapsed or updates are forced
        at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:459)
        at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifacts(DefaultArtifactResolver.java:262)
        at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolveArtifact(DefaultArtifactResolver.java:239)
        at org.apache.maven.repository.internal.DefaultModelResolver.resolveModel(DefaultModelResolver.java:122)
        ... 33 more
Caused by: org.eclipse.aether.transfer.ArtifactNotFoundException: Failure to find org.apache.maven:maven-parent:pom:8 in `http://127.0.0.1:8081/nexus/content/groups/public` was cached in the local repository, resolution will not be reattempted until the update interval of roger-nexus has elapsed or updates are forced
        at org.eclipse.aether.internal.impl.DefaultUpdateCheckManager.newException(DefaultUpdateCheckManager.java:232)
        at org.eclipse.aether.internal.impl.DefaultUpdateCheckManager.checkArtifact(DefaultUpdateCheckManager.java:206)
        at org.eclipse.aether.internal.impl.DefaultArtifactResolver.gatherDownloads(DefaultArtifactResolver.java:599)
        at org.eclipse.aether.internal.impl.DefaultArtifactResolver.performDownloads(DefaultArtifactResolver.java:518)
        at org.eclipse.aether.internal.impl.DefaultArtifactResolver.resolve(DefaultArtifactResolver.java:436)
        ... 36 more
[ERROR]
[ERROR] Re-run Maven using the -X switch to enable full debug logging.
[ERROR]
[ERROR] For more information about the errors and possible solutions, please read the following articles:
[ERROR] [Help 1] `http://cwiki.apache.org/confluence/display/MAVEN/PluginResolutionException`

我猜问题是我的网络组件阻止了对某些文件的访问。但令人困惑的是，我可以在没有nexus的情况下正常运行maven，所以我也怀疑我的setting.xml是错误的，这里是:

<?xml version="1.0" encoding="UTF-8"?>
<settings xmlns="http://maven.apache.org/SETTINGS/1.0.0" 
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
          xsi:schemaLocation="http://maven.apache.org/SETTINGS/1.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
  <localRepository>D:/DeveloperKit/maven_repos</localRepository>
  <pluginGroups>
  </pluginGroups>

  <proxies>
  </proxies>

  <servers>
    <server>
      <id>roger-nexus</id>
      <username>admin</username>
      <password>admin123</password>
    </server>
  </servers>

  <mirrors>
     <mirror>
      <id>roger-nexus</id>
      <mirrorOf>*</mirrorOf>
      <name>Mirror of roger</name>
      <url>http://127.0.0.1:8081/nexus/content/groups/public</url>
    </mirror>
  </mirrors>

  <profiles>
    <profile>
      <id>jdk-1.7</id>
      <activation>
        <jdk>1.7</jdk>
      </activation>
      <repositories>
        <repository>
          <id>jdk17</id>
          <name>Repository for JDK 1.7 builds</name>
          <url>http://127.0.0.1:8081/nexus/content/groups/public/</url>
          <layout>default</layout>
          <snapshotPolicy>always</snapshotPolicy>
        </repository>
      </repositories>
    </profile>
  </profiles>

  <activeProfiles>
    <activeProfile>jdk-1.7</activeProfile>
  </activeProfiles>
</settings>

Answer 1

使用 nexus is like the following 的默认设置:

<settings
    xmlns="http://maven.apache.org/POM/4.0.0"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/settings-1.0.0.xsd">
 <mirrors>
    <mirror>
      <!--This sends everything else to /public -->
      <id>nexus</id>
      <mirrorOf>*</mirrorOf>
      <url>http://localhost:8081/nexus/content/groups/public</url>
    </mirror>
  </mirrors>
  <profiles>
    <profile>
      <id>nexus</id>
      <!--Enable snapshots for the built in central repo to direct -->
      <!--all requests to nexus via the mirror -->
      <repositories>
        <repository>
          <id>central</id>
          <url>http://central</url>
          <releases><enabled>true</enabled></releases>
          <snapshots><enabled>true</enabled></snapshots>
        </repository>
      </repositories>
     <pluginRepositories>
        <pluginRepository>
          <id>central</id>
          <url>http://central</url>
          <releases><enabled>true</enabled></releases>
          <snapshots><enabled>true</enabled></snapshots>
        </pluginRepository>
      </pluginRepositories>
    </profile>
  </profiles>
  <activeProfiles>
    <!--make the profile active all the time -->
    <activeProfile>nexus</activeProfile>
  </activeProfiles>
</settings>

除了基于错误消息的内容:

Failure to find org.apache.maven:maven-parent:pom:8 in
`http://127.0.0.1:8081/nexus/content/groups/public` was cached in the local repository,
resolution will not be reattempted until the update interval of roger-nexus has 
elapsed or updates are forced -> 

这是由于您没有指定其他存储库的更新策略导致的。可能是您与 Maven Central 等的连接已超时(通过 Nexus)。

最好是删除本地存储库并重试。如果再次发生这种情况，请检查 Nexus 中的配置是否更改了某些默认设置。