java - 找不到 Maven 插件

Question

我使用的是 Maven 3.3.9。在学习maven的过程中，我创建了一个演示项目并运行这个命令来了解更多关于maven的编译器插件。

mvn help:describe -Dplugin =compiler

我收到以下错误:

INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building ex1 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-help-plugin:2.2:describe (default-cli) @ ex1 ---
Downloading: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-metadata.xml
Downloading: https://repo.maven.apache.org/maven2/org/codehaus/mojo/maven-metadata.xml
Downloaded: https://repo.maven.apache.org/maven2/org/apache/maven/plugins/maven-metadata.xml (13 KB at 5.6 KB/sec)
Downloaded: https://repo.maven.apache.org/maven2/org/codehaus/mojo/maven-metadata.xml (20 KB at 7.3 KB/sec)
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Skipping ex1
[INFO] This project has been banned from the build due to previous failures.
[INFO] ------------------------------------------------------------------------
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3.684 s
[INFO] Finished at: 2017-03-15T13:00:59+05:30
[INFO] Final Memory: 13M/245M
[INFO] ------------------------------------------------------------------------
[ERROR] Failed to execute goal org.apache.maven.plugins:maven-help-plugin:2.2:describe (default-cli) on project ex1: Plugin could not be found. If you believe it is correct, check your pluginGroups setting, and run with -U to update the remote configuration -> [Help 1]
[ERROR] 
[ERROR] To see the full stack trace of the errors, re-run Maven with the -e switch.
[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/MojoFailureException

查看构建失败，我运行了以下命令:

mvn clean install

一切都很顺利，如下所示:

[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building ex1 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ ex1 ---
[INFO] Deleting /Users/tiwaris/My Own Workspace/workspace/ex1/target
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ ex1 ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /Users/tiwaris/My Own Workspace/workspace/ex1/src/main/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ ex1 ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /Users/tiwaris/My Own Workspace/workspace/ex1/target/classes
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ ex1 ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory /Users/tiwaris/My Own Workspace/workspace/ex1/src/test/resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ ex1 ---
[INFO] Changes detected - recompiling the module!
[INFO] Compiling 1 source file to /Users/tiwaris/My Own Workspace/workspace/ex1/target/test-classes
[INFO] 
[INFO] --- maven-surefire-plugin:2.12.4:test (default-test) @ ex1 ---
[INFO] Surefire report directory: /Users/tiwaris/My Own Workspace/workspace/ex1/target/surefire-reports

-------------------------------------------------------
 T E S T S
-------------------------------------------------------
Running com.pg.AppTest
Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.027 sec

Results :

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0

[INFO] 
[INFO] --- maven-jar-plugin:2.4:jar (default-jar) @ ex1 ---
[INFO] Building jar: /Users/tiwaris/My Own Workspace/workspace/ex1/target/ex1-1.0-SNAPSHOT.jar
[INFO] 
[INFO] --- maven-install-plugin:2.4:install (default-install) @ ex1 ---
[INFO] Installing /Users/tiwaris/My Own Workspace/workspace/ex1/target/ex1-1.0-SNAPSHOT.jar to /Users/tiwaris/.m2/repository/com/pg/ex1/1.0-SNAPSHOT/ex1-1.0-SNAPSHOT.jar
[INFO] Installing /Users/tiwaris/My Own Workspace/workspace/ex1/pom.xml to /Users/tiwaris/.m2/repository/com/pg/ex1/1.0-SNAPSHOT/ex1-1.0-SNAPSHOT.pom
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.785 s
[INFO] Finished at: 2017-03-15T13:02:49+05:30
[INFO] Final Memory: 17M/310M
[INFO] ------------------------------------------------------------------------

搜索更多后，我想让我们删除整个 .m2 文件夹并重新开始。然而，这个错误仍然出现。原因是什么？

Answer 1

您需要删除等号之前的多余空格:

 mvn help:describe -Dplugin =compiler
                           ^

应该是

mvn help:describe -Dplugin=compiler