在使用Jenkins自动构建Java项目时，出现以下的错误。错误日志如下： 

+ /opt/maven/apache-maven-3.5.4/bin/mvn clean package -U -e -B -Dmaven.test.skip=true
[INFO] Error stacktraces are turned on.
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 0.096 s
[INFO] Finished at: 2018-10-17T19:09:42+08:00
[INFO] ------------------------------------------------------------------------
[ERROR] The goal you specified requires a project to execute but there is no POM in this directory (/root/.jenkins/workspace). Please verify you invoked Maven from the correct directory. -> [Help 1]
org.apache.maven.lifecycle.MissingProjectException: The goal you specified requires a project to execute but there is no POM in this directory (/root/.jenkins/workspace/). Please verify you invoked Maven from the correct directory.
    at org.apache.maven.lifecycle.internal.LifecycleStarter.execute (LifecycleStarter.java:85)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:305)
    at org.apache.maven.DefaultMaven.doExecute (DefaultMaven.java:192)
    at org.apache.maven.DefaultMaven.execute (DefaultMaven.java:105)
    at org.apache.maven.cli.MavenCli.execute (MavenCli.java:954)
    at org.apache.maven.cli.MavenCli.doMain (MavenCli.java:288)
    at org.apache.maven.cli.MavenCli.main (MavenCli.java:192)
    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.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)
[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/MissingProjectException
Build step '执行 shell' marked build as failure
SSH: Current build result is [FAILURE], not going to run.
Finished: FAILURE

去网上搜了一遍发现各种解决办法，但是没有什么作用。仔细分析了下文章中日志中的意思无非就是找不到POM文件。我去Jenkins的workspace里去查看发现下面多了一级子目录，也就是说pom文件不在workspace中的工程目录中。所以就会导致maven找不到pom文件。所以，我在构建的时候直接在构建前加一个进入工程实际目录的动作，在进行构建，就不会有问题了。

如下图：

就能直接构建成功了。这是最简便的方式。

事后分析了下造成这种情况：大概是拉取代码分支，代码分支裹了一层目录，所以拉过来就多了一级目录。