Maven说我在多模块项目中有一个循环引用,但无法弄清楚原因

Question

我有一个多模块项目,如下所示:

• 模块1
  • 的pom.xml
• 模块2
  • 的pom.xml
• 的pom.xml

module2中的pom.xml依赖于module1.

当我运行mvn clean编译时,我收到以下错误:

反应堆中的项目包含循环参考.

这是我在module1中的依赖项:

<dependencies>
    <dependency>
        <groupId>log4j</groupId>
        <artifactId>log4j</artifactId>
        <version>1.2.14</version>
    </dependency>
    <dependency>
        <groupId>org.slf4j</groupId>
        <artifactId>slf4j-log4j12</artifactId>
        <version>1.6.1</version>
    </dependency>
    <dependency>
        <groupId>com.jcraft</groupId>
        <artifactId>jsch</artifactId>
        <version>0.1.48</version>
    </dependency>
</dependencies>

我无法弄清楚为什么它说有一个循环引用.即使我做了mvn依赖:在module1上的树,我得到以下内容:

[INFO] +- log4j:log4j:jar:1.2.14:compile
[INFO] +- org.slf4j:slf4j-log4j12:jar:1.6.1:compile
[INFO] |  \- org.slf4j:slf4j-api:jar:1.6.1:compile
[INFO] +- com.jcraft:jsch:jar:0.1.48:compile
[INFO] \- junit:junit:jar:4.8.2:test

在我看来,在module1中没有对module2的任何引用.那么循环引用来自何处？

编辑:以下是调试日志:

+ Error stacktraces are turned on.
Apache Maven 2.2.1 (r801777; 2009-08-06 15:16:01-0400)
Java version: 1.6.0_31
Default locale: en_US, platform encoding: Cp1252
OS name: "windows 7" version: "6.1" arch: "amd64" Family: "windows"
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD FAILURE
[INFO] ------------------------------------------------------------------------
[INFO] The projects in the reactor contain a cyclic reference: Edge between 'Vertex{label='com.myorg:module2'}' and 'Vertex{label='com.myorg:module1'}' introduces to cycle in the graph com.myorg:module1 --> com.myorg:module2 --> com.myorg:module1
[INFO] ------------------------------------------------------------------------
[DEBUG] Trace
org.apache.maven.BuildFailureException: The projects in the reactor contain a cyclic reference: Edge between 'Vertex{label='com.myorg:module2'}' and 'Vertex{label='com.myorg:module1'}' introduces to cycle in the graph com.myorg:module1 --> com.myorg:module2 --> com.myorg:module1
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:295)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:138)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:362)
at org.apache.maven.cli.compat.CompatibleMain.main(CompatibleMain.java:60)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.codehaus.classworlds.Launcher.launchEnhanced(Launcher.java:315)
at org.codehaus.classworlds.Launcher.launch(Launcher.java:255)
at org.codehaus.classworlds.Launcher.mainWithExitCode(Launcher.java:430)
at org.codehaus.classworlds.Launcher.main(Launcher.java:375)
Caused by: hidden.org.codehaus.plexus.util.dag.CycleDetectedException: Edge between 'Vertex{label='com.myorg:module2'}' and 'Vertex{label='com.myorg:module1'}' introduces to cycle in the graph com.myorg:module1 --> com.myorg:module2 --> com.myorg:module1
at hidden.org.codehaus.plexus.util.dag.DAG.addEdge(DAG.java:143)
at hidden.org.codehaus.plexus.util.dag.DAG.addEdge(DAG.java:123)
at org.apache.maven.project.ProjectSorter.<init>(ProjectSorter.java:118)
at org.apache.maven.execution.ReactorManager.<init>(ReactorManager.java:99)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:288)
... 11 more
[INFO] ------------------------------------------------------------------------
[INFO] Total time: < 1 second
[INFO] Finished at: Thu Jul 05 17:21:21 EDT 2012    
[INFO] Final Memory: 3M/244M
[INFO] ------------------------------------------------------------------------

Answer 1

啊! 这是一个误导性的错误.

问题不在于module1和module2都相互依赖.问题是module2是一个Maven插件,在我的root pom.xml中,我在该部分中有插件.我从构建中删除了该插件并开始工作.

Answer 2

在这种情况下，它发生在我身上。

module_child_X 在 module_root pom.xml 中被指定了 2 次：

- 作为一个模块

(pom.xml of the root module)
<dependency>
    <groupId>module_root</groupId>
    <artifactId>module_child_X</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <type>jar</type>
</dependency>

- 作为依赖

(pom.xml of the root module)
<modules>
    <module>module_child_X</module>
    ...
</modules>

解决方案？

删除了 module_child_X 作为依赖项。它已经被指定为一个模块。