mvn：exec无法执行目标org.codehaus.mojo

Question

我使用maven，我有pom.xml：

    <plugin>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>2.0.2</version>
      <configuration>
        <source>1.6</source>
        <target>1.6</target>
      </configuration>
    </plugin>
    <plugin>
      <groupId>org.codehaus.mojo</groupId>
      <artifactId>exec-maven-plugin</artifactId>
      <configuration>
        <mainClass>test.main.Test</mainClass>
      </configuration>
    </plugin>

当我在命令行中使用时：

mvn exec:java -Dexec.mainClass=test.main.Test

我有一个错误：

[WARNING] 
java.lang.ClassNotFoundException: test.main.Test
    at java.net.URLClassLoader$1.run(URLClassLoader.java:202)
    at java.security.AccessController.doPrivileged(Native Method)
    at org.codehaus.mojo.exec.ExecJavaMojo$1.run(ExecJavaMojo.java:285)
    at java.lang.Thread.run(Thread.java:680)
[ERROR] Failed to execute goal org.codehaus.mojo:exec-maven-plugin:1.2.1:java (default-cli) on project TestApp: An exception occured while executing the Java class. test.main.Test -> [Help 1]

有什么问题？我不知道出了什么问题......