Eclipse Maven Plugin Configuration Problem

我在Eclipse里面 手动配置了 eclipse-maven3-plugin 的组件

打开Eclipse，项目第一次package 的时候没有问题。 

 clean 之后 再次package 就报如下错误 

         NFO] Compilation failure
        Unable to locate the Javac Compiler in:
        /usr/lib/jvm/java-6-openjdk/jre/../lib/tools.jar
        Please ensure you are using JDK 1.4 or above and
        not a JRE (the com.sun.tools.javac.Main class is required).
        In most cases you can change the location of your Java
        installation by setting the JAVA_HOME environment variable. 

我的jdk安装了两个 jdk7 和jdk6 path 配置的是jdk7

Eclispe 里面配置的也是jdk 7 。