解决com.sun.tools.javac.Main is not on the classpath / Unable to find a javac compiler 的问题

用ant编译nutch时报错：

<span style="font-size:18px;">  Unable to find a javac compiler; com.sun.tools.javac.Main is not on the classpath.  Perhaps JAVA_HOME does not point to the JDK.  It is currently set to “/usr/lib/jvm/java-7-openjdk-amd64"</span>

我把jdk安装目录lib/tools.jar拷贝到上面那个报错的路径里，

<span style="font-size:18px;">sudo cp /usr/lib/jvm/java/lib/tools.jar /usr/lib/jvm/java-7-openjdk-amd64/jre/</span>

问题了解决~