'version' contains an expression but should be a constant

[WARNING] Some problems were encountered while building the effective model for com.app:cache:jar:4.0.0
[WARNING] 'version' contains an expression but should be a constant. @ com.app:webapi:${myproject.version}, /usr/local/jenkins/webapi/pom.xml, line 8, column 14

[WARNING] Some problems were encountered while building the effective model for cy.nad.cyg:pay-web:war:3.0.2
[WARNING] 'version' contains an expression but should be a constant. @ cy.nad.cyg:pay:${myproject.version}, D:\workspace\idea\pay\pom.xml, line 7, column 14

这是因为Maven3 不允许出现version为非常量值的情况，我们就需要第三方插件来帮我们自动完成升级版本的工作。

参见下文：

http://mojo.codehaus.org/versions-maven-plugin/examples/update-child-modules.html

这个插件等于只需要我们在parent pom中变更一下版本号，然后执行

mvn -N versions:update-child-modules这个命令，就会将所有依赖的地方全部变成新的版本号，从而帮我们完成该问题。

http://www.cnblogs.com/beiyeren/p/4275032.html