在安装Alveole Studio MVC Web Project插件时，出现了一下错误：
An error occurred while collecting items to be installed
session context was:(profile=epp.package.jee, phase=org.eclipse.equinox.internal.p2.engine.phases.Collect, operand=, action=).
Unable to read repository at http://downloads.sourceforge.net/mvcwebproject/mvcwebproject-0.7.4.jar.
Read timed out
Unable to read repository at http://downloads.sourceforge.net/mvcwebproject/mvcwebprojecthelp-0.5.0.jar.
sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
我用网上的向security添加安全证书的方法，还有直接离线jar包方法安装，都没能解决问题，有没有人能告诉我这是因为什么啊？谢谢大家了。
