Groovy PermGen Full GC 问题解析以及解决

线上环境 使用Groovy脚本为业务提供自定义配置 结果 没几天就fullGC 并且持续很长时间，才降下来，
groovy 常见的三种引入方式都会有对应的问题，：
核心的问题是Groovy会缓存掉曾经执行的代码片段成为META-class ，如果每次执行的代码都不一样。那么缓存的类会越来越多。

相应的解决办法：

<dependency>
    <groupId>org.codehaus.groovy</groupId>
    <artifactId>groovy-all</artifactId>
    <version>2.4.7</version>
</dependency>

//清除groovy 里面的缓存， 防止fullGC,也可以定时来做
GroovyClassLoader groovyClassLoader = engine.getClassLoader();
Class[] classes = engine.getClassLoader().getLoadedClasses();
for (Class clazz : classes) {
    GroovySystem.getMetaClassRegistry().removeMetaClass(clazz);
    groovyClassLoader.clearCache();
    try {
        Field globalClassValue = ClassInfo.class.getDeclaredField("globalClassValue");
        globalClassValue.setAccessible(true);
        GroovyClassValue classValueBean = (GroovyClassValue) globalClassValue.get(null);
        classValueBean.remove(clazz);

    } catch (Throwable e) {

    }
}
groovyClassLoader.clearCache();
ClassInfo.clearModifiedExpandos();
/**
 * Using java beans (e.g. Groovy does it) results in all referenced class infos being cached in ThreadGroupContext. A valid fix
 * would be to hold BeanInfo objects on soft references, but that should be done in JDK. So let's clear this cache manually for now,
 * in clients that are known to create bean infos.
 */
Introspector.flushCaches();