請各位幫忙分析下，詳細描述如下：編寫了一個簡單的實體類Customer，和一個獲取Session的工具類，按照百度搜索的結果，檢查了hibernate配置文件和實體類映射文件，均沒有問題。但是執行到save方法時即報錯Unknown entity。打印獲取到的session信息為“SessionImpl(PersistenceContext[entityKeys=[],collectionKeys=[]];ActionQueue[insertions=ExecutableList{size=0} updates=ExecutableList{size=0} deletions=ExecutableList{size=0} orphanRemovals=ExecutableList{size=0} collectionCreations=ExecutableList{size=0} collectionRemovals=ExecutableList{size=0} collectionUpdates=ExecutableList{size=0} collectionQueuedOps=ExecutableList{size=0} unresolvedInsertDependencies=null])”