Java SE上的JPA：工具：entity.Customer@5e80188f不是已知的实体

我随着

https://glassfish.java.net/javaee5/persistence/persistence-example.html

在Java SE情形中测试JPA.
在Eclipse中,我：

>建设了一个新的JPA(2.1)项目;
>在options-> JPA->耐久类打点中,我选择了“自动发明带注释的类”,而不是“必需在persistence.xml中列出带注释的类”.

我乐成导入了zip文件(Client.java Customer.java Order.java)中的树Java类,并修改了persistence.xml文件以满意我的必要.可是在实行执行main时我获得以下错误.

[EL Info]: 2013-10-18 17:37:54.749--ServerSession(263489307)--EclipseLink,version: Eclipse Persistence Services - 2.5.1.v20130918-f2b9fc5
[EL Info]: connection: 2013-10-18 17:37:55.34--ServerSession(263489307)--file:/home/caterpillar/workspace/JPA_Java_SE/build/classes/_JPA_Java_SE login successful
[EL Warning]: metamodel: 2013-10-18 17:37:55.359--The collection of metamodel types is empty. Model classes may not have been found during entity search for Java SE and some Java EE container managed persistence units.  Please verify that your entity classes are referenced in persistence.xml using either 

$tree
.
├── build
│?? └── classes
│??     ├── client
│??     │?? └── Client.class
│??     ├── entity
│??     │?? ├── Customer.class
│??     │?? └── Order.class
│??     └── META-INF
│??         └── persistence.xml
├── sql
│?? ├── tables_derby.sql
│?? └── tables_oracle.sql
└── src
    ├── client
    │?? └── Client.java
    ├── entity
    │?? ├── Customer.java
    │?? └── Order.java
    └── META-INF
        └── persistence.xml

10 directories,10 files