Exception in thread "pool-2-thread-1" java.lang.NoClassDefFoundError:

其實這個錯誤情況根本無法給我準確的定位到錯誤代碼。

[color=blue]單例的代碼[/color]

public class DAOFactory {

	//....省略

	private static class SingletonHolder {
		//只有在調用的時候纔會初始化！而且線程安全。
        static DAOFactory instance = new DAOFactory();
    }  

	public static DAOFactory getInstance() {
		return SingletonHolder.instance;
	}
}

期間我加了個ControlDao的一些ibatis的class和module竟然報錯誤：
[color=red]Exception in thread "pool-2-thread-1" java.lang.NoClassDefFoundError: Could not initialize class com.xxxx.dao.DAOFactory$SingletonHolder
[/color]


找啊找，最後我試着改成，不用單例：

public class DAOFactory {

	//....省略

	public static DAOFactory getInstance() {
		return new DAOFactory():
	}
}

結果就出現了正確的ibatis錯誤定位了：
[color=red]java.lang.RuntimeException: Error occurred. Cause: com.ibatis.common.xml.NodeletException: Error parsing XML. Cause: java.lang.RuntimeException: Error parsing XPath '/sqlMapConfig/sqlMap'. Cause: com.ibatis.common.xml.NodeletException: Error parsing XML. Cause: java.lang.RuntimeException: Error parsing XPath '/sqlMap/insert'. Cause: com.ibatis.common.beans.ProbeException: There is no READABLE property named 'test' in class 'com.xxx.module.Control'[/color]

終於找到原因了，竟然是我的sql語句沒寫好，改好，再改回原來的單例，運行正常了。