druid数据连接池实例化失败的问题

最近在用druid的数据库连接池,在eclipse代码运行正常,当打包成jar就会报 

java.lang.NoClassDefFoundError: Could not initialize class***的错误,因为开发进度的原因只能抽时间查问题.后来发现是连接池类中static初始化的问题.原来参考的代码出处:点击打开链接.

其中涉及到静态块、静态变量、静态方法、构造函数的加载顺序，不清楚的可以自己写个简单的程序测试一下。

问题总结：

1.java.lang.NoClassDefFoundError: Could not initialize class错误提示不是找不到类，与NoClassFoundException错误不要混淆。

2.在IDE运行正常，但是打包后异常，可能与加载的properties等文件的编码格式错误读取不到有关。（应该不会有人忘记把相关文件放到目录下吧?）

3.应当熟悉单例模式内涵,关于单例模式大把的高人总结.

更改后代码:

import java.io.File;import java.io.FileInputStream;import java.io.InputStream;import java.sql.SQLException;import java.util.Properties;import com.alibaba.druid.pool.DruidDataSource;import com.alibaba.druid.pool.DruidDataSourceFactory;import com.alibaba.druid.pool.DruidPooledConnection;import com.since.emp.service.OrderSyncs;/** * 要实现单例模式，保证全局只有一个数据库连接池 */public class DbPoolConnection {String logTitle = "DBPoolConnection";private static DbPoolConnection dbPoolConnection = null;private static DruidDataSource druidDataSource = null;static  {              Init();     }      private DbPoolConnection() {         } private static void Init()  {try {Properties properties = loadPropertiesFile("db.properties");OrderSyncs.logger.info("【logTitle】"+"读取文件成功");druidDataSource = (DruidDataSource) DruidDataSourceFactory.createDataSource(properties); // DruidDataSrouce工厂模式} catch (Exception e) {OrderSyncs.logger.info("【logTitle】"+"获取配置失败");}} /** * 数据库连接池单例 *  * @return */public static synchronized DbPoolConnection getInstance() {if (null == dbPoolConnection) {dbPoolConnection = new DbPoolConnection();}return dbPoolConnection;}/** * 返回druid数据库连接 *  * @return * @throws SQLException */public DruidPooledConnection getConnection() throws SQLException {return druidDataSource.getConnection();}/** * @param string *            配置文件名 * @return Properties对象 */private static Properties loadPropertiesFile(String fullFile) {if (null == fullFile || fullFile.equals("")) {throw new IllegalArgumentException("Properties file path can not be null" + fullFile);}InputStream inputStream = null;Properties p = null;try {inputStream = new FileInputStream(new File(fullFile));//原来是决定路径,现在用相对路径p = new Properties();p.load(inputStream);} catch (Exception e) {e.printStackTrace();} finally {try {if (null != inputStream) {inputStream.close();}} catch (Exception e) {e.printStackTrace();}}return p;}}