无法初始化JDBCUtils的工具类

困扰很多天了，还没没找到原因。

错误信息

java.lang.NoClassDefFoundError: Could not initialize class com.imooc.utils.JDBCUtils
	com.imooc.dao.impl.UserDaoImpl.isRegisted(UserDaoImpl.java:50)
	com.imooc.service.impl.UserServiceImpl.regist(UserServiceImpl.java:13)
	com.imooc.web.action.RegistServlet.regist(RegistServlet.java:47)
	com.imooc.web.action.RegistServlet.doGet(RegistServlet.java:29)
	com.imooc.web.action.RegistServlet.doPost(RegistServlet.java:17)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:660)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:741)
	org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
	com.imooc.web.filter.CharsetEncodingFilter.doFilter(CharsetEncodingFilter.java:14)

JDBCUtils工具类

package com.imooc.utils;

import com.mchange.v2.c3p0.ComboPooledDataSource;

import javax.sql.DataSource;
import java.sql.*;

public class JDBCUtils {

    public static final ComboPooledDataSource dataSource = new ComboPooledDataSource();

    /**
     * 获得连接池
     * @return
     */
    public static DataSource getDataSource() {
        return dataSource;
    }

    /**
     * 获得连接
     * @return
     * @throws SQLException
     */
    public static Connection getConnection() throws SQLException {
        return dataSource.getConnection();
    }

    /**
     * 释放资源
     */
    public static void release(ResultSet rs,Statement stmt,Connection conn){
        if(rs != null){
            try {
                rs.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            rs = null;
        }
        if(stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            stmt = null;
        }
        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            conn = null;
        }
    }

    public static void release(Statement stmt,Connection conn){
        if(stmt != null){
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            stmt = null;
        }
        if(conn != null){
            try {
                conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
            conn = null;
        }
    }

}