MySQL超时到期后，c3p0的连接引发异常

我使用版本0.9.2.1的c3p0库在Web应用程序中创建连接池。MySQL超时后，我得到异常：

“ HTTP状态500-从服务器成功收到的最后一个数据包是627301毫秒之前。成功发送到服务器的最后一个数据包是627302毫秒之前。比服务器配置的'wait_timeout'值长。和/或在用于您的应用程序之前测试连接的有效性，增加服务器为客户端超时配置的值，或使用Connector / J连接属性'autoReconnect = true'来避免此问题。”

我试图将autoReconnect参数附加到JDBC url，但是也没有任何效果。因此，以这种方式，我在应用程序中使用了连接池：

为了进行测试，我将MySQL的wait_timeout设置为180秒

set @@global.wait_timeout=180;

show global variables like "wait_timeout";

+---------------+-------+
| Variable_name | Value |
+---------------+-------+
| wait_timeout  |  180  |
+---------------+-------+

以及接下来的几段代码

c3p0.properties

# JDBC paramters are ommited
# Basic pool configuration
c3p0.initialPoolSize=5
c3p0.minPoolSize=5
c3p0.maxPoolSize=50
c3p0.acquireIncrement=5
# Managing connection age
c3p0.maxConnectionAge=100
c3p0.maxIdleTime=90
# Configuring connection testing
c3p0.idleConnectionTestPeriod=30
c3p0.testConnectionOnCheckin=true
c3p0.preferredTestQuery=SELECT 1

DBConnectionUtil.java

public class DBConnectionUtil {
    // initialized through c3p0.properties
    private static ComboPooledDataSource ds = new ComboPooledDataSource();

    public static ComboPooledDataSource getConnectionPool() {
        return ds;
    }

    public static void destroyConnectionPool() {
        ds.close();
    }

    public static Connection getConnection() throws SQLException {
        return ds.getConnection();
    }
}

UserDAO.java

public class UserDAO {

    private Connection connection;

    public UserDAO() throws SQLException {
        connection = DBConnectionUtil.getConnection();
    }

    public User find(Integer id) throws SQLException {
        User user = null;
        PreparedStatement ps = connection.prepareStatement("SELECT * FROM `USERS` WHERE ID = ?");
        ps.setInt(1, id);
        ResultSet rs = ps.executeQuery();
        if (rs.next()) {
            user = new User();
            user.setId(rs.getInt("ID"));
            user.setName(rs.getString("NAME"));
            user.setUsername(rs.getString("USERNAME"));
            user.setPassword(rs.getString("PASSWORD"));
            user.setParentId(rs.getInt("PARENT_ID"));
        }
        rs.close();
        ps.close();
        return user;
    }
}

DAOUtil.java

public class DAOUtil {
    private static UserDAO userDAO;

    public static UserDAO getUserDAO() {
        return userDAO;
    }

    static {
        try {
            userDAO = new UserDAO();
        } catch (SQLException e) {
            throw new RuntimeException(e);
        }
    }
}

例如，在过期的MySQL wait_timeout之后，当我调用DAOUtil.userDAO.find（id）时，它将引发上面描述的异常。

您能帮我意识到我在做错什么吗？注意：我无法更改MySQL ini文件。