使用NetBeans在jsp tomcat中建立c3p0连接池

Question

I m performing a connection pooling operation in jsp. 我在jsp中执行连接池操作。 I created a static function in a particular class called MCE_Server.java and included the following 我在名为MCE_Server.java的特定类中创建了一个静态函数，并包含以下内容：

 public static void makeConnectionPool()
 {
    try
    {
        cpds = new ComboPooledDataSource();
        cpds.setDriverClass("com.mysql.jdbc.Driver");
        cpds.setJdbcUrl("jdbc:mysql://localhost:3306/mce_db");
        cpds.setUser("root");
        cpds.setPassword("xxxxxx");
        cpds.setMaxPoolSize(100);
        cpds.setMinPoolSize(10);
        cpds.setAcquireIncrement(20);
    } 
    catch (PropertyVetoException ex) 
    {

        Logger.getLogger(MCE_Server.class.getName()).log(Level.SEVERE, null, ex);
    }

 }

Following static function is called from a jsp page 从jsp页面调用以下静态函数

http://................/dbActivatePage.jsp

where i have included the function 我已包含功能的地方

      <%@page import="xxxxx.MCE_Server"%>
      <html>
      .
      .
      .
      <body>
      <%
              MCE_Server.makeConnectionPool();
      %>
      .
      .
      .
      </body>
      </html>

I m planning to get the required Connection as per the static function included in MCE_Server.java as follows: 我计划按照MCE_Server.java中包含的静态函数来获取所需的Connection，如下所示：

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

ie whenever i need to get a connection. 即每当我需要获得连接。 I'll include MCE_Server.getConnectionfromPool() . 我将包含MCE_Server.getConnectionfromPool() 。

Now the Problem im having is im receiving an error 现在的问题是我收到错误

java.sql.SQLException: Connections could not be acquired from the underlying database!

Why I m getting this......?? 为什么我得到这个......

On Further trial and error method.... i found out that the statements below the code cpds = new ComboPooledDataSource(); 关于进一步的试验和错误方法...。我发现代码cpds = new ComboPooledDataSource();下面的语句cpds = new ComboPooledDataSource(); is getting executed. 正在执行。

So, what might be the problem here. 因此，这里可能是问题所在。 Is my approach correct ? 我的方法正确吗？

Answer 1

this is not a good approach. 这不是一个好方法。 stuff inside <% ... %> of a JSP gets executed every time a client hits your page. 每当客户点击您的页面时，JSP的<％...％>中的内容就会执行。 a Connection pool should be created only once per web application, not once per-user request! 每个Web应用程序只能创建一次连接池，而不是每个用户请求一次！

my favorite way to set up a Connection pool in a web-app is to set up a ServletContextListener that creates the pool in contextInitialized(ServletContextEvent sce), and also binds it to a name in the application scope (ie it sets a ServletContext attribute). 我最喜欢的在Web应用程序中设置连接池的方法是设置一个ServletContextListener，它在contextInitialized（ServletContextEvent sce）中创建该池，并将其绑定到应用程序范围内的名称（即，它设置ServletContext属性）。。 the pool should be close()ed in the contextDestroyed method of ServletContextListener. 池应该在ServletContextListener的contextDestroyed方法中关闭（）。

if that seems like too much work, just change your makeConnectionPool() to a private method and call it only from inside a static initializer block. 如果这看起来工作量过多，则只需将makeConnectionPool（）更改为私有方法，然后仅从静态初始化程序块内部调用即可。 get rid of <% MCE_Server.makeConnectionPool(); 摆脱<％MCE_Server.makeConnectionPool（）; %> entirely. ％>完全。 then makeConnectionPool() will be called only once, when the MCE_Server class is loaded. 那么当MCE_Server类被加载时，makeConnectionPool（）将仅被调用一次。 but since you never destroy the pool, you'll find leaks of Threads and other resources if you unload and hot redeploy your application (ie you modify and reload the war file without quitting the Servlet container's JVM). 但是由于您从不破坏该池，因此，如果您卸载并热重新部署应用程序（即，在不退出Servlet容器的JVM的情况下修改并重新加载war文件），则会发现线程和其他资源的泄漏。

Answer 2

Well looking at the error ur showing. 好吧，我们看一下显示的错误。

java.sql.SQLException: Connections could not be acquired from the underlying database! . 。

It seems like your c3p0 configuration is right although i agree with Waldman's idea of using ServletContextListener. 尽管我同意Waldman使用ServletContextListener的想法，但您的c3p0配置似乎正确。 In your case, I strongly believe that the problem has to do something with mysql class path. 在您的情况下，我坚信问题必须与mysql类路径有关。 Please Check whether u have properly included the mysql connector. 请检查您是否已正确包含mysql连接器。

使用NetBeans在jsp tomcat中建立c3p0连接池

问题描述

2 个解决方案

解决方案1
3 2013-02-06 10:43:04

解决方案2
1 已采纳

使用NetBeans在jsp tomcat中建立c3p0连接池

问题描述

2 个解决方案

解决方案1 3 2013-02-06 10:43:04

解决方案2 1 已采纳

解决方案1
3 2013-02-06 10:43:04

解决方案2
1 已采纳