C3P0连接池在Servlet / Tomcat中不起作用

Question

基于C3P0 ComboPooledDataSource类创建了一个Datasource类。它适用于测试代码但不能在tomcat容器下的servlet中工作。有谁知道为什么？

class Datasource{
   private ComboPooledDataSource cpds;
   private Datasoruce datasource;

   private Datasource(){
   //setup cpds
   cpds.new ComboPooledDataSource();
   cpds.setUser("abcd");
   ...
 }

 public static getInstance(){
     if( datasource == null ) datasource = new Datasource();
     return datasource;
 }

  public Connection getConnection(){
     return cpds.getConnection();
 }
}

//test code works if put in indepedent main() with multithreading.
  Datasource ds = Datasource.getInstance();
  Connection conn = ds.getConnection();

//Above test code won't work if put inside servlet doGet() with tomcat.

错误是＆＃34;客户端尝试签出连接的尝试已在getConnection（）的行中超时。