数据库连接高手请进！答者有分！

[offsider]

我建了一个有10个连接的连接池，用jsp调用连接池中的连接，刚开始是一切正常，
但过一段时间就报错：

java.lang.NullPointerException
at _default._jspService(_default.java, Compiled Code)
at oracle.jsp.runtime.HttpJsp.service(HttpJsp.java, Compiled Code)
at oracle.jsp.app.JspApplication.dispatchRequest(JspApplication.java, Compiled Code)
at oracle.jsp.JspServlet.doDispatch(JspServlet.java, Compiled Code)
at oracle.jsp.JspServlet.internalService(JspServlet.java, Compiled Code)
at oracle.jsp.JspServlet.service(JspServlet.java, Compiled Code)
at javax.servlet.http.HttpServlet.service(HttpServlet.java, Compiled Code)
at org.apache.jserv.JServConnection.processRequest(JServConnection.java, Compiled Code)
at org.apache.jserv.JServConnection.run(JServConnection.java, Compiled Code)
at java.lang.Thread.run(Thread.java, Compiled Code)


重起Webserver就好了，
后来我把连接池改为100个，也不解决问题。
请问那位大哥知道是怎么回事？马上给分，在线等待！