sqlserver+jsp

我用JSP访问SQLSERVER数据库常会出现如下问题，请大家帮忙分析一下：（而且对于同一个页面，第一次访问时正确，再次访问时就可能出现该问题）
com.microsoft.sqlserver.jdbc.SQLServerException: 接收 TDS 预登录响应时发生 I/O 错误。
at com.microsoft.sqlserver.jdbc.SQLServerException.makeFromDriverError(Unknown Source)
at com.microsoft.sqlserver.jdbc.DBComms.Prelogin(Unknown Source)
at com.microsoft.sqlserver.jdbc.DBComms.<init>(Unknown Source)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connectHelper(Unknown Source)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.loginWithoutFailover(Unknown Source)
at com.microsoft.sqlserver.jdbc.SQLServerConnection.connect(Unknown Source)
at com.microsoft.sqlserver.jdbc.SQLServerDriver.connect(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at java.sql.DriverManager.getConnection(Unknown Source)
at org.sunxin.lesson.jsp.bookstore.ListServlet.doGet(ListServlet.java:49)
at org.sunxin.lesson.jsp.bookstore.ListServlet.doPost(ListServlet.java:168)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
at java.lang.Thread.run(Unknown Source)