//初始化上下文
                   Context cxt = new InitialContext();
//查找数据源
DataSource ds = (DataSource)cxt.lookup("java:comp/env/mydata");
conn = ds.getConnection();
程序执行到这里报了下面这个错,
javax.naming.NameNotFoundException: Name mydata is not bound in this Context
at org.apache.naming.NamingContext.lookup(NamingContext.java:770)
at org.apache.naming.NamingContext.lookup(NamingContext.java:140)
at org.apache.naming.NamingContext.lookup(NamingContext.java:781)
at org.apache.naming.NamingContext.lookup(NamingContext.java:140)
at org.apache.naming.NamingContext.lookup(NamingContext.java:781)
at org.apache.naming.NamingContext.lookup(NamingContext.java:153)
at org.apache.naming.SelectorContext.lookup(SelectorContext.java:137)
at javax.naming.InitialContext.lookup(Unknown Source)
at org.svse.util.DBconnection.getConn(DBconnection.java:21)
at org.apache.jsp.Dbconn_jsp._jspService(Dbconn_jsp.java:66)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
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:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
at java.lang.Thread.run(Unknown Source)
大家帮忙看下是什么错啊  mydata 数据源 我也有啊,为什么会在上下文中找不到呢?