servlet傳直到jsp問題

[cklonger (22)]

我在serlve將二惟array存在session
之後到jsp再取出來

int size  = 0;
int n =0;
size =
session.getAttribute("sized")==null?0:Integer.parseInt(session.getAttribute("sized").toString());
        //  out.println(size);


        String a[][] = new String[2][size];

        a =(String[][])session.getAttribute("valuesd");
         out.println("<table border = '1'><tr><td>Domain name</td><td>Alert numbers</td></tr>");
        for(n = 0; n<size;n++){
        out.println("<tr><td>"+a[0][n]+"</td>");
        out.println("<td>"+a[1][n]+"</td></tr>");
        }
        out.println("</table>");
        //out.println(a.length);

        a = null;


但是會有 第一次load jsp 值印不出來
要重整網頁才印出來

我加了一個迴圈 想要判斷 array取到了再列印

while(a.length <=0){

        }

但是會出現錯誤訊息

2008/9/4 銝鲳? 06:13:42 org.apache.catalina.core.StandardWrapperValve invoke
?湧??? Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
        at
org.apache.jsp.chart_002dnewall_jsp._jspService(chart_002dnewall_jsp.java:178)
        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(Thread.java:595)


請問有什麼方法可以讓網頁第一次就取到session的值

或是讓out.print可以等到array assign ok再列印

--

refresh
因為會讓網頁其他部分的呈現跑掉
所以不能採用

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◆ From: 210.241.25.133
推 TonyQ:if (xxx!=null){ /* run the body ....*/ };
→ cklonger:請問XXX是什麼 這個code要寫在jsp還是javascript funtion
※ 編輯: cklonger        來自: 218.166.12.250       (09/04 20:53)
推 slalala:xxx應該是某instance
推 slalala:要不要寫個dispatcher 當session==null 導向error page?
推 TonyQ:我猜 xxx是 a , 因為裡面看起來只有a比較有可能產生NullPoin
→ cklonger:是a null沒錯 a是用來存session的矩陣
→ cklonger:有方法能知道a 已經存好值 因為一定要能存到 else要寫
推 TonyQ:if(a!=null){  /* run the body */  };