以下是我的JSP页面：
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@page import="connection.*" %>
<%@page import="java.sql.*" %>
<%@page import="javax.servlet.*" %>
<!DOCTYPE html>
<html>
<head>
<meta charset="ISO-8859-1">
<title>VIEW REPORTS</title>
</head>
<body>
<div align="center"><b>View Reports</b></div>
<form action="GetRole" method="get">
<p>Enter user id:
<input type="text" name="userid"><br>
<input type="submit" value="submit"><br>
</form>
</body>
</html>
<%Object obj=request.getAttribute("substr");%>
<%String[] substr=(String[])obj;
System.out.println("In the second time execution of JSP after getting data from the servlet");
for(int i=0;i<substr.length;i++)
{
System.out.println(""+substr[i]);
}%>
此JSP正在与另一个servlet getRole进行交互。现在我的目标是使用来自getRole的数据在同一个jsp中使用。如果你观察到，</html>标记之后的jsp的结尾部分是处理来自servlet的数据。现在的问题是，当调用JSP时，它正在执行</html>的后期部分，并自然地抛出nullpointerexception。
那么请根据我的要求建议如何执行部分jsp？
PS：我知道不建议在JSP中使用scriptlet，但这又是一个临时项目;所以我采取了一些自由。
更新我的servlet如下：
package all_packages;
import connection.*;
import java.io.IOException;
import java.sql.*;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
//import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class GetRole extends HttpServlet {
private static final long serialVersionUID = 1L;
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
try {
Connection con=getConnection.getConnectionBuilder();
System.out.println(""+con.toString());
String userid=request.getParameter("userid");
String roleid="";
String files="";
System.out.println(" "+userid);
PreparedStatement pstmt=con.prepareStatement("select role_id from users where user_id=?");
pstmt.setString(1,userid);
ResultSet rs=pstmt.executeQuery();
if(rs!=null)
{
while(rs.next())
{
System.out.println(" "+rs.getString(1));
roleid=rs.getString(1);
}
pstmt.close();
}
PreparedStatement pstmt1=con.prepareStatement("select files from access_files where role_id=?");
pstmt1.setString(1,roleid);
ResultSet rs1=pstmt1.executeQuery();
System.out.println(""+rs1.toString());
if(rs1!=null)
{
System.out.println("check");
while(rs1.next())
{
System.out.println(" "+rs1.getString(1));
files=rs1.getString(1);
}
pstmt1.close();
}
String substr[]=files.split(",");
for (int j=0;j<substr.length;j++)
{
System.out.println(""+substr[j]);
}
request.setAttribute("substr", substr);
RequestDispatcher rd=request.getRequestDispatcher("Reports.jsp");
rd.include(request, response);
} catch (SQLException e) {
System.out.println("Connection unsuccessful");
e.printStackTrace();
}
}
}
堆栈跟踪
In the second time execution of JSP after getting data from the servlet
7 Dec, 2014 10:11:14 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [/Final_Bank] threw exception [An exception occurred processing JSP page /Reports.jsp at line 24
21: <%Object obj=request.getAttribute("substr");%>
22: <%String[] substr=(String[])obj;
23: System.out.println("In the second time execution of JSP after getting data from the servlet");
24: for(int i=0;i<substr.length;i++)
25: {
26: System.out.println(""+substr[i]);
27: }%>
Stacktrace:] with root cause
java.lang.NullPointerException
at org.apache.jsp.Reports_jsp._jspService(Reports_jsp.java:90)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:727)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:303)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:208)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:220)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:122)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:501)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:103)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:950)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:116)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1070)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:611)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:314)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)