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서블릿에서 정보를 얻으려고합니다. 여기 내 JSP 페이지의 코드입니다.서블릿을 통해 데이터베이스에서 정보 얻기
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"
import="java.util.*, DB.DBServlet"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<link href="css/bootstrap.min.css" rel="stylesheet">
<title>Lab4</title>
</head>
<body>
<div id='chekboxOfCompanies'>
<%Iterator itr;%>
<% List data= (List)request.getAttribute("country");
for (itr=data.iterator(); itr.hasNext();) {
out.println("<input type='checkbox'>");
}%>
</div>
<div id=''></div>
</body>
</html>
다음은 정보를 가져 오는 서블릿 코드입니다.
public class DBServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
public String page = "main.jsp";
/**
* @see HttpServlet#HttpServlet()
*/
public DBServlet() {
super();
// TODO Auto-generated constructor stub
}
/**
* @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
PrintWriter out = response.getWriter();
String protocol = "jdbc:derby:";
Connection conn = null;
ArrayList<Statement> statements = new ArrayList<Statement>();
Statement s = null;
ResultSet rs = null;
String dbName = "Lab4DB";
ArrayList<String> dataList = new ArrayList<String>();
try {
conn = DriverManager.getConnection(protocol + dbName);
System.out.println("Connected to database " + dbName);
conn.setAutoCommit(false);
s = conn.createStatement();
statements.add(s);
s.executeQuery("SELECT company from companies");
rs = s.getResultSet();
while(rs.next()){
dataList.add(rs.getString("country"));
}
rs.close();
s.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
request.setAttribute("country", dataList);
RequestDispatcher dispatcher = request.getRequestDispatcher(page);
if (dispatcher != null) {
dispatcher.forward(request, response);
}
}
/**
* @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
}
이 코드를 실행하려고하면 Null 포인터 예외가 발생합니다. 콘솔의 출력.
SEVERE: Servlet.service() for servlet [jsp] in context with path [/Lab4DWP] threw exception [java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at org.apache.jsp.main_jsp._jspService(main_jsp.java:80)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
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:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:695)
10.02.2014 15:11:12 org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet [jsp] in context with path [/Lab4DWP] threw exception [java.lang.NullPointerException] with root cause
java.lang.NullPointerException
at org.apache.jsp.main_jsp._jspService(main_jsp.java:80)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
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:728)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:895)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:918)
at java.lang.Thread.run(Thread.java:695)
어떤 변수가 null 값을 가져 옵니까? 어떻게 피할 수 있습니까?
콘솔에서 정보를 인쇄하려고 할 때 : java.sql.SQLException : jdbc : derby : Lab4DB에 적합한 드라이버가 없습니다. –
또한 입력을 위해 닫는 태그가 필요하지 않습니다. –
드라이버는 어디에 지정해야합니까? –