我是程序员，是jsp的新手，试图编写一些代码。
我写的像
<%
int i=1;
String connectionURL = "jdbc:mysql://localhost:3306/registration";
Connection connection = null;
Statement stmt = null;
ResultSet rset = null;
Statement stmt1 = null;
ResultSet rset1 = null;
Class.forName("com.mysql.jdbc.Driver").newInstance();
int updateQuery = 0;
try {
connection = DBUtil.createConnection();//DriverManager.getConnection(connectionURL, "root", "root");
String queryString = "select * from course";
System.out.println("select all from course table");
stmt = connection.createStatement();
System.out.println("Statment object "+ stmt );
rset = stmt.executeQuery(queryString);
System.out.println("Result set " + rset );
while (rset.next()) {
System.out.println(" Results...");
String s1 = rset.getString(1);
Double amount = rset.getDouble("amount");
String loginid = rset.getString("loginid");
String queryString1 = "select * from users where loginid = '"+ loginid +"'";
System.out.println("select user details from users table");
System.out.println(queryString1);
stmt1 = connection.createStatement();
System.out.println("Statment object "+ stmt1 );
rset1 = stmt1.executeQuery(queryString1);
System.out.println("Result set " + rset1 );
System.out.println(" name -> " + rset1.getString(2));
%>
<tr class="subtext1">
<td align="left"><%=i%> </td>
<td align="left"><%=rset.getString("name")%></td>
<td align="left"><%=rset.getString("loginid")%></td>
<td align="left"><%=rset.getString("name")%></td>
<td align="left"><%=rset.getString("email")%></td>
<td align="left"><%=rset.getString("iimbtrack")%></td>
<td align="left"><%=rset.getString("result")%></td>
<td align="left">CourseFee/<%=rset.getString("product")%></td>
<td align="left"><%=amount%></td>
<td align="left"><%=rset.getString("fdate")%></td>
</tr>
当我尝试打印时，它会出错。但是当我删除这一行时：
System.out.println(" name -> " + rset1.getString(2));
有效。我哪里错了？
这是我得到的错误
statment object com.mysql.jdbc.Statement@429be9
Result set com.mysql.jdbc.ResultSet@10a0d51
java.sql.SQLException: Before start of result set
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:910)
at com.mysql.jdbc.ResultSet.checkRowPos(ResultSet.java:703)
at com.mysql.jdbc.ResultSet.getStringInternal(ResultSet.java:5653)
at com.mysql.jdbc.ResultSet.getString(ResultSet.java:5597)
at org.apache.jsp.WEB_002dINF.jsp.secure.transaction.feesreports_jsp._jspService(feesreports_jsp.java:235)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:98)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:331)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:329)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:265)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:679)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:461)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:399)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:301)
at org.apache.struts.action.RequestProcessor.doForward(RequestProcessor.java:1056)
at org.apache.struts.tiles.TilesRequestProcessor.doForward(TilesRequestProcessor.java:261)
at org.apache.struts.action.RequestProcessor.processForwardConfig(RequestProcessor.java:388)
at org.apache.struts.tiles.TilesRequestProcessor.processForwardConfig(TilesRequestProcessor.java:316)
at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:231)
at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1158)
at org.apache.struts.action.ActionServlet.doGet(ActionServlet.java:397)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:627)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:269)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:188)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:172)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:108)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:174)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:875)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:665)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:528)
at org.apache.tomcat.util.net.LeaderFollowerWorkerThread.runIt(LeaderFollowerWorkerThread.java:81)
答案 0 :(得分：3)
您需要调用ResultSet#next()将光标移动到下一行，否则您无法访问该行中的任何数据。如果您期望多行，请在while循环中执行此操作：
while (rset1.next()) {
System.out.println(" name -> " + rset1.getString(2));
}
或者如果您只想要一行，那么请在if语句中执行此操作：
if (rset1.next()) {
System.out.println(" name -> " + rset1.getString(2));
}
尽管如此，老实说这段代码不是实现从HTML表格中显示数据的功能要求的正确方法。此数据库交互任务不应在JSP文件中完成，而应在真正的Java类中完成。 JSP页面应保留 scriptlet -free。
答案 1 :(得分：1)
您得到的确切错误是什么？我怀疑当你要求第二列数据时，“用户”表中只有一列。或者，如果没有数据，则“rset1”将为null。
我强烈建议您寻找MVC模式。
答案 2 :(得分：1)
您应该明确列出要请求的列，而不是使用通配符。否则，无法保证结果集中列的顺序。考虑如果某人在表格中间添加了一个列会发生什么（是的，这个会发生）。