当我运行以下servlet时：
// package projectcodes;
public void doPost(HttpServletRequest request,HttpServletResponse response) throws ServletException,IOException {
String UserID = request.getParameter("UserID");
String UserPassword = request.getParameter("UserPassword");
String userName = null;
String Email = null;
Encrypter encrypter = new Encrypter();
String hashedPassword = null;
try {
hashedPassword = encrypter.hashPassword(UserPassword);
Context context = new InitialContext();
DataSource ds = (DataSource)context.lookup("java:comp/env/jdbc/photog");
Connection connection = ds.getConnection();
String sqlStatement = "SELECT email,firstname FROM registrationinformation WHERE password='" + hashedPassword + "'";
PreparedStatement statement = connection.prepareStatement(sqlStatement);
ResultSet set = statement.executeQuery();
userName = set.getString(1); // <<---------- Line number 28
response.sendRedirect("portfolio_one.jsp");
// userName = set.getString("FirstName");
Email = set.getString(3);
if(set.wasNull() || Email.compareTo(UserID) != 0) {
// turn to the error page
response.sendRedirect("LoginFailure.jsp");
} else {
// start the session and take to his homepage
HttpSession session = request.getSession();
session.setAttribute("UserName", userName);
session.setMaxInactiveInterval(900); // If the request doesn't come withing 900 seconds the server will invalidate the session
RequestDispatcher rd = request.getRequestDispatcher("portfolio_one.jsp");
rd.forward(request, response); // forward to the user home-page
}
}catch(Exception exc) {
System.out.println(exc);
}
我得到以下例外情况：
INFO: java.sql.SQLException: Invalid operation at current cursor position.
at org.apache.derby.client.am.SQLExceptionFactory40.getSQLException(Unknown Source)
at org.apache.derby.client.am.SqlException.getSQLException(Unknown Source)
at org.apache.derby.client.am.ResultSet.getString(Unknown Source)
at com.sun.gjc.spi.base.ResultSetWrapper.getString(ResultSetWrapper.java:155)
-----> at projectcodes.ValidateDataForSignIn.doPost(ValidateDataForSignIn.java:28
at javax.servlet.http.HttpServlet.service(HttpServlet.java:754)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847)
at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:281)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:98)
at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:91)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:162)
at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:330)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:174)
at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:828)
at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:725)
at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1019)
at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225)
at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
at java.lang.Thread.run(Thread.java:722)
Caused by: org.apache.derby.client.am.SqlException: Invalid operation at current cursor position.
at org.apache.derby.client.am.ResultSet.checkForValidCursorPosition(Unknown Source)
at org.apache.derby.client.am.ResultSet.checkGetterPreconditions(Unknown Source)
... 30 more
服务器上面的日志显示第28行是导致异常的原因。但我无法得到例外的原因。表中的所有列都具有varchar的数据类型。
我在servlet代码中突出显示第28行（根据服务器日志的异常原因）。
答案 0 :(得分：33)
您应该先使用next语句。
ResultSet set = statement.executeQuery();
if (set.next()) {
userName = set.getString(1);
//your logic...
}
更新
正如Java 6文档所说
ResultSet游标最初位于第一行之前;对方法的第一次调用使得第一行成为当前行;第二个调用使第二行成为当前行，依此类推。
这意味着当你执行句子时
ResultSet set = statement.executeQuery();
将创建ResultSet set并指向第一个数据结果之前的行。你可以这样看：
SELECT email，firstname FROM registrationinformation
email | firstname
____________________________________
0 <= set points to here
1 email1@gmail.com | Email1 Person
2 foo@bar.com | Foo Bar
因此，在打开ResulSet之后，执行方法next将其移动到第一行。
if(set.next())
现在set看起来像这样。
email | firstname
____________________________________
0
1 email1@gmail.com | Email1 Person <= set points to here
2 foo@bar.com | Foo Bar
如果需要读取ResultSet中的所有数据，则应使用while而不是if：
while(set.next()) {
//read data from the actual row
//automatically will try to forward 1 row
}
如果set.next()返回false，则表示没有要读取的行，因此while循环将结束。
更多信息here。
答案 1 :(得分：1)
您必须将指针设置为正确的位置：
while(set.hasNext()){
set.next();
String a = set.getString(1);
String b = set.getString(2);
}
答案 2 :(得分：0)
ResultSet set = statement.executeQuery（）;
迭代该集合，然后获取String。
while(set.next()) {
me = set.getString(1); // <<---------- Line number 28
}
答案 3 :(得分：0)
检查光标是否有行，例如
if(rs.next()){
//your all other works should go here
}
答案 4 :(得分：0)
您可以使用rs.first()