我写的代码是
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Search extends HttpServlet {
/**
* Processes requests for both HTTP
* <code>GET</code> and
* <code>POST</code> methods.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException, ClassNotFoundException, SQLException {
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
Connection con =null;
Statement stmt = null;
ResultSet rs = null;
String veh_no = request.getParameter("vehicle_no");
try {
/* TODO output your page here. You may use following sample code. */
Class.forName("com.mysql.jdbc.Driver");
con = DriverManager.getConnection ("jdbc:mysql://localhost:3306/pay_n_park","root","admin");
stmt = con.createStatement();
rs = stmt.executeQuery("select block_no from vehicle where vehicle_no='"+veh_no+"' and out_time=NULL");
if(rs != null){
out.println("<!DOCTYPE html>");
out.println("<html>");
out.println("<head>");
out.println("<title>Search Results</title>");
out.println("</head>");
out.println("<body>");
out.println("<h1>Search Results :</h1>");
out.print("<br/> Vehicle No: " + veh_no);
out.print("<br/> Block No : " + rs.getString("block_no"));
out.println("</body>");
out.println("</html>");
}
} finally {
out.close();
}
}
// <editor-fold defaultstate="collapsed" desc="HttpServlet methods. Click on the + sign on the left to edit the code.">
/**
* Handles the HTTP
* <code>GET</code> method.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try {
processRequest(request, response);
} catch (ClassNotFoundException ex) {
Logger.getLogger(Search.class.getName()).log(Level.SEVERE, null, ex);
} catch (SQLException ex) {
Logger.getLogger(Search.class.getName()).log(Level.SEVERE, null, ex);
}
}
/**
* Handles the HTTP
* <code>POST</code> method.
*
* @param request servlet request
* @param response servlet response
* @throws ServletException if a servlet-specific error occurs
* @throws IOException if an I/O error occurs
*/
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
try {
processRequest(request, response);
} catch (ClassNotFoundException ex) {
Logger.getLogger(Search.class.getName()).log(Level.SEVERE, null, ex);
} catch (SQLException ex) {
Logger.getLogger(Search.class.getName()).log(Level.SEVERE, null, ex);
}
}
/**
* Returns a short description of the servlet.
*
* @return a String containing servlet description
*/
@Override
public String getServletInfo() {
return "Short description";
}
}// </editor-fold>
结果集rs只有一条记录。如果我执行rs.next()，它就来自if，我不想要那样。我该怎么做才能打印此记录，在两种情况下它都是从if中出来的。
返回的ResultSet是从不 null。您确实需要调用ResultSet#next()将光标设置到下一行。它的默认位置是before第一行。不这样做只会导致
所以，只需替换
if(rs != null){
作者
if (rs.next()) {
您应该已经准备就绪。
如果要处理“未找到结果”的情况，只需在else的if中进行处理：
if (rs.next()) {
// At least one record found.
} else {
// No records found.
}
Unrelated涉及到具体问题，此代码还有其他严重问题：存在巨大的SQL注入攻击漏洞，并且数据库资源正在被泄漏掉。这是不对的。