我正在学习用Java编程以及servlet和jsp页面的使用。
我在理解如何与数据库建立连接时遇到了一些麻烦。 特别是，我有一个名为Database.java的Java页面，在其中创建与数据库的连接，并在其中执行所有功能。 我创建了一个名为Prenotation.java的页面，在其中必须执行一些操作。我的问题是，我不想在该页面上保留数据库连接（从代码中可以看到），但是我想通过Database.java页面建立连接。 我已经尝试了几次，但我不知道该怎么做。 你能给我一些建议吗？谢谢。
Database.java
package db;
import java.math.BigDecimal;
import java.sql.*;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Date;
import java.util.GregorianCalendar;
import java.util.concurrent.TimeUnit;
import entity.*;
public class Database {
private Connection connection = null;
private PreparedStatement statement = null;
private ResultSet rs = null;
private String dbname = "Hotel";
String nomeutente = "root";
String password = "123456789";
private static Database db = null;
public static synchronized Database getDatabase() {
if (db == null) {
db = new Database();
}
return db;
}
private Database() {
try {
Class.forName("com.mysql.jdbc.Driver").newInstance();
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/" + dbname
+ "?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC",
nomeutente, password);
} catch (Exception exc) {
exc.printStackTrace();
}
}
public Connection getConnection() {
return connection;
}
public boolean checkUser(String email, String password) throws SQLException {
boolean result = false;
String query = "select password from users where email=?";
statement = connection.prepareStatement(query);
statement.setString(1, email);
rs = statement.executeQuery();
if (rs.next() && password.equals(rs.getString("password"))) {
result = true;
}
rs.close();
statement.close();
return result;
}
public boolean existingMail(String email) throws SQLException {
String query = "select * from users where email=?";
boolean result = true;
statement = connection.prepareStatement(query);
statement.setString(1, email);
rs = statement.executeQuery();
if (rs.next()) {
result = true;
} else {
result = false;
}
rs.close();
statement.close();
return result;
}
public boolean insertUtente(Utente u,String password) throws SQLException {
String query = "INSERT INTO users (email,nome,cognome,luogodinascita,datadinascita,indirizzo,password) VALUES (?,?,?,?,?,?,?)";
if(existingMail(u.getEmail())) {
return false;
}
statement = connection.prepareStatement(query);
statement.setString(1, u.getEmail());
statement.setString(2, u.getNome());
statement.setString(3, u.getCognome());
statement.setString(4, u.getLuogodinascita());
statement.setString(5, u.getDatadinascita());
statement.setString(6, u.getIndirizzo());
statement.setString(7, password);
statement.execute();
statement.close();
return true;
}
public Utente getUtente(String email) throws SQLException {
String query= "select * from users where email=?";
statement = connection.prepareStatement(query);
statement.setString(1, email);
rs=statement.executeQuery();
if(!rs.next()) {
return null;
}
Utente u=new Utente(email,rs.getString("nome"),rs.getString("cognome"),rs.getString("datadinascita"),rs.getString("luogodinascita"),rs.getString("indirizzo"));
rs.close();
statement.close();
return u;
}
public boolean modificaPassword(String email, String password) throws SQLException {
String query="UPDATE users SET password='"+password+"' WHERE email='"+email+"'";
Statement statement=connection.createStatement();
statement.executeUpdate(query);
statement.close();
return true;
}
public boolean modificaProfilo(Utente u) throws SQLException {
String query="UPDATE users SET nome = ?, cognome = ?, datadinascita = ?, luogodinascita = ?, indirizzo = ? WHERE email = ?";
statement = connection.prepareStatement(query);
statement.setString(1, u.getNome());
statement.setString(2, u.getCognome());
statement.setString(3, u.getDatadinascita());
statement.setString(4, u.getLuogodinascita());
statement.setString(5, u.getIndirizzo());
statement.setString(6, u.getEmail());
statement.executeUpdate();
statement.close();
return true;
}}
这是我所说的页面
package servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.*;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
import javax.swing.JOptionPane;
import db.Database;
import entity.Prenotazione;
/**
*
* @author OOPs
*/
public class Prenotation extends HttpServlet {
private static final String ResultSet = null;
protected void processRequest(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
HttpSession session=request.getSession();
String idPrenotazione = request.getParameter("idPrenotazione");
String email = request.getParameter("email");
int typeRoom = Integer.parseInt(request.getParameter("typeRoom"));;
String arrivalDate = request.getParameter("arrivalDate");
String departureDate = request.getParameter("departureDate");
response.setContentType("text/html;charset=UTF-8");
PrintWriter out = response.getWriter();
try {
Class.forName("com.mysql.cj.jdbc.Driver");
// out.println("driver loaded");
Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/Hotel?useUnicode=true&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC","root" ,"123456789");
out.println("Connect");
Statement st = con.createStatement();
// Statement stmt = con.createStatement();
out.println("connection successfull");
int total = 0;
PreparedStatement ps = con.prepareStatement( "SELECT COUNT(*) as total FROM reservation WHERE typeRoom = ? AND (? >= arrivaldate AND ? <= departuredate) OR (? >= arrivaldate AND ? <= departuredate)");
int c = 0;
ps.setInt(++c, typeRoom);
ps.setString(++c, arrivalDate);
ps.setString(++c, departureDate);
ps.setString(++c, arrivalDate);
ps.setString(++c, departureDate);
ResultSet rs = ps.executeQuery();
// ResultSet rs2 = stmt.executeQuery(check);
out.println("<h1> Stringa check eseguito </h1>");
if( total > 0) {
// response.sendRedirect("home.jsp");
response.sendRedirect("PrenotazioneNegata.jsp");
}
else {
st.executeUpdate("insert into reservation (email,typeRoom,arrivalDate,departureDate)values ('"+email+"','"+typeRoom+"','"+arrivalDate+"','"+departureDate+"')");
response.sendRedirect("PrenotazioneAvvenuta.jsp");
}
out.println("<h1> Registrazione Eseguita </h1>");
}catch(Exception e){
out.println("Errore." +e);
}
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 {
processRequest(request, response);
}
/**
* 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 {
processRequest(request, response);
}
/**
* Returns a short description of the servlet.
*
* @return a String containing servlet description
*/
@Override
public String getServletInfo() {
return "Short description";
}// </editor-fold>
}