Servlet的數據庫連接問題

Question

我試圖連接servlet與mysql數據庫......但在servlet代碼.. 聲明：

Class.forName(driver)顯示與tooltip-

Syntax error on token-"driver",VariableDeclaratorId expected after this token. 

紅色下劃線錯誤

我爲什麼會這樣，只是無法得到它..

這裏是servlet代碼：

package Servlets; 

import java.io.IOException; 
import java.sql.*; 

import javax.servlet.ServletException; 

import javax.servlet.http.HttpServlet; 

import javax.servlet.http.HttpServletRequest; 

import javax.servlet.http.HttpServletResponse; 

public class LoginServlet extends HttpServlet 
{ 

    private static final long serialVersionUID = 1L; 

    public LoginServlet() 
    { 
     super(); 
    } 
    Connection con = null; 

    String url = "jdbc:mysql://localhost:3306/"; 

    String db = "abc"; 

    String driver = "com.mysql.jdbc.Driver"; 

    Class.forName(driver); 


    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
    { 
    } 
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 

    { 
     String username= request.getParameter("username"); 
     String password= request.getParameter("password"); 
     con = DriverManager.getConnection("url+db","root","root"); 
     Statement st = con.createStatement(); 
     int val = st.executeUpdate("INSERT login values("+username+","+password+")"); 
     System.out.println("1 row affected"); 

     response.sendRedirect("login.jsp"); 

    } 

} 

Answer 1

我把

Class.forName("com.mysql.jdbc.Driver").newInstance(); 

線略高於

con = DriverManager.getConnection("url+db","root","root"); 

記住，servlet需要是多線程的，這樣你

Connection con = null; 

可能當兩個用戶同時嘗試登錄時會造成問題。

此外，您還需要關閉連接正確

try { 
    if(con != null) 
     con.close(); 
     } catch(SQLException e) {} 

最後你將需要處理任何異常，數據庫訪問可能會導致這樣一個try catch塊包裹。

package Servlets; 

import java.io.IOException; 
import java.sql.*; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 

public class LoginServlet extends HttpServlet 
{ 

private static final long serialVersionUID = 1L; 

public LoginServlet() 
{ 
    super(); 
} 

String url = "jdbc:mysql://localhost:3306/"; 
String db = "abc"; 
String driver = "com.mysql.jdbc.Driver"; 

protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 
{ 
} 
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException 

{ 
    try{ 
    Connection con = null; 
    String username= request.getParameter("username"); 
    String password= request.getParameter("password"); 
    Class.forName(driver).newInstance(); 
    con = DriverManager.getConnection("url+db","root","root"); 
    Statement st = con.createStatement(); 
    int val = st.executeUpdate("INSERT login values("+username+","+password+")"); 
    System.out.println("1 row affected"); 

    response.sendRedirect("login.jsp"); 
    }catch(SQLException e){} 
    finally{ 
    try { 
     if(con != null) 
     con.close();con=null; 
     } catch(SQLException e) {} 
    } 

} 
} 

或類似的東西。

作爲最後一點，使用「連接池」會更好。

Answer 2

Class.forName("com.mysql.jdbc.Driver"); 
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/rental","root","root") ; 
Statement st = conn.createStatement(); 
String sql = "select * from login"; 
ResultSet rs = st.executeQuery(sql); 

Answer 3

的Class.forName（ 「com.mysql.jdbc.Driver」）; Connection conn = DriverManager.getConnection（「jdbc：mysql：// localhost：3306/rental」，「root」，「root」）;

Answer 4

添加一個MySQL連接器5.1.0 bin jar文件..將jar文件添加到您的項目庫中。

鏈接http://www.java2s.com/Code/Jar/m/Downloadmysqldatabase1610jar.htm