Servlet 数据库连接问题

Question

我正在尝试将 servlet 与 mysql 数据库连接...但在 servlet 代码中... 声明：

Class.forName(driver) 在工具提示上显示带有红色下划线的错误-

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

我就是不明白为什么会这样……

这里是servlet代码：

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

我会放

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

就在上面一行

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

请记住，servlet 需要是多线程的，以便您的

Connection con = null;

当两个用户尝试同时登录时，可能会给您带来问题。

另外，你需要正确关闭连接

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

最后，您需要处理数据库访问可能导致的任何异常，因此请将其包装在 try catch 块中。

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) {}
  }

}
}

或者类似的东西。

最后一点，最好使用“连接池”。

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

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

Answer 4

添加一个 mysql 连接器 5.1.0 bin jar 文件.. 在您的项目库中添加 jar 文件。

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