这个SQL语法有什么问题？

Question

我想用java servlet构建注册系统。并将数据插入到mySQL数据库中。但是我得到一个语法错误。我刚刚读完Wiley mySQL和Java开发人员指导书。

我对servlet编程还不太熟悉，所以如果有简单的方法可以做，请告诉我。

package com.app.base; 

import java.io.IOException; 
import java.io.PrintWriter; 
import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.ResultSet; 
import java.sql.Statement; 

import javax.servlet.RequestDispatcher; 
import javax.servlet.ServletException; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 

import com.app.pojo.*; 

public class RegisterServlet extends HttpServlet{ 

MySqlDB mysql; 

@Override 
public void init() throws ServletException { 
    // TODO Auto-generated method stub 
    mysql = new MySqlDB(); 

} 

@Override 
protected void doPost(HttpServletRequest req, HttpServletResponse resp) 
     throws ServletException, IOException { 

    PrintWriter out = null; 
    //Connection connection = null; 
    //Statement statement; 
    //ResultSet rs; 

    resp.setContentType("text/html"); 
    out = resp.getWriter(); 


    try{ 
     mysql.createConnection(); 
    }catch(Error e){ 
     out.write("Couldn't connect to mysql"); 
    } 
    String fname = req.getParameter("fname"); 
    String lname = req.getParameter("lname"); 
    String email = req.getParameter("email"); 
    String password = req.getParameter("password"); 
    String city = req.getParameter("city"); 
    String country = req.getParameter("country"); 

    if(fname == null){ 
     String destination = "signup.jsp?error=Complete All Fields"; 
     RequestDispatcher rd = getServletContext().getRequestDispatcher(destination); 
     rd.forward(req, resp); 
    }else if(lname == null){ 
     String destination = "signup.jsp?error=Complete All Fields"; 
     RequestDispatcher rd = getServletContext().getRequestDispatcher(destination); 
     rd.forward(req, resp); 
    }else if(email == null){ 
     String destination = "signup.jsp?error=Complete All Fields"; 
     RequestDispatcher rd = getServletContext().getRequestDispatcher(destination); 
     rd.forward(req, resp); 
    }else if(password == null){ 
     String destination = "signup.jsp?error=Complete All Fields"; 
     RequestDispatcher rd = getServletContext().getRequestDispatcher(destination); 
     rd.forward(req, resp); 
    }else if(city == null){ 
     String destination = "signup.jsp?error=Complete All Fields"; 
     RequestDispatcher rd = getServletContext().getRequestDispatcher(destination); 
     rd.forward(req, resp); 
    }else if(country == null){ 
     String destination = "signup.jsp?error=Complete All Fields"; 
     RequestDispatcher rd = getServletContext().getRequestDispatcher(destination); 
     rd.forward(req, resp); 
    }else{ 

     String sql = "INSERT INTO main.users(first_name, last_name, email, password, city, country, registered_time) VALUES(" 
       + fname +", "+ lname + ", "+ email +", " + password +", " + city +"," + country + ",Now());"; 
     int answer = mysql.insertSQL(sql); 
     if(answer == 1){ 
      resp.sendRedirect("index.jsp?registered=true"); 
      //String destination = "index.jsp?registered=true"; 
      //RequestDispatcher rd = getServletContext().getRequestDispatcher(destination); 
      //rd.forward(req, resp); 
     } 
    } 


} 

} 

这是MySql类来连接。

package com.app.pojo; 

import java.sql.Connection; 
import java.sql.DriverManager; 
import java.sql.ResultSet; 
import java.sql.SQLException; 
import java.sql.Statement; 

public class MySqlDB{ 

private static String username = "root", password = "root"; 

public Connection createConnection(){ 
    Connection connection = null; 
    try{ 
     //Load the JDBC driver 
     Class.forName("com.mysql.jdbc.Driver"); 

     connection = DriverManager.getConnection("jdbc:mysql://localhost:3306,/main", username, password); 
     //Create a connection to the database 


    }catch(SQLException ex){ 
     System.out.println(ex); 
    }catch(ClassNotFoundException e){ 
     System.out.println(e); 
    } 

    return connection; 
} 

public void runSqlStatement(String sql){ 
    try{ 
     Statement statement = createConnection().createStatement(); 
     //statement executeQuery(Query) 
     boolean rs = statement.execute(sql); 
    }catch(SQLException ex){ 
     System.out.println(ex); 
    } 
} 

public ResultSet executeSQL(String sql){ 

    Statement statement = null; 
    ResultSet rs = null; 

    try{ 
     statement = createConnection().createStatement(); 
     rs = statement.executeQuery(sql); 

     /*while(rs.next()){ 
      System.out.println(rs.getString(1)); 
     }*/ 


    //   rs.close(); 
    //   statement.close(); 
    }catch (SQLException e) { 
     System.out.println(e); 
    } 

    return rs; 
} 

public int insertSQL(String sql){ 

    int rs; 

    try{ 
     Statement statement = createConnection().createStatement(); 
     rs = statement.executeUpdate(sql); 
     return rs; 

    }catch(SQLException ex){ 
     System.out.println(ex); 
     return 0; 
    } 


} 
} 

这是tomcat的控制台

INFO: Reloading Context with name [/Map] has started 
Apr 21, 2012 12:59:14 AM org.apache.catalina.loader.WebappClassLoader clearReferencesJdbc 
SEVERE: The web application [/Map] registered the JDBC driver [com.mysql.jdbc.Driver] but failed to unregister it when the web application was stopped. To prevent a memory leak, the JDBC Driver has been forcibly unregistered. 
Apr 21, 2012 12:59:17 AM org.apache.catalina.core.StandardContext reload 
INFO: Reloading Context with name [/Map] is completed 

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near '********,Colombo,Sri Lanka,Now())' at line 1 

Answer 1

尝试......

Connection con = mysql.createConnection(); 
String sql = "INSERT INTO main.users(first_name, last_name, email, password, city, 
country, registered_time) VALUES(?, ?, ?, ?, ?, ?, ?);"; 
PreparedStatement insertStatement = con.prepareStatement(sql); 
insertStatement.setString(1, first_name); 
insertStatement.setString(2, last_name); 
insertStatement.setString(3, email); 
insertStatement.setString(4, password); 
insertStatement.setString(5, city); 
insertStatement.setString(6, country); 
insertStatement.setString(7, new Date()); 
insertStatement.execute(); 

问候。

Answer 2

你需要逃出/报价，您有串在你VALUES部分。您的JDBC驱动程序将为您执行此操作，例如using a PreparedStatement。

请注意，如果您保留现有代码或只是添加周围的引号，则您确实存在SQL injection attack的危险。

Answer 3

试着把单引号放在你的变量中。

例：

VALUES('" + myString + "', '" + myOtherString + "')

Answer 4

Colombo,Sri Lanka,Now())' at line 1 

看起来像你缺少你周围的字符串单引号。

Answer 5

String sql = "INSERT INTO main.users(first_name, last_name, email, password, city, country, registered_time) VALUES('" 
       + fname +"', '"+ lname + "', '"+ email +"', '" + password +"',' " + city +"','" + country + "',Now())";