Question

我正在尝试将此Java Web应用程序插入数据库。下图显示了我遇到的错误。

问题：当我调用insertDB()时它起作用了，因为id列正在计数1，2，3，...，但是当我全部传递customers36表中的其余数据时，它们都是空白数据输入。display()方法有效，但插入方法无效，而且我用光了它可能要用的东西。

Image showing that the data is not getting to the database.

注意： selectDB（）//也可以

力求尽可能具体。 db中的数据是所有字符串，但id列除外。这就是为什么我将所有字符串发送到数据库的原因。

//Code is for a java bank application.    
package Business;

import java.sql.*;
import java.util.logging.Level;
import java.util.logging.Logger;

/**
 * @author DEVGRU
 */
public class Customer
{
    //properties
    private String custId;
    private String custPassword;
    private String custFname;
    private String custLname;
    private String address;
    private String email;
    Connection con = null;

    //Constructors
    public Customer()
    {
        custId = "";
        custPassword = "";
        custFname = "";
        custLname = "";
        address = "";
        email = "";
    }

    public Customer( String id, String pw, String fn, String ln, String add, String em )
    {
        custId = id;
        custPassword = pw;
        custFname = fn;
        custLname = ln;
        address = add;
        email = em;
    }

    //Setters and getters.
    public void setCustId( String id )
    {
        custId = id;
    }

    public String getCustId()
    {
        return custId;
    }

    public void setCustPassword( String pw )
    {
        custPassword = pw;
    }

    public String getCustPassword()
    {
        return custPassword;
    }

    public void setCustFirstName( String fn )
    {
        custFname = fn;
    }

    public String getCustFirstName()
    {
        return custFname;
    }

    public void setCustLastName( String ln )
    {
        custLname = ln;
    }

    public String getCustLastName()
    {
        return custLname;
    }

    public void setAddress( String add )
    {
        address = add;
    }

    public String getAddress()
    {
        return address;
    }

    public void setEmail( String em )
    {
        email = em;
    }

    public String getEmail()
    {
        return email;
    }

    //Db Management and Manipulation methods

    /**
     * @param id@throws ClassNotFoundException
     */
    public void selectDb( String id ) throws ClassNotFoundException
    {
        Class.forName( "com.mysql.jdbc.Driver" );
        try
        {
            //Get the connection and stick it in con.
            con = DriverManager.getConnection( Settings.mysql_connstring, Settings.mysql_user, Settings.mysql_password );
            Statement stmt = con.createStatement();
            String sql;                                             //Single Quotes Arround String Data.Pay Attention.
            sql = "Select * from `JavaChatBankDB`.`Customers` where CustID = '" + id + "'";
            System.out.println( sql );
            ResultSet rs;
            //Execute
            rs = stmt.executeQuery( sql );
            //Process

            while ( rs.next() )
            {
                custId = rs.getString( 1 );
                custPassword = rs.getString( 2 );
                custFname = rs.getString( 3 );
                custLname = rs.getString( 4 );
                address = rs.getString( 5 );
                email = rs.getString( 6 );

            }//End while              
        }
        catch ( SQLException ex )
        {
            System.out.println( "Error somewhere. " + ex );
        }
        finally
        {
            try
            {
                con.close();
            }
            catch ( SQLException ex )
            {
                Logger.getLogger( LoginServlet.class.getName() ).log( Level.SEVERE,
                        null, ex );
            }//End Try/Catch on connection.close() -- sqlexception.
        }//End Finally
    }//End Select Db

    public void insertDB( String id, String pw, String fn, String ln, String add,
            String em ) throws ClassNotFoundException
    {
        Class.forName( "com.mysql.jdbc.Driver" );
        try
        {
            //Get the connection and stick it in con.
            con = DriverManager.getConnection( Settings.mysql_connstring, Settings.mysql_user, Settings.mysql_password );
            Statement stmt = con.createStatement();
            //Single Quotes Arround String DataPay Attention.
            String sql = "INSERT INTO `JavaChatBankDB`.`Customers36` (`CustId`,`CustPassword`, `CustFirstName`, `CustLastName`, `CustAddress`, `CustEmail`)"
                         + "VALUES ('" + custId + "','" + custPassword + "','" + custFname + "','" + custLname + "','" + address + "','" + email + "')";
            System.out.println( sql );
            int answer = stmt.executeUpdate( sql );
            if ( answer >= 1 )
            {
                System.out.println( "Success on Inserting Data into the Database. Go Check!!!" );
            }
            else
            {
                System.out.println( "An error occured while attempting to update database" );
            }

            custId = id;
            custPassword = pw;
            custFname = fn;
            custLname = ln;
            address = add;
            email = em;
        }
        catch ( SQLException ex )
        {
            System.out.println( "Error somewhere. " + ex );
        }
        finally
        {
            try
            {
                con.close();
            }
            catch ( SQLException ex )
            {
                Logger.getLogger( LoginServlet.class.getName() ).log( Level.SEVERE, null, ex );
            }//End Try/Catch on connection.close() -- sqlexception.
        }//End Finally
    }//End Select Db

    public void display()
    {
        System.out.println( "_________Display___________" );
        System.out.println( "                           " );
        System.out.println( "Customer Id: " + custId );
        System.out.println( "Customer Password:" + custPassword );
        System.out.println( "Customer First Name: " + custFname );
        System.out.println( "Custoner Last Name: " + custLname );
        System.out.println( "Customer Address: " + address );
        System.out.println( "Customer Email: " + email );

    }

    public static void main( String[] args ) throws ClassNotFoundException
    {
        //Customer c1 = new Customer("4567","root","mike","baules","afghanistan","camels@sandbox.org");

        Customer c2 = new Customer();
        //c2.selectDb("3006");
        c2.insertDB( "3007", "apple", "Steve", "Jobs", "cali", "apple@apple.com" );
        c2.display();

    }
}//End Class

Answer 1

在发送查询之后，您将为查询设置值。好，为时已晚，查询已发送（使用默认值或先前值）。所以代替：

String sql = "INSERT INTO `JavaChatBankDB`.`Customers36` (`CustId`,`CustPassword`, `CustFirstName`, `CustLastName`, `CustAddress`, `CustEmail`)"
               + "VALUES ('"+custId+"','"+custPassword+"','"+custFname+"','"+custLname+"','"+address+"','"+email+"')";
int answer = stmt.executeUpdate(sql);
[...]
custId = id;
custPassword = pw;
custFname = fn;
custLname = ln;
address = add;
email = em;

您必须交换订单或完全不使用变量custId，custPassword等，而使用方法参数值id，pw等等。

此外，对于具有可变输入的查询，应使用准备好的语句，以防止任何SQL注入。请阅读https://docs.oracle.com/javase/tutorial/jdbc/basics/prepared.html，了解如何在Java中将预处理语句与JDBC一起使用。

Answer 2

代码应分为多个类，例如DbHelper和Customer。请更具体地说明您的问题，因为我只看到您插入1个ID为3007类型字符串的客户？还可以考虑将Long用作id或AtomicLong。

MySQL数据库未插入数据

2 个答案: