[讨论]javabean连接mysql的问题 — 编程爱好者社区

主题：[讨论]javabean连接mysql的问题

pulm [专家分：10] 发布于 2008-04-23 06:26:00

小弟新手，遍了一个ＪＡＶＡＢＥＡＮ连接ＭＹＳＱＬ的代码，不知道那里有问题，麻烦大哥大姐帮忙看看，代码有点长，十分感谢那些耐心看完帖子并给出回复的人．．．．

ＪＡＶＡＢＥＡＮ的包如下

package opendb;

import java.sql.*;

public class opendb
{
String dbdriver="org.gjt.mm.mysql.driver";
String url="jdbc:mysql:/localhost/staffinfo";
String user="root";
String password="Lee_0593";

Connection conn=null;
ResultSet rs=null;
Statement stmt;

public opendb()
{
try{
Class.forName(dbdriver);
conn= DriverManager.getConnection(url,user,password);
stmt=conn.createStatement();
}
catch(java.lang.ClassNotFoundException e)
{
System.err.println("dbconnaccess():"+e.getMessage());
}
catch(java.sql.SQLException exp)
{
System.err.println("dbconnaccess():"+exp.getMessage());
}
}
public Statement getstmt()
{
return stmt;
}

public ResultSet exesql(String sql)
{
rs=null;
try {rs=stmt.executeQuery(sql);}
catch (SQLException ex) { System.err.println("aq.excutequery:"+ex.getMessage());}
return rs;
}

public boolean executeupdate(String sql)
{
try{
stmt.executeUpdate(sql);
return true;
}
catch(SQLException ea) {System.err.println("aq.executeupdate:"+ea.getMessage()); }
return false;
}
public void closedb()
{
try{
if(rs != null)
rs.close();
if(stmt != null)
stmt.close();
if(!conn.isClosed() || conn != null)
conn.close();
}
catch(Exception e){System.out.println(e.toString());}
}

}

ＪＳＰ代码如下

<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*"%>
<jsp:useBean id="db" scope="page" class="opendb.opendb"/>

<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>用户登录</title>
  </head>
  <body >
  <center>
<%
    String uid=request.getParameter("staff_name");
    String pwd=request.getParameter("password");
    String query="select * from staff where staff_name='"+uid+"' and password='"+pwd+"'";
    ResultSet rs = db.exesql(query);
    if(rs.next())
    {
      rs.close();

      %>
      welcome <%=uid %>
      <%
    }
    else
    {
      rs.close();
    %>
     <p>sorry!the password is incorrect!</p>
     <p><input type="button" name="Button2" value="back" onClick="backward()"></p>
    <%}
%>
  </center>
  </body>
</html>

错误信息

HTTP Status 500 -

--------------------------------------------------------------------------------

type Exception report

message

description The server encountered an internal error () that prevented it from fulfilling this request.

exception

javax.servlet.ServletException: opendb/opendb (Unsupported major.minor version 49.0)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:244)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

root cause

java.lang.UnsupportedClassVersionError: opendb/opendb (Unsupported major.minor version 49.0)
    java.lang.ClassLoader.defineClass0(Native Method)
    java.lang.ClassLoader.defineClass(ClassLoader.java:539)
    java.security.SecureClassLoader.defineClass(SecureClassLoader.java:123)
    org.apache.catalina.loader.WebappClassLoader.findClassInternal(WebappClassLoader.java:1634)
．．．．．．．．．．
．．．．．．．．．．
note The full stack trace of the root cause is available in the Apache Tomcat/5.0.28 logs.

问题已经解决,正确的代码如下.

JAVABEAN代码

package opendb;

import java.sql.*; //完成环境设置，导入java.sql包

public class opendb {

//declare variable
private Connection conn = null;
private ResultSet rs = null;
private String server = "localhost"; // Can't use localhost , you must use IP or CNAME
private String db = "staffinfo"; //change to your db name
private String user = "root"; //change to your username
private String pass = "Lee_0593"; //change to your password
private String drivername="org.gjt.mm.mysql.Driver"; //mysql driver
private String URL="jdbc:mysql://"+server+"/"+db+"?useUnicode=true&characterEncoding=GBK&user="+user+"&password="+pass;

public opendb()
{
}

public Connection getConn(){ //get database connection
try{
Class.forName(drivername).newInstance(); //载入驱动器
conn = DriverManager.getConnection(URL); //连接到数据库
}
catch(Exception e){
e.printStackTrace();
}
return conn ;
}

public ResultSet executeSQL(String str) {
try{
Statement stmt = conn.createStatement(); //语句接口
rs = stmt.executeQuery(str); //获得结果集
}
catch(Exception e){
e.printStackTrace();
}
return rs;
}
}

JSP代码

<%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*"%>
<jsp:useBean id="db" scope="page" class="opendb.opendb"/>

<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
    <title>用户登录</title>
  </head>
  <body >
  <center>
<%
    ResultSet rs=null;
    Connection conn=null;
    conn=db.getConn();
    String uid=request.getParameter("staff_name");
    String pwd=request.getParameter("password");
    rs=db.executeSQL("select * from staff where staff_name='"+uid+"' and password='"+pwd+"'");
    if(rs.next())
    {
      rs.close();
      %>
      welcome <%=uid %>
      <%
    }
    else
    {
      rs.close();
    %>
     <p>sorry!the password is incorrect!</p>
     <p><input type="button" name="Button2" value="back" onClick="history.back()"></p>
    <%}
%>
  </center>
  </body>
</html>

值得注意的是上面的这个错误
exception
javax.servlet.ServletException: opendb/opendb (Unsupported major.minor version 49.0)
专门找了个帖子详细解释Unsupported major.minor version 49.0错误以及解决方法,
连接如下
http://www.blogjava.net/Unmi/archive/2007/12/04/165035.html
如果有类似的错误,请参考上面连接

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