JSP连接mysql报错

jsp连接mysql报错，org.apache.jasper.JasperException: Unable to compile class for JSP

<%@ page contentType="text/html; charset=gb2312" %>
<%@ page language="java" %>
<%@ page import="com.mysql.jdbc.Driver" %>
<%@ page import="java.sql.*" %> 

<%
//驱动程序名
String driverName="com.mysql.jdbc.Driver";
//数据库用户名
String userName="";
//密码
String userPasswd="";
//数据库名
String dbName="";
//表名
String tableName="";
//联结字符串
String url="jdbc:mysql://localhost/"+dbName+"?user="+userName+"&password="+userPasswd;
Class.forName("com.mysql.jdbc.Driver").newInstance();
Connection connection=DriverManager.getConnection(url);
Statement statement = connection.createStatement();
String sql="SELECT * FROM "+tableName;
ResultSet rs = statement.executeQuery(sql); 
//获得数据结果集合
ResultSetMetaData rmeta = rs.getMetaData();
//确定数据集的列数，亦字段数
int numColumns=rmeta.getColumnCount();
	out.print("id"); 	
	out.print("| ");
	out.print("username");
	out.print("| ");
	out.print("password");
	out.print("<br>");
	while(rs.next()) {
		out.print(rs.getString(1)); 
		out.print("   |   ");
		out.print(rs.getString(2));
		out.print("   |   "); 
		out.print(rs.getString(3));
		out.print("<br>"); 
	}
	out.print("<br>");
	out.print("数据库操作成功，恭喜你"); 
	rs.close(); 
	statement.close(); 
	connection.close(); 
%>

 最后确定是java home等相关变量未建立

java_home=
classpath=
path=

重启tomcat即可。