关于 MySql JDBC 在netbeans中连接不上的问题

Question

 Connection con;
            Statement sql = null;
            ResultSet rs = null;
            try {
                Class.forName("com.mysql.jdbc.Driver");
            } catch (ClassNotFoundException e) {
                out.print(e);
            }
            try {
                String url="jdbc:mysql://localhost:3306/ChatDB";
                con = DriverManager.getConnection(url,
                        "wtc", " 9999999");
            } catch (SQLException e) {
                out.print(e);
            }
            sql = con.createStatement();
错误为
G:\programming\Netbeans\WebApplication1\build\generated\src\org\apache\jsp\index_jsp.java:84: 可能尚未初始化变量 con
      sql = con.createStatement();应该是上面的con没有得到连接上的值  请大家帮帮忙 谢谢！！！！

Answer 1

下面是服务器日志An error occurred at line: 39 in the jsp file: /index.jsp
The local variable con may not have been initialized
36:                 {
37:                     out.print(e);
38:                 }
39:             sql=con.createStatement();
40:             //rs=sql.executeQuery()
41:         %>
42:     </body>
Stacktrace:
        at org.apache.jasper.compiler.DefaultErrorHandler.javacError(DefaultErrorHandler.java:92)
        at org.apache.jasper.compiler.ErrorDispatcher.javacError(ErrorDispatcher.java:330)
        at org.apache.jasper.compiler.JDTCompiler.generateClass(JDTCompiler.java:423)
        at org.apache.jasper.compiler.Compiler.compile(Compiler.java:317)
        at org.apache.jasper.compiler.Compiler.compile(Compiler.java:295)
        at org.apache.jasper.compiler.Compiler.compile(Compiler.java:282)
        at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:586)
        at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:317)
        at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
        at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:390)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:286)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:845)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:583)
        at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:447)
        at java.lang.Thread.run(Thread.java:619)
2009-11-9 22:18:29 org.apache.catalina.core.StandardWrapperValve invoke
严重: Servlet.service() for servlet jsp threw exception
org.apache.jasper.JasperException: Unable to compile class for JSP: 

Answer 2

你是在jsp页面上连接数据库的啊？给的部分代码貌似没问题。
把整个页面粘出来看一下

Answer 3

Connection con=null;
再试试

Answer 4

package com.car.util;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;public class DBCon {
public static String driver="oracle.jdbc.driver.OracleDriver";
public static String url="jdbc:oracle:thin:@127.0.0.1:1521:orcl";
public static String user="scott";
public static String pwd="tiger";

public static Connection getConnection(){
try {
Class.forName(driver);
Connection con=DriverManager.getConnection(url, user, pwd);
System.out.println("OK");
return con;
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return null;
}

public static void close(Connection con,Statement stm,ResultSet rs){
if(con!=null){
try {
con.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(stm!=null){
try {
stm.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(rs!=null){
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}

public static void main(String[] args) {
DBCon.getConnection();
}
}给你个例子 
不过是在MyEclipse里面写的

Answer 5

改成null也是不行的 编译的时候错误会消失，但是运行的时候总是错误HTTP500  
HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException: java.lang.NullPointerException
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:522)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:416)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:390)
root cause java.lang.NullPointerException
org.apache.jsp.index_jsp._jspService(index_jsp.java:85)
org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:390)仍然是没有获得  空指针错误

Answer 6

出现空指针的错误  我觉得肯定就是没有连上MySql    tomcat应该没有问题，我用的是netbeans原带的
tomcat 执行非数据库操作的JSP文件都是可以执行的。请各位说一下MySql失败的原因啊？
谢谢