学习struts阶段，数据库总是报错，在学校就没事，

错误信息：
at java.sql.DriverManager.getConnection(DriverManager.java:512)

at java.sql.DriverManager.getConnection(DriverManager.java:171)

at db.DBHelper.getConnection(DBHelper.java:18)

at dao.DAOHelperUser.login(DAOHelperUser.java:19)

at action.UserAction.login(UserAction.java:26)
我的代码：
package db;

import java.sql.*;

public class DBHelper {
private static Connection conn = null;
private static String url = null;
private static String serverName = null;
private static String portNumber = null;
private static String databaseName = null;
private static String uid = null;
private static String pwd = null;
public DBHelper() {
try {
Class.forName("com.microsoft.jdbc.sqlserver.SQLServerDriver");
} catch (ClassNotFoundException ex) {
ex.printStackTrace();
}
}
private static String getConnectionUrl()
{
url = "jdbc:microsoft:sqlserver://";
serverName = "127.0.0.1";
portNumber = "1433";
databaseName = "test";
uid = "sa";
pwd = "";

return url + serverName + ":" + portNumber + ";databaseName=" + databaseName + ";";
}

public static Connection getConnection()
{
try {
conn = DriverManager.getConnection(getConnectionUrl(),uid,pwd);
} catch (SQLException ex) {
ex.printStackTrace();
}
if ( conn != null )
{
System.out.println("连接成功");
}
return conn;
}
}
总报错，在学校就没事。高手们帮看看阿。。

谢谢，谢谢。
可是还是不行的。。。
代码应该没问题啊，像你那样写，我也写了N次了。。。
在学校的机器上就能跑。

都打过的，用桥连连的上。。。

java.sql.SQLException: [Microsoft][SQLServer 2000 Driver for JDBC]Error establishing socket.

at com.microsoft.jdbc.base.BaseExceptions.createException(Unknown Source)

at com.microsoft.jdbc.base.BaseExceptions.getException(Unknown Source)

at com.microsoft.jdbc.base.BaseExceptions.getException(Unknown Source)

at com.microsoft.jdbc.sqlserver.tds.TDSConnection.<init>(Unknown Source)

at com.microsoft.jdbc.sqlserver.SQLServerImplConnection.open(Unknown Source)

at com.microsoft.jdbc.base.BaseConnection.getNewImplConnection(Unknown Source)

at com.microsoft.jdbc.base.BaseConnection.open(Unknown Source)

at com.microsoft.jdbc.base.BaseDriver.connect(Unknown Source)

at java.sql.DriverManager.getConnection(DriverManager.java:512)

at java.sql.DriverManager.getConnection(DriverManager.java:171)

at db.DB.getConnection(DB.java:17)

at dao.DAO.login(DAO.java:14)

at action.loginAction.login(loginAction.java:24)

at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)

at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)

at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)

at java.lang.reflect.Method.invoke(Method.java:324)

at org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:280)

at org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:216)

at org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)

at org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)

at org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)

at org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:709)

at javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:237)

at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:157)

at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:214)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)

at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)

at org.apache.catalina.core.StandardContextValve.invokeInternal(StandardContextValve.java:198)

at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:152)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)

at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)

at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:137)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)

at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:117)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:102)

at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)

at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)

at org.apache.catalina.core.StandardValveContext.invokeNext(StandardValveContext.java:104)

at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:520)

at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:929)

at org.apache.coyote.tomcat5.CoyoteAdapter.service(CoyoteAdapter.java:160)

at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:799)

at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:705)

at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:577)

at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)

at java.lang.Thread.run(Thread.java:534)

这样的。

不行，而且调试，连接那是没报异常，可是是NULL，用桥连的上。。。

exception

javax.servlet.ServletException
    org.apache.struts.action.RequestProcessor.processException(RequestProcessor.java:545)
    org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:486)
    org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
    org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
    org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

root cause

java.lang.NullPointerException
    dao.DAO.login(DAO.java:16)
    action.loginAction.login(loginAction.java:24)
    sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
    sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
    java.lang.reflect.Method.invoke(Method.java:324)
    org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:280)
    org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:216)
    org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
    org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
    org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
    org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:802)

是混合，我都把数据库，卸了装，装了卸，好几次了。。。