struts+Eclipse的问题
本人是初学者，现在在Eclipse环境下用struts写的web程序，编译正常，但是当我按提交按钮处理数据的时候，却出错：
警告:   Unhandled   exception
警告:   Exception   from   exceptionCommand   'servlet-exception '
严重:   Servlet.service()   for   servlet   action   threw   exception
java.lang.NullPointerException
at   j2eebbs.DB. <init> (DB.java:16)
at   j2eebbs.user.action.RegistrationAction.execute(RegistrationAction.java:37)
at   org.apache.struts.chain.commands.servlet.ExecuteAction.execute(ExecuteAction.java:53)
at   org.apache.struts.chain.commands.AbstractExecuteAction.execute(AbstractExecuteAction.java:64)
at   org.apache.struts.chain.commands.ActionCommandBase.execute(ActionCommandBase.java:48)
at   org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
at   org.apache.commons.chain.generic.LookupCommand.execute(LookupCommand.java:304)
at   org.apache.commons.chain.impl.ChainBase.execute(ChainBase.java:190)
at   org.apache.struts.chain.ComposableRequestProcessor.process(ComposableRequestProcessor.java:280)
at   org.apache.struts.action.ActionServlet.process(ActionServlet.java:1858)
at   org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:459)
at   javax.servlet.http.HttpServlet.service(HttpServlet.java:710)
at   javax.servlet.http.HttpServlet.service(HttpServlet.java:803)
at   org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at   org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at   org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:228)
at   org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
at   org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:128)
at   org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:104)
at   org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at   org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:216)
at   org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:844)
at   org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:634)
at   org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:445)
at   java.lang.Thread.run(Thread.java:595)

========================我的代码   原文件如下==========================
===DB.java================
package   j2eebbs;

import   javax.sql.DataSource;
import   java.sql.Connection;
import   java.sql.Statement;
import   java.sql.ResultSet;
import   java.sql.SQLException;

public   class   DB   {

Connection   connect   =   null;
ResultSet   rs   =   null;
public   DB(DataSource   dataSource)   {

try   {
connect   =   dataSource.getConnection();     //======16行出错
}
catch(SQLException   e)   {
e.printStackTrace();
}
}

public   ResultSet   OpenSql(String   sql)   {