问题描述
我用的方式是现在一个JSP页面通过一个按钮通过form跳转到servlet里面，然后用servlet链接数据库。首先是我的JSP的主要内容<%Stringpath=request.getContextPath();StringbasePath=request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";%><head><metahttp-equiv="Content-Type"content="text/html;charset=utf-8"><title>Inserttitlehere</title></head><body><formid="form1"name="form1"method="post"action="<%=basePath%>test"><inputname="AddBtn"type="submit"id="AddBtn"value="提交"/></form>进入这个jsp页面时成功的。然后是我的一个bean这是连接的类：publicConnectioncon=null;Statementstmt=null;ResultSetrs=null;privateResultSetMetaDatarsmd=null;publicDBConnect(){try{StringdatabaseName="";Stringhost="sqld.duapp.com";Stringport="4050";Stringusername="";//用户名(apikey);Stringpassword="";//密码(secretkey)StringdriverName="com.mysql.jdbc.Driver";StringdbUrl="jdbc:mysql://";StringserverName=host+":"+port+"/";StringconnName=dbUrl+serverName+databaseName;System.out.println(connName);Class.forName(driverName);con=DriverManager.getConnection(connName,username,password);这是查询的类：publicResultSetexecuteQuery(StringSqlQuery){try{（42行）stmt=con.createStatement(ResultSet.TYPE_SCROLL_SENSITIVE,ResultSet.CONCUR_UPDATABLE);rs=stmt.executeQuery(SqlQuery);}catch(java.sql.SQLExceptionsql){sql.printStackTrace();}returnrs;}下面是我的servlet的内容：response.setContentType(CONTENT_TYPE);DBConnectconnect=newDBConnect();PrintWriterout=response.getWriter();StringCheckIDSql="select*fromtest";（40行）ResultSetrs=connect.executeQuery(CheckIDSql);System.out.println("ddddd");try{while(rs.next()){Stringstr=rs.getString("id");System.out.println(str);out.print(str);}}catch(SQLExceptione){//TODOAuto-generatedcatchblocke.printStackTrace();protectedvoiddoPost(HttpServletRequestrequest,HttpServletResponseresponse)throwsServletException,IOException{（59行）doGet(request,response);//TODOAuto-generatedmethodstub}下面是点击了按钮之后跳转到servlet里面的错误信息（错误行数在上文中标出了）：错误类型是500typeExceptionreportmessagedescriptionTheserverencounteredaninternalerrorthatpreventeditfromfulfillingthisrequest.exceptionjava.lang.NullPointerExceptionpublicUse.DBConnect.executeQuery(DBConnect.java:42)tst.test.doGet(test.java:40)tst.test.doPost(test.java:59)javax.servlet.http.HttpServlet.service(HttpServlet.java:647)javax.servlet.http.HttpServlet.service(HttpServlet.java:728)noteThefullstacktraceoftherootcauseisavailableintheApacheTomcat/7.0.47logs.