从JSP页面调用查询语句就报空指针，但是从java文件中调用缺显示正常

[zhoujiao2008]

<%
	}else if("edit".equals(action)){
		Integer id = Integer.parseInt(request.getParameter("id"));
		
		CalendarDao calendarDao = new CalendarDaoImpl();
		Calendar calendar = new CalendarDaoImpl().findById(id);

这个是JSP文件里调用的findById方法，

	Calendar calendar = calendarService.findById(id);
			String start = calendar.getStart();

这个是java文件中调用的findById方法；

@Override
	public Calendar findById(Integer id) {
		// TODO Auto-generated method stub
		System.out.println(id);
		String sql = "select * from  fullcalendar where id = "+id;	
		List<Map<String, Object>> list = null;
		try{
			list = jdbcTemplate.queryForList(sql);
		}catch(Exception e){
			e.printStackTrace();
		}
		Map<String, Object> map = list.get(0);
		Calendar calendar = new Calendar();
		calendar.setId(Integer.parseInt(map.get("id").toString()));
		calendar.setTitle(map.get("title").toString());
		calendar.setStart(map.get("start").toString());
		calendar.setEnd(map.get("end").toString());
		calendar.setAllDay(Integer.parseInt(map.get("allday").toString()));
		calendar.setColor(map.get("color").toString());
		return  calendar;
	}

这个是dao层里面的方法。
我从java文件里面调用这个方法都能打印出来，为什么从JSP文件里调用就提示空指针，错误如下：

SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
	at com.njceb.dao.impl.CalendarDaoImpl.findById(CalendarDaoImpl.java:97)
	at org.apache.jsp.pages.event_jsp._jspService(event_jsp.java:190)
	at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:374)
	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.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:88)
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at com.njceb.interceptor.JspReqFilter.doFilter(JspReqFilter.java:108)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:235)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
	at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
	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(Unknown Source)

这个只是我写的一个日程控件的Demo，初学者，只想知道什么原因，请大侠们能够给错误说下原理，接触JAVA不久，还请多多指教。

[zhoujiao2008]

list = jdbcTemplate.queryForList(sql);这一行报空指针，我说了不是每次调用都是空指针，是调用位置不一样才会显示空指针，麻烦问题看清楚。

[Kiln]

LZ，你是采用的是注入的方式吧。你从jsp里面直接new一个是拿不到数据库连接的。你的数据库连接应该是从spring的ioc的方式获取的。所以你在JSP里面肯定就报空指针了。

[zhoujiao2008]

ID是传递过去了，打印出来的SQL语句也是正常的，但是就是报LIST为空。我是想知道原因，资料上没有查到相关的东西。

[rumlee]

单步打印一下看看具体是哪一行报空指针不就知道了。这种问题都搞不定那你可怎么办啊？

[sinat_15114467]

Server 把得到的list传到jsp不就好了 request.getAttribute() ------------------------------ 你jsp页面又没连接数据库

[master_y]

at com.njceb.dao.impl.CalendarDaoImpl.findById(CalendarDaoImpl.java:97) 97行的代码问题，代码贴出来看看

[qq_26004821]

把 数据库的jar驱动包拷贝到你Tomcat的lib下 相信你就可以成功了

[ht15602261894]

楼主解决没?我也遇到了同样的问题.

[ht15602261894]

爱;找了挺久;终于知道了;因为myEclipse或者自己装的tomcatlib目录下没有数据库驱动,你将驱动jar包放在tomcat下的lib目录下就可以了.亲自试验了

[什么都不能]

没查到记录，数据库里没指定ID的记录

[Scaarf]

把

 List<Map<String, Object>> list = null;

改成

 List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();

试试

[Scaarf]

2015-01-07