空指针错误求帮助

空指针异常求帮助
出错提示

java.lang.NullPointerException
	at com.tchManage.dao.PostDAO.findAllPost(PostDAO.java:39)
	at com.tchManage.servlet.PostController.findAll(PostController.java:131)
	at com.tchManage.servlet.PostController.doPost(PostController.java:40)
	at com.tchManage.servlet.PostController.doGet(PostController.java:147)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
	at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
	at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
	at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
	at org.apache.tomcat.util.net.AprEndpoint$SocketProcessor.run(AprEndpoint.java:1822)
	at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
	at java.lang.Thread.run(Thread.java:619)

com.tchManage.dao.PostDAO.java

public List<Post> findAllPost(int currentPage) throws SQLException,ClassNotFoundException{
		try{
			ResultSet rs=pl.pageList(5,"userinfo",currentPage,"desc","id");（39）
			System.out.println(rs);
			rs.beforeFirst();
			List<Post> list=new ArrayList<Post>();
			
			while(rs.next()){
				Post u=new Post();
				u.setId(rs.getInt("id"));
				u.setTitle(rs.getString("title"));
				u.setContent(rs.getString("content"));
				u.setTime(rs.getString("time"));
				
				list.add(u);	
			}
			return list;
			
		}catch(Exception e){
			e.printStackTrace();
		}

com.tchManage.servlet.PostController.java

//查找所有公告
	private void findAll(HttpServletRequest request,
			HttpServletResponse response) {
		try{
			//request.setAttribute("pageinfo",postdao.pageSize());
			//String currpage=request.getParameter("currentPage");
			
			int currentPage=1;
			//if(currpage!=null){
			//	currentPage=Integer.parseInt(currpage);
			//}	
			List<Post> list = new ArrayList<Post>();
			list = postdao.findAllPost(currentPage);
			request.setAttribute("findAll", list);
			RequestDispatcher rd = request.getRequestDispatcher("index.jsp");
			rd.forward(request, response);
			
		}catch(Exception e){
			e.printStackTrace();
		}
		
	}

PageList.java pageList()分页方法

public ResultSet pageList(int pagesize, String tablename, int currentePage,