无法调用servlet /relogin.jsp的service()方法
应用服务器：websphere(已设置好数据源jdbc/DLTK，测试通过)
数据库：DB2
我想通过文件relogin.jsp提取数据，可是运行时总是提示错误：“无法调用 servlet /relogin.jsp 的 service() 方法。抛出异常：java.lang.NullPointerException”
哪位高手知道这是怎么回事？
relogin.jsp相关代码如下：
<%String ls_sql;
Connection conn = null; 
Statement stmt = null; 
Context context = null;
ResultSet rs = null;
DataSource ds = null;
ls_sql = "select username from HEYONG.WAS_USER";
ds =(DataSource)context.lookup("java:comp/env/jdbc/DLTK");
conn = ds.getConnection();
stmt = conn.createStatement();
rs = stmt.executeQuery(ls_sql);%>

------解决方案--------------------
<%String ls_sql; 
Connection conn = null; 
Statement stmt = null; 
Context context = null; 
ResultSet rs = null; 
DataSource ds = null; 
ls_sql = "select username from HEYONG.WAS_USER"; 
ds =(DataSource)context.lookup("java:comp/env/jdbc/DLTK"); 
conn = ds.getConnection(); // 最好用之前测试下是否为空 应该是这行出问题了
stmt = conn.createStatement(); 
rs = stmt.executeQuery(ls_sql);%>
我的异常网推荐解决方案：Servlet.service() for servlet default threw exception,http://www.myexception.cn/eclipse/181756.html