Servlet.service（）進行的servlet [com.jagrut.GroupServlet]在上下文中與路徑[/ jaagrut]拋出異常

Question

爲什麼這個錯誤即將..

Mar 29, 2013 2:04:26 PM org.apache.catalina.core.StandardWrapperValve invoke 
SEVERE: Servlet.service() for servlet [com.jagrut.GroupServlet] in context with path   [/jaagrut] threw exception 
    java.lang.NullPointerException 
at com.jagrut.GroupServlet.doPost(GroupServlet.java:170) 
at javax.servlet.http.HttpServlet.service(HttpServlet.java:647) 
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$AbstractConnectionHandler.process(AbstractProtocol.java:589) 
at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312) 
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source) 
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source) 
at java.lang.Thread.run(Unknown Source) 

下面是代碼

try { 
         String queryString = "INSERT INTO groups(course_id,group_name,location,batch_no)" 
           + " VALUES ('" 
           + ccode 
           + "','" 
           + group 
           + "','" 
           + loc 
           + "','" + batch + "')"; 



           st = con.createStatement(); 

           last_id = st.executeUpdate(queryString); 

           System.out.println(">>>>>>>llll" + last_id); 
           /* Getrting Group_id from groups table */ 

           if(last_id == 0){ 

             out.print("Group Already Available."); 
             //return; 
           } 

            try{ 
            st1 = con.createStatement(); 
            rs1 = st1.executeQuery("SELECT group_id from groups Where group_name='"+ group + "'"); 
            while (rs1.next()) { 
            group_id = rs1.getInt(1); 
            } 
            System.out.print(">>>>>>>" + group_id); 
            /* Inserting DATA to Student Group */ 
            }catch (SQLException ex1) { 

             System.out.print("Unable to Create Group.Duplicate Entry "); 
             ex1.printStackTrace(); 

            } 
            try { 
              stmt1 = con.createStatement(); 
              for (int i = 0; i < stud.length; i++) { 
               //System.out.println(stud[i]); 
               String sql = "Insert into student_group(group_id,s_id)Values('" + group_id + "','" + stud[i] + "')"; 
               stmt1 = con.createStatement(); 
               updateQuery = stmt1.executeUpdate(sql); 
              } 
             } catch (Exception ex1) { 

              out.println("Unable to Insert Student Into Group."); 
              ex1.printStackTrace(); 
             } 

             /* Inserting teacher into the group */ 
             try { 
             String query = "Insert into teacher_group(group_id,t_id,join_date)Values('" + group_id + "','" + teacher + "','" + sqlDate + "')"; 

               st2 = con.createStatement(); 

               updateQuery = st2.executeUpdate(query); 

               if (updateQuery != 0) { 
                out.println("Group Created Successfully"); 
               } 
              } catch (Exception ex2) { 

               out.println("Unable to Insert Teacher Into Group."); 
               ex2.printStackTrace(); 
              } 
             } catch (SQLException ex) { 
              out.print("Group Already Available."); 
               System.out.print("Unable to Create Group.Duplicate Entry "); 
               ex.printStackTrace(); 

              } 
             finally { 
              // close all the connections. 
              try { 
               rs.close(); 
               stmt.close(); 
               st.close(); 
               rs1.close(); 
               stmt1.close(); 
               st1.close(); 
               st2.close(); 
               con.close(); 
              } catch (SQLException e) { 


             e.printStackTrace(); 
            } 
           } 

Answer 1

你的最後一塊應該是：

finally { 
    try { 
    if(rs != null) { 
    rs.close(); 
    } 

    if(stmt != null) { 
    stmt.close(); 
    } 


    if(st != null) { 
    st.close(); 
    } 
    } catch (SQLException e) { 
    }//end try 
}//end finally