自定义Exception

DaoException，ServiceException都是自定义异常类，
DaoException继承自ServiceException，ServiceException继承自Exception类。

显示代码：

 1 package com.wei.exception;
 2 
 3 public class DaoException extends ServiceException{
 4     
 5     public DaoException(){
 6         super("dao层异常");
 7     }
 8     
 9     public DaoException(String msg){
10         super(msg);
11     }
12     
13     public DaoException(Exception e){
14         super("dao层异常",e);
15     }
16     
17     public DaoException(String msg , Exception e){
18         super(msg,e);
19     }
20 }

 1 package com.wei.dao.impl;
 2 
 3 // class created by wwei 2011-12-11 下午01:32:45 
 4 
 5 public class DaoImpl {
 6     public void testDaoExce() throws DaoException{
 7         try {
 8             User user = null;
 9             user.printUser();  //空值调用方法，必报异常java.lang.NullPointerException
10         } catch (Exception e) {
11             throw new DaoException("dao层testDaoExce方法异常",e);
12         }
13     }
14 }

显示代码：

 1 package com.wei.exception;
 2 
 3 // class created by wwei 2011-12-11 下午02:15:47 
 4 
 5 public class ServiceException extends Exception{
 6     public ServiceException(){
 7         super("service层异常");
 8     }
 9     
10     public ServiceException(String msg){
11         super(msg);
12     }
13     
14     public ServiceException(Exception e){
15         super("service层异常",e);
16     }
17     
18     public ServiceException(String msg , Exception e){
19         super(msg,e);
20     }
21 }

 1 package com.wei.service.impl;
 2 
 3 // class created by wwei 2011-12-11 下午02:16:59 
 4 
 5 public class ServiceImpl {
 6 
 7     DaoImpl daoImpl = new DaoImpl();
 8     
 9     public void testServiceExce(int num) throws ServiceException{
10             try {
11                 int a = 2/num;     //参数num若为0，报异常java.lang.ArithmeticException: / by zero
12             } catch (Exception e) {
13                 throw new ServiceException("num为零,零不能做除数！",e);
14             }
15             daoImpl.testDaoExce();
16     }
17 }

 1 package com.wei.test;
 2 
 3 // class created by wwei 2011-12-11 下午01:32:45 
 4 
 5 public class Test {
 6     public static void main(String[] args) {
 7         ServiceImpl service = new ServiceImpl();
 8         try {
 9             int num = 0;
10             service.testServiceExce(num);
11         } catch (Exception e) {
12             e.printStackTrace();
13         }
14     }
15 }

当num为0时，报的是Service层的错。

com.wei.test.ServiceException: num为零,零不能做除数！
    at com.wei.test.ServiceImpl.testServiceExce(ServiceImpl.java:13)
    at com.wei.test.Test.main(Test.java:10)
Caused by: java.lang.ArithmeticException: / by zero
    at com.wei.test.ServiceImpl.testServiceExce(ServiceImpl.java:11)
    ... 1 more

当num不为0时，报的是dao层的错

com.wei.test.DaoException: dao层testDaoExce方法异常
    at com.wei.test.DaoImpl.testDaoExce(DaoImpl.java:11)
    at com.wei.test.ServiceImpl.testServiceExce(ServiceImpl.java:15)
    at com.wei.test.Test.main(Test.java:10)
Caused by: java.lang.NullPointerException
    at com.wei.test.DaoImpl.testDaoExce(DaoImpl.java:9)
    ... 2 more