Servlet 

    1. public class BusinessAServlet extends HttpServlet {
    2.     //servlet拥有接口类型的businessA属性，具体实现由实现类来处理，如果想更换实现类，改这一行就可以啦
    3.     private BusinessAServiceInterface businessA = new BusinessAServiceImpl();
    4.     @Override
    5.     protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    7.         //业务逻辑处理
    8.         businessA.businessAServiceTest1();
    9.         businessA.businessAServiceTest2();
    10.         businessA.businessAServiceTest3();
    11.     }
    13. }

    service 层
    具体业务接口层

    1. public interface BusinessAServiceInterface {
    2.     public abstract void businessAServiceTest1();
    3.     public abstract void businessAServiceTest2();
    4.     public abstract void businessAServiceTest3();
    5. }

    具体业务实现层

    1. public class BusinessAServiceImpl implements BusinessAServiceInterface{
    2.     //拥有接口类型的Dao,如果以后想更换实现类，改这一行就可以了
    3.     private BusinessADaoInterface businessADaoInterface = new BusinessADaoImpl();
    4.     @Override
    5.     public void businessAServiceTest1() {
    6.         System.out.println("businessAServiceTest1");
    7.         //Dao删除数据
    8.         businessADaoInterface.delete(1);
    9.     }
    11.     @Override
    12.     public void businessAServiceTest2() {
    13.         System.out.println("businessAServiceTest2");
    14.     }
    16.     @Override
    17.     public void businessAServiceTest3() {
    18.         System.out.println("businessAServiceTest3");
    19.     }
    20. }

    Dao层
    具体Dao接口层

    1. public interface BusinessADaoInterface {
    2.     public abstract Object get(Integer id);
    3.     public abstract void delete(Integer id);
    4. }

    具体Dao实现层

    1. public class BusinessADaoImpl implements BusinessADaoInterface {
    2.     @Override
    3.     public Object get(Integer id) {
    4.         return null;
    5.     }
    7.     @Override
    8.     public void delete(Integer id) {
    10.     }
    11. }