If you have an apple and I have an apple and we exchange these apples then you and I will still each have one apple.

But if you have an idea and I have an idea and we exchange these ideas, then each of us will have two ideas.

jigsaw wrote:; zyzhang wrote:
1. Page 3, VOs should be replaced with interfaces. We should *not* pass objects between layers, but interfaces. Each layer could have its own implementation of the interfaces. The interfaces should belong to the business layer(why???)

>>> Will it be a overkill to replace VO w/ interface? IMHO, most small projects dont have to hide vo's implementation between layers.

>>>> Value Object (Named "Transfer Object" in J2EE Design Pattern), is widely used as a way to pass object between layers(for example, from integration tier or business tier to web tier). Generally, it's plain java object.

2. Page 4, add/remove/update methods should have parameter user, not integer. Don't expose implementation. What if one day we need to change this id to 36 digit guid? Changing from 3-digit to 4 caused an earthquake in my working company, what if more than that?

>>> yes sure. Command pattern.

>>>>I always forget this point,and end up with a lot of tedious work when new change comes up. I am trying to use refactoring to improve the code.

3. Page 4, yes, normally we shouldn't care about db shifting in business applications, unless we are doing some middleware or like, e.g., forums/jive.
>>> agree w/ u.

>>>> I have a big headache on the db shifting problem.The application needs to deploy in differenct app servers and databases, we configure the db selection in the property file. but in data access layer, we 've been using vendor specific JDBC extension API(like CachedPrepareStatement,CachedResultSet, etc), and even worse, the data access layer isnot got good abstract(like DAO). We really need to get a elegant way to solve this problem.

4. Page 6, yes, start from db side, get schema done first, then use middlegen hibernate to generate hbm files, then use tools to generate java classes(be careful here when you go hbm-->java, if you have inheritance, you have to read in parent hbms first before you read in child hbms). One more note: After we settle the business layer, the schema could be derived in several ways, read scott ambler's articles for 4 ways to do this.
>>> is there any class generator for ibatis? i hate to do it by hand.

>>>>where's scott ambler's artichles?

5. Page 7, JDBCTemplates etc could be done better in the following:
a. queryForObject/Long/Int should be improved to return a uniform object, like in SQLExecutor interface. Same as input. SQLExecutor's interface is nices to api callers.
>>> i dont see a reason to queryForLong/Int...casting can be done out of jdbc layer w/o pain.

>>>> I 've noticed that this kind of interface(specific for different data type) are in a lot of API design. There could be other reason why not returning a uniform object.

b. not sure about callbacks and inner classes, seems we just do what SQLExecutor does, it will be good enough.
>>> callback and inner classes seem to be more elegant as i think..hehe

>>>> In some situation, the callback handler can provide an elegant way to do pre and post processing ,extensing,or plug-in support.

6. Page 10, on datasource. The settings for different layers should be in seperate files(although we may read all of them into the context) so each layer is independent of others. Sample code constantly misleads this. And I don't like to read settings from resources from classpath because the collision is uncontrollable.
>>> err..dont catch ur meaning...if settings are not read from res in classpath, where do they locate?

7. Page 11, web layer.
General speaking, there are 3 kinds of presentation tools:
a. velocity: scripting based
b. xml: xslt, xml based
c. tapestry: object based
jsp based is somewhere in the middle. Others are faces, tiles, portlets.
MVC model(well, not really mvc) - reads professional jsp chapter 7(new version) or 12(old version) for models, especially model 2 and 2x.
Hell to struts and hail to spring, .
What's wrong with spring's mvc? abuse of templates! This abuse breaks the workflow's logic(This workflow is to send output to browsers). The usage pattern is more like swing applications. You have to do things in a certain way, certain order. BUT the underlying is doing right, so still the best one so far.
>>> err...=( i dont have experienced other view technologies than jsp...

page 14. spring bean package: doesn't have a way to write back to files. Swing applications need this feature, like firewall settings, etc. Once users config'd, they want to save them.
>>> we are talking abt web app, aren't we?

page 15. AOP, not sure about this. If we combine AOP and python, that's going to be something. Check Thinking in java's author's website on python.
BTW, there is a Jython out there too.
>>> aop...never tried that b4...=P

Others:
Transactions.

questions:
Why do we use spring transactions rather than Connection's autocommit or jta/jts?
>>> I have the same question. IMO CMT is enough.

>>> I have transaction context propogate problem with POJO(with jdbc ,jta) from business tier(session bean).it seems Spring address this problem,and give good solution on this.
Why do we use spring web mvc rather than struts?
>>> have no chances to use spring web mvc...

What's the difference between beanfactory and applicationcontext?
>>> err...=P...never thought of that...

Page9: Encapsulate SQLException
I do agree the way spring handle the SQLException. Actually, runtime and checked exception sometimes are not easy to decide and choose. There are some debate, guidelines and best practice on the java exception handling in the onjava web site. Logging also need to pay more attention, Maybe AOP can give elegant solution on them.

Jove wrote:
在第二部分的实例部分，有两个接近实际需求的假想项目
其中的第4页谈到了基于AOP的事务管理，以及使用MVC的Web开发方式
希望能继续得到各位的指正

Jove wrote:
继续抛砖引玉，以下为文档第二部分和示意代码

jigsaw wrote:
to hitaco abt exceptions:
no matter DAO/EJB throws RuntimeException or checked exception,
client class is expected to catche them, since exceptions are return from method.
However SQLException contains not enought infos abt wot's happening,
so we have to wrap it w/ app-spec exception to tell client class wot's
going on there.
if a wrapper of low level exception is not able to tell in a non-ambiguous way, it should be defined as a runtime exception which means client dont have to catch it, just let CMT to rollback and display a common error message to end user.

floater wrote:
Jove,
Somewhere in your controller code, you didn't call the errors.getModel(), just create your Map and pass it the ModelAndView. This will create exception in you jsp, right? Because you didn't pass the errors's model, so in jsp the spring:bind would blow up.
...

public void createOrderWithDAO_JTA() {
  
  Exception caught = null;

  /*
   * This DAO expects the caller to demarcate the transaction using JTA.  This DAO access database1.
   */
  WarehouseDAO dao1 = MyDAOFactory.getWarehouseJTA_DAO();

  /*
   * This DAO expects the caller to demarcate the transaction using JTA.   This DAO access database2.
   */
  OrderDAO dao2 = MyDAOFactory.getOrderJTA_DAO();

  /*
   * This publisher publishes messages to a JMS Topic  and expects the caller to demarcate the transaction. 
   * When creating session, make sure it is transacted.
   */  
  MessagePublisher publisher = null;

  UserTransaction utx = ResourceManager.getUserTransaction();

  try {
    /*                                                      
     * Execute the transaction. 
     * This transaction accesses three resources:
     *   1) a JMS Topic. 
     *   2) two different JDBC DataSources.
     */

    utx.begin();

      dao2.createOrder(....);

      dao1.updateWareHouse(....);

      publisher.publishTextMessage("Order Confirm Message....");

    utx.commit();

  } catch (Exception ex) {
    log.error(ex);
    caught = ex;
    if (utx != null) {
      try {
        utx.rollback();
      } catch (SystemException sysex) {
        log.error(sysex);
      }
    }
  } finally {
    if (dao != null) {
      dao.close();
      dao = null;
    }
    if (publisher != null) {
      publisher.close();
      publisher = null;
    }
    if (caught != null) {
      throw new DAORuntimeException(caught);
    }
  }
}

.....
In dao implementation:  
 conn = DBUtil.getXADBConnection();
 .....