设计模式之模板方法

模板方法是用得最广泛的设计模式之一，特别是在应用框架中经常用模板方法来实现控制反转（Inversion of Control, IoC)。

比如在批处理框架中，每个批处理任务都从框架的层面上都可以分成如下三个步骤:

1. 初始化

2. 处理

3. 结束清理

在EL中，BaseEscrowLedgerApp定义了一个process方法，该方法规定了每个EscrowLedgerApp应用的总体处理流程

1. init
2. validateRequest
3. processInternally
4. commit
5. handleResponse

View Code

 1     public BaseEscrowLedgerResponse process(BaseEscrowLedgerRequest request){
 2         boolean successAction = false;
 3         try {
 4             //init
 5             init(request);
 6             
 7             // validate request
 8             validateRequest();
 9 
10             // process request internally
11             processInternally();
12 
13             // commit db change
14             commit();
15             
16             //build response
17             buildResponse();
18             
19             //successAction
20             successAction = true;
21         } catch (Exception e) {
22             handleException(e);
23         } finally {
24             // clear up
25 // clear UOW token
26             cleanup(successAction);
27         }    
28         return getResponse();
29     }

process方法即为模板方法，而其他的几个方法除commit之外都是抽象方法。每个具体的EscrowLedgerApp应用根据自己的实际情况来实现上述抽象方法。
commit方法由于对各个子类来说都是提交封装在EmsPaymentBo中的数据变化，所以在BaseEscrowLedgerApp中提供一个默认实现是比较合理的。代码如下。

View Code

1     protected void commit() throws CreateException, UpdateException {
2         EmsPaymentBo payment = getPaymentChanges();
3         if(payment != null){
4             EmsPaymentAggregatorBOF.getInstance().executeBulkOperations(payment);
5         }
6     }

以CreateLienApp为例，
init

View Code

1     protected void init(BaseEscrowLedgerRequest request) {
2         m_request = (CreateLienRequest) request;
3         m_response = new CreateLienResponse();
4         m_paymentChanges = new EmsPaymentBo();
5         m_lienTrx = m_request.getLienTrxInfo();
6     }

validateRequest

View Code

 1     protected void validateRequest() throws EmsValidationException {
 2         m_lienTrx = m_request.getLienTrxInfo();
 3         if(m_lienTrx == null){
 4             throw EmsExceptionHelper.newValidationFailedException("LienTrxInfo", "lienTrxInfo is missing");
 5         }
 6         
 7         if (m_lienTrx.getPayerId() <= 0) {
 8             throw EmsExceptionHelper.newValidationFailedException("PayerId", "payerId is missing");
 9         }
10         if (m_lienTrx.getPayeeId() <= 0)    {
11             throw EmsExceptionHelper.newValidationFailedException("PayeeId", "payeeId is missing");
12         }
13         
14         if (m_lienTrx.getExternalOrderId() == null) {
15             throw EmsExceptionHelper.newValidationFailedException("ExternalOrderId", "external order id is missing");
16         }
17 
18         if (m_lienTrx.getExternalContractId() == null) {
19             throw EmsExceptionHelper.newValidationFailedException("ExternalContractId", "external contract id is missing");
20         }
21         if (m_lienTrx.getExternalContractIdType() == null) {
22             throw EmsExceptionHelper.newValidationFailedException("ExternalContractType", "external contract type is missing");
23         }
24 
25         if (m_lienTrx.getLienAmount() == null ) {
26             throw EmsExceptionHelper.newValidationFailedException("LienAmount", "LienAmount is missing");
27         } else if ( !m_lienTrx.getLienAmount().isPositive() ) {
28             throw EmsExceptionHelper.newValidationFailedException("LienAmount", "LienAmount should be positive");
29         } 
30         
31     }

processInternally

View Code

 1     protected void processInternally() throws Exception {
 2         //load emsTrxns
 3         loadEmsTrxns();
 4          
 5          //check duplicate        
 6         if(checkDuplicate()){            
 7             return;
 8         }
 9                 
10         //validate lien amount
11         validateLienAmount();
12         
13         //create lien
14         createLien();
15     }

5.buildResponse

View Code

1     @Override
2     protected void buildResponse() {
3         EscrowLienTrx escrowLienTrx = new EscrowLienTrx(m_emsAdjTrx);
4         m_response.setEscrowLienTrx(escrowLienTrx);
5         EmsResponseCodeEnum resCode = m_isDuplicatedRequest ? EmsResponseCodeEnum.DUPLICTE_REQUEST_ERROR
6                 : EmsResponseCodeEnum.SUCCESS;
7         m_response.setResponseCode(resCode);    
8     }