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

    public BaseEscrowLedgerResponse process(BaseEscrowLedgerRequest request){
        boolean successAction = false;
        try {
            //init
            init(request);
            
            // validate request
            validateRequest();

            // process request internally
            processInternally();

            // commit db change
            commit();
            
            //build response
            buildResponse();
            
            //successAction
            successAction = true;
        } catch (Exception e) {
            handleException(e);
        } finally {
            // clear up
// clear UOW token
            cleanup(successAction);
        }    
        return getResponse();
    }

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。

    protected void commit() throws CreateException, UpdateException {
        EmsPaymentBo payment = getPaymentChanges();
        if(payment != null){
            EmsPaymentAggregatorBOF.getInstance().executeBulkOperations(payment);
        }
    }

以CreateLienApp为例，
init

    protected void init(BaseEscrowLedgerRequest request) {
        m_request = (CreateLienRequest) request;
        m_response = new CreateLienResponse();
        m_paymentChanges = new EmsPaymentBo();
        m_lienTrx = m_request.getLienTrxInfo();
    }

validateRequest

    protected void validateRequest() throws EmsValidationException {
        m_lienTrx = m_request.getLienTrxInfo();
        if(m_lienTrx == null){
            throw EmsExceptionHelper.newValidationFailedException("LienTrxInfo", "lienTrxInfo is missing");
        }
        
        if (m_lienTrx.getPayerId() <= 0) {
            throw EmsExceptionHelper.newValidationFailedException("PayerId", "payerId is missing");
        }
        if (m_lienTrx.getPayeeId() <= 0)    {
            throw EmsExceptionHelper.newValidationFailedException("PayeeId", "payeeId is missing");
        }
        
        if (m_lienTrx.getExternalOrderId() == null) {
            throw EmsExceptionHelper.newValidationFailedException("ExternalOrderId", "external order id is missing");
        }

        if (m_lienTrx.getExternalContractId() == null) {
            throw EmsExceptionHelper.newValidationFailedException("ExternalContractId", "external contract id is missing");
        }
        if (m_lienTrx.getExternalContractIdType() == null) {
            throw EmsExceptionHelper.newValidationFailedException("ExternalContractType", "external contract type is missing");
        }

        if (m_lienTrx.getLienAmount() == null ) {
            throw EmsExceptionHelper.newValidationFailedException("LienAmount", "LienAmount is missing");
        } else if ( !m_lienTrx.getLienAmount().isPositive() ) {
            throw EmsExceptionHelper.newValidationFailedException("LienAmount", "LienAmount should be positive");
        } 
        
    }

processInternally

    protected void processInternally() throws Exception {
        //load emsTrxns
        loadEmsTrxns();
         
         //check duplicate        
        if(checkDuplicate()){            
            return;
        }
                
        //validate lien amount
        validateLienAmount();
        
        //create lien
        createLien();
    }

5.buildResponse

    @Override
    protected void buildResponse() {
        EscrowLienTrx escrowLienTrx = new EscrowLienTrx(m_emsAdjTrx);
        m_response.setEscrowLienTrx(escrowLienTrx);
        EmsResponseCodeEnum resCode = m_isDuplicatedRequest ? EmsResponseCodeEnum.DUPLICTE_REQUEST_ERROR
                : EmsResponseCodeEnum.SUCCESS;
        m_response.setResponseCode(resCode);    
    }