模板模式应用一例

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设计模式

CTO给的设计是这样的：一个管理类DataLoaderManager，一个接口DataLoader，n个DataLoader实现。

我添加了一个对DataLoader的抽象类AbstractDataLoader，抽出实现中普遍用到的方法。

java 代码

public interface DataLoader {
/**
* load data
* @param dataMessage
* @return true - if successful
* @throws DataLoadException
* @see
*/
public boolean loadData(VoDataLoad dataload) throws DataLoadException;
}

java 代码

public abstract class AbstractDataLoader {
public void lockDataLoad(VoDataLoad dataload) throws DataLoadException {
// implement code
}
public void processErrorDataLoad VoDataLoad dataload) throws DataLoadException {
// implement code
sendEmailToAdmin(dataload);
}
public void sendEmailToAdmin(VoDataLoad dataload) {
// implement code
}

}

一个实现：

java 代码

public class FxRateLoader extends AbstractDataLoader implements DataLoader {
public boolean loadData(VoDataLoad dataload) throws DataLoadException {
try {
// call getFxRateListget() to get a Vo array
} catch (Exception e) {
// process exception
}
// process other biz
}
private VoFXRate[] getFxRateList(VoDataLoad dataload) throws Exception {
// code
}

}

另外个接口实现

java 代码

public class GlobalIndexLoader extends AbstractDataLoader implements DataLoader {
public boolean loadData(VoDataLoad dataload) throws DataLoadException {
try {
// call getIndexList() to get a Vo array
} catch (Exception e) {
// process exception
}
// process other biz
}
private VoIntIndex[] getIndexList(VoDataLoad dataload) throws Exception {
// code
}

}

不难发现，他们的流程几乎完全一致，可以用模板模式改造一下：

首先改造他们的抽象类AbstractDataLoader，把它的子类的实现流程拿上来，构造流程中的抽象方法，让子类实现。这样的话，第三个，第四个实现就无需重复很多代码了。

java 代码

public abstract class AbstractDataLoader implements DataLoader {
private static Logger logger = Logger.getInstance(DataLoaderManager.class.getName());
/**
* load data, subclass must implement all abstract method
* @param dataload
* @return true if ok, else false.
* @throws DataLoadException
*/
public boolean loadData(VoDataLoad dataload) throws DataLoadException {
if (dataload == null) throw new IllegalArgumentException();
Object[] voList = null;
try {
this.getVoList(dataload);
} catch (Exception e) {
this.processException(dataload, e);
}
if (voList != null) {
return this.processVoList(dataload, voList);
} else {
return false;
}
}
/**
* lock dataload if can not update now
* @param dataload
* @throws DataLoadException
*/
public void lockDataLoad(VoDataLoad dataload) throws DataLoadException {
DataLoadBo bo = new DataLoadBo();
dataload.setDataStatus(CdaConstants.LOCKED);
try {
bo.updateStatus(dataload);
} catch (AppSystemException e1) {
logger.error("error", e1);
throw new DataLoadException(e1.getMessage());
}
}
/**
* if something wrong, we set dataload status to be E, which means error.
* @param dataload
* @throws DataLoadException
*/
protected void processErrorDataLoad(VoDataLoad dataload) throws DataLoadException {
DataLoadBo bo = new DataLoadBo();
dataload.setDataStatus(CdaConstants.ERROR);
try {
bo.updateStatus(dataload);
} catch (AppSystemException e) {
throw new DataLoadException(e.getMessage());
}
sendEmailToAdmin(dataload);
}
/**
* get array of VO, such as VoIntIndex, VoFXRate
* @param dataload
* @return
* @throws DataLoadException
*/
protected abstract Object[] getVoList(VoDataLoad dataload) throws DataLoadException;
/**
* Everything is OK, we process Vo array
* @param dataload
* @param voList
* @return
* @throws DataLoadException
*/
protected abstract boolean processVoList(VoDataLoad dataload, Object[] voList) throws DataLoadException;
/**
* If something is wrong, before set dataload to be Error,
* we should try to extract error message and process this exception
* @param dataload
* @param e
* @throws DataLoadException
*/
protected abstract void processException(VoDataLoad dataload, Exception e) throws DataLoadException;
/**
* send email to notify administrator
* @param dataload
* @throws DataLoadException
*/
public void sendEmailToAdmin(VoDataLoad dataload) throws DataLoadException{
// TODO waiting for Jiang's assign
}
}

改造第一个接口实现为：

java 代码

public class FxRateLoader extends AbstractDataLoader implements DataLoader {
protected Object[] getVoList(VoDataLoad dataload) throws DataLoadException {
// code
}
protected void processException(VoDataLoad dataload, Exception e) throws DataLoadException {
// code
}
protected boolean processVoList(VoDataLoad dataload, Object[] fxRateList) throws DataLoadException {
// code
}
}