Tapestry之Cache组件

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有许多页面的一部分或者这个页面是很少更新的，他们通常是由外部文件来生成这个部分。所以我们可以把这部分内容cache住，当有新的请求时，我们就response cache，这样可以减少服务器的负担，还可以提高性能。其中oscache已经可以实现页面的cache和页面部分cache。oscache使用jsp tags来实现局部cache的。拿到Tapestry中肯定是行不通的。在同事的提醒下，想到写这个Tapestry的cache组件来达到重用的目的。

 

说干就干，先在头脑中想好要怎样使用cache（页面上的布局）。ok。 我想好了。

    //Cache body, which is the content you want to cache.

这里有2个参数，updateCondition 当为true时，我们就绕过cache， cacheProvider 我把他定义为一个接口，这样用户可以把cache存在任何地方。而且提供这样的一个接口，用户可以更好的操作cache。先看看jwc对cache组件的定义。

 

"-//Apache Software Foundation//Tapestry Specification 4.0//EN"
"http://jakarta.apache.org/tapestry/dtd/Tapestry_4_0.dtd">

  
   Cache component, this component can inclue any content as its body, and cache its body.
    This is useful in rarely updated content.
   

   
     The flag that need to refresh cache, it would casue tapestry render not use the cache.
   


    
     You need to provider an cache provider to store its body content. for some simply use.
    Please see     @com.live.spaces.dengyin2000.tapestry.tfancomponents.components.SimpleHtmlSourceCacheProvider
   

下面的是ICacheProvider接口

 

public interface ICacheProvider {
/**
*
* @param cacheKey
* @param cacheContent
*/
public void storeCache(String cacheKey, String cacheContent);
/**
*
* @param cacheKey
* @return
*/
public String getCacheContent(String cacheKey);
/**
* This method provider to user, so that user can controll cache manaully.
* @param cacheKey
*/
public void removeCache(String cacheKey);
/**
* This method provider to user, so that user can controll cache manaully.
* Clear all caches
*
*/
public void reset();
}

ok。 再来看看Cache组件的代码。

 

public abstract class Cache extends AbstractComponent {
protected static final Log logger = LogFactory.getLog(Cache.class);
public abstract boolean getUpdateCondition();
public abstract ICacheProvider getCacheProvider();
@Override
protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle) {
if (getUpdateCondition()){
renderComponentWithCache(writer, cycle);
}else{
if (getCacheProvider().getCacheContent(this.getIdPath()) != null){
//response cache html content.
writer.printRaw(getCacheProvider().getCacheContent(this.getIdPath()));
}else{
renderComponentWithCache(writer, cycle);
}
}

}
private void renderComponentWithCache(IMarkupWriter writer, IRequestCycle cycle) {

logger.debug("We need to refresh cache now.");
CacheWriterWrapper cacheWrapper =new CacheWriterWrapper();
super.renderBody(buildCacheMarkupWriter(cacheWrapper.getPrintWriter(), writer), cycle);
String cacheContent = cacheWrapper.getCacheContent();
logger.debug("fetched cache content, ready to put it into cache.");

getCacheProvider().storeCache(this.getIdPath(), cacheContent);
// response html content.
writer.printRaw(cacheContent);
}
private IMarkupWriter buildCacheMarkupWriter(PrintWriter writer, IMarkupWriter sourceWriter){
return this.getPage().getRequestCycle().getInfrastructure().getMarkupWriterSource().newMarkupWriter(writer, new ContentType(sourceWriter.getContentType()));
}
class CacheWriterWrapper{
private StringWriter sw;
private PrintWriter pw;
public CacheWriterWrapper() {
sw = new StringWriter();
pw = new PrintWriter(sw);
}

public String getCacheContent(){
return sw.getBuffer().toString();
}
public PrintWriter getPrintWriter(){
return pw;
}
}
}

主要是得到cache组件body的内容，然后把body的内容cache住，下次的话就response Cache的内容。 其实也是满简单的。

我自己还写了一个简单CacheProvider。

 

public class SimpleHtmlSourceCacheProvider implements ICacheProvider {
private Map cache = new HashMap();
public String getCacheContent(String cacheKey) {
return cache.get(cacheKey);
}

public void storeCache(String cacheKey, String cacheContent) {
cache.put(cacheKey, cacheContent);
}

public void removeCache(String cacheKey) {
cache.remove(cacheKey);
}

public void reset() {
cache.clear();
}
}

在使用中你可以把CacheProvider放到Global或者Visit对象中。注意要使用同一个CacheProvider。

我在google code host上面建了一个probject地址是http://code.google.com/p/tfancomponents/ 有兴趣的同学可以看看， 这是一个maven项目。