转载：Tapestry5: Caching Method Results_JAVA_编程开发_程序员俱乐部

Tapestry5: Caching Method Results

Assume you have methods that (almost) always return the same result for the same input arguments. If preparing method result is a heavy operation and/or it consumes time, it is reasonable to cache these results.

One way of building method cache in Tapestry5 is by implementing?MethodAdvice?interface like this:

public class CacheMethodResultAdvice implements MethodAdvice {

    private static final Logger logger = LoggerFactory.getLogger(CacheMethodResultAdvice.class);
    
    private final Cache cache;
    private final Class<?> advisedClass;
    private final Object nullObject = new Object();
    
    public CacheMethodResultAdvice(Class<?> advisedClass, Cache cache) {
        this.advisedClass = advisedClass;
        this.cache = cache;
    }
    
    @Override
    public void advise(Invocation invocation) {
        String invocationSignature = getInvocationSignature(invocation);
        
        String entityCacheKey = String.valueOf(invocationSignature.hashCode());

        Object result;
        
        if (cache.containsKey(entityCacheKey))
        {
            result = cache.get(entityCacheKey);

            logger.debug("Using invocation result ({}) from cache '{}'", invocationSignature, result);

            invocation.overrideResult(result);
        }
        else 
        {
            invocation.proceed();
            
            if (!invocation.isFail())
            {
                result = invocation.getResult();
                
                cache.put(entityCacheKey, result);
            }
        }
    }

    private String getInvocationSignature(Invocation invocation) {
        StringBuilder builder = new StringBuilder(150);
        builder.append(advisedClass.getName());
        builder.append('.');
        builder.append(invocation.getMethodName());
        builder.append('(');
        for (int i = 0; i < invocation.getParameterCount(); i++) {
            if (i > 0) {
                builder.append(',');
            }
            Class<?> type = invocation.getParameterType(i);
            builder.append(type.getName());
            builder.append(' ');

            Object param = invocation.getParameter(i);
            builder.append(param != null ? param : nullObject);
        }
        builder.append(')');
        
        return builder.toString();
    }
    
}

?Implementation of?getInvocationSignature(...)?is not ideal, but you may improve it to match your requirements. One issue I see here is building invocation signature for?null-value parameters in a clustered environment (which is GAE). In this implementation method?nullObject.toString()?will return something like?java.lang.Object@33aa9b. And this value will vary in different instances of your application. You may replace?nullObject?with just?"null"?string. Just keep in mind that?"null" != null.