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.

To make this advice working you should declare it in your AppModule.java:

@SuppressWarnings("unchecked")
    @Match("IPResolver")
    public static void adviseCacheIPResolverMethods(final MethodAdviceReceiver receiver, Logger logger, PerthreadManager perthreadManager) {
        try {
            Map props = new HashMap();

            //  IP address of URL may change, keep it in cache for one day
            props.put(GCacheFactory.EXPIRATION_DELTA, 60 * 60 * 24);
            
            CacheFactory cacheFactory = CacheManager.getInstance().getCacheFactory();
            Cache cache = cacheFactory.createCache(props);
            
            LocalMemorySoftCache cache2 = new LocalMemorySoftCache(cache);
            
            //  We don't want local memory cache live longer than memcache
            //  Since we don't have any mechanism to set local cache expiration
            //  we will just reset this cache after each request
            perthreadManager.addThreadCleanupListener(cache2);
            
            receiver.adviseAllMethods(new CacheMethodResultAdvice(IPResolver.class, cache2));
        } catch (CacheException e) {
            logger.error("Error instantiating cache", e);
        }
    }

    @Match("LocationResolver")
    public static void adviseCacheLocationResolverMethods(final MethodAdviceReceiver receiver, Cache cache) {
        //  Assume that location of IP address will never change, 
        //  so we don't have to set any custom cache expiration parameters
        receiver.adviseAllMethods(new CacheMethodResultAdvice(LocationResolver.class, cache));
    } 

 These declarations tell Tapestry5 to add our advice to all methods of services that implement IPResolver andLocationResolver interfaces.