Guice Caching And Interceptors

A little while ago I wanted to try out Guice 2′s Interceptors. And amazingly enough, I managed to create an integration towards ehcache in a couple of hours and had fun too.

The result is this

// Calculator.java
package org.slurry.cache4guice;

public interface Calculator {

        public int calculateSomethingWild(Integer number) throws InterruptedException ;

        public int calculateSomethingWild(Integer number,Integer number2) throws InterruptedException ;

}

// CalculatorImpl.java
package org.slurry.cache4guice;

import org.slurry.cache4guice.annotation.Cached;

public class CalculatorImpl implements Calculator {

        @Cached
        public int calculateSomethingWild(Integer number)
                        throws InterruptedException {
                Thread.sleep(2000);

                return number;

        }

        @Cached
        public int calculateSomethingWild(Integer number, Integer number2)
                        throws InterruptedException {
                Thread.sleep(2000);

                return number + number2;
        }

}

And bind it in your module

// GuiceModule.java
package org.slurry.cache4guice;

import com.google.inject.AbstractModule;

public class GuiceModule extends AbstractModule {

        @Override
        protected void configure() {
                bind(Calculator.class).to(CalculatorImpl.class);

        }

}

So what’s backing those annotations in line 19 and 28 of the first source code box, whats doing all the magic?
1. An annotation, dada

package org.slurry.cache4guice.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.METHOD)
public @interface Cached {

}

2. An interceptor, more interesting, look at line 18 the most important thing in the interceptor implementation

package org.slurry.cache4guice.aop;

import net.sf.ehcache.Cache;
import net.sf.ehcache.CacheManager;
import net.sf.ehcache.Element;

import org.aopalliance.intercept.MethodInterceptor;
import org.aopalliance.intercept.MethodInvocation;

import com.google.inject.Inject;

public class CacheInterceptor implements MethodInterceptor {

        private CacheManager cacheManager;

        private CacheKeyGenerator cacheKeyGenerator;

        public Object invoke(MethodInvocation invocation) throws Throwable {
                setupCacheIfNecessary(invocation);

                return getResultFromCacheOrMethod(invocation);

        }

...

3. Some Guice setup, in a module look at line 18,19 and 20. And actually line 19 are only needed if you need something injected into your interceptor

package org.slurry.cache4guice.module;

import net.sf.ehcache.CacheManager;

import org.slurry.cache4guice.annotation.Cached;
import org.slurry.cache4guice.aop.CacheInterceptor;
import org.slurry.cache4guice.aop.CacheKeyGenerator;
import org.slurry.cache4guice.cache.StringBasedKeyGenerator;

import com.google.inject.AbstractModule;
import com.google.inject.matcher.Matchers;

public class CacheModule extends AbstractModule {
        protected void configure() {

                bind(CacheManager.class).toInstance(CacheManager.create());
                bind(CacheKeyGenerator.class).to(getCacheKeyGeneratorClass());
                CacheInterceptor cacheInterceptor = new CacheInterceptor();
                requestInjection(cacheInterceptor);
                bindInterceptor(Matchers.any(), Matchers.annotatedWith(Cached.class),
                                cacheInterceptor);
        }

        protected Class getCacheKeyGeneratorClass() {

                return StringBasedKeyGenerator.class;
        }
}

So could it be easier? I mean theres only 3 steps. Now I haven’t shown all the code, only the relevant ones for guice. There’s a little more to it. And I should probably expand the functionality, so there’s a evict from cache annotation, that can evict certain caches. So did you need a cache for guice or did you want to play with interceptors, now you got both

All hosted here, with source code and tests,  if you have additions please contribute

http://code.google.com/p/slurry/

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