Craig Andrews

HTTP caching is both important, as it reduces bandwidth use and improves performance, and complex, as the rules are far from simple. In my experience, most Java and Android applications either don’t do HTTP caching, or they roll their own and up doing it wrong or in way too complicated a fashion. In other words, they create a non-standard, one off, unmaintainable solution. And IMHO, that’s no solution at all.

If you find yourself using HttpClient, you can use HttpClient-Cache, which is an easy drop in for Java. See my previous post about HttpClient-Cache for Android. But if you’re using HttpUrlConnection (aka java.net.URL.openConnection()), there’s no good solution for regular Java or Android. Well, in Android 4.0 and later, you can use HttpResponseCache, but with only a small percentage of Android devices using 4.0 or later, that’s not a terribly good solution. If you use Android 4.0+’s HttpResponseCache as recommended by Google, then all previous Android versions end up with no HTTP response caching – this causes excess load on your servers, slower performance for the app, and unnecessary bandwidth use.

To fix this problem, I grabbed all the code from AOSP that implements Android 4.0′s HttpResponseCache and made it a separate library. This library is easy to use, works on Java 1.5+, all versions of Android, and is licensed under APLv2 (just like everything else in AOSP). Really, there’s no reason not to use it! You can even use in Java server applications, such as those that use Spring.

To use it, if you’re using Maven, simply add this block to your pom.xml (all artifacts are in Maven Central):
<dependency>
<groupId>
<com.integralblue</groupId>
<artifactId>httpresponsecache</artifactId>
<version>1.0.0</version>
</dependency>
If you’re not using Maven, you’ll need to add the httpresponsecache jar and its dependency, disklrucache.jar, to your project.

When your application starts, before it makes any HTTP requests, execute this method:
com.integralblue.httpresponsecache.HttpResponseCache.install(File directory, long maxSize);
If you’re using Android, and you want to use Android 4.0′s HttpResponseCache if it’s available, and fallback to this library if it’s not available:
final long httpCacheSize = 10 * 1024 * 1024; // 10 MiB
final File httpCacheDir = new File(getCacheDir(), "http");
try {
Class.forName("android.net.http.HttpResponseCache")
.getMethod("install", File.class, long.class)
.invoke(null, httpCacheDir, httpCacheSize);
} catch (Exception httpResponseCacheNotAvailable) {
Ln.d(httpResponseCacheNotAvailable, "android.net.http.HttpResponseCache not available, probably because we're running on a pre-ICS version   of Android. Using c$
try{
com.integralblue.httpresponsecache.HttpResponseCache.install(httpCacheDir, httpCacheSize);
}catch(Exception e){
Ln.e(e, "Failed to set up com.integralblue.httpresponsecache.HttpResponseCache");
}
}

The source code to the library is available on GitHub. I’m already using it in my CallerID Android app. If you end up using this library, please leave me a comment.

That’s it – enjoy easy to use HTTP caching!