为Java / Spring / Tomcat Web应用程序淘汰MongoDB或Couch的Hibernate / Mysql

Question

I have an application that is undergoing massive rework, and I've been exploring different options - chug along 'as is', redo the project in a different framework or platform, etc.

When I really think about it, here are 3 major things I really dislike about java:

1. Server start/stops when modifying controllers or other classes. Dynamic languages are a huge win over Java here.
2. Hibernate, Lazyloading exceptions (especially those that occur in asynchronous service calls or during Jackson JSON marshalling) and ORM bloat in general. Hibernate, all by itself, is responsible for slow integration start up times and insanely slow application start up times.
3. Java stupidity - inconsistent class-loading problems when running your app inside of your IDE compared to Tomcat. Granted once you iron out these issues, you most likely won't see them again. Even still, most of these are actually caused by Hibernate since it insists on a specific Antlr version and so on.

After thinking about the problem... I could solve or at least improve the situation in all 3 of these areas if I just got rid of Hibernate.

Have any of you reworked a 50+ entity java application to use mongo or couch or similar database? What was the experience like? Do you recommend it? How long did it take you assuming you have some pretty great unit/integration tests? Does the idea sound better than it really is?

My application would actually benefit in many areas if I could store documents. It would actually open up some very cool and interesting features for this application. However, I do like being able to create dynamic queries for complex searches... and I'm told that Couch can't do those.

I'm really green when it comes to NoSQL databases, so any advice on migrating (or not migrating) a big java/spring project would be really helpful. Also, if this is a good idea, what books would you recommend I pick up to get me up to speed and really make use of them for this application in the best way possible?

Thanks

Answer 1

In any way, your rant doesn't just cover problems with the previously made (legacy) decision for Hibernate but also with your development as a programmer in general.

This is how I would do it, should a similar project be dropped in my lap and in dire need of refactoring or improvement.

It depends on the stage in your software's lifetime and the time pressure involved if you should make big changes or stick with smaller ones. Nevertheless, migrating in increments seems to be your best option in the long term.

Keeping the application written in Java for the short term seems wise, a major rewrite in another language will definitely break acceptance and integration tests.

Like suggested by Joseph, make the step from Hibernate to JPA. It shouldn't cost too much time. And from there you can switch the back-end to some other way of storage. Work towards a way of seperating concerns. Pick whatever concept seems best, some prefer MVC while others might opt for CQRS and still others adore another style of segmentation/seperation.

Since the JVM supports many languages, you can always switch to any of those or at least partially implement functionality in more dynamic languages. This will solve part of the problem where you keep bumping into the "stupidity" of Java, while still retaining the excellent optimizations of current JVMs at runtime.

In addition, you might want to set up automatic integration tests... since the application will hopefully never be run from your IDE, these tests will give you honest results.

Side note: I never trust my IDE to get dependencies right if the IDE has capabilities to inject its own libraries into my build or runtime path.

So to recap in short: small steps; lose Hibernate and go more abstract to JPA; if Java becomes stupid, then gradually switch to a clever language. Your primary concern should be to restructure the code base without losing functionality, keeping in mind to have an open design which will make adding interesting and cool features easier later on.

Answer 2

Well, much depends on things like "what exactly are the pain points with Hibernate?" (I know, you gave three examples...)

But those aren't core issues over the long haul. What you're running into is the nature of a compiled language vs. a dynamic one; at runtime, it works out better for you (as Java is faster and more scalable than the dynamic languages, based on my not-quite-exhaustive tests), but at development time, it's less amenable to just hacking crap together and hoping it works.

NoSQL isn't going to fix things, although document stores could, but there's a migration step you're going to have to go through.

Important: I work for a vendor in this space, which explains my experience in the area, as well as the bias in the next paragraph:

You're focusing on open source projects, I suppose, although what I would suggest is using a commercial product: GigaSpaces (http://gigaspaces.com). There's a community edition, that would allow you to migrate JPA-based java objects to a document model (via the SpaceDynamicProperties annotation); you could use JPA for the code you've written and slowly migrate to a fully document-oriented model at your convenience, plus complex queries aren't an issue.

Answer 3

All of those points are usually causing problems due to incompetence, rather than hibernate or java being problematic:

• apart from structural modifications (adding fields or methods), all changes in the java code are hot-swapped in debug mode, so that you can save & test (without any redeploy).

• the LazyInitializationException is a problem for hibernate-beginners only. There are many and clear solutions to it, and you'll find them with a simple google or SO search. And you can always set your collections to fetch=FetchType.EAGER . Or you can use Hibernate.initialize(..) to initialize lazy collections.

• It is entirely normal for a library to require a specific version of another library (the opposite would be suspicious and wrong). If you keep your classpath clean (for example by using maven or ivy), you won't have any classloading issues. I have never had.

Now, I will provide an alternative. spring-data is a new portfolio project by springsource, that allows you to use your entities for a bunch of NoSQL stores.