There's been lots of debate this year over whether or not Sun should open source Java. I've talked at OSCon to quite a few Java guys, many long term Apache developers, who are disgruntled at Sun for not open sourcing Java. I totally share their frustration as Sun have done 95-99% of all the right things. Part of the frustration is there's only a little step further to go, we're all so close.

I think Sun's done a fantastic job of growing and protecting the Java platform. There's just one more step they need to take - to open source some Java source code - and we're all happy. However up to now I think the problem has been that no-one's managed to explain to Sun why they should do it or even what 'open sourcing Java' means in real practical terms.

Sun is clearly very concerned that any kind of move in this direction could undermine the Java platform, leading to fragmenting of the platform and brand etc. I guess this reluctance should be seen as a very good thing - they are being very careful and protecting Java. However sometimes a parent can smother a child and wrap it in too much cotton wool...

So here's hoping this proposal can help show why and how Sun could do it, making lots of open source hackers very happy and growing the Java platform even more, especially faced with stiff competition from .NET / Mono.

What's more I'm not even proposing it open sources Java but something a little different. Lets start out with a couple of use cases...


Use Case A

You're a developer in a large company or ISV or consultancy of some kind. You develop enterprise applications for your customers, using the right tools for the job etc. Now let's assume that you like Java and develop most of your enterprise software in Java due to the diversity of tools, technologies (open source and commercial) available and so forth. (So here we're talking about most of the developers in the Java community today.)

However increasingly you're finding that X per cent of the time you need to write or interface closely with some .NET / Mono code. e.g. you need to put some code inside Word/Excel/Access/InfoPath to write some rich client thingy. Or maybe you need to hack some existing .NET/Mono project etc.

The value of X might not be very big. I know many large companies where X will be zero. For some I know it'll be 5-10%. I know of some companies where this will be much higher - though in the circles I move it's not very big, but YMMV. (BTW you could argue Web services is a solution here, but really sometimes you just need to hack inside the .NET/Mono worlds).

Whatever the value of X, let's assume that for a reasonable amount of people it's gonna be greater than zero and a significant value. Now to build code that works on .NET / Mono today, there's only really one safe option - ditch Java, the language, the JVM, the tools, the frameworks, and jump wholesale into the .NET / Mono world using C# and VisualStudio and all that stuff MS is doing.

This means you've now 2 platforms and code bases to work on, 2 sets of build tools, libraries and so forth. This is not ideal. Indeed I can imagine many companies, to save having both .NET experts and Java experts and having 2 sets of tools and internal Java vs .NET wars, will try and just pick one and use that one tool for everything. I can therefore imagine quite a few of these developers just switching to .NET / Mono. Why might they do this?

• They need to hack on windows-only technology like Office.
• Using one platform saves money.
• Moving to .NET is seen as an easier choice, since once you've made that choice you get everything you need from MS - no need to choose the best IDE, the best build tool, the best app server, Web app framework and all those things - just use what MS gives you. Some folks in technology just want an easy life, even if it's not the best tool for the job, it's an easy life and no one ever got sacked for choosing MS etc.
• They may get their heads turned by some whizzy new rich client UI stuff that MS/.NET has (like InfoPath or neato Office stuff if MS were to innovate in Office again or, who knows, maybe some of this Longhorn stuff isn't just catchup-to-OS X, but might actually be new and innovative. At least now MS has an incentive to innovate.
• VB looks easy to hack stuff together.
  

Maybe there are other reasons to switch. From the Java camp, who cares what the reasons are, people will switch.

So whats the (.)net result?

• Java the platform loses users and grows less popular.
• There's a clear pressure on developers to switch to .NET / Mono especially by their business who love Excel or whatnot.
• For those users who don't switch completely, they now have 2 platforms to support which is a PITA and adds more cost and complexity to their job.
• For users who do switch to the .NET/Mono they've just lost a lot of their choice, they've lost a lot of the benefits of the Java platform and open APIs and community and are now mostly vendor locked into MS with no plan B.

Clearly this is not good for Sun, the Java platform or the users in Use Case A. But its great for MS and Mono!


Use Case B

This one is pretty much the same as above, except you're a highly Linux/C focussed developer. You may work with lots of C code, work on open source Linux C projects or you may even be some kind of Linux distributor. Either way you'd like to use a language and tools that make your job easier yet work nicely in your C / GPL environment. Something that can fit right in, turn easily into shared libraries / DLLs or executables and be easily distributed to your users.

Java is not as easy as it might be at integrating into C code or Linux worlds or being easy to redistribute in typically Linux/GPL worlds. There's another option - Mono. This is welcoming the Linux platform and developers with open arms. Java could be a possible solution in this space (as a language, set of tools, standard APIs etc). However due to restrictions on licensing issues, Mono seems a much better option for Linux folks to use today - purely due to licensing restrictions rather than any technical issue.

The net result to Java for this situation? Linux/C based developers don't move to Java (or move away from Java) and move to Mono. A kinda knock on benefit for .NET as it looks like .NET is more popular thanks to Mono


Conclusions

So we've just described 2 massive communities of developers above and why the current licensing of Java is causing them pain and how its badly affecting the Java platform to the benefit of .NET / Mono.

For Use Case A, developers could stick on the Java platform. They could keep their investment in the Java tools, languages, frameworks and so forth. But for those times where they need to be inside .NET for neater Office integration or to work inside a .NET/Mono project, they could compile their Java code and any dependent code they use to .NET IL. Java is mostly bytecode which is easily translatable and the .NET CLR is very similar to the JVM so its not that hard to do.

Indeed IKVM does exactly this today. We can today use .NET as a platform on which to run Java code. The downside is, IKVM isn't allowed to use the rt.jar thats part of the JDK / JRE due to licence restrictions. So it must use GNU classpath, which is a little buggy and not totally compliant with its real, certified JVM / JRE equivalent code. It's pretty good - Eclipse works fine inside IKVM for example, but there are buggy areas. (e.g. Geronimo doesn't run yet inside IKVM due to IO / classloader bugs).

Now the users in Use Case A are not trying to subvert the Java brand or fool anyone into thinking that .NET / Mono is a Java platform. They just wan to get their job done and use one set of languages and tools, to save money, and have an easier life and try avoid being caught in the cross-fire of a developer mindshare war.

Hey, one of Java's goals is to write once run anywhere. Yet this clearly does not yet include running inside .NET / Mono. These should be valid platforms for folks to use Java on!

Similarly for users in Use Case B - developers could use the Java platform, yet turn all their Java code/libraries into shared libraries, DLLs, and executables. They can do this completely today with gcj. It works fine, however like above it must use GNU classpath which is buggy and incomplete.

Again the WORA vision is broken since C libraries are not considered to be a platform on which Java should run - which thanks to gcj it could be - it's just not really supported or possible, again due to licensing issues.


A Proposed Solution

So what should Sun do to help both of these massive communities of developers? Firstly its clearly Sun's fault as it's Sun licensing agreements which are the problem here. So here's what Sun can do to both protect the Java platform from fragmentation and to grow the Java platform into these 2 large areas of developers while still keeping a steely grip on the Java platform and brand...

Sun should set up an open source project called JRT. It's not Java, it's not a Java platform - it's something else, it's JRT. It's a bunch of Java source code for some java.* and javax.* APIs and implementation classes which are used to implement part of the JDK / JRE - basically the source code which when compiled to bytecode makes the rt.jar which goes into the JVM. Parts of this are already open sourced (XML parsers, DOM, SAX etc). So its already been done in part. We're just making a bigger chunk of this code open source.

Note it's not the JVM though - there's lots of C code for implementing that and there's all that really cool hotspot stuff too - I'm not proposing any of this is open sourced (yet) - though that could be kinda cool, the Mono guys could really help out and reuse that stuff.

So JRT is just an open sourced Java project - under a very liberal licence, say Apache 2.0 licenced so folks can use it inside GPL and BSD open source projects or inside commercial products if need be. Note that the JRT project also includes a few C header files for when JRT's Java code has to call out to native C functions that any VM must implement.

Now Sun is sole committer on JRT; they decide what goes into JRT when. However now that a huge bulk of the code for the JVM is out there now we all benefit because...

• More eyeballs are now looking closely at the code.
• Previous GNU-classpath developers can now work with Sun developers to help maintain and improve JRT.
• Folks can easily submit patches.
• This has no effect on the Java brand or platform, since JRT != Java, its just some java code for some of the java libraries.
• Sun keeps the Java trademark, brand and compatibility tests so 'Java' is protected.

So far, nothing too earth shattering or risky for Sun. They're already done part of this (for XML). They've not open sourced Java, the JVM, or the platform. They've just open sourced some Java source code (and some C header files) that are used to create rt.jar.


Now what this now means is that the IKVM and the gcj guys can reuse JRT freely. They can redistribute JRT source code or compile it into some format and call it anything they like. (There would be restrictions, like you can't modify JRT and call it JRT, or you can't claim that you are a Java platform unless you pass Sun's TCK etc). Redistributing JRT doesn't affect the Java brand, since no one is saying it is Java - no one is allowed to say it is Java.

However now the IKVM & gcj guys don't have to try keep GNU classpath in sync with JRT; they can just share the code. This then means they can make .NET / Mono / gcj into a platform on which Java code can be run. Lets call this a JRT-platform. JRT-platform = a platform which your Java code is likely to run, but it might not. i.e. it's not a certified Java platform but it might be close.

Now developers have a choice; they can write their code in Java and deploy on any Java platform, or they could try their luck on a JRT platform too - that's their choice. Choice is good. JRT platforms are not necessarily a Java platform, so it's a little risky and there might be a few bugs and suchlike, but hey it might work. (It already does for Eclipse and so could well work for many projects). It doesn't have to work for everyone; so long as it works for some folks, we've all gained.

So far so good. We've already got Java platforms, officially sanctioned and certified platforms on which developers can have total confidence. Or there could be these new JRT platforms, which have specific close integration with .NET stuff or C or whatnot which could be used too. This is good - we've got more choice now and everyone's happy. There are other non-Java platforms developers can try if they want to and the GNU-classpath guys can just help fix and tune JRT instead. Win-win!


But wait. The IKVM or gcj guys could try certify their JRT platforms as fully fledged 'Java platforms.' This is by no means necessary; things would be OK if there were Java and JRT platforms, but the ideal would be for IKVM and gcj to both certify so that they become Java platforms too, passing any certification tests Sun comes up with to ensure developers have complete confidence that their stuff will run. This would be a truly great step and I think both these platforms could get there without too much work (since they're really close now and the JRT code is the missing link). IKVM for example is the work of mostly one person!

Think about that for a second. We could test and certify that .NET / Mono (with IKVM) and gcj would completely pass all of Sun's compatibility tests and so could then call themselves a fully fledged Java platform and JVM.

If we get there then

• We have one really massive Java platform now; all of the JVMs available today plus .NET, Mono, Rotor, and gcj. That makes pretty much anything a possible Java platform (which may not use the Java VM but use another VM, like the CLR - who cares how it works so long as it's compatible).
  
• Sun protects the Java brand still, defines the TCKs and for anyone who tries to pass off a non-compliant Java platform as a Java platform it can sue and protect us all from Java brand fragmentation.
  
• Folks who don't have the resources to go the whole hog and certify as a Java platform, can be a 2nd class JRT-platform but still be useful to Java developers even though they are not a real, true, compliant Java platform.
  
• We'd get more competition in the VMs; who knows the .NET VM migth one day run Java code better than Sun's? Or maybe Mono? Or vice versa - the Sun JVM might run .NET / Mono code better? e.g. Mono users could take advantage of hotspot. Competition is good!
  
• Folks who are using C / gcj / .NET / Mono today could be tempted to use some of the great stuff available in the Java ecosystem inside their platform (since their platforms could now be certified as Java platforms). i.e. folks could start switching to not from Java.
  
• We could end all these ports of Java open source projects to C# just to get clean integration with .NET / Mono, we could just use Java code to run on both platforms. (Or we could write a C# compiler for the JVM similarly, to reuse any C# open sourced code - of which there's little today but that might change in the future.)

This would be a win-win for Java, Sun, developers, and Mono/gcj too. We would all now standardize on one set of languages, tools, frameworks, IDEs, APIs yet when we needed to work closely with lots of C or lots of Mono / .NET stuff, we wouldn't have to switch platforms and tooling, we could stay on the Java platform (if they are certified, or use a JRT-platform with a little more work/risk).

From time to time we might switch APIs from java.something to System.whatnot when it makes sense to do so. But hey, healthy competition for APIs is a good thing. Use the right tool for the job and let's avoid unnecessary platform wars.

The only folks who could possibly be hurt by this are MS since they would not be locking anyone into .NET any more. However they're free to innovate and compete by building better APIs and tools to tempt folks to use MS-only stuff. This is fine and competition is healthy and we all win. Let's have an open playing field with no artificial barriers!

So please Sun, go for it. Make the first step and open source JRT. It's no biggie and doesn't affect the Java brand. There are many people in the open source world who'd bend over backwards to help you do it. We'd all love you for it! We'ld help you develop, support, document, and tune JRT for free. You'd keep ownership of the IPR and sole rights over it and I'm sure Apache or codehaus would happily host the project for nothing - it would't cost you a penny.

Once you've taken that first step, some of us could then try help turn .NET, Mono, and gcj into Java platforms - and then we'd all really win.