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I'm attempting to migrate a Maven application to Java 11 (OpenJDK 11).
To start, I am looking to compile my Java 8 project utilizing Java 11 via the release compiler option to target 8.
The compilation works fine, however when running my JUnit tests, the tests fail with various issues (Maven MyBatis tests fail when running Java 8 project compiled with Java 11).
In an attempt to eliminate variables, I've simplified the process and compiled the application with the Java 8 compiler (vs. Java 11, targeting Java 8) and then ran my tests with the Java 11 runtime - I'm still experiencing exceptions.
My understanding is that you should be able to run Java 8 applications with Java 11 as it should be backwards compatible.
What am I missing?
My understanding is that you should be able to run Java 8 applications with Java 11 as it should be backwards compatible.
What am I missing?
This is incorrect. Java merely promises not to break compatibility lightly. They've been interpreting 'lightly' somewhat differently, especially in the 8 to 9 transition (which broke rather a lot, really).
There are a few fairly well known issues. Post the errors and you may get some insights. At any rate, no, there is no such guarantee: Even when compiling with --release 8. It also sounds like the thing you compile it with is completely irrelevant here - the only variable that decides whether you get errors or not, is if you run the resulting class files on JDK8 or on JDK11.
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i would like to update from Oracle Java to Adopt OpenJDK.
Therefore i have some question before i start doing the update:
Some information about the application i use:
2 applications
Application 1 uses Java 8
Application 2 uses Java 11
My Questions:
Are there any known problems updating from oracle Java 8 to AdoptOpenJDK 8?
Are there any known problems updating from oracle Java 11 to Adopt OpenJDK 11?
Is it even possible to run a Java 8 Application on Java 11? (Can i use Adopt OpenJDK 11 for both applications?)
Is there any guideline to update from Oracle to Adopt? (Or just straigt forward?)
best regards
For a given Java version (since Java 8), the various commercially-supported OpenJDK builds are almost drop-in replacements for the Oracle JDK.
If you're writing an application with a GUI, you'll find some differences in the fonts, and in colour profiles. The Oracle JDKs also have better support for Java Flight Recorder (if anybody uses that). There's little support in OpenJDK for the ancient Java Web Start, but there are alternatives.
In my experience (which is nearly all in middleware), choice of JDK (for a given version) is almost always a decision about support, and rarely about features. I've rarely encountered any technical problems moving from Oracle JDK to OpenJDK, or vice versa.
I've also not found any problems running Java 8 applications with Java 11 and later. However, Java 11 decoupled several components -- again most related to GUI applications -- into separate JARs.
But, in the end, this is all a matter of testing, isn't it? If your testing is sufficiently thorough, any problems with compatibility will be flushed out. I certainly wouldn't rely on anybody else's claims of backward compatibility without thorough testing.
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We want to migrate all our production services to Java 10 from Java 8. As I understood, we might face issues with builds (gradle etc.), dependencies etc. for development. But when it comes just to the JVM itself, i.e. running services, will we face any issues if we just install JVM 10 in production to run our jar services?
I'm not sure why this has been downvoted since it seems a reasonable question.
Oracle's own guidance for moving applications from JDK 8 and earlier to JDK 9 and later is "applications that just use java.se should just work". If you have not used (directly or indirectly via a third-party library or framework) any JDK internal APIs (sun.misc.Unsafe is the most infamous) then you can leave all your application code on the classpath and this will most likely work without change. There are a few differences that might catch you out with changes to things like command line flags.
I've written two blogs on this, which might be helpful to you:
https://www.azul.com/jdk-9-pitfalls-for-the-unwary/
https://www.azul.com/jdk-10-pitfalls-for-the-unwary/
You should also bear in mind that it doesn't make any sense to migrate to JDK 10. JDK 11 will be released next month and, at that point, updates for JDK 10 will stop. It would be better to migrate to JDK 11. If you're looking for long-term support Oracle is now charging for this. Check out our Zulu OpenJDK builds.
A good starting point is the JDK Migration Guides on the Oracle download site. The JDK 10 Migration Guide covers migration from JDK 8 to JDK 10 and can be found here:
https://docs.oracle.com/javase/10/migrate/toc.htm
Another good resource is the JDK release notes as these include notes on the known source, binary and behavioural compatibility issues. You can find the release notes for the JDK 9 and JDK 10 releases linked from here:
https://www.oracle.com/technetwork/java/javase/jdk-relnotes-index-2162236.html
Another resource is the videos from conferences. I've prepared several times on the topic of migrating to JDK 9 and beyond. A recent one from Devoxx BE 2017 can be found here:
https://www.youtube.com/watch?v=uSR5JroBp34
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The target environments of my code use older Java versions (Java 7, Java 8). I use JDK 7 for development.
Will there be advantages if I use the most up-to-date JDK for my development, which is JDK 9 (and specify source=1.7 and target=1.7)?
I am aware that my code must not use any API which is not availabke on the target platform.
For the can I? Yes. Since backwards compatibility is important in Java, there's no technical reason why you couldn't do it. Sometimes company policies mandate a specific JDK version for development though.
In general the main advantage of using a later version of the JDK than what you're developing for is getting familiar with the later version. This may also increase your interest to migrate the software itself to a later version, if you notice it to be useful: for example you notice you love lambdas, so you migrate from Java 7 to Java 8.
Since the resulting bytecode is the same (not that it really matters) and the tools you use usually don't depend on the JDK, it has very little other effect. You can (usually) run code safely on newer JREs, so there's no difference with that either.
For the should I?
Whether you should start using JDK 9 now is primarily a matter of opinion. As Oleg pointed out it's not actively pushed everywhere, so at least you're not late and have time to consider moving forward for a while still (maybe toy around with it first before considering it for work use). Due to the large architectural differences between Java 8 and Java 9, I'd expect there to be a lot bigger gap in acceptance than between older versions.
However it's not all gloomy. There's a pretty good wrap-up of the features here and even if you are sticking to Java 7/8 projects for the time being, I see no reason not to do that on JDK 9 when you feel you're ready to have a look at it (and there is no hurry). I haven't installed it yet, although I've read about the decisions (good choice they didn't remove Unsafe).
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I have some big projects running on Java 6. But I plan to start building them in Java 8 since a lot of build tools have moved away from Java 6.
Is it safe for me to simply compile them with Java 8 and then deploy them in a web container running Java 8? If not, what are the considerations?
FYI, they don't have a proper automated test suite in place.
The problems can be related to:
deprecated methods that are removed in java 8 and you used in the old java 6 code
different behaviour for some methods:
There are aspects of the platform's behavior that are intentionally unspecified and the underlying implementation may change in a platform release.
configuration of web container that can be different from a version supporting java 6 and the version supporting java 8
external libraries that changed during the passage from java 6 to java 8 removing old methods so that your code can't compile
So yes it is possible that the passage from java 6 to java 8 can broke your code.
But if the code compile it is quite sure that the behaviour of the code is the same, because generally (but not always) a retro compatibility is granted. You can be sure of that only running a complete set of unit tests both on java 6 and java 8 versions.
Here some example of not compatibility between java 6 and java 7:
JDK-6527962 : Retire the non-standard package com.sun.image.codec.jpeg. If your code use this package the it doesn't compile on java 8
JDK-6563734 : Path2D.Float and Path2D.Double should have final getPathIterator methods If your code ovewrite the methods declared final the code will not compile passing to java 8
Here a complete official list of incompatibilities between java 6 and java 7
Here a complete official list of incompatibilities between java 7 and java 8
It usually should be, since most of the features are backward compatible. However, there are no guarantees. Please do follow the proper process and do testing before rolling out to production.
For web container , with jdk, version would also have changed. This may cause some problems depending upon the software vendor and what all services you are using from the container ( JNDI, connection pooling etc).I once had a problem in migrating application to higher version of JDK. We also upgraded Websphere. We were using JSF, and higher version of WAS had JSF jars included, which was clashing with our application jars.
Your apps may be using a lot of 3rd party library which may be impacted. Again, mostly you should be Ok, but there can be small issues. Without knowing your applications, I can only suggest migrate and test to confirm.
You need to test things very thoroughly. If there are bugs, then it is imperative to find them and fix them before you move on to the next version. If you have a sunny day scenario and do not have bugs coming from the upgrade, then at least you know that for sure after the testing.
However, you need to know what to focus on. You need to read about changes applied on version 7 and on version 8.
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Should I always use the latest JRE version of Java 7 for a ubuntu production server ? Or should I be careful while upgrading between these minor versions too ?
Does the same rule apply to while making a choice between minor versions of Tomcat7 server?
I'm asking this in context of making a choice only amongst the minor versions of Java 7. Also please mind I'm asking this for a PRODUCTION server so I need extra carefulness.
This is a security issue; the minors are almost always security updates. Use the latest of whichever JRE (Oracle, OpenJDK) you choose.
I would suggest you to use the latest one, but at the same time, i would suggest to move your updates first on a stage server , test them thoroughly be fore moving to production. This is because, many time the project code uses library/jars who are compatible only with certain version of JRE, and upgrading JRE version might break them. So, either you need to update those library /jar as well or you live with current JRE version.
If those jars are not being maintained, you may be out of luck.