I read a few posts about JVM at Stack Overflow and would like to download a binary copy of the Hotspot JVM, yet I am not able to find it on http://www.java.net.
Beside that, what is the difference between Hotspot JVM and JVMs found at Oracle
Is Oracle JVM good for a production website?
Overview:
This SO question may clear up your questions regarding "What is JVM, Hotspot and OpenJDK".
Basically:
JVM means Java Virtual Machine. The JVM is the underlying runtime that executes java bytecode. There are multiple different implementations out there, all implementing the Java Virtual Machine Specification
HotSpot is the most used implementation of the JVM concept. It is used in both, Oracle JDK and OpenJDK. Oracle's JDK can be downloaded on oracle's website, currently http://www.oracle.com/technetwork/java/javase/downloads/index.html. This is "the typical JVM you will find on a normal user's windows machine".
OpenJDK is the open source project maintaining and impelmenting the HotSpot JVM, but also many other projects beside the JVM such as Graal or VisualVM. On Ubuntu for example you can install this OpenJDK (current version 8) by running sudo apt-get install openjdk8.
Conclusion:
While this explaination is not really perfect, it may be good enough to understand that there is no big difference between Oracle JDK and OpenJDK. If you are interested in a little more info on this, have a look at the SO question Differences between Oracle JDK and Open JDK
JDK / JVM sourcecode:
If you are interested in the source code, OpenJDK is the way to go. Here you can find the current OpenJDK 8 (which includes the HotSpot JVM). Its source code can be found here. It also states how to download the source code:
The jdk8u-dev forest for ongoing development can be cloned using this command: hg clone http://hg.openjdk.java.net/jdk8u/jdk8u-dev;cd jdk8u-dev;sh get_source.sh .
The corresponding master forest jdk8u can be cloned using this command: hg clone http://hg.openjdk.java.net/jdk8u/jdk8u;cd jdk8u;sh get_source.sh .
In addition, the source code for the last release, 8u66, is available by cloning the 8u master forest : http://hg.openjdk.java.net/jdk8u/jdk8u and using the 'jdk8u66-b17' mercurial tag.
Related
I try to install mobicents-Restcomm-JBoss-AS7
but - found many src distributions, i don't want to go down the road - compiling the whole src tree.
Many docs point some urls - that i should look mobicents-Restcomm-JBoss-AS7-*-zip.
On github jss7-8.0.0-179 is a source distrib.
any working link with binary?
going with source build - is a little pain to do a proof of concept...
if it matters:
CentOS Linux release 7.6.1810 (Core)
java version "1.7.0_221"
OpenJDK Runtime Environment (rhel-2.6.18.0.el7_6-x86_64 u221-b02)
OpenJDK 64-Bit Server VM (build 24.221-b02, mixed mode)
Seems all the binary have been removed from repo. You might to get binaries if you have it installed before now.
I am getting following error while running /tmp/jprofiler8/bin/jpenable
No suitable Java Virtual Machine could be found on your system.
The version of the JVM must be at least 1.6 and at most 1.7.
Please define INSTALL4J_JAVA_HOME to point to a suitable JVM.
You can also try to delete the JVM cache file
I have also set INSTALL4J_JAVA_HOME to point to suitable JVM.
Java version on my machine is 1.4.2.
Can anyone please suggest what might be wrong or missing?
Unfortunately you did not mention details about your environment, so I don't know which Linux distribution you use.
There are some options though:
install a current JRE alongside the installer for JProfiler
As you can't install or update Java, you could provide a JRE in a kind of "portable application" setup. Simply unzip the server jre Oracle provides or (if you are not on an x64 architecture) unzip the jdk you also can download from Oracle.
But if the code you want to profile is limited to your pre-installed Java 1.4 you will run into another problem, because as far as I know Java 1.5 is the minimum JProfiler expects
use a different machine for profiling
Unless your code depends heavily on the environment you run it in you can even take a Windows 8.1 machine and profile the code there. Code that is slow is slow on any operating system. Or make use of a different Linux computer.
OpenJDK currently does not have support for a JRE on MIPS processors (there's a port in progress, but who knows how long that will take).
I'm trying to understand how the JRE works, and what is standing in the way of using OpenJDK on our embedded system running Linux on a MIPS processor. If I have a custom JVM that is capable of running on MIPS designed to work with OpenJDK (in this case, I'm referring to JamVM 2.0), is there anything else preventing the JRE from running on the MIPS board? Are any other parts of the JRE platform-dependent?
My understanding is that the JRE is (mostly) composed of two units: the virtual machine, which abstracts the hardware and which is platform-dependent, and the collection of Java libraries which run on the virtual machine and which are not platform-dependent.
To be clear, my questions is: aside from the JVM, is any part of the Java Runtime Environment platform-dependent?
"aside from the JVM, is any part of the Java Runtime Environment platform-dependent?"
That depends on where you place the boundary where the VM ends and the JRE begins. I would consider memory management and code execution as 'the VM', everything more specific part of the JRE.
Thats means every binding to the operating system, be it I/O, Graphics etc. is part of the JRE. Thus the JRE has many platform dependent parts; you usually just don't notice them because your code uses their abstractions (e.g. File, Socket, Window).
So when you say "a port to MIPS" it doesn't mean anything without specifying an OS (ok, your link says Linux); a VM ported to a processor architecture by itself does not make a working java environment. It also requires a port of the native parts of the JRE that allow the java program to actually communicate with things outside the VM; thats where the OS platform comes in.
Since Linux is already supported for x64, the MIPS port should be able to reuse most of the JRE to platform bindings from that.
I'm running Minecraft on a headless Linux server with OpenJDK. I've added a bunch too many mods and its lagging (even on my local network) without using too much CPU or memory (e.g. its lagging, but its still got resources it can use). So I'm pretty sure its a mod fault.
To save the hassle of removing/adding mods one by one to see whats causing the error, my research led me to VisualVM where you can profile the java application and see which entities are doing what and with what resources. With any luck it should point out the mod consuming the most resources, and the most ticks.
Given its a headless server, and VisualVM is a window/GUI application, I've successfully managed to get it running and passing the GUI back to my Windows client using X over SSH.
Trouble is now, that its telling me that I need to use JDK and not JRE. Which is fair enough. Except OpenJDK has JDK in its name, rendering all googling futile. I cannot for the life of me, find if JDK is included in OpenJDK, what its named, and where it may be located. The other problem is, most of the troubleshooting guides I find are for Windows, and dont help me find the JDK on linux.
As some background information, I'm running Debian, and I know OpenJDK's JRE is installed here: /usr/lib/jvm/java-7-openjdk-amd64/jre
Can someone tell me please, if JDK is in OpenJDK, or I need to install it as well? If I do need to install it, is there an OpenJDK equivelant for JDK? If its already included, can someone provide some tips on locating it, so I can point VisualVM at it instead of the JRE?
The OpenJDK has a JDK, but there is also a cut down version which is just the JRE. I would use locate javac and if it can't find it, you need to install the JDK.
I understand that the Oracle Java SE contains closed source extensions and tools that are not part of the OpenJDK however is the Oracle Java SE JVM identical to the OpenJDK JVM or does Oracle make changes to the OpenJDK JVM before releasing it as a Java SE JVM?
Update 1:
I found some info from the JDK7 updates projects: http://openjdk.java.net/projects/jdk7u/qanda.html
Will the 7 Update Project receive security fixes from Oracle?
Yes.
As with OpenJDK 6, security fixes are first kept confidential and applied to a private forest before being pushed to the public forest as part of the general synchronized publication of the fix to effected JDK release trains. In addition, they will not go through the public code review and putback approval process, and their corresponding issues in the Project's issue tracker will not be publicly visible.
OpenJDK is the reference implementation of Java as of version 7.
OpenJDK 7 is the starting point for the version that Oracle distributes as Oracle JDK. Other vendors (e.g. RedHat for IcedTea) may also use OpenJDK as their starting point.
In terms of the differences between OpenJDK and a vendor VM, there may be patches which a vendor wants to apply but which the overall OpenJDK community has not accepted into mainline.
Vendor VMs must, of course, be able to prove that they are in conformance with the TCK if they want to use the Java trademarks to describe their product.
Oracle JDK is also not open-source. This is possible because of Java's dual licensing arrangements, and the fact that Oracle own Java overall.
Do you have more specific questions - as posed, your question is a bit vague. What specific aspects are you interested in?