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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?
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OpenJ9 is generally known for much faster starting and much lower memory usage initially, while HotSpot may run more efficiently overall for long-running apps. Both are well-regarded, well-worn, and available with distributions of OpenJDK.
Oracle HotSpot JVM is based on OpenJDK HotSpot project. So, they are mostly the same VM, except that Oracle JVM has a few additional commercial features, mainly, Java Flight Recorder, Application Class Data Sharing and Cooperative Memory Management.
HotSpot, released as Java HotSpot Performance Engine, is a Java virtual machine for desktop and server computers, developed by Sun Microsystems and now maintained and distributed by Oracle Corporation. It features improved performance via methods such as just-in-time compilation and adaptive optimization.
HotSpot is a dynamic compiler. It combines the best features of a JIT compiler and an interpreter, combining the two in a single package. That two-in-one combination provides a number of important benefits for code performance, as you will shortly see.
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.
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