I have a trial task which includes writing simple http server using only Oracle JRE 1.6 standard libraries. Here simple HTTP server in Java using only Java SE API
I found the statement:
Since Java 1.6, there's a builtin HTTP server in Sun Oracle JDK (note: JDK, not JRE).
But I thought that all runtime libraries are included in JRE, and JDK is JRE + some development tools. Also, I have downloaded JRE 1.6 and found that HttpServer is included there in the rt.jar file.
So, my questions are:
Is it correct for me to use this implementation?
Why it is stated that JDK has libraries that are not in JRE? Do JDK provide any additional libraries to JRE?
Before I answer, please note that I am not familiar with the implementation you're referring to (I generally pull in Jetty and embed it when I need an HTTP server in my modules). So I'll answer somewhat generally, but maybe this gets your mind thinking in a direction that's helpful.
Is it correct for me to use this implementation?
That depends on the constraints on the trial task. Assuming that the implementation meets those constraints, and you are willing to live with any shortcomings it has, then there is nothing intrinsically wrong with using it. If it's available, it's fair game.
Why it is stated that JDK has libraries that are not in JRE? Do JDK provide any additional libraries to JRE?
First off, the statement made in that question is observably false. Clearly that implementation is included in the JRE.
More generally though, the JDK always has the option to do this, and there are definitely libraries deployed with a JDK that are not deployed with a JRE (see this page). Moreover, depending on the install, it's possible that there are installed extensions to the JRE in place (see this page).
Related
This question already has answers here:
How can I get Java 11 run-time environment working since there is no more JRE 11 for download?
(4 answers)
Closed 3 years ago.
We are planning to migrate our Java 8 project to use Java 11. But I noticed that Java 11 doesn't have a JRE folder.
In Java 9 and Java 10, folder structures are changed i.e. java\jdk1.x or java\jre1.x, where x is Java 9 or 10.
But in Java 11, I am getting only one folder, i.e. java\jdk-11. How will my client use my application without jre?
What I understood is that Java 11 is enforcing to modularize our application, and using jlink is needed to create our own jre to run the application in client.
Is my understanding correct?
For 20 years, the JDK shipped with a JRE which was just a subset of its functionality installed in a different directory on your system.
In fact, it shipped with TWO identical JREs, one installed inside the JDK installation directory and one outside it.
This has always puzzled me as it's a complete waste of effort on the part of the maintainers to make this so, and a complete waste of disk space on the computer you install it on, as that JRE just duplicates some of the things the JDK can do already.
Finally, with Java 11, Oracle and the OpenJDK team decided to end this silliness and just distribute a single thing, the JDK.
This JDK when installed is actually smaller on your hard disk than the old JRE alone used to be, removing even the somewhat valid argument that you'd want a separate JRE for devices with limited disk space, an argument that never explained why 2 JREs would be installed with a single JDK in the first place but was made to justify the need for a JRE as a stripped down runtime environment for the JDK.
Ergo, there is no need for a separate JRE, and there hasn't been one for a long time, let alone for including and forcibly installing it as part of the JDK installation.
And no, you don't need to create your own JRE. Just install the OpenJDK on the client machines and make sure you add the $JAVA_HOME/bin to the system path, just as you had to do with old JREs.
And oh, strip the Windows directory tree of any java*.exe files which some versions of the old JRE installer were wont to place there, as well as the system path which also had some weird entries added by some JRE installers.
tl;dr
How will my client use my application without jre?
➥ Bundle a Java implementation within your Java-based app.
Learn about:
Java Platform Module System
jlink (JEP 282)
jpackage (JEP 343)
Details
What I understood is that Java 11 is enforcing to modularize our application
No, modularization is not required, strictly speaking. Most existing apps can run as-is in Java 11. You can continue to develop in Java 11 without modularizing your code. But in your case, for a GUI desktop or mobile app, then you need to package a JVM within your app. Modularizing and using jlink tooling is probably the best way to go about that. In contrast a server-side Servlet-based app or Microservices server need not yet modularize, though likely a good idea to do so eventually.
I noticed that Java 11 doesn't have a JRE folder.
Oracle no longer intends for end-users to be installing a JRE or a JDK. Java Applets in a browser and Java Web Start app delivery are both being phased out, leaving the end-user with no need for a JRE. Java-based apps are expected to bundle their own Java implementation. The only folks consciously installing a JDK will be developers & server-side sysadmins.
Some folks are disappointed to see the passing of the Java Everywhere dream. And they may be annoyed to have to make a build of their app for every host OS (macOS, Linux, Windows, etc.). On the other hand, some developers are happy to be bundling a Java implementation (now smaller than ever) with their app, as that eliminates the hassle for the end-user to download-install-update a system-wide Java implementation. Also eliminates wrestling with corporate IT departments to install Java on users’ PCs. And bundling Java with app simplifies testing and support, as you know and control exactly what version and distribution of Java is involved. By the way, this bundling-Java-with-app is not exactly new: It has been supported by Apple for many years in the macOS & iOS app stores.
Important:
Understand clearly the nature of the OpenJDK project, as explained in Wikipedia
Read this white paper by Oracle of 2018-03, Java Client Roadmap Update
Read the white paper Java Is Still Free, authored by key members of the Java community.
Here is a flowchart diagram that may help you finding and deciding amongst the various vendors providing a Java 11 implementation.
Look at the AdoptOpenJDK project website to download the latest JRE and JDK.
I have used their nightly builds to work around the problem of missing JRE in JDK package. Just unpack JRE into JDK folder and this is going to be it.
I wonder what is the use case for jdk-slim docker image?
In which cases should I use jdk-slim instead of jre?
Are there any well-known issues (e.g. some monitoring tools are not working on jre?)
jdk - stand for Java Development Kit, so it includes development tools (e.g. javac)
jre - Java Runtime Environment (no Javac, for instance).
slim - This image installs the -headless package of OpenJDK and so is missing many of the UI-related Java libraries and some common packages contained in the default tag
Do you need to build something with your image? => jdk or jdk-slim.
Do you need just to run already build app? => jre or jre-slim
P.S. It's too late for the author. Hopefully, it will be useful for somebody else.
Are the Oracle Java and OpenJDK implementations for com.sun.net.httpserver fully compatibile? Should I expect some problems when I develop on Oracle Java, but ship for OpenJDK (docker)?
Eclipse warns me for using 'restricted' package, which makes me some worries, however, Eclipse's warnings are flawed in many domains (maven the most prominent one from my daily life).
Is there a good reason as for current stand (Java 8) for discouraging using of this package in first line? If there is, is it relevant for Oracle vs. OpenJDK or they are fully compatibile for that package?
That package is part of an exported, JDK-specific API, per https://docs.oracle.com/javase/9/docs/api/jdk.httpserver-summary.html . Exported means you can use it. JDK-specific means it's in both OpenJDK and Oracle JDK, but doesn't necessarily have to be in every implementation. Please see http://openjdk.java.net/jeps/179 for details.
I have opened/imported the accumulo "examples-simple" maven project into netbeans. Do I need to set the Java Platform?
Properties indicate "Java SDK 7.1". I know that accumulo-1.4.3 runs on JDK 1.6.0.
My current version is java version "1.6.0_32"
I am pretty sure the answer is yes, but it never hurts to ask!
Thanks,
Chris
As answered by Josh Elser on the Apache Accumulo Mailing List, where this was cross-posted to:
No, you don't need to.
Currently, all versions of Accumulo are still guaranteed to work against
1.6. So, if you hypothetically contributed anything back to Accumulo,
you would need to make sure that it runs on a 1.6 JVM. As such, it's a
good idea to ensure that you're building with a 1.6 JVM, but not a
requirement if you're just developing things locally for yourself.
I'm about to release a new version of my app. I'd prefer to stick with Java 1.6 since it's been fully tested using that JVM. I use install4J.
On the Mac I don't package a JVM, relying on the presence of Apple's JVM. As I understand it they've disabled the browser plugin by default so security isn't an issue.
I do however package a 1.6 JVM with the windows version. Am I correct in believing that the packaged 1.6 JVM doesn't have and more security risks than the latest 1.7 JVM since it won't be used by the browsers?
Thanks.
Thats just a question of updated software, older versions still safe. but using then in the browser can be such a problem just because of websites checking java version.
http://www.java.com/en/download/faq/remove_olderversions.xml
take a look at that link it should help