I have to install a lower version of Java on some clients but some of them have a new version already installed. Do you know which one will take precedence? Is there a way to force Java to use a certain version without uninstalling the other? We have an application that requires the certain lower version.
By client I suppose you mean some Windows machine?
You can control which version is used by setting:
The system path to include the java.exe you want used at runtime.
The JAVA_HOME variable to point to the JDK library, only if development takes place on the machine.
If the client you are using does NOT have the option to setup JDK, then it will look into what ever JAVA_HOME you have defined in your OS environment variable.
There are clients, such as Eclipse, where you can define any version of JDK installed on your machine.
Also, if you are just launching your app using Java (and the app itself is not invoking any Java), you may be able to get away with just setting the shortcut that launches the app:
...\my\path\to\java\java.exe NameOfAppMainClassInYourJar.class
and setting the classpath as indicated here.
Related
I'm new to java programming and I haven't used any java IDE,
I intalled Java JDK 8 on my computer and been doing some coding through Notepad++ and compiling it via cmd commands.
Since now that i'm comfortable coding manually, I wanna try to use IDE and decided to get the latest "Eclipse IDE for Java Developers". what I got is actually a .zip file no installation or something which is odd.
My question is does the eclipse uses the JDK I installed on my computer or it has it's own? if so how would I know which version of java does my eclipse run?
and if does use the JDK on my computer, if I want to update the JDK intalled on my computer do I have to uninstall the old one or I can just overwrite it with the new JDK build??
Thanks,
CC
Eclipse uses externally installed JDKs to run itself (it's written in Java, after all) and to provide the core libraries for the code you write (such as the java.* packages). By default, Eclipse will use its own compiler, ECJ, that has deep integrations with the IDE to provide features such as detailed error reporting and sometimes even partial compilation of invalid classes.
It's possible to override the compiler via some plugin (for example, you can explicitly specify a compiler in a POM via m2eclipse, though the default there still uses ECJ), but that's uncommon if you're still compiling Java code.
Eclipse has support for using multiple JDKs, for example for different versions (maybe you have backwards compatibility with 1.6) or different vendors. Depending on how your OS is set up, if your main JAVA_HOME is set through a symlink, you may not need to update Eclipse at all if you perform a minor upgrade. In the case of a major upgrade, though, you will probably need to go to "Installed JREs" and add or modify an entry.
1.the jdk you installed in your computor is global situation. it can effect anywhere if you have configured the environment variables.
2.configured the environment variables,run cmd like this,the java version will be show,enter image description here
3.generally, one JDK , one computor is enough.if you want to update jdk, just download new jdk and override the old jdk .
Hopefully someone can help me because I am apparently brain dead. I have searched and read through a lot of this forum as well as others for help in resolving my problem and I am just not getting it.
I have 2 Java WebApps that I need to run for Johnson Control HVAC units. The one unit is old and strictly requires Java 1.6.0_21. There are no upgrade options available for this unit. Just hundreds of thousands of dollars to replace the whole system. But the system works just fine so I am not interested in replacing it.
Now I have another unit which my company just took over at another location that uses a similar control unit but runs on Java 1.7.0_49 or 69 I can't remember. I have both versions installed on my computer but only the newer unit with Java 1.7 works. My older one now comes up with Unable to Launch Application Error. I have tried all these things and either I am just plain doing it wrong or something else that I am not catching is up.
I tried going into the Java Control Panel and unchecking Enable 1.7. That had no affect, even after rebooting.
I went into the Environmental Variables and under Path I have no Path to Java. So I added the path to the Java 1.6 version which also had no affect.
I have a batch file on my desktop to run the older app because it's web URL is a mile long. In this batch file I tried to add set JAVA_HOME variable and a set PATH variable for Java 1.6 which also had no affect.
I tried just doing java -version:1.6 from the cmd prompt which also did not allow the program to start.
I got it so when I did java -version from the cmd prompt it would tell me 1.6.0_21 for the version but I still can't get the program to load.
So I uninstalled 1.7 from the computer and tried it again. Still would not load the program. I had to reinstall the 1.6 before the older program worked. But once I reinstalled 1.7 I was back in the same boat.
I tried re-installing both programs using the STATIC=1 command through cmd prompt and still only version 1.7 runs and the older 1.6 does not.
I do get a message when I try to load the 1.6 that says, the program has requested an older outdated version of the program. Open with new version recommended or open in the older requested version 1.6.0_21. I select open in the older version but still get the Can Not Launch Application Error.
I have also tried going into the advanced settings and unchecking Internet Explorer for the Browser in the 1.7 control panel and going into the 1.6 control panel and checking Internet Explorer.
What am I doing wrong here or what am I missing? Any help would be appreciated.
This is a Windows XP 32 bit computer. Nothing special, just a word processor mostly.
You are swimming upstream, but it isn't a very large or strong stream, and this can be done.
The upstream part is that most instructions for doing this assume you are going to run only one version of the JVM on a given machine.
The good news is that Java doesn't require this, and is not set up so that it is difficult to run two at the same time. You just have to be rigorous about where each of them get their information.
I would recommend not "installing" EITHER of them. Do not put the executables' or the libraries' directories on your path variable, and do not define a CLASSPATH variable on the machine globally. You will need to unpack a runtime environment for each JVM, each in their own directory tree.
Make one batch file to run each version. It will define its own path variable, and its own classpath (either with SET CLASSPATH= or using the classpath JVM argument).
Good luck.
My application will support only java 1.6 version and I need to execute all test cases using java 1.7 compiled class files code.
My question how to reach above requirement...
Is it possible to install both java 1.6 and java 1.7 versions in my machine?
If possible how can i set java 1.6 path for my application and how i can set path for java 1.7 version to execute test cases using java 1.7 compile files.
Application will not open with Java 1.7, but I need to use java 1.7 compiled files only.
Yes , it is possible. You need to change JAVA_HOME environmental variable. You can set it in the script that is used to start the application.
This article might help you
Yes it is possible.
You can install multiple java versions in single system.
To make it simple. You can use eclipse , or Netbeans IDE. In that you can use different java versions to compile.
Like any program, you need to specify the directory of the program you want to run, either directly by giving the full path name, or indirectly by setting an environment variable like PATH or JAVA_HOME OR JDK_HOME
You can install any number of updates/versions of Java until you run out of disk space. To configure each program to use a specific version you need to look at how they are started and set appropriate directory to use Java from for that program.
I've got a curious problem. After installing java jdk 6u25 I tested the installation by typing java in the command prompt. Everything worked fine , the console displayed the usage options as expected. This was about 3 weeks ago - I recently reinstalled windows 7 on my machine- Now I would like to get started with the play framework and followed a tutorial. I got a new application with play new but couldn't use play run because of this:
play! 1.2.3, http://www.playframework.org
Ctrl+C to stop
Could not execute the java executable, please make sure the JAVA_HOME environment variable is set properly .
The funny thing is that typing java in the console still displays usage options and neither eclipse or netbeans complained about a missing jdk. Nevertheless I checked my environment variables and was surprised to find:
No reference to java at all.
Seriously I got no idea how the console, eclipse and netbeans found my java. As a first countermeasure I once again reinstalled java hoping that the installer might set the path correctly. It didn't. Now I would like your advise: Should I just create the JAVA_HOME variable ? If I do, will further versions of the jdk override the variable to point to the new version or will I have to change the variable manually everytime? What about eclipse and netbeans. I would guess that they have been downloaded with their "own" jdk. If I want to update java on my machine, will it update their versions, too ?
Update:
I set the environment variable manually and restarted the pc. Now everything works fine but I would like to know what symbolic link is. Could you just give me a link in a comment or explain briefly ?
Eclipse and netbeans use a different way of finding your java installation than command line tools likes play, ant, maven, gradle etc.
IDEs may search your registry, guess default locations, or even have the JRE prepackaged with the installation.
Command-line tools usually rely on JAVA_HOME variable. And you have to set that manually.
Should I just create the JAVA_HOME variable ?
There are several tools that use that environment variable, so I'd recommend creating it.
If I do, will further versions of the jdk override the variable to point to the new version or will I have to change the variable manually everytime?
If you install your new Java version into the same folder (or if you create symbolic links), then no.
What about eclipse and netbeans. I would guess that they have been downloaded with their "own" jdk. If I want to update java on my machine, will it update their versions, too ?
That depends on whether the JDK is prebundled and how the configuration is done. I can't speak for Netbeans but in Eclipse, you could add this to your eclipse.ini:
-vm
C:/Java/jre/bin
Note that this is an example path to the bin folder. If you don't add versions there or use symbolic links (see above) then you'd not have to update the path when installing a new version.
It is possible that you have a (older?) java.exe in C:\windows or other common directory.
Make sure that the java you get on the command line is the one you think it is:
java -version
I make my executable jar in exe format, but I want to add JRE with this because if JRE is not present in their machine, they can use it with this included JRE.
But I do not want to install this JRE in their machine. This JRE is only used by this application only. It will just like game or other application. I use launch4j to make jar to exe but i did not find any option from where it can attach JRE and it has no option from where I can link my jar dynamically.
How do I achieve that?
If there is other free installer then mention it, and please give the procedure with example.
Since it has been established that your app. has a GUI, I will suggest Java Web Start as the answer.
But I do not want to install this JRE in their machine.
That is not a sensible requirement. The user might already have a usable JRE installed, if they don't they probably also don't want every Java based application to be installing its own 'private' JRE.
Oracle's deployJava.js can do the checking, and help guide the user through the steps of installing (which basically comes down to click 'OK' when prompted).
I make my executable jar in exe format,..
If you only intend to support Windows, what is the attraction of coding in Java? JWS supports any platform for which Java is available. That brings a lot more potential customers for the app.
I want to use free installer.
JWS is entirely free. Just like the JRE.
..please give the procedure with example.
Do you run an IDE? If not, do you otherwise have Ant installed? If that is a yes to either one, check out my small JNLP API examples. Each comes with complete source and a build file (an Ant build.xml).
Within a couple of keystrokes & a few moments, you can see the app. installed and launched on your desktop. For the end user, it is even simpler. Just click a link in a web page, and it all happens automatically (possibly with a security prompt - for the protection of the user).
I like JSmooth. You can give it a try here:
http://jsmooth.sourceforge.net/features.php
Flexible automatic Java VM detection
Detects the location of any Sun JVM installed. The wrappers use
several strategies to detect all the JVM available on a computer,
using windows registry, environment variables, windows path.
Detects
and uses Microsoft's JView (for 1.0 and 1.1 Java applications), if
available.
The JVM search sequence is fully customizable using the
GUI. You can force the executable to search in the path first, and in
the registry last, or in JAVA_HOME first. We have all the flavours!
Sometimes it's more convenient to bundle a JRE with your application.
JSmooth can deal with that too, you just need to define in which
folder the JRE is expected. It falls back nicely to a standard JVM
search if the JRE is not where it should be.
Specify which versions of
the JVM are compatible with your software. You can set a minimum
version, but also a maximum JVM version.
Documentation: http://jsmooth.sourceforge.net/docs/jsmooth-doc.html
Take a look at launch4j.
I had to use it, and it worked out very well.
You can set a minimum version of a needed JRE, bundle a JRE, or if a JRE is not found (and not bundled) the launcher may lead the user to a download location of an appropriate JRE.
There are various further features launch4j offers, and as opposed to another suggestion here, launch4j is activly developed
http://launch4j.sourceforge.net/