JRE : Java Glossary

Java Runtime Environment. This is the subset of Sun’s Java Development Kit JDK/SDK that you can ship with your application. It is free.

The JRE, described here, is for people who just want to run Java programs or browse Applets on the web. You must use the much larger JDK if you want to write your own Java programs. You don’t need both.

Downloading the JRE	Multiple JREs
Testing Your JRE	Links
Silent JRE Installs

Downloading the JRE

You can find the various downloads with your browser.

Sun’s Download SDM

(Sun Download Manager) then manage your downloads. SDM is more awkward to use since you must determine the URLs and paste them into it. Its main function is recovering from partly completed downloads. It is probably not worth the bother unless you have a dial-up connection.

For Vista, make sure you are logged in as an administrator before you install. Some suggest it is best also to turn on UAC (that irritating Visa User Account control) during the install. The downloads are labeled as updates, but they are complete in themselves. You don’t need to install a previous version.

Below is how to get Java for Windows, Linux and Solaris. For other platforms (e.g. various Unices) see your OS vendor’s site. For example for NetBSD Unix Java is included in pkgsrc (the Packages System).

Version	Executables	Notes
JRE 1.6.0_17 (current)	Download 16 Mb self-installing executable. Look for the fourth entry, Java Runtime Environment (JRE) 6 Update 16. Then click Download. Then tick the licence agreement and Click Windows off-line Installation, Multi-language. This is most likely the version you want to download. For Vista, make sure you are logged in as an administrator before you install. The install will work more smoothly if you launch the install of the download with “run as administrator” and if you have UAC turned on.	The download includes the Java Plug-in for Applets and Java Web Start. It includes the JVM and the standard class library files, but no source, and no javac.exe. It does not include JavaMail or JAF. It will install in C:\Program Files\java\jre6. If you want to write your own Java programs, install the JDK instead.
any older JRE	In the Sun’s documentation on archives you can find nearly every JRE Sun ever released, using a fill in the blanks description of what you want.	If you get a broken link try composing the URL from this pattern: http://java.sun.com/products/archive/j2se/5.0_18/index.html
JRE 1.5.0_22 (old)	Sun’s documentation on download ( 15.8 mb ) Look under Java Runtime Environment (JRE) 5.0 Update 21.	It includes the Java Plug-in and Java Web Start. It includes the JVM and the standard class library files, but no source, and no javac.exe. It does not include JavaMail or JAF. JRE version 1.5 is slated for end of life 2009-10-30, last updated on 2009-09-08.
JRE 1.4.2_19 (old)	Download	It includes the Java Plug-in and Java Web Start. It includes the JVM and the standard class library files, but no source, and no javac.exe. It does not include JavaMail or JAF. No longer supported.
JRE 1.3.1 (old)	Download	It includes the Java Plug-in. It includes the JVM and the standard class library files, but no source, and no javac.exe. No longer supported.
JRE 1.2 (old)	Download	It includes the JVM and the standard class library files, but no source, and no javac.exe. The java.exe file it contains is renamed to jre.exe. No longer supported.

You might want to manually set your JAVA_HOME environment variable to the JRE directory e.g. C:\Program Files\java\jre6. Some software finds Java using this variable rather than poking around in the registry.

Polishing and Testing Your JRE

Testing your JRE is more complicated that you might expect. You want to find out if Java is working properly on the desktop, and in each of your browsers. Further, you want to test that Java Web Start is working properly on the desktop, and in each of your browsers. Just because Java/Java Web Start works in one browser, does not mean it will automatically work in another.

Configure your set environment for the CLASSPATH. If you are not sure use CLASSPATH=. See environment for details of how. See classpath for details.
Copy your various library jars into the C:\Program Files\java\jre6\lib\ext directory.Sooner or later you will have to reinstall the JDK/JRE and you will lose your ext directories. You can quickly rebuild them if you maintain a bat file like this and run it after every JRE/JDK install. Adjust the file to account for where your ext dirs are and where the jars are you need.
In Internet Explorer, go into Tools ⇒ Internet option ⇒ Advanced ⇒ Java(Sun). Make sure Sun Java is checked.
In Internet Explorer, make sure all three boxes under Tools Internet option ⇒ Advanced ⇒ Microsoft VM are checked.
In Internet Explorer 7+, you must OK allow blocked content permission to run Active X on the site, (even your own when running off-line). This also gives permission to run Java. Since Java is perfectly safe because it runs it a sandbox, logically it should not need special permission. This roadblock to Java is just part of Microsoft’s war on Sun and Java.
Test your JRE on the desktop by typing in a DOS box:
```
java.exe -version
```
You should see the expected version you just installed, probably 1.6.0_17. It can be problematic to have more than one version installed at a time.
Run Sun’s formal Applet test of the Java JRE in a browser.
Test your JRE browser’s ability to run Applets by running Sun’s
Sun’s documentation on Sort demo
.
Test your JRE browser’s ability to run signed Applets by running Wassup.
It should tell you that your browser is using the JVM version you just installed, probably 1.6.0. Look for the line marked java.version. If Wassup does not run, or you have the wrong version, go into Settings ⇒ Control Panel ⇒ Java Plug-In ⇒ Browser and turn off each browser, then click apply, then turn them on again, then hit apply again. Then retest with Wassup. If that still does not work, turn on the Java console, try Wassup again and look for clues.
Test Java Web Start on the desktop by typing javaws.exe and running any sample application.
Check that the associations for the *.jnlp extension is set to point to the appropriate javaws.exe and *.jar is set to point to javaw.exe. Confirm this in any My Computer directory display with tools ⇒ folder options ⇒ file types.
Set up associations for *.jar files to make them double clickable, following the instructions here.
Check that Java Web Start is working in each browser by testing SetClock. Click SetClock to test.
Check the Opera browser’s quick preferences to make sure you have Java enabled. Turn on the console with tools ⇒ advanced ⇒ Java console to get some hints why it may not be working. Make sure Opera has *.jnlp files associated with mime type application-x-java-jnlp-file in preferences ⇒ files.
If you can’t get it to work, follow the failed install instructions.

Silent JRE Installs

If you want to install the JRE on many machines, or an install triggered by an utter novice, you would prefer a command-line style install that did not ask any questions as it progressed. That is called a silent install. It does not mean stealthily installing the JRE or other app on a machine without the owner’s notice.

Sun’s JDK Technote Guide on silent JRE installs : available:

on the web at java.sun.com
in the current JDK 1.6.0_17 on your local Windows J: drive.

Linux

Installing a JRE under Linux is much more complicated that under Windows. You need to perform half a dozen manual installation steps. You also need to set up a soft link from each of your browser plug-ins to the corresponding Java *.so libraries. Download and study the install instructions. You will never guess them. Consult your browser for documentation on the soft links.

Multiple JREs

If you want to install multiple JREs, first uninstall all your JDKs and JREs, then install the JREs and JDKs the oldest version first and install them in order. If you want the JDK, there in no need to install the corresponding JRE as well.

Then instead of saying java.exe, use the fully qualified name to select which version of the java run time you want e.g. C:\Program Files\java\jre6\bin\java.exe.

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