Selecting the correct Java, JRE and JDK versions when building an executable JAR for distribution?

Question

I am putting together my first Java package for distribution to users, and am running into some difficulties. I have jar packages that I've built that users can't run; the error messages vary, but are all "version" something or another. I suspect I'm selecting the wrong build paths, and I'm not quite sure where to start troubleshooting because I don't clearly understand the differences between the Java executable ( javaw.exe ), the JDK and the JRE; I have some questions that I'd like answered which will help in that understanding. I'm used to the way that C# executables compile in VS; wrapping my head around how executable jar files come together is still a little mysterious to me.

Although I've done a few google searches, most of what I'm finding is how to build a jar file, but not how to manipulate/use/select the Java, JRE and JDK versions appropriately to ensure compatibility. I do understand that the JRE includes the virtual machine that allows Java bytecode to run anywhere, and that the JDK includes development tools...but as to figuring out which version I AM running, vs which version is used when building jar files and which version SHOULD be used...I am completely lost.

I'm using Eclipse Indigo under 64-bit Win7. My build path includes the following:

JRE System Library: C:\\Program Files\\java\\jre7\\*

External paths: C:\\<MyDocuments>\\java\\lib\\commons-io-2.4*

I also have, installed on my machine, the following paths which are NOT included in the build:

C:\Program Files (x86)\java\jre7\
C:\Program Files (x86)\java\jre1.5.0_22\
C:\Program Files (x86)\java\jdk1.7.0_21\

The users that will be running this executable file are only supported (by corporate IT) up to JRE5. I suspect that my building this pointing it jre7 is one of the things that's messing with me.

My first stupid question is whether there's a difference between "Java" and the "JRE" when it comes to version numbers. For instance, when I read about JavaSE7 or JavaEE7, are they talking about the JRE version for the standard or enterprise editions? Are the development kits and runtime environments just components to JavaSE/EE? Or are they separate and distinct products?

Then, my understanding is that I should build this jar using the lowest-common-denominator JRE expected from my users. In this particular case, because the corporate standard is JRE5, I should build this pointing to JRE5 instead of JRE7. Is that a correct assumption?

Does it matter if I build using the 64bit or 32bit version? Some older machines may still be 32bit running JRE5, so I need to make sure I'm backwards compatible.

The Program Files (x86) naming conventions confuse me. JRE7 installed as \\jre7 . However, JRE5 installed as \\jre1.5.0_22 , and I also have jdk1.7.0_21 , which, based on the JRE name, I assume to be the Java7 Development Kit. Do I need to install the Java5 Development Kit to properly build this program? And am I properly interpreting the versions from the filenames? that 1.5 represents Java5 and 1.7 represents Java7?

Then, my last question I know there's an Eclipse option to copy the external libraries to the project. I assume that if I do this, this will be included with the jar so the users do NOT need to have the Apache Commons jars on their local machines in order for this to run properly. Does the manifest include any confirmations that these files were included? I've been unable to find any references...so I'm trying to verify if I'm even pulling the Commons libraries over and where to look to get that confirmation.

Answer 1

This is just speculation, but I think you may have to re-write the program with the java5 jdk, because some of the APIs/libraries used in java7's jdk may not be recognized by the java5 jre. (Just like it wouldn't be possible to play PS4 games on a PS2... without any serious modding)

If you write the program in Eclipse, you can just select what library you want to use as you create the Java project. At the "Create a Java Project" screen, you can select the "Use an execution environment JRE:" or "Use a project specific JRE" or "Use default JRE" option. (I have jdk6 and jdk7 installed on my computer so I'm able to select those two options; which is why you may have install the jdk5 in order to create a java 5 project.)

You are properly interpreting the filenames. jre1.5.0_22 is java 5 update 22.

There is a way to specify which JRE is used to run the jar file.

cmd prompt > "C:\\Program Files (x86)\\java\\jre1.5.0_22\\bin\\javaw.exe" -jar "filepath_filename.jar"

Drop the "w" from the javaw.exe, and you'll be able to see any console and/or stack trace output.