Setting the JAVA_HOME environment variable

Many Java programs launched from batch files, such as Ant and Cocoon, check for
the JAVA_HOME environment variable. If it is missing, the program may not
start, or it may display a message such as
Warning: JAVA_HOME environment variable is not set.

How do I check whether JAVA_HOME exists?

If you are not sure the variable exists,
you can easily check on Windows. Run
set > vystup.txt or simply set
at the command prompt (Start >> Run >> cmd). In the first case,
the output is written to vystup.txt, and in the second it is printed
on the screen. If the variable exists, it will appear in output
like the following:

[In this example output, identifiers and network paths have been replaced with fictional examples.]

ALLUSERSPROFILE=C:\Documents and Settings\All Users
  APPDATA=C:\Documents and Settings\example-user\Application Data
  COMMANDER_PATH=C:\Tools\TotalCommander
  CommonProgramFiles=C:\Program Files\Common Files
  COMPUTERNAME=EXAMPLE-WORKSTATION
  ComSpec=C:\WINNT\system32\cmd.exe
  HOMEDRIVE=H:
  HOMEPATH=\\example.invalid\example-share\example-user
  JAVA_HOME=c:\tools\Java\j2sdk1.4.2_02

Where should JAVA_HOME point?

JAVA_HOME must point to the directory where
Java is installed. That directory directly contains the bin and lib directories.
If Java is installed in c:\tools\Java\j2sdk1.4.2_02 (and c:\tools\Java\j2sdk1.4.2_02\bin and c:\tools\Java\j2sdk1.4.2_02\lib exist),
set JAVA_HOME to c:\tools\Java\j2sdk1.4.2_02.

Where do I set JAVA_HOME?

The simplest and somewhat laborious way is to add a line to the startup batch file:
set JAVA_HOME=adresář Javy, for example JAVA_HOME=c:\tools\Java\j2sdk1.4.2_02. A more
elegant option is to set JAVA_HOME as an environment variable
as follows on Windows:

My Computer >> System Properties >> Advanced >> Environment Variables

In the Environment Variables window you have two choices. A user variable applies
only to one user, and a system variable is visible to all users.
I recommend creating a system variable and restarting
the computer afterward.