Adding up to @Joni's answer, you can get the Java installation directory from the registry and use script constants to set your environment variable:
(EDIT: thanks to @TLama for code correction!)
[Registry]
Root: HKCU; Subkey: "Environment"; ValueType:string; ValueName:"JAVA_HOME"; ValueData:"{code:GetJava32Path|6}"; Flags: preservestringtype
[Code]
const
RegKeyJRE = 'SOFTWARE\JavaSoft\Java Runtime Environment\';
function GetJava32Path(MinVersion: string): string;
var
I: Integer;
Path: string;
Versions: TArrayOfString;
begin
Result := '';
if RegGetSubkeyNames(HKLM, RegKeyJRE, Versions) then
for I := 0 to GetArrayLength(Versions)-1 do
if (Versions[I][2] = '.') and (Versions[I][3] >= MinVersion) and
RegQueryStringValue(HKLM32, RegKeyJRE + Versions[I], 'JavaHome', Path) then
begin
Result := Path;
Exit;
end;
end;
(N.B. I'm far from being a Pascal-script expert, the code could be a lot better, though now it was corrected by @TLama :))