Check Java is present before installing

Question

I\'m creating an Inno Setup installer for a jar app. What I want to do right now is to check if java is present before proceeding with the install. So I only need to be sure the

Answer 1

There is another way now. You can include a Stub setup - online installer, which will download and install actual setup.
The filename name as for now is JavaSetup8u121.exe, which suggests it might be version specific. I don't have an older one to test if it will download actual or specific, older version.
And for now, it seems it only does install 32bit JRE.

[Files]
#define JavaInstaller "JavaSetup8u121.exe"
Source: "include\{#JavaInstaller}"; DestDir: "{tmp}";

[Code]
const
  REQUIRED_JAVA_VERSION = '1.7';

function isJavaInstalled(): Boolean;
var
  JavaVer : String;
  tmpFileName,
  pathJavaExe: String;
  isGoodJavaVersion,
  isFoundJavaPath: Boolean;
  ResultCode: Integer;
  ExecStdout: AnsiString;
begin

  { *** check in registry }
  { sets variables: }
  {   JavaVer }
  {   isGoodJavaVersion }
  if RegQueryStringValue(HKLM, 'SOFTWARE\JavaSoft\Java Runtime Environment',
           'CurrentVersion', JavaVer) AND (JavaVer <> '') OR
     RegQueryStringValue(HKLM64, 'SOFTWARE\JavaSoft\Java Runtime Environment',
           'CurrentVersion', JavaVer) AND (JavaVer <> '') then begin
    Log('* Java Entry in Registry present. Version: ' + JavaVer);
    isGoodJavaVersion := CompareStr(JavaVer, REQUIRED_JAVA_VERSION) >= 0;
  end;

  { add additional checks, for example by searching the PATH, }
  { or by running `java -version` }

  Result := isGoodJavaVersion;
end;

[Run]
Filename: "{tmp}\{#JavaInstaller}"; Parameters: "SPONSORS=0"; \
   StatusMsg: "Java Runtime Enviroment not installed on your system. Installing..."; \
   Check: not isJavaInstalled

Searches for 32 and 64 bit versions in registry, internal function CompareStr() is actually usable for comparing versions in String, you can change >= 0 to =0 if you want to check against the exact version and not 'at least'.

Alternatively Exec() could be used instead of [Run], if you want to cancel the whole install in case when the user will not go through with the Java install by cancelling it or because of an error.