When dealing with Windows services (like Tomcat) that need environment variables, you'll quickly discover that simply setting variables in System Properties won't work for services. Windows services run under different contexts and don't inherit user-level environment variables.

The common methods don't work because:

• System environment variables (set via Control Panel) won't propagate to existing services
• User-level variables never reach services running under SYSTEM or specific service accounts
• .bat file variables only work for manual startup, not service-controlled processes

For Tomcat specifically (but applicable to any Windows service), follow these steps:

1. Open command prompt as Administrator
2. Stop the Tomcat service: net stop Tomcat9
3. Use SC command to set environment:
   sc config Tomcat9 binPath= "\"C:\path\to\tomcat\bin\tomcat9.exe\" //US//Tomcat9 --Environment=\"MY_VAR=my_value\""
4. Start the service: net start Tomcat9

For system-wide persistence across reboots:

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tomcat9\Parameters]
"Environment"=hex(7):4d,00,59,00,5f,00,56,00,41,00,52,00,3d,00,6d,00,79,00,76,\
  00,61,00,6c,00,75,00,65,00,00,00,00,00

Note: The hex value represents "MY_VAR=my_value" in UTF-16 format.

After implementing either solution, verify in your Java webapp:

@WebServlet("/env")
public class EnvServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) 
      throws ServletException, IOException {
        String myVar = System.getenv("MY_VAR");
        response.getWriter().println("MY_VAR value: " + myVar);
    }
}

• Always restart the service after making changes
• For Tomcat, check catalina.out if the variable doesn't appear
• Use Process Explorer to verify environment variables in running processes
• Test with simple values before moving to production configuration

When dealing with Windows services (like Tomcat running as a service), environment variables behave differently compared to regular console applications. The service control manager doesn't inherit user-level environment variables, which creates headaches for Java developers needing to access them via System.getenv().

Method 1: Registry Modification (Permanent Solution)

Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tomcat8\Parameters\Environment]
"MY_VAR"="your_value_here"

Save as tomcat_env.reg and merge. Requires service restart.

Method 2: Service Wrapper Configuration

For Tomcat specifically, edit service.bat installer script:

set SERVICE_ENV=MY_VAR=your_value
tomcat8 //US//%SERVICE_NAME% ++Environment "%SERVICE_ENV%"

Using Java System Properties Instead

// In catalina.bat or setenv.bat
set "JAVA_OPTS=%JAVA_OPTS% -DMY_VAR=your_value"

// Java access:
String myVar = System.getProperty("MY_VAR");

PowerShell Deployment Script

$service = Get-WmiObject -Class Win32_Service -Filter "Name='Tomcat8'"
$service.Change($null,$null,$null,$null,$null,$null,"MY_VAR=your_value",$null,$null,$null,$null)
Restart-Service -Name Tomcat8

• Always restart the service after changes
• Check environment in-process using Java Management MXBeans
• For Tomcat, verify setenv.bat isn't overriding your variables