Java: block System.exit() using a SecurityManager

no-system-exit.jsp

<%--
  JSP page that demonstrates blocking System.exit()
  with a SecurityManager.
  Do NOT use on production systems unless you know
  EXACTLY what you are doing!
--%>
<%@page 
  contentType="text/plain" 
  pageEncoding="UTF-8"
  import="
    java.lang.SecurityManager,
    java.lang.SecurityException,
    java.security.Permission,
    java.util.Date
  "
%>
<%!
private static class ExitBlocker extends SecurityManager {
    
  static void activate() {
    System.setSecurityManager(new ExitBlocker());          
  }
  
  /** Block System.exit */    
  public void checkExit(int status) {
    throw new SecurityException("Blocking System.exit at " + new Date()
        + ", check stack trace to find out where it was called");
  }
  
  /** Allow everything else */
  public void checkPermission(Permission perm) {
  }
}

/** Use a named class so it shows in the stack trace for our demo */
private static class ExitCommand {
    ExitCommand() {
        System.exit(42);
    }
}
%>

<%
if(request.getParameter("exit") != null) {
    %>Attempting System.exit()!<%
  new ExitCommand();
} else {
  ExitBlocker.activate();
}
%>
    
All good, <%= System.getSecurityManager() %> is active!