Spring @Controllers, @Services, and @Repositorys are singletons by default, meaning only one instance of the class is ever instantiated in the application. Typically such a class might have a few static members, such as a logger, but all non-static members should be managed by Spring. That is, they should have the @Autowired annotation.

Having non-@Autowired members in one of these classes could indicate an attempt to manage state. Because they are singletons, such an attempt is almost guaranteed to eventually expose data from User1's session to User2.

This rule raises an issue when a singleton @Controller, @Service, or @Repository has non-static, non-@Autowired members.

Noncompliant Code Example

@Controller
public class HelloWorld {

  private String name = null;

  @RequestMapping("/greet", method = GET)
  public String greet(String greetee) {

    if (greetee != null) {
      this.name = greetee;
    }

    return "Hello " + this.name;  // if greetee is null, you see the previous user's data
  }
}