How to create a Spring Interceptor for Spring RESTful web services

Question

I have some Spring RESTful (RestControllers) web services with no web.xml and I am using Spring boot to start the services.

I want to add authorization layer for the web services and wanted to route all the http requests to one front controller before actually calling the web service itself. (I have a code to simulate sessions behavior at the autherisation layer, to validate a user based on a generated key that I send with each of the httpRequest from the client).

Is there any Standard Spring solution on routing all the requests to a filter /front controller?

Thanks in advance, Praneeth

Edit: Adding my code

Controller: `

@RestController
public class UserService {
    UserDAO userDAO = new UserDAO();

    @RequestMapping(value="/login", method = RequestMethod.POST)
    @LoginRequired
    public String login(@RequestParam(value="user_name") String userName, @RequestParam(value="password") String password, HttpServletRequest request){
        return userDAO.login(userName, password);
    }
}`

Interceptor:

`

public class AuthenticationInterceptor implements HandlerInterceptor  {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler)
        throws Exception {
        System.out.println("In Interceptor");
        //return super.preHandle(request, response, handler);
        return true;
    }
    @Override
    public void postHandle( HttpServletRequest request, HttpServletResponse response,
            Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("---method executed---");
    }
    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response,
            Object handler, Exception ex) throws Exception {
        System.out.println("---Request Completed---");
    }
}

`

Interface. `

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
public @interface LoginRequired {
}

`

Answer 1

Following steps can be taken to implement the interceptor with Spring:

• Implement an interceptor class extending HandlerInterceptorAdapter class. Following is how the code could look like:

  public class LoginInterceptor extends HandlerInterceptorAdapter {
  
      @Override
      public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception exception)
      throws Exception {
      // TODO Auto-generated method stub
  
      }
  
      @Override
      public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView)
      throws Exception {
      // TODO Auto-generated method stub
  
      }
  
      @Override
      public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
  
          HandlerMethod handlerMethod = (HandlerMethod) handler;
  
          String emailAddress = request.getParameter("emailaddress");
          String password = request.getParameter("password");
  
          if(StringUtils.isEmpty(emailAddress) || StringUtils.containsWhitespace(emailAddress) ||
          StringUtils.isEmpty(password) || StringUtils.containsWhitespace(password)) {
              throw new Exception("Invalid User Id or Password. Please try again.");
          }
  
          return true;
      }
  
  
  }
  

• Implement an AppConfig class or add the addInterceptors in one of the existing Configuration class. Note the path pattern specified with the LoginInterceptor instance

  @Configuration  
  public class AppConfig extends WebMvcConfigurerAdapter  {  
  
      @Override
      public void addInterceptors(InterceptorRegistry registry) {
         registry.addInterceptor(new LoginInterceptor()).addPathPatterns("/account/login");
      }
  } 
  

• Implement the controller method such as following:

  @Controller
  @RequestMapping("/account/login")
  public class LoginController {
  
      @RequestMapping(method = RequestMethod.GET)
      public String login() {
          return "login";
      }
  }