title: swagger read documentation from properties file
body: <p><br>
  I am trying to get Swagger to read the API documentation from a properties file <code>swagger.properties</code> but can't. In <code>@ApiOperation</code> annotation there is an error saying: <code>Attribute value must be constant</code>. Any suggestions about how to solve this and be able to read the documentation from a properties file?<br>
  Here is the Controller code:</p>
  
  <pre><code>package com.demo.student.demo.controller;
  
  import com.demo.student.demo.entity.Student;
  import com.demo.student.demo.service.StudentService;
  import io.swagger.annotations.Api;
  import io.swagger.annotations.ApiOperation;
  import org.springframework.beans.factory.annotation.Autowired;
  import org.springframework.beans.factory.annotation.Value;
  import org.springframework.web.bind.annotation.*;
  
  import java.util.List;
  
  @RestController
  @RequestMapping(value = "/v1/students")
  @Api(description = "Set of endpoints for Creating, Retrieving, Updating and Deleting of Students.")
  public class StudentController {
      private final String message;
  
      public StudentController(@Value("${test.swagger.message}") String message){
          this.message=message;
      }
  
      @Autowired
      private StudentService studentService;
  
      @GetMapping
      @ApiOperation(message)
      public List&lt;Student&gt; findAll(){
          return studentService.findAl();
      }
  
  }
  </code></pre>
  
  <p>And also, how can I inject a value at the class level in the @API(description)?</p>