Logo Questions Linux Laravel Mysql Ubuntu Git Menu
 

Spring Boot Controller - Enum parameter as Value

I have a spring boot controller, one of my parameters is an Enum. The enum has a string value. I want to pass as the parameter the value of the enum and the controller to give me the Enum. Can this be done?

 @RequestMapping(value = "/")
public MyResponse getResponse ( @RequestParam(value = "version") final ProjectVersion version ) {
   ...bla bla bla...
}

public enum ProjectVersion {
    VERSION_1 ("1.00")
    VERSION_2 ("2.00")

    private final String version;

    ProjectVersion ( String version ) {
        this.version = version;
    }

     @Override
     public String toString() {
        return this.version;
     }

}

I want to be able to make a request as follows:

http://myhost.com/mypath?version=1.00

And get in the controller the ProjectVersion.VERSION_1

Any ideas?

like image 272
Panos Avatar asked Apr 06 '17 09:04

Panos


People also ask

How do you pass enum as parameter in spring boot?

Use Enums as Request Parameters mode=ALPHA, the request parameter is a String object. Spring can try to convert this String object to an Enum object by using its StringToEnumConverterFactory class. The back-end conversion uses the Enum. valueOf method.

Can enum be used as variable value?

An enum type is a special data type that enables for a variable to be a set of predefined constants. The variable must be equal to one of the values that have been predefined for it.

Can you use an enum as a parameter in Java?

Yes, you can pass enum constants to methods, but you shouldn't use the 'enum' keyword in the method declaration, just like you don't use the 'class' keyword in a method declaration.

Can we assign value to enum?

You can assign different values to enum member. A change in the default value of an enum member will automatically assign incremental values to the other members sequentially.


2 Answers

This is not possible as is. You have to create your custom converter to convert from a String to ProjectVersion.

For example first defines the converter from a String to ProjectVersion:

public class ProjectVersionConverter implements ConditionalGenericConverter {

  @Override
  public boolean matches(TypeDescriptor sourceType, TypeDescriptor targetType) {
    return targetType.getType().equals(ProjectVersion.class);
  }

  @Override
  public Set<ConvertiblePair> getConvertibleTypes() {
    return Collections.singleton(new ConvertiblePair(String.class , ProjectVersion.class));
  }

  @Override
  public Object convert(Object source, TypeDescriptor sourceType, TypeDescriptor targetType) {
    return ProjectVersion.findByVersion((String)source);
  }
}

Then register it:

@Configuration
public class CustomWebMvcConfigurerAdapter extends WebMvcConfigurerAdapter {

  @Override
  public void addFormatters(FormatterRegistry registry) {
    registry.addConverter(new ProjectVersionConverter());
  }
}

You can skip the registration if you define ProjectVersionConverter as a Spring bean. (This code has not be tested).

like image 68
Nicolas Labrot Avatar answered Sep 24 '22 02:09

Nicolas Labrot


Because you need to pass (for each request) the argument to the Controller method, the clean solution would be to use HandlerMethodArgumentResolver, so that Spring container can dynamically inject your ProjectVersion argument to the Controller method as shown below:

ProjectVersionArgumentResolver class:

public class ProjectVersionArgumentResolver implements 
                                    HandlerMethodArgumentResolver {

    @Override
    public boolean supportsParameter(MethodParameter methodParameter) {
        return methodParameter.getParameterType().equals(ProjectVersion.class);
    }

    @Override
    public Object resolveArgument(MethodParameter methodParameter,
                   ModelAndViewContainer modelAndViewContainer,
                   NativeWebRequest nativeWebRequest,
                   WebDataBinderFactory webDataBinderFactory) throws Exception {

        return ProjectVersion.fromString(nativeWebRequest.getParameter("version"));
    }
}

Spring-boot ApplicationLauncher class:

public class MyProjectApplicationLauncher extends WebMvcConfigurerAdapter {

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> 
                                           argumentResolvers) {
        //add the new resolver
        argumentResolvers.add(new MyMethodArgumentResolver());
    }

    public static void main(String[] args) {
        SpringApplication.run(MyProjectApplicationLauncher.class, args);
    }
} 

ProjectVersion class:

public enum ProjectVersion {

    //add your existing code

    //Add fromString method to convert string to enum 
    public static ProjectVersion fromString(String input) {
        for (ProjectVersion projectVersion : ProjectVersion.values()) {
          if (projectVersion.version.equals(input)) {
            return projectVersion;
          }
        }
        return null;
     }
}
like image 32
developer Avatar answered Sep 24 '22 02:09

developer