Spring MVC. Default values for fields of method parameter

问题

I have a simple controller with method test:

 @RequestMapping(produces = "application/json")
    @ResponseBody
    public HttpEntity<Void> test(Test test) {
        return new ResponseEntity<>(HttpStatus.OK);
    }

Test class looks like this:

    public class Test {
    private String name;
    private Date date;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Date getDate() {
        return date;
    }

    @DateTimeFormat(iso= DateTimeFormat.ISO.DATE)
    public void setDate(Date date) {
        this.date = date;
    }
}

And I need default values for fields of Test object. If I had a primitive param, I would be able to use @RequestParam(required = false, defaultValue = "someValue"). But with non-primitive param this approach doesn't seem to work. I see a couple of variants how to deal with it:

Assign values in a constructor. Not very good, because may be I will need different defaults for different methods.
Write custom DataBinder. Better, but the problem with different defaults still exists.
Write custom DataBinder and custom annotation with defaults.

Am I missing something and there is a built in feature which can solve my problem?

回答1:

You can lean on argument resolving, in four easy steps, similiar as you suggested in your third point.

Create an annotation e.g.

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface TestDefaultValues {
    String[] value();
}

Write a resolver e.g.

public class TestArgumentResolver implements HandlerMethodArgumentResolver {

    public boolean supportsParameter(MethodParameter parameter) {
        return parameter.getParameterAnnotation(TestDefaultValues.class) != null;
    }

    public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer mavContainer, NativeWebRequest webRequest,
            WebDataBinderFactory binderFactory) throws Exception {
        TestDefaultValues attr = parameter.getParameterAnnotation(TestDefaultValues.class);
        String[] value = attr.value();
        Test test = new Test();
        test.setName(value[0]);
        test.setDate(new Date(value[1]));
        return test;
    }

}

<mvc:annotation-driven>
        <mvc:argument-resolvers>
            <bean class="your.package.TestArgumentResolver"></bean>
        </mvc:argument-resolvers>
</mvc:annotation-driven>

use an annotation in your controller method e.g.

 public HttpEntity<Void> test(@TestDefaultValues({"foo","11/12/2014"}) Test test) {

instantiating date is just to get the gist of the implementation, obviously you'll use whatever is your idea

来源：https://stackoverflow.com/questions/29469887/spring-mvc-default-values-for-fields-of-method-parameter

标签

java

Spring

spring-mvc