Spring RequestMapping for controllers that produce

问题:

With multiple Spring controllers that consume and produce application/json, my code is littered with long annotations like:

    @RequestMapping(value = "/foo", method = RequestMethod.POST,
            consumes = MediaType.APPLICATION_JSON_VALUE,
            produces = MediaType.APPLICATION_JSON_VALUE)

Is there a way to produce a "composite/inherited/aggregated" annotation with default values for consumes and produces, such that I could instead write something like:

    @JSONRequestMapping(value = "/foo", method = RequestMethod.POST)

How do we define something like @JSONRequestMapping above? Notice the value and method passed in just like in @RequestMapping, also good to be able to pass in consumes or produces if the default isn't suitable.

I need to control what I'm returning. I want the produces/consumes annotation-methods so that I get the appropriate Content-Type headers.

回答1:

As of Spring 4.2.x, you can create custom mapping annotations, using @RequestMapping as a meta-annotation. So:

Is there a way to produce a "composite/inherited/aggregated" annotation with default values for consumes and produces, such that I could instead write something like:

@JSONRequestMapping(value = "/foo", method = RequestMethod.POST)

Yes, there is such a way. You can create a meta annotation like following:

@Target({ElementType.METHOD, ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@RequestMapping(consumes = "application/json", produces = "application/json")
public @interface JsonRequestMapping {
    @AliasFor(annotation = RequestMapping.class, attribute = "value")
    String[] value() default {};

    @AliasFor(annotation = RequestMapping.class, attribute = "method")
    RequestMethod[] method() default {};

    @AliasFor(annotation = RequestMapping.class, attribute = "params")
    String[] params() default {};

    @AliasFor(annotation = RequestMapping.class, attribute = "headers")
    String[] headers() default {};

    @AliasFor(annotation = RequestMapping.class, attribute = "consumes")
    String[] consumes() default {};

    @AliasFor(annotation = RequestMapping.class, attribute = "produces")
    String[] produces() default {};
}

Then you can use the default settings or even override them as you want:

@JsonRequestMapping(method = POST)
public String defaultSettings() {
    return "Default settings";
}

@JsonRequestMapping(value = "/override", method = PUT, produces = "text/plain")
public String overrideSome(@RequestBody String json) {
    return json;
}

You can read more about AliasFor in spring's javadoc and github wiki.

回答2:

The simple answer to your question is that there is no Annotation-Inheritance in Java. However, there is a way to use the Spring annotations in a way that I think will help solve your problem.

@RequestMapping is supported at both the type level and at the method level.

When you put @RequestMapping at the type level, most of the attributes are 'inherited' for each method in that class. This is mentioned in the Spring reference documentation. Look at the api docs for details on how each attribute is handled when adding @RequestMapping to a type. I've summarized this for each attribute below:

• name: Value at Type level is concatenated with value at method level using '#' as a separator.
• value: Value at Type level is inherited by method.
• path: Value at Type level is inherited by method.
• method: Value at Type level is inherited by method.
• params: Value at Type level is inherited by method.
• headers: Value at Type level is inherited by method.
• consumes: Value at Type level is overridden by method.
• produces: Value at Type level is overridden by method.

Here is a brief example Controller that showcases how you could use this:

package com.example;

import org.springframework.http.MediaType;
import org.springframework.web.bind.annotation.*;

@RestController
@RequestMapping(path = "/", 
        consumes = MediaType.APPLICATION_JSON_VALUE, 
        produces = MediaType.APPLICATION_JSON_VALUE, 
        method = {RequestMethod.GET, RequestMethod.POST})
public class JsonProducingEndpoint {

    private FooService fooService;

    @RequestMapping(path = "/foo", method = RequestMethod.POST)
    public String postAFoo(@RequestBody ThisIsAFoo theFoo) {
        fooService.saveTheFoo(theFoo);
        return "http://myservice.com/foo/1";
    }

    @RequestMapping(path = "/foo/{id}", method = RequestMethod.GET)
    public ThisIsAFoo getAFoo(@PathVariable String id) {
        ThisIsAFoo foo = fooService.getAFoo(id);
        return foo;
    }

    @RequestMapping(path = "/foo/{id}", produces = MediaType.APPLICATION_XML_VALUE, method = RequestMethod.GET)
    public ThisIsAFooXML getAFooXml(@PathVariable String id) {
        ThisIsAFooXML foo = fooService.getAFoo(id);
        return foo;
    }
}

回答3:

You can use the @RestController instead of @Controller annotation.

回答4:

You shouldn't need to configure the consumes or produces attribute at all. Spring will automatically serve JSON based on the following factors.

• The accepts header of the request is application/json
• @ResponseBody annotated method
• Jackson library on classpath

You should also follow Wim's suggestion and define your controller with the @RestController annotation. This will save you from annotating each request method with @ResponseBody

Another benefit of this approach would be if a client wants XML instead of JSON, they would get it. They would just need to specify xml in the accepts header.

回答5:

There are 2 annotations in Spring: @RequestBody and @ResponseBody. These annotations consumes, respectively produces JSONs. Some more info here.