🌱 Spring @RequestParam @ResponseBody

public @interface RequestParam {

	@AliasFor("name")
	String value() default "";

	@AliasFor("value")
	String name() default "";

	boolean required() default true;

	String defaultValue() default ValueConstants.DEFAULT_NONE;

}

@GetMapping("hello-string")
@ResponseBody
public String helloString(@RequestParam("name") String name) {
    return "hello " + name;
}

@GetMapping("hello-string")
@ResponseBody
public String helloString(String name) {
    return "hello " + name;
}

package org.springframework.web.method.annotation;
...

public class RequestParamMethodArgumentResolver extends AbstractNamedValueMethodArgumentResolver
		implements UriComponentsContributor {

	...

	@Override
	protected NamedValueInfo createNamedValueInfo(MethodParameter parameter) {
		RequestParam ann = parameter.getParameterAnnotation(RequestParam.class);
		return (ann != null ? new RequestParamNamedValueInfo(ann) : new RequestParamNamedValueInfo());
	}

	...

}

private static class RequestParamNamedValueInfo extends NamedValueInfo {

		public RequestParamNamedValueInfo() {
			super("", false, ValueConstants.DEFAULT_NONE);
		}

		public RequestParamNamedValueInfo(RequestParam annotation) {
			super(annotation.name(), annotation.required(), annotation.defaultValue());
		}
	}

@GetMapping("hello-api")
@ResponseBody
public Hello helloApi(@RequestParam("name") String name) {
    Hello hello = new Hello();
    hello.setName(name);
    return hello;
}

static class Hello {
    private String name;

    public String getName() {
        return name;
    }

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

Exception processing template "hello-api": Error resolving template [hello-api], template might not exist or might not be accessible by any of the configured Template Resolvers

public interface HttpMessageConverter<T> {

	boolean canRead(Class<?> clazz, @Nullable MediaType mediaType);

	boolean canWrite(Class<?> clazz, @Nullable MediaType mediaType);

	List<MediaType> getSupportedMediaTypes();

	default List<MediaType> getSupportedMediaTypes(Class<?> clazz) {
		return (canRead(clazz, null) || canWrite(clazz, null) ?
				getSupportedMediaTypes() : Collections.emptyList());
	}

	T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
			throws IOException, HttpMessageNotReadableException;

	void write(T t, @Nullable MediaType contentType, HttpOutputMessage outputMessage)
			throws IOException, HttpMessageNotWritableException;

}

public abstract class AbstractJackson2HttpMessageConverter extends AbstractGenericHttpMessageConverter<Object> {
		...
}