我想实现一个自定义的ResponseBodyAdvice
,它只需查找Page<?>
,然后将总元素数添加到响应标头中。
@ControllerAdvice
public class PageResponseAdvice implements ResponseBodyAdvice<Object> {
@Override
public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
return Page.class.isAssignableFrom(returnType.getParameterType());
}
@Override
public Object beforeBodyWrite(Object body, MethodParameter returnType, MediaType selectedContentType, Class<? extends HttpMessageConverter<?>> selectedConverterType, ServerHttpRequest request, ServerHttpResponse response) {
((Page<?>) body).getTotalElements();
...
}
}
问题是:
为什么
body
(在beforeBodyWrite
方法中)是MappingJacksonValue
类型?有更好的方法来实现这一点吗?/我用错拦截器了吗?
我不想处理包装类,不过我只想在beforeBodyWrite
方法中使用未修改的Page
对象。
编辑:
我现在只是extend AbstractMappingJacksonResponseBodyAdvice
。这很有效,但感觉不对。也许还有人有更好的主意。
这是Page -> Content-Range Header
:的代码
@ControllerAdvice
public class PageResponseAdvice extends AbstractMappingJacksonResponseBodyAdvice {
@Override public boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType) {
return super.supports(returnType, converterType) && Page.class.isAssignableFrom(returnType.getParameterType());
}
@Override protected void beforeBodyWriteInternal(MappingJacksonValue bodyContainer, MediaType contentType, MethodParameter returnType, ServerHttpRequest request, ServerHttpResponse response) {
Page<?> page = ((Page<?>) bodyContainer.getValue());
Long from = null;
Long to = null;
if(page.getTotalElements() > 0 && page.getNumberOfElements() > 0) {
from = Integer.valueOf(page.getNumber()).longValue()*page.getSize();
to = from + page.getNumberOfElements() - 1;
}
response.getHeaders().add(
HttpHeaders.CONTENT_RANGE,
ContentRangeEncoder.encode(
"items",
from,
to,
page.getTotalElements()
)
);
response.getHeaders().add(
HttpHeaders.ACCEPT_RANGES,
"items"
);
}
}
(如果有人感兴趣的话。这是ContentRangeEncoder
):
public class ContentRangeEncoder {
private static final Pattern TYPE_PATTERN = Pattern.compile("[a-zA-Z0-9]+");
private static final Predicate<String> TYPE_PATTERN_PREDICATE = TYPE_PATTERN.asPredicate();
public static <T extends Number & Comparable<T>> String encode(String unit, T from, T to, T length) {
StringBuilder sb = new StringBuilder();
if(unit != null) {
Assert.isTrue(TYPE_PATTERN_PREDICATE.test(unit));
sb.append(unit).append(" ");
}
if(from == null && to == null) {
sb.append("*");
} else {
Assert.notNull(from);
Assert.notNull(to);
Assert.isTrue(from.compareTo(to) <= 0);
sb.append(from).append("-").append(to);
}
sb.append("/");
if(length == null) {
sb.append("*");
} else {
Assert.isTrue(to == null || length.compareTo(to) > 0);
sb.append(length);
}
return sb.toString();
}
}
至于主体类型为MappingJacksonValue
的原因,取决于您的配置和特定处理程序方法的返回值。
附带说明一下,WebMvcConfigurationSupport
将JsonViewResponseBodyAdvice
添加到RequestMappingHandlerAdapter
中,如果这个ResponseBodyAdvice
bean在您之前被调用,这将解释为什么主体是MappingJacksonValue
。主体从一个ResponseBodyAdvice
bean传递到下一个,每个bean都以它认为合适的任何"形式"返回主体。
以下是JsonViewResponseBodyAdvice
的超类"AbstractMappingJacksonResponseBodyAdvice"的摘录,以了解身体会发生什么:
public final Object beforeBodyWrite(@Nullable Object body,
MethodParameter returnType, ..., ..., ..., ...) {
//...
MappingJacksonValue container = getOrCreateContainer(body);
//...
return container;
}