jersey/jackson-基于查询参数的过滤器属性

Question

使用Jackson过滤掉属性非常简单：

final FilterProvider filters = new SimpleFilterProvider().
    addFilter(... the name of the filter ...,
    SimpleBeanPropertyFilter.filterOutAllExcept(... enumeration of properties ...));

<object mapper>.writer(filters).writeValueAsString(... the bean ...);

我正在尝试将其集成到我的Jersey REST应用程序中。API用户可以通过提供查询字符串来过滤属性：

https://the-api/persons?fields=name,age,location,gender

在泽西岛最优雅的方式是什么？我可以很容易地在我的资源方法中执行上述操作，但这不知何故破坏了Jersey的优雅。此外，我认为为每个请求创建一个新的ObjectMapper会导致性能下降。

我可以编写一个MessageBodyWriter，它从UriInfo上下文中获取字段查询参数，并将实体序列化为json，同时应用基于字段查询参数的过滤器。这是最好的方法吗？这样地：

@Provider
@Produces(MediaType.APPLICATION_JSON)
public class JustTesting implements MessageBodyWriter<Object> {
    @Context
    UriInfo uriInfo;
    @Context
    JacksonJsonProvider jsonProvider;

    public boolean isWriteable(Class<?> aClass, Type type, Annotation[] annotations, MediaType mediaType) {
        return MediaType.APPLICATION_JSON_TYPE.equals(mediaType);
    }

    public long getSize(Object object, Class<?> aClass, Type type, Annotation[] annotations, MediaType mediaType) {
        return -1;
    }

    public void writeTo(Object object, Class<?> aClass, Type type, Annotation[] annotations, MediaType mediaType, MultivaluedMap<String, Object> stringObjectMultivaluedMap, OutputStream outputStream) throws IOException, WebApplicationException {
        final FilterProvider filters = new SimpleFilterProvider().addFilter("MyFilter", SimpleBeanPropertyFilter.filterOutAllExcept(uriInfo.getQueryParameters().getFirst("fields")));

        jsonProvider.locateMapper(aClass, mediaType).writer(filters).writeValue(outputStream, object);
    }
}

这似乎有效，但我不确定这样做是否明智。我是新泽西州图书馆的新员工。

Answer 1

我目前对类似问题的解决方案是注册以下servlet过滤器：

@Singleton
public class ViewFilter implements Filter {
    private @Inject Provider<ViewBeanPropertyFilter> filter;

    @Override
    public void init(FilterConfig filterConfig) throws ServletException { }

    @Override
    public void destroy() { }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
        ObjectWriterInjector.set(new ObjectWriterModifier() {
            @Override
            public ObjectWriter modify(EndpointConfigBase<?> endpoint, MultivaluedMap<String, Object> responseHeaders, Object valueToWrite, ObjectWriter w, JsonGenerator g) throws IOException {
                return w.with(new FilterProvider() {
                    @Override
                    public BeanPropertyFilter findFilter(Object filterId) {
                        if(filterId.equals(ViewFilterJacksonModule.FILTER_NAME)) {
                            return filter.get();
                        }
                        return null;
                    }
                });
            }
        });
        chain.doFilter(request, response);
    }

    public static class ViewBeanPropertyFilter extends SimpleBeanPropertyFilter {
        private @Inject ViewManager manager;

        @Override
        protected boolean include(BeanPropertyWriter writer) {
            Class<?> cls = writer.getMember().getDeclaringClass();
            return manager.isFieldInView(cls, writer.getMember().getName());
        }

        @Override
        protected boolean include(PropertyWriter writer) {
            return true;
        }
    }
}

它比您提供的解决方案要复杂一些，但保留了标准的JacksonJsonProvider序列化。

它可以通过通过Config（）. getFilterProvider（）提取（可能）现有的FilterProviderm.get并在过滤器之前/之后委托给它来改进。