public RouteBuilder produces(Iterable<MediaType> produceTypes) {
        ensureUniqueMediaTypes(produceTypes, "produceTypes");
        produces = ImmutableSet.copyOf(produceTypes);
        return this;
    }
Sets the {@link Route} to produce the specified {@link MediaType}s. If not set,
the mapped {@link HttpService} accepts {@link HttpRequest}s that have any
{@link HttpHeaderNames#ACCEPT}. In order to get this work, {@link #methods(Iterable)} must be set.
core/src/main/java/com/linecorp/armeria/server/RouteBuilder.java