ResourceUtils.java 文件源码

/**
 * Lookup a resource of given <code>resourceType</code> type, either using a suitable {@link ContextResolver} if
 * <code>providers</code> is not <code>null</code> and a {@link ContextResolver} for given <code>resourceType</code>
 * is available, or trying to obtain the resource from {@link Context} using given <code>resourceType</code> as
 * context resource key.
 * @param <R> Resource type
 * @param caller Caller class
 * @param resourceType Resource type to lookup (not null)
 * @param providers JAX-RS {@link Providers}, if available
 * @return Resource instance, or an empty optional if not available
 */
public static <R> Optional<R> lookupResource(Class<?> caller, Class<R> resourceType, Providers providers) {
    ObjectUtils.argumentNotNull(resourceType, "Resource type must be not null");

    R resource = null;

    // try to use a ContextResolver, if available
    ContextResolver<R> resolver = providers.getContextResolver(resourceType, null);
    if (resolver != null) {
        resource = resolver.getContext(caller);
    }

    if (resource == null) {
        // lookup in context
        resource = Context.get()
                .resource(resourceType,
                        (caller != null) ? caller.getClassLoader() : ClassUtils.getDefaultClassLoader())
                .orElse(null);
    }

    return Optional.ofNullable(resource);
}