How to get resource method matched to URI before Jersey invokes it?
java, jersey, jersey-1.0
Solution
I figured out how to solve my problem using only Jersey. There's apparently no way to match a request's URI to the method that will be matched before that method is invoked, at least in Jersey 1.x. However, I was able to use a `ResourceFilterFactory` to create a `ResourceFilter` for each individual resource method - that way these filters can know about the destination method ahead of time.
Here's my solution, including the validation for required query params (uses Guava and JSR 305):
public final class ValidationFilterFactory implements ResourceFilterFactory {
@Override
public List<ResourceFilter> create(AbstractMethod abstractMethod) {
//keep track of required query param names
final ImmutableSet.Builder<String> requiredQueryParamsBuilder =
ImmutableSet.builder();
//get the list of params from the resource method
final ImmutableList<Parameter> params =
Invokable.from(abstractMethod.getMethod()).getParameters();
for (Parameter param : params) {
//if the param isn't marked as @Nullable,
if (!param.isAnnotationPresent(Nullable.class)) {
//try getting the @QueryParam value
@Nullable final QueryParam queryParam =
param.getAnnotation(QueryParam.class);
//if it's present, add its value to the set
if (queryParam != null) {
requiredQueryParamsBuilder.add(queryParam.value());
}
}
}
//return the new validation filter for this resource method
return Collections.<ResourceFilter>singletonList(
new ValidationFilter(requiredQueryParamsBuilder.build())
);
}
private static final class ValidationFilter implements ResourceFilter {
final ImmutableSet<String> requiredQueryParams;
private ValidationFilter(ImmutableSet<String> requiredQueryParams) {
this.requiredQueryParams = requiredQueryParams;
}
@Override
public ContainerRequestFilter getRequestFilter() {
return new ContainerRequestFilter() {
@Override
public ContainerRequest filter(ContainerRequest request) {
final Collection<String> missingRequiredParams =
Sets.difference(
requiredQueryParams,
request.getQueryParameters().keySet()
);
if (!missingRequiredParams.isEmpty()) {
final String message =
"Required query params missing: " +
Joiner.on(", ").join(missingRequiredParams);
final Response response = Response
.status(Status.BAD_REQUEST)
.entity(message)
.build();
throw new WebApplicationException(response);
}
return request;
}
};
}
@Override
public ContainerResponseFilter getResponseFilter() {
return null;
}
}
}
And the `ResourceFilterFactory` is registered with Jersey as an init param of the servlet in `web.xml`:
<init-param>
<param-name>com.sun.jersey.spi.container.ResourceFilters</param-name>
<param-value>my.package.name.ValidationFilterFactory</param-value>
</init-param>
At startup, `ValidationFilterFactory.create` gets called for each resource method detected by Jersey.
Credit goes to this post for getting me on the right track: How can I get resource annotations in a Jersey ContainerResponseFilter
Problem
I'm trying to implement a `ContainerRequestFilter` that does custom validation of a request's parameters. I need to look up the resource method that will be matched to the URI so that I can scrape custom annotations from the method's parameters. Based on this answer I should be able to inject `ExtendedUriInfo` and then use it to match the method: ``` public final class MyRequestFilter implements ContainerRequestFilter { @Context private ExtendedUriInfo uriInfo; @Override public ContainerRequest filter(ContainerRequest containerRequest) { System.out.println(uriInfo.getMatchedMethod()); return containerRequest; } } ``` But `getMatchedMethod` apparently returns `null`, all the way up until the method is actually invoked (at which point it's too late for me to do validation). How can I retrieve the `Method` that will be matched to a given URI, before the resource method is invoked? For those interested, I'm trying to roll my own required parameter validation, as described in JERSEY-351.