Dropwizard /Jersey: Pass query-parameter with multiple values as List (maybe using a filter) - list

Question

I have clients passing in IDs like this: /v1/path?id=1,2,3
What I have and want
I have a resource class for Dropwizard/Jersey.
I'd like to show up the query-parameter id=1,2,3 as a List parameter in my resource's GET method
// Resource class
public List<Something> getFilteredList(#QueryParam("id") List<String> ids) {
// filter the List<Something> based on a list of ids
}
Right now, the ids list contains 1 string which is "1,2,3".
What I tried
I tried a filter but the query parameters given by Jersey's
ContainerRequestContext.getUriInfo().getQueryParameters()
is immutable.
Questions
I would like to apply a filter and change any comma separated query parameters into multi-valued parameters so that the resource method gets a list instead.
Is there a way to change the existing query parameters using a Jersey filter?
What's a good way to solve this problem?

Answer 1

The best way I can think of is to just create a wrapper class for the list. This makes it easier to take advantage of the specified functionality of Jersey. You can see what I mean at Passing custom type query parameter.
For example
public class IdFilter {
private List<String> ids = new ArrayList<>();
public List<String> getIds() { return ids; }
public static IdFilter valueOf(String param) {
IdFilter filter = new IdFilter();
for (String id: param.split(",") {
filter.getIds().add(id);
}
}
}
getFilteredList(#QueryParam("id") IdFilter ids) {
We don't need to do anything else. Just having the static valueOf is enough for Jersey to know how to parse the query string.

Answer 2

3 ways to solve it:
use the generic context-parameter UriInfo , which is not very expressive
add an explicit custom type that can parse a comma-separated list
stay with #QueryParam List<String> requiring a concatenated query like ?id=1&id=2&id=3 given as URI
I would prefer the second as most-expressive, like answered already by Paul. This way you can concisely pass a single CSV like ?id=1,2,3,3 and also use a Set to ensure unique ID values, e.g. resulting in only [1, 2, 3].
Generic context-param UriInfo
One way would be to use a generic parameter #Context UriInfo to get the list in the method's body:
public List<Something> getFilteredList( #Context UriInfo uriInfo ) {
List<String> idList = uriInfo.getQueryParameters().get("id"); // before was #QueryParam("id")
System.out.println("idList: " + idList);
// filter a given list by ids
var somethingFiltered = getSomethingList().stream()
.filter(s -> idList.contains(s.getId()))
.collect(toList());
return Response.status(Status.OK).entity(somethingFiltered).build();
}
See the tutorial in Java Vogue(2015): QueryParam Annotation In Jersey -
Custom type with static valueOf(String) factory-method
The other way is to design a custom type which can be constructed using a String:
class IdSet {
Set<String> values;
// a factory method, can also be named valueOf
public static IdSet fromString(String commaSeparated) {
return new HashSet( Arrays.asList( commaSeparated.split(",") ) );
}
}
public List<Something> getFilteredList(#QueryParam("id") IdSet ids) {
System.out.println("ids (Set): " + ids.values);
// filter a given list by ids
var somethingFiltered = getSomethingList().stream()
.filter(s -> ids.values.contains(s.getId()))
.collect(toList());
return Response.status(Status.OK).entity(somethingFiltered).build();
}
See Jersey's JavaDocs for #QueryParam:
The type T of the annotated parameter, field or property must either:
Be a primitive type
Have a constructor that accepts a single String argument
Have a static method named valueOf or fromString that accepts a single String argument (see, for example, Integer.valueOf(String))
Have a registered implementation of ParamConverterProvider that returns a ParamConverter instance capable of a "from string" conversion for the type.
Be List<T>, Set<T> or SortedSet<T>, where T satisfies 2, 3 or 4 above. The resulting collection is read-only.
Use a collection interface with multiple key-value pairs
When the calling client uses following URI pattern: /something?id=1&id=2&id=3 then JAX-RS can deserialize them to a single parameter of List<String> id having given multiple elements:
public List<Something> getFilteredList(#QueryParam("id") List<String> ids) {
System.out.println("ids : "+ids);
// filter a given list by ids
var somethingFiltered = getSomethingList().stream()
.filter(s -> ids.contains(s.getId()))
.collect(toList());
return Response.status(Status.OK).entity(somethingFiltered).build();
}
See Mkyong: JAX-RS #QueryParam example where explained the multiple occurrences of orderBy in the GET query:
#QueryParam will convert the query parameter “orderBy=age&orderBy=name” into java.util.List automatically.
See also
Handling Multiple Query Parameters in Jersey
Deserializing List<Map<String, String>> QueryParam in jersey 1
Jersey, #QueryParam List<String>