Read another parameter within jersey's ParamConverter

Question

I've made a ParamConverter which provides an Instant (Date) when given a string formatted as either Instant's native ISO-8601, or as an integer number of milliseconds since the epoch. This is working fine, but I also need to be able to support other date formats (the customers are fussy).

To avoid the classic dd/mm/yyyy vs mm/dd/yyyy ambiguity, I'd like to have the customer specify their preferred format as part of the request*. e.g:

GET http://api.example.com/filter?since=01/02/2000&dateformat=dd/mm/yyyy

passed to a method which looks like:

@GET
String getFilteredList( final @QueryParam( "since" ) Instant since ) {
    ...
}

(time & timezone parts omitted for clarity)

So I'd like my ParamConverter<Instant> to be able to read the dateformat parameter.

I've been able to use a combination of a filter which sets a ContainerRequestContext property and an AbstractValueFactoryProvider to do something similar, but that needs the parameter to have a custom annotation applied and doesn't let it work with QueryParam/FormParam/etc., making it far less useful.

Is there any way to get other parameters, or the request object itself, from inside a ParamConverter?

_{[*] In the real world this would be from a selection of pre-approved formats, but for now just assume they're providing the input to a DateTimeFormatter}

---

For clarity, here's the code I have:

public class InstantParameterProvider implements ParamConverterProvider {
    private static final ParamConverter<Instant> INSTANT_CONVERTER =
            new ParamConverter<Instant>( ) {
                @Override public final T fromString( final String value ) {
                    // This is where I would like to get the other parameter's value
                    // Is it possible?
                }

                @Override public final String toString( final T value ) {
                    return value.toString( );
                }
            };

    @SuppressWarnings( "unchecked" )
    @Override public <T> ParamConverter<T> getConverter(
            final Class<T> rawType,
            final Type genericType,
            final Annotation[] annotations
    ) {
        if( rawType == Instant.class ) {
            return (ParamConverter<T>) INSTANT_CONVERTER;
        }
        return null;
    }
}

Answer 1

As mentioned here, the key to this is injecting some context object with javax.inject.Provider, which allows us to retrieve the object lazily. Since the ParamConverterProvider is a component managed by Jersey, we should be able to inject other components.

The problem is that the component we need is going to be in a request scope. To get around that, we inject javax.inject.Provider<UriInfo> into the provider. When we actually call get() in the Provider to get the actual instance of UriInfo, it will be be in a request. The same goes for any other component that requires a request scope.

For example

public class InstantParamProvider implements ParamConverterProvider {
    
    @Inject
    private javax.inject.Provider<UriInfo> uriInfoProvider;

    @Override
    public <T> ParamConverter<T> getConverter(Class<T> rawType, 
                                              Type genericType, 
                                              Annotation[] annotations) {

        if (rawType != Instant.class) return null; 

        return new ParamConverter<T>() {
            @Override
            public T fromString(String value) {
                UriInfo uriInfo = uriInfoProvider.get();
                String format = uriInfo.getQueryParameters().getFirst("date-format");
                
                if (format == null) {
                     throw new WebApplicationException(Response.status(400)
                             .entity("data-format query parameter required").build());
                } else {
                    try {
                        // parse and return here
                    } catch (Exception ex) {
                        throw new WebApplicationException(
                            Response.status(400).entity("Bad format " + format).build());
                    }
                }
            }

            @Override
            public String toString(T value) {
                return value.toString();
            }  
        };
    }  
}

---

UPDATE

Here is a complete example using Jersey Test Framework

import java.lang.annotation.Annotation;
import java.lang.reflect.Type;
import java.time.LocalDate;
import java.time.format.DateTimeFormatter;
import java.util.logging.Logger;

import javax.inject.Inject;
import javax.ws.rs.GET;
import javax.ws.rs.Path;
import javax.ws.rs.QueryParam;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.Response;
import javax.ws.rs.core.UriInfo;
import javax.ws.rs.ext.ParamConverter;
import javax.ws.rs.ext.ParamConverterProvider;

import org.glassfish.jersey.filter.LoggingFilter;
import org.glassfish.jersey.server.ResourceConfig;
import org.glassfish.jersey.test.JerseyTest;

import org.junit.Test;
import static org.junit.Assert.*;
import static org.junit.matchers.JUnitMatchers.*;

public class LocalDateTest extends JerseyTest {

    public static class LocalDateParamProvider implements ParamConverterProvider {

        @Inject
        private javax.inject.Provider<UriInfo> uriInfoProvider;

        @Override
        public <T> ParamConverter<T> getConverter(Class<T> rawType,
                Type genericType,
                Annotation[] annotations) {

            if (rawType != LocalDate.class) {
                return null;
            }
            return new ParamConverter<T>() {
                @Override
                public T fromString(String value) {
                    UriInfo uriInfo = uriInfoProvider.get();
                    String format = uriInfo.getQueryParameters().getFirst("date-format");

                    if (format == null) {
                        throw new WebApplicationException(Response.status(400)
                                .entity("date-format query parameter required").build());
                    } else {
                        try {
                            return (T) LocalDate.parse(value, DateTimeFormatter.ofPattern(format));
                            // parse and return here
                        } catch (Exception ex) {
                            throw new WebApplicationException(
                                    Response.status(400).entity("Bad format " + format).build());
                        }
                    }
                }

                @Override
                public String toString(T value) {
                    return value.toString();
                }
            };
        }
    }

    @Path("localdate")
    public static class LocalDateResource {

        @GET
        public String get(@QueryParam("since") LocalDate since) {
            return since.format(DateTimeFormatter.ofPattern("MM/dd/yyyy"));
        }
    }

    @Override
    public ResourceConfig configure() {
        return new ResourceConfig(LocalDateResource.class)
                .register(LocalDateParamProvider.class)
                .register(new LoggingFilter(Logger.getAnonymousLogger(), true));
    }

    @Test
    public void should_return_bad_request_with_bad_format() {
        Response response = target("localdate")
                .queryParam("since", "09/20/2015")
                .queryParam("date-format", "yyyy/MM/dd")
                .request().get();
        assertEquals(400, response.getStatus());
        assertThat(response.readEntity(String.class), containsString("format yyyy/MM/dd"));
        response.close();
    }

    @Test
    public void should_return_bad_request_with_no_date_format() {
        Response response = target("localdate")
                .queryParam("since", "09/20/2015")
                .request().get();
        assertEquals(400, response.getStatus());
        assertThat(response.readEntity(String.class), containsString("query parameter required"));
        response.close();
    }

    @Test
    public void should_succeed_with_correct_format() {
        Response response = target("localdate")
                .queryParam("since", "09/20/2015")
                .queryParam("date-format", "MM/dd/yyyy")
                .request().get();
        assertEquals(200, response.getStatus());
        assertThat(response.readEntity(String.class), containsString("09/20/2015"));
        response.close();
    }
}

Here's the test dependency

<dependency>
    <groupId>org.glassfish.jersey.test-framework.providers</groupId>
    <artifactId>jersey-test-framework-provider-grizzly2</artifactId>
    <version>${jersey2.version}</version>
    <scope>test</scope>
</dependency>