以集合为实体的javax.ws.rs.core.Response

Question

I have the following code:

    @GET
    @Path("v1/entity")
    @ApiOperation(
            value = "List",
            notes = "Enables you to List.",
            tags = { "List" })
    @ApiImplicitParams(
            {
                @ApiImplicitParam(name = "pageSize",
                    value = "Page Size",
                    dataType = "int",
                    paramType = "formData",
                    example = "50"),
                @ApiImplicitParam(name = "sortAscending",
                    value = "Sort Ascending",
                    dataType = "boolean",
                    paramType = "formData",
                    example = "false")
            })
    public Response list(@ApiParam(hidden = true) Integer pageSize,
            @ApiParam(hidden = true) Boolean sortAscending) {
        Collection<EntityData> dataCollection;
        if (pageSize == null || sortAscending == null || pageSize <= 0) {
            dataCollection = storeController.list();
        } else {
            SortDirection sortDirection = sortAscending ? SortDirection.ASC : SortDirection.DESC;
            dataCollection= storeController.list(pageSize, sortDirection);
        }
        logger.info("List contains {} elements", dataCollection.size());
        GenericEntity<Collection<EntityData>> response = new GenericEntity<Collection<EntityData>>(dataCollection){};
        return Response.ok(response).build();
        //return ResponseEntity.ok(dataCollection);
    }

Both methods from storeController object only return an ArrayList of EntityData, whose structure is below:

public class EntityData implements Serializable {

    private String document;

    private String validTo;

    private String validFrom;

    private String entityAlias;

    public String getDocument() {
        return document;
    }

    public void setDocument(String document) {
        this.document= document;
    }

    public String getValidTo() {
        return validTo;
    }

    public void setValidTo(String validTo) {
        this.validTo = validTo;
    }

    public String getValidFrom() {
        return validFrom;
    }

    public void setValidFrom(String validFrom) {
        this.validFrom = validFrom;
    }

    public String getEntityAlias() {
        return entityAlias;
    }

    public void setEntityAlias(String entityAlias) {
        this.entityAlias = entityAlias;
    }
}

When I call the API, I get this error:

No message body writer has been found for class java.util.ArrayList, ContentType: */*

I used this as a reference , but it didn't work. I've also tried to, instead of using Response to retrieve the contents, using ResponseEntity<Collection<EntityData>> , but the error persists. Just as using directly the " ArrayList " in the Response (without wrapping on GenericEntity ).

If I change the last line to return Response.ok().build(); it works, but I need the Collection to be retrieved... The logger indicates that the Collection has 9 elements when I run.

I know I am missing something here, but I can't see it. Can you help me?

Answer 1

Make sure your resource method (or the entire resource class) is annotated either with:

• @Produces("applicaton/json") or;
• @Produces(MediaType.APPLICATION_JSON) .

Then ensure you have a JSON provider, such as Jackson, in the classpath:

<dependency>
  <groupId>com.fasterxml.jackson.jaxrs</groupId>
  <artifactId>jackson-jaxrs-json-provider</artifactId>
  <version>${jackson.version}</version>
</dependency> 

Depending on how the JAX-RS implementation is configured, adding the jackson-jaxrs-json-provider artifact to your classpath is enough to use Jackson as a JSON provider. Otherwise you need to register JacksonJsonProvider .