We Keep Coding

How to make json deserialization fail when detecting duplicate properties in API POST request body

I have a POST endpoint which accepts a JSON as request body.
#Path("/drink")
#Produces(MediaType.APPLICATION_JSON)
#Consumes(MediaType.APPLICATION_JSON)
public class DrinkResource {
#POST
public Drink getDrink(Fruit fruit) {
return new Drink(fruit.getName());
}
}
The request body is supposed to be deserialized into this POJO :
public class Fruit {
private final String name;
#JsonCreator
public Fruit(#JsonProperty("name") String name) {
this.name = name;
}
public String getName() {
return name;
}
}
I'm using Jackson for the deserialization.
Is it possible to make the deserialization fail when the JSON in the request body has duplicate keys ?
For example, if the request body looks like this : {"name" : "banana", "name" : "orange"}, I would like to get a 500 status code or another kind of error instead of having the json deserialized with the last property.
Basically, I'm looking for a solution with the same logic as the JsonParser.Feature.STRICT_DUPLICATE_DETECTION with the ObjectMapper but for a POST endpoint.
I'm also using quarkus so I don't know if there is a property for this. Something similar to quarkus.jackson.fail-on-unknown-properties=true but for the duplicate properties.

Add the following:
#Singleton
public class MyCustomizer implements ObjectMapperCustomizer {
#Override
public void customize(ObjectMapper objectMapper) {
objectMapper.enable(JsonParser.Feature.STRICT_DUPLICATE_DETECTION);
}
}
If you do, the ObjectMapper that Quarkus uses will throw a JsonParseException thus leading to a HTTP 400 response.

Customize Json serializer instead of Jersey's default?

I am using Jersey to implement RESTful webservice. Now the MediaType in which I return data is JSON.
#GET
#Produces({MediaType.APPLICATION_JSON })
public Response service() {
return Response
.ok(entity)
.header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON)
.build();
}
Here I set CONTENT_TYPE to json and my entity will be converted to json by Jersey framework.
Now I want to customize my json response.
Eg: I want to remove the empty elements or change the keys name of my Json object.
Default Jersey's Json conversion:
{
"cinter" : {
"state" : 1,
"checks" : 10,
}
}
What I want:
{
"cin" : {
"st" : 1,
"cs" : 10,
}
}
I know I can use Jackson library's my own ObjectMapper to customize my Json according to my needs.
But is this the standard way to do it if I want JSON conversion in a different way than Jersey's default conversion ??
Or can I change paramaters in Jersey's ObjectMapper ??
Should I be using my own ObjectMapper ?

Here is my thoughts about your options. First of all
So for every different response I should configure ObjectMapper
differently ?
If you want to use both json versions in different places like this
public Response getObject() // returns {"cinter" : {"state" : 1,"checks" : 10}}
public Response getShortNamesObject() // returns {"cin" : {"st" : 1,"cs" : 10}}
Than yep, you have to use multiple ObjectMappers.
But if you just want to use 1 representation everywhere, then you probably will be able to setup Jackson once with custom mixin for you classes. Anyway here is how you can do both options: And lets look at simple case with just 1 json version needed
public class TestBean {
private String name;
private int id;
//getters and setters
}
public interface TestBeanMixin {
#JsonProperty("short_field_name")
String getName();
#JsonProperty("short_field_id")
int getId();
}
#Provider
#Priority(1)
public class MixInJacksonJsonProvider extends JacksonJaxbJsonProvider {
private static final ObjectMapper mapper = createMapper();
public MixInJacksonJsonProvider() {
setMapper(mapper);
}
private static ObjectMapper createMapper() {
final ObjectMapper result = new ObjectMapper();
result.addMixIn(TestBean.class, TestBeanMixin.class);
return result;
}
}
This code will produce short names for you POJO fields everywhere. and to implement different behavior for different request we have to add new custom annotation like this:
#Retention(RetentionPolicy.RUNTIME)
#Target({ElementType.METHOD, ElementType.TYPE})
public #interface MixIn {}
Controller will look like this:
#Path("test")
public class MyResource {
#GET
#MixIn // <== Here is important part
#Produces(MediaType.APPLICATION_JSON )
public Response getShortName() {
return Response.ok(demoObj()).build();
}
#POST
#Produces(MediaType.APPLICATION_JSON )
public Response postLongName() {
return Response.ok(demoObj()).build();
}
}
And our MixInJacksonJsonProvider will have 2 more #Override:
//.. same as before
#Override
public boolean isReadable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
return super.isReadable(type, genericType, annotations, mediaType) && hasMixInAnnotation(annotations);
}
#Override
public boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
return super.isWriteable(type, genericType, annotations, mediaType) && hasMixInAnnotation(annotations);
}
public static boolean hasMixInAnnotation(Annotation[] annotations){
for(Annotation annotation: annotations){
if (annotation instanceof MixIn){
return true;
}
}
return false;
}
}
Here is demo code for you to play: https://github.com/varren/jersey2-jacksonsetup/tree/master/src/main/java/ru/varren

Web Service accepting Object[]. What JSON it accepts?

I am writing a web service which should accept type Object[]. Its universal and needs to accept different number and types of parameters in different scenarios.
Request object looks like this:
#XmlRootElement
public class SimilarityRequest {
private Object[] params;
private String similarity;
public Object[] getParams() {
return params;
}
public void setParams(Object[] params) {
this.params = params;
}
public String getSimilarity() {
return similarity;
}
public void setSimilarity(String similarity) {
this.similarity = similarity;
}
}
This is WebService:
#SessionScoped
#Path("/similarity/")
#Produces({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON})
#Consumes({MediaType.APPLICATION_XML, MediaType.APPLICATION_JSON})
#Stateful
#StatefulTimeout(600000) // 10 minutes
public class SimilarityResource {
#POST
#Path("/")
public List<SimilarityResult> universalSimilarity(JAXBElement<SimilarityRequest> sr) {
Object[] params = sr.getValue().getParams();
String similarity = sr.getValue().getSimilarity();
}
}
I dont know what json it accepts for params in this case? I tried "params":{5,10} and "params":{"0":5,"1":10} and also "params":[5,10]. Something throws 500 and something 400 (bad request). Any ideas?

I've successfully implemented the service using Jersey, the code is the same, I've just removed the JAXBElement wrapper and the #XmlRootElement annotation.
The WEB-INF.xml file must include the folder containing the SimilarityRequest class in the
com.sun.jersey.config.property.packages parameter section and the com.sun.jersey.api.json.POJOMappingFeature parameter must be true.
The service receives correctly the following json:
{ "similarity": "test", "params":[5,10] }
The object array contains two Integer values.

Jersey JSON serialization with external classes

I am trying to create a rest api server on top of my quartz scheduler. I want to be able to return the org.quartz.Trigger and org.quartz.JobDetail objects as JSON. The problem is that I cannot add the #XmlRootElement to these classes without having to recompile the jar and this causes problems with future upgrades etc. I have tested and am able to serialize a list of classes when adding the #XmlRootElement but when I try to return a List I get the error "A message body writer for Java class java.util.ArrayList, and Java type java.util.List, and MIME media type application/json was not found". I have tried adding a custom MessageBodyWriter but that does not seem to fix the problem either. Is there a way to marshal the quartz classes to JSON without having to modify the quartz code to add the #XmlRootElement. I am using this in an embedded web server with jetty btw.
#Path("/jobs")
public class JobsResource {
#GET
#Produces(MediaType.APPLICATION_JSON)
public List<Trigger> listScheduledJobs() throws SchedulerException {
return TaskEngine.getInstance().listScheduledJobs();
}
}
Web server configuration
public class TaskEngineWebServer {
private static final Logger logger = Logger.getLogger(TaskEngineWebServer.class.getName());
private Server server;
public TaskEngineWebServer() {
this(8585);
}
public TaskEngineWebServer(Integer port) {
server = new Server(port);
logger.info("Configuring rest service to start at url /r");
ServletContextHandler handler = new ServletContextHandler(ServletContextHandler.NO_SECURITY);
//handler.getInitParams().put("com.sun.jersey.api.json.POJOMappingFeature", "true");
PackagesResourceConfig packagesResourceConfig = new PackagesResourceConfig("com.hp.vf.scheduler.server.rest");
ServletContainer servletContainer = new ServletContainer(packagesResourceConfig);
handler.addServlet(new ServletHolder(servletContainer), "/r/*");
server.setHandler(handler);
logger.info("Done configuring rest service");
}
public void start() throws Exception {
server.start();
}
public void stop() throws Exception {
server.stop();
}
public boolean isStarted() {
return server.isStarted();
}
public boolean isStopped() {
return server.isStopped();
}
}

I dont think you can return a List as JSON directly. You need to have a wrapper class which contains this list. For eg try something like this
#XmlRootElement
#XmlAccessorType(XmlAccessType.FIELD)
public class TriggerWrapper{
private List<Triggers> triggers;
public List<Triggers> getTriggers(){
if(triggers==null){
triggers = new ArrayList<Triggers>();
}
return triggers;
}
}
Then in your rest service class :
#Path("/jobs")
public class JobsResource {
#GET
#Produces(MediaType.APPLICATION_JSON)
public TriggerWrapper listScheduledJobs() throws SchedulerException {
TriggerWrapper response = new TriggerWrapper();
List<Triggers> triggers = TaskEngine.getInstance().listScheduledJobs();
response.getTriggers.addAll(triggers);
return response;
}
}
Your json would something like this :
{
"triggerwrapper": {
"triggers": [
{
"triggerid": 1
},
{
"triggerid": 2
}
]
}
}
And ofcourse if you want you can drop the root element tag from your json its configurable in jersey.

I finally figured out a clean solution, it involves creating my own MediaBodyWriter class and adding it as a provider. You have to make sure you are not using the jersey-bundle jar as the default jaxb to json provider will override yours.
jars required
jersey-core
jersey-servlet
jersey-server
jackson-annotations
jackson-databind
jackson-core
I found this MediaWriter example on the web somewhere. Sorry for not having the url but thanks to whoever write it.
#Provider
#Produces({ MediaType.APPLICATION_JSON })
public class JacksonWriter implements MessageBodyWriter<Object> {
private static final ObjectMapper MAPPER = new ObjectMapper();
#Override
public boolean isWriteable(Class<?> aClass, Type type, Annotation[] annotations, MediaType mediaType) {
return true;
}
#Override
public long getSize(Object value, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {
return -1;
}
#Override
public void writeTo(Object value, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType, MultivaluedMap<String, Object> httpHeaders,
OutputStream entityStream) {
try {
MAPPER.writeValue(entityStream, value);
} catch (IOException ex) {
throw new RuntimeException(ex);
}
}
}
When it loads you will see a log message that your provider was loaded.
This gave me the json output I was expecting as it does not rely on the JAXB annotations and simply uses the object mapper/ reflection. Probably less efficient but for my case it does not matter.

How to get a Map parameter in a REST service for different mime types?

How can I specify a map as one of the parameters of a REST service e.g
#Path("/servicepath")
#Consumes(MediaType.APPLICATION_XML)
public class MyResource {
#POST
public Response getMap(Map<String, List<Object>>) {
//code here
}
}
or
#Path("/servicepath")
#Consumes(MediaType.APPLICATION_JSON)
public class MyResource {
#POST
public Response getMap(Map<String, List<Object>>) {
//code here
}
}
I am using Jersey. Should I implement a MessageBodyReader for that? But implementing a reader for a generic type like Map seems a bad way for me. Maybe I should write a wrapper class on top of the Map object.
What is your ideas? Thanks.

The JAX-RS specification (section 4.2.4) does require that implementors (like jersey) provide a MessageBodyReader implementation for MultivaluedMap<String, String> which is used to consume application/x-www-form-urlencoded mime types. So for example, you can do something like this:
#Path("/servicepath")
#POST
#Consumes("application/x-www-form-urlencoded")
#Produces("text/plain")
public String doTheFormThing(MultivaluedMap<String, String> formdata) {
return formdata.toString();
}
Is this not sufficient for what you're trying to do?