How to include only specific properties when serializing with Jackson - json

I am trying to implement a universal method which serializes the given object to JSON, but only those properties which are passed in a collection. If possible I want to get this functionality without specifying #JsonFilter on the class. For this I am trying to use FilterExceptFilter from Jackson 2.4.1. Dependencies:
jackson-core-2.4.1.jar
jackson-databind-2.4.1.jar
jackson-annotations-2.4.0.jar
Here is what I have at the moment:
public static String serializeOnlyGivenFields(Object o,
Collection<String> fields) throws JsonProcessingException {
if ((fields == null) || fields.isEmpty()) return null;
Set<String> properties = new HashSet<String>(fields);
SimpleBeanPropertyFilter filter =
new SimpleBeanPropertyFilter.FilterExceptFilter(properties);
SimpleFilterProvider fProvider = new SimpleFilterProvider();
fProvider.addFilter("fieldFilter", filter);
fProvider.setDefaultFilter(filter);
ObjectMapper mapper = new ObjectMapper();
mapper.setFilters(fProvider);
String json = mapper.writeValueAsString(o);
return json;
}
However, the filter is never applied. It always serializes all properties.
Set<String> fields = new HashSet<String>(); fields.add("name");
String json = Serializer.serializeOnlyGivenFields(e, fields);
System.out.println(json);
{"name":"Test entity","description":"Test description"}
I have also tried to register the FilterProvider on the ObjectWriter, but same result:
String json = mapper.writer(fProvider).writeValueAsString(o);
What am I missing? Is there a nice way to achieve this with Jackson?

Based on http://www.cowtowncoder.com/blog/archives/2011/09/entry_461.html an alternate way to set up the filter is setting up a class that extends JacksonAnnotationIntrospector and overrides findFilterId. You can then specify to find your filter in the findFilterId. This could be made to be as robust if you want based on some other map or algorithm. Below is sample code. Not sure if the performance is better than the solution above but it seems to be simpler and probably more easily extensible. I was doing this for serializing CSV using Jackson. Any feedback is welcome!
public class JSON {
private static String FILTER_NAME = "fieldFilter";
public static String serializeOnlyGivenFields(Object o,
Collection<String> fields) throws JsonProcessingException {
if ((fields == null) || fields.isEmpty()) fields = new HashSet<String>();
Set<String> properties = new HashSet<String>(fields);
SimpleBeanPropertyFilter filter =
new SimpleBeanPropertyFilter.FilterExceptFilter(properties);
SimpleFilterProvider fProvider = new SimpleFilterProvider();
fProvider.addFilter(FILTER_NAME, filter);
ObjectMapper mapper = new ObjectMapper();
mapper.setAnnotationIntrospector( new AnnotationIntrospector() );
String json = mapper.writer(fProvider).writeValueAsString(o);
return json;
}
private static class AnnotationIntrospector extends JacksonAnnotationIntrospector {
#Override
public Object findFilterId(Annotated a) {
return FILTER_NAME;
}
}
}

One additional thing is that you have to indicate Java classes for which filter is to be used by #JsonFilter annotation:
#JsonFilter("fieldFilter")
public class MyType { }
and then it should apply.

I have found a solution based on Jackson: How to add custom property to the JSON without modifying the POJO. I override BeanSerializer#serializeFields to always use BeanSerializer#serializeFieldsFiltered instead. This way the filter is always applied.
Performance-wise not a very good solution, since an ObjectMapper has to be constructed at every method call. Feel free to post improvements or suggestions!
Module implementation:
public class FilteredModule extends SimpleModule {
private static final long serialVersionUID = 1L;
#Override
public void setupModule(SetupContext context) {
super.setupModule(context);
context.addBeanSerializerModifier(new BeanSerializerModifier() {
#Override
public JsonSerializer<?> modifySerializer(
SerializationConfig config,
BeanDescription beanDesc,
JsonSerializer<?> serializer) {
if (serializer instanceof BeanSerializerBase) {
return new FilteredBeanSerializer(
(BeanSerializerBase) serializer);
}
return serializer;
}
});
}
private class FilteredBeanSerializer extends BeanSerializer {
public FilteredBeanSerializer(BeanSerializerBase source) {
super(source);
}
#Override
protected void serializeFields(Object arg0, JsonGenerator arg1,
SerializerProvider arg2) throws IOException,
JsonGenerationException {
super.serializeFieldsFiltered(arg0, arg1, arg2);
}
}
}
API method:
public static String serializeOnlyGivenFields(Object o,
Collection<String> fields) throws JsonProcessingException {
if ((fields == null) || fields.isEmpty()) fields = new HashSet<String>();
Set<String> properties = new HashSet<String>(fields);
SimpleBeanPropertyFilter filter =
new SimpleBeanPropertyFilter.FilterExceptFilter(properties);
SimpleFilterProvider fProvider = new SimpleFilterProvider();
fProvider.addFilter("fieldFilter", filter);
fProvider.setDefaultFilter(filter);
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new FilteredModule());
String json = mapper.writer(fProvider).writeValueAsString(o);
return json;
}
Example
Entity e = new Entity("Test entity", "Test description");
Set<String> fields = new HashSet<String>(); fields.add("name");
String json = JSON.serializeOnlyGivenFields(e, fields);
System.out.println(json);
{"name":"Test entity"}
Benchmark: 1000 iterations on the same object
serializeOnlyGivenFields: 536 ms
serialize (reuses ObjectMapper): 23 ms

Related

How to dynamically ignore a property on Jackson serialization

I have an entity with multiple #ManyToOne associations. I am using spring-boot to expose a REST API. Currently, I have multiple REST API's which return a JSON response of the whole entity, including associations.
But I don't want to serialize all associated objects in all REST APIs.
For example
API-1 should return parent + associationA object
API-2 should return parent + associationA + associationB object
API-3 should return parent + associationB + associationC + associationD
So, in my serialization process, I want to ignore all association except associationA for API-1.
For API-2 I want to ignore other associations except A and B
How do I dynamically ignore these properties during Jackson serialization?
Notes:
I'm using the same class for each; I am not interested in creating a DTO for each API.
Any suggestions are kingly appreciated.
I've put together three approaches for performing dynamic filtering in Jackson. One of them must suit your needs.
Using #JsonView
You could use #JsonView:
public class Views {
interface Simple { }
interface Detailed extends Simple { }
}
public class Foo {
#JsonView(Views.Simple.class)
private String name;
#JsonView(Views.Detailed.class)
private String details;
// Getters and setters
}
#RequestMapping("/foo")
#JsonView(Views.Detailed.class)
public Foo getFoo() {
Foo foo = new Foo();
return foo;
}
Alternatively you can set the view dynamically with MappingJacksonValue.
#RequestMapping("/foo")
public MappingJacksonValue getFoo() {
Foo foo = new Foo();
MappingJacksonValue result = new MappingJacksonValue(foo);
result.setSerializationView(Views.Detailed.class);
return result;
}
Using a BeanSerializerModifier
You could extend BeanSerializerModifier and then override the changeProperties() method. It allows you to add, remove or replace any of properties for serialization, according to your needs:
public class CustomSerializerModifier extends BeanSerializerModifier {
#Override
public List<BeanPropertyWriter> changeProperties(SerializationConfig config,
BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) {
// In this method you can add, remove or replace any of passed properties
return beanProperties;
}
}
Then register the serializer as a module in your ObjectMapper:
ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new SimpleModule() {
#Override
public void setupModule(SetupContext context) {
super.setupModule(context);
context.addBeanSerializerModifier(new CustomSerializerModifier());
}
});
Check examples here and here.
Using #JsonFilter with a SimpleBeanPropertyFilter
Another approach involves #JsonFilter:
#JsonFilter("customPropertyFilter")
public class Foo {
private String name;
private String details;
// Getters and setters
}
Extend SimpleBeanPropertyFilter and override the serializeAsField() method according to your needs:
public class CustomPropertyFilter extends SimpleBeanPropertyFilter {
#Override
public void serializeAsField(Object pojo, JsonGenerator jgen,
SerializerProvider provider,
PropertyWriter writer) throws Exception {
// Serialize a field
// writer.serializeAsField(pojo, jgen, provider, writer);
// Omit a field from serialization
// writer.serializeAsOmittedField(pojo, jgen, provider);
}
}
Then register the filter in your ObjectMapper:
FilterProvider filterProvider = new SimpleFilterProvider()
.addFilter("customPropertyFilter", new CustomPropertyFilter());
ObjectMapper mapper = new ObjectMapper();
mapper.setFilterProvider(filterProvider);
If you want to make your filter "global", that is, to be applied to all beans, you can create a mix-in class and annotate it with #JsonFilter("customPropertyFilter"):
#JsonFilter("customPropertyFilter")
public class CustomPropertyFilterMixIn {
}
Then bind the mix-in class to Object:
mapper.addMixIn(Object.class, CustomPropertyFilterMixIn.class);
public static <T> String getNonNullFieldsSerialized(T object, ObjectMapper objectMapper)throws JsonProcessingException {
Map<String, Object> objectMap = objectMapper.convertValue(object, new TypeReference<Map<String, Object>>() {});
Map<String, Object> objectMapNonNullValues = objectMap.entrySet().stream()
.filter(stringObjectEntry -> Objects.nonNull(stringObjectEntry.getValue()))
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
return objectMapper.writeValueAsString(objectMapNonNullValues);
}
This will basically ignore all the fields that are non-null. Similarly you can ignore other fields by changing the map filter condition.
I have implemented dynamic filter on data getting from db and returning it using rest api.I have avoided using MappingJacksonValue.As it was getting issue while object chaining
#GetMapping("/courses")
public ResponseEntity<JpaResponse> allCourse() throws Exception {
JpaResponse response = null;
ObjectMapper mapper = new ObjectMapper();
mapper.setSerializationInclusion(JsonInclude.Include.NON_NULL);
List<Course> course = service.findAllCourse();
SimpleBeanPropertyFilter filter = SimpleBeanPropertyFilter.filterOutAllExcept("name","reviews");
FilterProvider filterProvider = new SimpleFilterProvider().addFilter("jpafilter", filter).setFailOnUnknownId(false);
ObjectWriter writer = mapper.writer(filterProvider);
String writeValueAsString = writer.writeValueAsString(course);
List<Course> resultcourse = mapper.readValue(writeValueAsString,List.class);
response = new JpaResponse(HttpStatus.OK.name(),resultcourse);
return new ResponseEntity<>(response, HttpStatus.OK);
}
public class JpaResponse {
private String status;
private Object data;
public JpaResponse() {
super();
}
public JpaResponse(String status, Object data) {
super();
this.status = status;
this.data = data;
}
}

Gson: Is there more efficient ways to do custom (de)serialization of a verbose Json object

I am working with some json objects that I call verbose:
{
"user": {
"name": "username",
"email": "blah#blah.com",
"time_zone": "America/New_York"
}
}
But I'd prefer to just deal with them in terms of java POJOs like:
class UserDetails {
String name;
String email;
String timeZone;
...
}
Note that I have no control over the POJO as it is generated code.
My two requirements for (de)serialization is that
the timeZone field maps to time_zone in JSON
the outer user is ignored
So I have some customer (de)serializers:
class UserDeserializer implements JsonDeserializer<UserDetails> {
#Override
public UserDetails deserialize(JsonElement je, Type type, JsonDeserializationContext jdc)
throws JsonParseException {
JsonElement content = je.getAsJsonObject().get("user");
UserDetails userDetails = new GsonBuilder()
.setFieldNamingStrategy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
.create()
.fromJson(content, UserDetails.class);
return userDetails;
}
}
class UserSerializer implements JsonSerializer<UserDetails> {
#Override
public JsonElement serialize(UserDetails userDetails, Type typeOfSrc,
JsonSerializationContext context) {
JsonObject obj = new JsonObject();
JsonElement je = new GsonBuilder()
.setFieldNamingStrategy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
.create().toJsonTree(userDetails);
obj.add("user", je);
return obj;
}
}
I feel like creating new Gson objects in the (de)serializer logic is not ideal/efficient just to add and remove the outermost user key.
EDIT: Actually .setFieldNamingStrategy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES) does work fine on deserialization.
I don't really think it's a good idea in general, and you should probably better have a single Wrapper<T> for all "top-most" purposes (if you don't want your inner objects to be considered "verbose").
But you're right when you say
I feel like creating new Gson objects in the (de)serializer logic is not ideal/efficient just to add and remove the outermost user key.
So:
Creating a Gson is a relatively expensive operation.
This just creates unnecessary objects and hits the heap.
Gson may be configured in a special way and you might want to share the same Gson configuration everywhere.
JsonSerializer and JsonDeserializer operate on JSON trees (JsonElement and its subclasses), therefore it creates an intermediate in-memory tree representations before/after serialization/deserialization.
You might consider a faster solution, that's free of those items.
final class VerboseTypeAdapterFactory
implements TypeAdapterFactory {
private final Map<Class<?>, String> mappings;
private VerboseTypeAdapterFactory(final Map<Class<?>, String> mappings) {
this.mappings = mappings;
}
static TypeAdapterFactory get(final Map<Class<?>, String> mappings) {
// Create a defensive copy to make sure the map is not modified from outside
final Map<Class<?>, String> mappingsCopy = mappings
.entrySet()
.stream()
.collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue));
return new VerboseTypeAdapterFactory(mappingsCopy);
}
#Override
public <T> TypeAdapter<T> create(final Gson gson, final TypeToken<T> typeToken) {
final Class<? super T> rawType = typeToken.getRawType();
// Not something we can handle?
if ( !mappings.containsKey(rawType) ) {
// Then let Gson do its job elsewhere
return null;
}
// Getting a property name we want to use for a particular class
final String propertyName = mappings.get(rawType);
// And getting the original type adapter for this class (effectively ReflectiveTypeAdapterFactory.Adapter)
final TypeAdapter<T> delegateTypeAdapter = gson.getDelegateAdapter(this, typeToken);
return VerboseTypeAdapter.get(propertyName, delegateTypeAdapter);
}
private static final class VerboseTypeAdapter<T>
extends TypeAdapter<T> {
private final String propertyName;
private final TypeAdapter<T> delegateTypeAdapter;
private VerboseTypeAdapter(final String propertyName, final TypeAdapter<T> delegateTypeAdapter) {
this.propertyName = propertyName;
this.delegateTypeAdapter = delegateTypeAdapter;
}
private static <T> TypeAdapter<T> get(final String propertyName, final TypeAdapter<T> delegateTypeAdapter) {
return new VerboseTypeAdapter<>(propertyName, delegateTypeAdapter)
// A convenient method to simplify null-handling
.nullSafe();
}
#Override
#SuppressWarnings("resource")
public void write(final JsonWriter out, final T object)
throws IOException {
// Open the object with `{`
out.beginObject();
// Prepend the object with its reserved name
out.name(propertyName);
// Write the object
delegateTypeAdapter.write(out, object);
// And close the object with `}`
out.endObject();
}
#Override
public T read(final JsonReader in)
throws IOException {
// Assume the very first token is `{`
in.beginObject();
// Peeking what's the actual property name
final String actualPropertyName = in.nextName();
// And if it's not we expect, throw a JSON parse exception
if ( !actualPropertyName.equals(propertyName) ) {
throw new JsonParseException("Expected " + propertyName + " but was " + actualPropertyName);
}
// Otherwise read the value led by the property name
final T object = delegateTypeAdapter.read(in);
// And make sure there are no more properties
if ( in.hasNext() ) {
throw new JsonParseException(propertyName + " is expected to be the only top-most property");
}
// Assume the very last token is `}` (this works for the check above, but we made it more semantical)
in.endObject();
return object;
}
}
}
So, for example, the following code
private static final Gson gson = new GsonBuilder()
.setFieldNamingStrategy(FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES)
.registerTypeAdapterFactory(VerboseTypeAdapterFactory.get(ImmutableMap.of(UserDetails.class, "user")))
.create();
...
final UserDetails userDetails = gson.fromJson(jsonReader, UserDetails.class);
System.out.println(userDetails.name);
System.out.println(userDetails.email);
System.out.println(userDetails.timeZone);
final String json = gson.toJson(userDetails);
System.out.println(json);
produces
username
blah#blah.com
America/New_York
{"user":{"name":"username","email":"blah#blah.com","time_zone":"America/New_York"}}
As the conclusion:
No more excessive Gson instantiation.
Original Gson instance configuration inherited (i.e. FieldNamingPolicy.LOWER_CASE_WITH_UNDERSCORES set once).
No intermediate JsonElement instances.

Serialize only mentioned fields in Spring MVC to JSON response

I am writing a rest service using spring MVC which produces JSON response. It should allow client to select only the given fields in response, means client can mention the fields he is interested in as url parameter like ?fields=field1,field2.
Using Jackson annotations does not provide what I am looking for as it is not dynamic also the filters in Jackson doesnt seem to be promising enough.
So far I am thinking to implement a custom message converter which can take care of this.
Is there any other better way to achieve this? I would like if this logic is not coupled with my services or controllers.
From Spring 4.2, #JsonFilter is supported in MappingJacksonValue
Issue : SPR-12586 : Support Jackson #JsonFilter
Commit : ca06582
You can directly inject PropertyFilter to MappingJacksonValue in a controller.
#RestController
public class BookController {
private static final String INCLUSION_FILTER = "inclusion";
#RequestMapping("/novels")
public MappingJacksonValue novel(String[] include) {
#JsonFilter(INCLUSION_FILTER)
class Novel extends Book {}
Novel novel = new Novel();
novel.setId(3);
novel.setTitle("Last summer");
novel.setAuthor("M.K");
MappingJacksonValue res = new MappingJacksonValue(novel);
PropertyFilter filter = SimpleBeanPropertyFilter.filterOutAllExcept(include);
FilterProvider provider = new SimpleFilterProvider().addFilter(INCLUSION_FILTER, filter);
res.setFilters(provider);
return res;
}
or you can declare global policy by ResponseBodyAdvice. The following example implements filtering policy by "exclude" parameter.
#ControllerAdvice
public class DynamicJsonResponseAdvice extends AbstractMappingJacksonResponseBodyAdvice {
public static final String EXCLUDE_FILTER_ID = "dynamicExclude";
private static final String WEB_PARAM_NAME = "exclude";
private static final String DELI = ",";
private static final String[] EMPTY = new String[]{};
#Override
protected void beforeBodyWriteInternal(MappingJacksonValue container, MediaType contentType,
MethodParameter returnType, ServerHttpRequest req, ServerHttpResponse res) {
if (container.getFilters() != null ) {
// It will be better to merge FilterProvider
// If 'SimpleFilterProvider.addAll(FilterProvider)' is provided in Jackson, it will be easier.
// But it isn't supported yet.
return;
}
HttpServletRequest baseReq = ((ServletServerHttpRequest) req).getServletRequest();
String exclusion = baseReq.getParameter(WEB_PARAM_NAME);
String[] attrs = StringUtils.split(exclusion, DELI);
container.setFilters(configFilters(attrs));
}
private FilterProvider configFilters(String[] attrs) {
String[] ignored = (attrs == null) ? EMPTY : attrs;
PropertyFilter filter = SimpleBeanPropertyFilter.serializeAllExcept(ignored);
return new SimpleFilterProvider().addFilter(EXCLUDE_FILTER_ID, filter);
}
}
IMHO, the simplest way to do that would be to use introspection to dynamically generate a hash containing selected fields and then serialize that hash using Json. You simply have to decide what is the list of usable fields (see below).
Here are two example functions able to do that, first gets all public fields and public getters, the second gets all declared fields (including private ones) in current class and all its parent classes :
public Map<String, Object> getPublicMap(Object obj, List<String> names)
throws IllegalAccessException, IllegalArgumentException, InvocationTargetException {
List<String> gettedFields = new ArrayList<String>();
Map<String, Object> values = new HashMap<String, Object>();
for (Method getter: obj.getClass().getMethods()) {
if (getter.getName().startsWith("get") && (getter.getName().length > 3)) {
String name0 = getter.getName().substring(3);
String name = name0.substring(0, 1).toLowerCase().concat(name0.substring(1));
gettedFields.add(name);
if ((names == null) || names.isEmpty() || names.contains(name)) {
values.put(name, getter.invoke(obj));
}
}
}
for (Field field: obj.getClass().getFields()) {
String name = field.getName();
if ((! gettedFields.contains(name)) && ((names == null) || names.isEmpty() || names.contains(name))) {
values.put(name, field.get(obj));
}
}
return values;
}
public Map<String, Object> getFieldMap(Object obj, List<String> names)
throws IllegalArgumentException, IllegalAccessException {
Map<String, Object> values = new HashMap<String, Object>();
for (Class<?> clazz = obj.getClass(); clazz != Object.class; clazz = clazz.getSuperclass()) {
for (Field field : clazz.getDeclaredFields()) {
String name = field.getName();
if ((names == null) || names.isEmpty() || names.contains(name)) {
field.setAccessible(true);
values.put(name, field.get(obj));
}
}
}
return values;
}
Then you only have to get the result of one of this function (or of one you could adapt to your requirements) and serialize it with Jackson.
If you have custom encoding of you domain objects, you would have to maintain the serialization rules in two different places : hash generation and Jackson serialization. In that case, you could simply generate the full class serialization with Jackson and filter the generated string afterwards. Here is an example of such a filter function :
public String jsonSub(String json, List<String> names) throws IOException {
if ((names == null) || names.isEmpty()) {
return json;
}
ObjectMapper mapper = new ObjectMapper();
Map<String, Object> map = mapper.readValue(json, HashMap.class);
for (String name: map.keySet()) {
if (! names.contains(name)) {
map.remove(name);
}
}
return mapper.writeValueAsString(map);
}
Edit : integration in Spring MVC
As you are speaking of a web service and of Jackson, I assume that you use Spring RestController or ResponseBody annotations and (under the hood) a MappingJackson2HttpMessageConverter. If you use Jackson 1 instead, it should be a MappingJacksonHttpMessageConverter.
What I propose is simply to add a new HttpMessageConverter that could make use of one of the above filtering functions, and delegate actual work (and also ancilliary methods) to a true MappingJackson2HttpMessageConverter. In the write method of that new converter, it is possible to have access to the eventual fields request parameter with no need for an explicit ThreadLocal variable thanks to Spring RequestContextHolder. That way :
you keep a clear separation of roles with no modification on existing controllers
you have no modification in Jackson2 configuration
you need no new ThreadLocal variable and simply use a Spring class in a class already tied to Spring since it implements HttpMessageConverter
Here is an example of such a message converter :
public class JsonConverter implements HttpMessageConverter<Object> {
private static final Logger logger = LoggerFactory.getLogger(JsonConverter.class);
// a real message converter that will respond to ancilliary methods and do the actual work
private HttpMessageConverter<Object> delegate =
new MappingJackson2HttpMessageConverter();
// allow configuration of the fields name
private String fieldsParam = "fields";
public void setFieldsParam(String fieldsParam) {
this.fieldsParam = fieldsParam;
}
#Override
public boolean canRead(Class<?> clazz, MediaType mediaType) {
return delegate.canRead(clazz, mediaType);
}
#Override
public boolean canWrite(Class<?> clazz, MediaType mediaType) {
return delegate.canWrite(clazz, mediaType);
}
#Override
public List<MediaType> getSupportedMediaTypes() {
return delegate.getSupportedMediaTypes();
}
#Override
public Object read(Class<? extends Object> clazz, HttpInputMessage inputMessage) throws IOException, HttpMessageNotReadableException {
return delegate.read(clazz, inputMessage);
}
#Override
public void write(Object t, MediaType contentType, HttpOutputMessage outputMessage)
throws IOException, HttpMessageNotWritableException {
// is there a fields parameter in request
String[] fields = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes())
.getRequest().getParameterValues(fieldsParam);
if (fields != null && fields.length != 0) {
// get required field names
List<String> names = new ArrayList<String>();
for (String field : fields) {
String[] f_names = field.split("\\s*,\\s*");
names.addAll(Arrays.asList(f_names));
}
// special management for Map ...
if (t instanceof Map) {
Map<?, ?> tmap = (Map<?, ?>) t;
Map<String, Object> map = new LinkedHashMap<String, Object>();
for (Entry entry : tmap.entrySet()) {
String name = entry.getKey().toString();
if (names.contains(name)) {
map.put(name, entry.getValue());
}
}
t = map;
} else {
try {
Map<String, Object> map = getMap(t, names);
t = map;
} catch (Exception ex) {
throw new HttpMessageNotWritableException("Error in field extraction", ex);
}
}
}
delegate.write(t, contentType, outputMessage);
}
/**
* Create a Map by keeping only some fields of an object
* #param obj the Object
* #param names names of the fields to keep in result Map
* #return a map containing only requires fields and their value
* #throws IllegalArgumentException
* #throws IllegalAccessException
*/
public static Map<String, Object> getMap(Object obj, List<String> names)
throws IllegalArgumentException, IllegalAccessException {
Map<String, Object> values = new HashMap<String, Object>();
for (Class<?> clazz = obj.getClass(); clazz != Object.class; clazz = clazz.getSuperclass()) {
for (Field field : clazz.getDeclaredFields()) {
String name = field.getName();
if (names.contains(name)) {
field.setAccessible(true);
values.put(name, field.get(obj));
}
}
}
return values;
}
}
If you want the converter to be more versatile, you could define an interface
public interface FieldsFilter {
Map<String, Object> getMap(Object obj, List<String> names)
throws IllegalAccessException, IllegalArgumentException, InvocationTargetException;
}
and inject it with an implementation of that.
Now you must ask Spring MVC to use that custom message controller.
If you use XML config, you simply declare it in the <mvc:annotation-driven> element :
<mvc:annotation-driven >
<mvc:message-converters>
<bean id="jsonConverter" class="org.example.JsonConverter"/>
</mvc:message-converters>
</mvc:annotation-driven>
And if you use Java configuration, it is almost as simple :
#EnableWebMvc
#Configuration
public class WebConfig extends WebMvcConfigurerAdapter {
#Autowired JsonConverter jsonConv;
#Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.add(jsonConv);
StringHttpMessageConverter stringConverter = new StringHttpMessageConverter();
stringConverter.setWriteAcceptCharset(false);
converters.add(new ByteArrayHttpMessageConverter());
converters.add(stringConverter);
converters.add(new ResourceHttpMessageConverter());
converters.add(new SourceHttpMessageConverter<Source>());
converters.add(new AllEncompassingFormHttpMessageConverter());
converters.add(new MappingJackson2HttpMessageConverter());
}
}
but here you have to explicitely add all the default message converters that you need.
I've never done this but after looking at this page http://wiki.fasterxml.com/JacksonFeatureJsonFilter it seems that it would be possible to do what you want this way:
1) Create a custom JacksonAnnotationIntrospector implementation (by extending default one) that will use a ThreadLocal variable to choose a filter for current request and also create a custom FilterProvider that would provide that filter.
2) Configure the message converter's ObjectMapper to use the custom introspector and filter provider
3) Create an MVC interceptor for REST service that detects fields request parameter and configures a new filter for current request via your custom filter provider (this should be a thread local filter). ObjectMapper should pick it up through your custom JacksonAnnotationIntrospector.
I'm not 100% certain that this solution would be thread safe (it depends on how ObjectMapper uses annotation introspector and filter provider internally).
- EDIT -
Ok I did a test implementation and found out that step 1) wouldn't work because Jackson caches the result of AnnotationInterceptor per class. I modified idea to apply dynamic filtering only on annotated controller methods and only if the object doesn't have anoter JsonFilter already defined.
Here's the solution (it's quite lengthy):
DynamicRequestJsonFilterSupport class manages the per-request fields to be filtered out:
public class DynamicRequestJsonFilterSupport {
public static final String DYNAMIC_FILTER_ID = "___DYNAMIC_FILTER";
private ThreadLocal<Set<String>> filterFields;
private DynamicIntrospector dynamicIntrospector;
private DynamicFilterProvider dynamicFilterProvider;
public DynamicRequestJsonFilterSupport() {
filterFields = new ThreadLocal<Set<String>>();
dynamicFilterProvider = new DynamicFilterProvider(filterFields);
dynamicIntrospector = new DynamicIntrospector();
}
public FilterProvider getFilterProvider() {
return dynamicFilterProvider;
}
public AnnotationIntrospector getAnnotationIntrospector() {
return dynamicIntrospector;
}
public void setFilterFields(Set<String> fieldsToFilter) {
filterFields.set(Collections.unmodifiableSet(new HashSet<String>(fieldsToFilter)));
}
public void setFilterFields(String... fieldsToFilter) {
filterFields.set(Collections.unmodifiableSet(new HashSet<String>(Arrays.asList(fieldsToFilter))));
}
public void clear() {
filterFields.remove();
}
public static class DynamicIntrospector extends JacksonAnnotationIntrospector {
#Override
public Object findFilterId(Annotated annotated) {
Object result = super.findFilterId(annotated);
if (result != null) {
return result;
} else {
return DYNAMIC_FILTER_ID;
}
}
}
public static class DynamicFilterProvider extends FilterProvider {
private ThreadLocal<Set<String>> filterFields;
public DynamicFilterProvider(ThreadLocal<Set<String>> filterFields) {
this.filterFields = filterFields;
}
#Override
public BeanPropertyFilter findFilter(Object filterId) {
return null;
}
#Override
public PropertyFilter findPropertyFilter(Object filterId, Object valueToFilter) {
if (filterId.equals(DYNAMIC_FILTER_ID) && filterFields.get() != null) {
return SimpleBeanPropertyFilter.filterOutAllExcept(filterFields.get());
}
return super.findPropertyFilter(filterId, valueToFilter);
}
}
}
JsonFilterInterceptor intercepts controller methods annotated with custom #ResponseFilter annotation.
public class JsonFilterInterceptor implements HandlerInterceptor {
#Autowired
private DynamicRequestJsonFilterSupport filterSupport;
private ThreadLocal<Boolean> requiresReset = new ThreadLocal<Boolean>();
#Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
if (handler instanceof HandlerMethod) {
HandlerMethod method = (HandlerMethod) handler;
ResponseFilter filter = method.getMethodAnnotation(ResponseFilter.class);
String[] value = filter.value();
String param = filter.param();
if (value != null && value.length > 0) {
filterSupport.setFilterFields(value);
requiresReset.set(true);
} else if (param != null && param.length() > 0) {
String filterParamValue = request.getParameter(param);
if (filterParamValue != null) {
filterSupport.setFilterFields(filterParamValue.split(","));
}
}
}
requiresReset.remove();
return true;
}
#Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
}
#Override
public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
Boolean reset = requiresReset.get();
if (reset != null && reset) {
filterSupport.clear();
}
}
}
Here's the custom #ResponseFilter annotation. You can either define a static filter (via annotation's value property) or a filter based on request param (via annotation's param property):
#Target({ElementType.METHOD, ElementType.TYPE})
#Retention(RetentionPolicy.RUNTIME)
#Documented
public #interface ResponseFilter {
String[] value() default {};
String param() default "";
}
You will need to setup the message converter and the interceptor in the config class:
...
#Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.add(converter());
}
#Bean
JsonFilterInterceptor jsonFilterInterceptor() {
return new JsonFilterInterceptor();
}
#Override
public void addInterceptors(InterceptorRegistry registry) {
registry.addInterceptor(jsonFilterInterceptor);
}
#Bean
DynamicRequestJsonFilterSupport filterSupport() {
return new DynamicRequestJsonFilterSupport();
}
#Bean
MappingJackson2HttpMessageConverter converter() {
MappingJackson2HttpMessageConverter converter = new MappingJackson2HttpMessageConverter();
ObjectMapper mapper = new ObjectMapper();
mapper.setAnnotationIntrospector(filterSupport.getAnnotationIntrospector());
mapper.setFilters(filterSupport.getFilterProvider());
converter.setObjectMapper(mapper);
return converter;
}
...
And finally, you can use the filter like this:
#RequestMapping("/{id}")
#ResponseFilter(param = "fields")
public Invoice getInvoice(#PathVariable("id") Long id) { ... }
When request is made to /invoices/1?fields=id,number response will be
filtered and only id and number properties will be returned.
Please note I haven't tested this thoroughly but it should get you started.
Would populating a HashMap from the object not suite the requirements? You could then just parse the HashMap. I have done something similar with GSON in the past where I had to provide a simple entity and ended up just populating a HashMap and then serializing it, it was far more maintainable than over engineering a whole new system.

Jersey client read json response into custom object

public class RESTDataServiceClient{
private Client client;
private String dataServiceUri;
private String dataServiceResource;
private CustomData customData;
public RESTDataServiceClient(String dataServiceUri, String dataServiceResource, Client client){
this.client = client;
this.dataServiceUri = dataServiceUri;
this.dataServiceResource = dataServiceResource;
}
#Override
public CustomData getCustomData() {
WebTarget dataServiceTarget = client.target(dataServiceUri).path(dataServiceResource);
Invocation.Builder invocationBuilder = dataServiceTarget.request(MediaType.APPLICATION_JSON_TYPE);
Response response = invocationBuilder.get();
myCustomData = response.readEntity(CustomData.class);
return myCustomData;
}
}
CustomData.java
public class CustomData{
private TLongObjectMap<Map<String, TIntIntMap>> data;
public CustomData() {
this.data = new TLongObjectHashMap<>();
}
//getter and setter
}
sample json content
{"50000":{"testString":{"1":10}},"50001":{"testString1":{"2":11}} }
I am trying to get data from a data service which is going to return data in a JSON format. I am trying to write a client to read that JSON into a custom object. The CustomData contains a nested trove map datastructure. we wrote a custom serializer for that and the server part works fine. I am unable to get the rest client read the data into an object, but reading into string works. I tried above pasted code with the sample data and i get the error below.
javax.ws.rs.ProcessingException: Error reading entity from input stream.
at org.glassfish.jersey.message.internal.InboundMessageContext.readEntity(InboundMessageContext.java:866)
at org.glassfish.jersey.message.internal.InboundMessageContext.readEntity(InboundMessageContext.java:783)
at org.glassfish.jersey.client.ClientResponse.readEntity(ClientResponse.java:326)
at org.glassfish.jersey.client.InboundJaxrsResponse$1.call(InboundJaxrsResponse.java:111)
at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
at org.glassfish.jersey.internal.Errors.process(Errors.java:228)
at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:399)
at org.glassfish.jersey.client.InboundJaxrsResponse.readEntity(InboundJaxrsResponse.java:108)
at com.sample.data.RESTDataServiceClient.getCustomData(RESTDataServiceClient.java:42)
Caused by: com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException: Unrecognized field "50000" (class com.sample.data.CustomData), not marked as ignorable (0 known properties: ])
at [Source: org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$UnCloseableInputStream#2cb89281; line: 1, column: 14] (through reference chain: com.sample.data.CustomData["50000"])
at com.fasterxml.jackson.databind.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:51)
at com.fasterxml.jackson.databind.DeserializationContext.reportUnknownProperty(DeserializationContext.java:671)
at com.fasterxml.jackson.databind.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:773)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownProperty(BeanDeserializerBase.java:1297)
at com.fasterxml.jackson.databind.deser.BeanDeserializerBase.handleUnknownVanilla(BeanDeserializerBase.java:1275)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.vanillaDeserialize(BeanDeserializer.java:247)
at com.fasterxml.jackson.databind.deser.BeanDeserializer.deserialize(BeanDeserializer.java:118)
at com.fasterxml.jackson.databind.ObjectReader._bind(ObjectReader.java:1233)
at com.fasterxml.jackson.databind.ObjectReader.readValue(ObjectReader.java:677)
at com.fasterxml.jackson.jaxrs.base.ProviderBase.readFrom(ProviderBase.java:777)
at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$TerminalReaderInterceptor.invokeReadFrom(ReaderInterceptorExecutor.java:264)
at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor$TerminalReaderInterceptor.aroundReadFrom(ReaderInterceptorExecutor.java:234)
at org.glassfish.jersey.message.internal.ReaderInterceptorExecutor.proceed(ReaderInterceptorExecutor.java:154)
at org.glassfish.jersey.message.internal.MessageBodyFactory.readFrom(MessageBodyFactory.java:1124)
at org.glassfish.jersey.message.internal.InboundMessageContext.readEntity(InboundMessageContext.java:851)
... 38 more
TLongObjectMap is not deserializable out of the box, so how you made a custom serializer you also need to implement a custom deserializer. You can package these up nicely in a module and add it to your ObjectMapper.
It looks like there is a Trove module in development right now, which you can download and add to your ObjectMapper the same as the example below. The TIntObjectMapDeserializer implementation in that link is much more robust then my solution, so I would recommend using that class in your project if possible.
If you want to try and write it yourself, here's a starting point that properly deserializes your provided example:
public class FakeTest {
#Test
public void test() throws Exception {
ObjectMapper om = new ObjectMapper();
om.registerModule(new CustomModule());
String s = "{\"50000\":{\"testString\":{\"1\":10}},\"50001\":{\"testString1\":{\"2\":11}} }";
CustomData cd = om.readValue(s, CustomData.class);
System.out.println(cd.getData());
}
public static class CustomData {
private TLongObjectMap<Map<String, TIntIntMap>> data;
public CustomData() {
this.data = new TLongObjectHashMap<>();
}
public TLongObjectMap<Map<String, TIntIntMap>> getData() { return data; }
public void setData(TLongObjectMap<Map<String, TIntIntMap>> data) { this.data = data; }
}
public static class CustomModule extends SimpleModule {
public CustomModule() {
addSerializer(CustomData.class, new CustomSerializer());
addDeserializer(CustomData.class, new CustomDeserializer());
}
public static class CustomSerializer extends JsonSerializer<CustomData> {
#Override
public void serialize(CustomData value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
// add custom serializer here
}
}
public static class CustomDeserializer extends JsonDeserializer<CustomData> {
#Override
public CustomData deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
TLongObjectMap<Map<String, TIntIntMap>> data = new TLongObjectHashMap<>();
ObjectNode node = jsonParser.getCodec().readTree(jsonParser);
Iterator<Map.Entry<String,JsonNode>> fields = node.fields();
while (fields.hasNext()) {
Map.Entry<String, JsonNode> entry = fields.next();
ObjectNode value = (ObjectNode) entry.getValue();
Map.Entry<String, JsonNode> innerField = value.fields().next();
ObjectNode innerNode = (ObjectNode) innerField.getValue();
Map.Entry<String, JsonNode> innerInnerField = innerNode.fields().next();
TIntIntMap intMap = new TIntIntHashMap();
intMap.put(Integer.parseInt(innerInnerField.getKey()), innerInnerField.getValue().asInt());
Map<String, TIntIntMap> innerMap = Collections.singletonMap(innerField.getKey(), intMap);
data.put(Long.parseLong(entry.getKey()), innerMap);
}
CustomData customData = new CustomData();
customData.setData(data);
return customData;
}
}
}
}

How to indicate a specific Serializer for an object?

I have a model like :
SomeModel
public Long id;
public String name;
public Integer age;
public String address;
public Profile profile;
In my templates, I'd like to render a simpler version of this model, only id and name.
If I do Json.toJson(SomeModel.find.findList()); it will render a list of the SomeModels in the database, but with the complete form.
I've written a Serializer that just returns id and name, but how can I tell Json.toJson to use this serializer ?
public class SimpleSomeModelSeralizer extends JsonSerializer<SomeModel> {
#Override
public void serialize(SomeModel someModel, JsonGenerator generator, SerializerProvider serializer) throws IOException,JsonProcessingException {
if (someModel == null) return;
generator.writeStartObject();
generator.writeNumberField("id", someModel.getId());
generator.writeStringField("name", someModel.getName());
generator.writeEndObject();
}
}
I've looked at the code in Play, and of course, toJson is a simple version, that doesn't take some serializer as parameter, so I guess I have to write a longer code, but I don't know what/how to do it.
Code in Play of Json.toJson :
public static JsonNode toJson(final Object data) {
try {
return new ObjectMapper().valueToTree(data);
} catch(Exception e) {
throw new RuntimeException(e);
}
}
Is it possible to do something like this? :
new ObjectMapper().useSerializer(SimpleSomeModelSeralizer.class).valueToTree(SomeModel.find.findList());
Ok so, here's what I did. On the SomeModel class, I added a static method that returns the list as JsonNode, and I simply call it from my templates :
public static JsonNode findItemsAsJson() {
ObjectMapper mapper = new ObjectMapper();
SimpleModule someModelModule = new SimpleModule("SomeModel", new Version(1, 0, 0, null));
someModelModule.addSerializer(SomeModel.class, new SimpleSomeModelSeralizer());
mapper.registerModule(someModelModule);
return mapper.valueToTree(SomeModel.find.findList());
}
The drawback of this method is that you are bound to the query hard coded (SomeModel.find.findList()) but you can easily add a parameter to that method that is the query :
public static JsonNode findItemsAsJson(Query<SomeModel> query) {
ObjectMapper mapper = new ObjectMapper();
SimpleModule someModelModule = new SimpleModule("SomeModel", new Version(1, 0, 0, null));
someModelModule.addSerializer(SomeModel.class, new SimpleSomeModelSeralizer());
mapper.registerModule(someModelModule);
return mapper.valueToTree(query.findList());
}
And you call it with :
SomeModel.findItemsAsJson(SomeModel.find.like("name", "B%").query());
Hope it'll helps :)