I have the following JSON...
{
"name":"MyThings",
"things":[
{
"num":"123"
},
{
"num":"456"
}
]
}
So far I have this much of the mapping...
#JsonIgnoreProperties(ignoreUnknown = true)
public class ThingList {
private String name;
private int[] nums;
}
How do I essentially do a map from object array to int array using Jackson?
You can use a custom deserializer for this:
class DeSerializer extends StdDeserializer<ThingList> {
protected DeSerializer() {
super(ThingList.class);
}
#Override
public ThingList deserialize(JsonParser p, DeserializationContext ctxt) {
// use p.getText() and p.nextToken to navigate through the xml and construct ThingList object
return something;
}
Initialize the parser as follows with the deserializer:
ObjectMapper mapper = new ObjectMapper();
SimpleModule module = new SimpleModule("configModule", Version.unknownVersion());
module.addDeserializer(ThingList.class, new DeSerializer());
mapper.registerModule(module);
ThingList tl = mapper.readValue(<json string>, ThingList.class);
Consider a json of type "Clothing":
{
"id":"123",
"version":2,
"apparel":{
"category":[
{
"id":"a1",
"style":"top",
"comments":[
{
"header":{
"type":"apparel.detail.Summary",
"major_version":1,
"minor_version":0
},
"summary": "notes"
}]
}
]
},
"accessories":[
{
"header":{
"type":"accessories.detail.Handbag",
"major_version":1,
"minor_version":0
},
"details":{
"brand":"Gucci",
"sno.":"G12"
},
"color":"Red",
},
{
"header":{
"type":"accessories.detail.Hat",
"major_version":1,
"minor_version":0
},
"details":{
"brand":"Adidas",
"sno.":"A12"
}
}
]
}
"Clothing" is not accessible to me and I cannot add any field level or class level json annotations.
There is a property "header" in json that helps me to determine the type of class I want to convert that entity into. I will remove the header from my json once the class type is determined (since header is not defined in my target class type because of which deserialization will fail)
I need to write a custom deserializer that returns a generic class type object. It will check if there is header, fetch target class name, remove header and deserialize it to the fetched target class and return.
This is the code that I have written, but it does not work and I am not even sure if it is possible to have a custom deserializer injected in SimpleModule with a generic return type.
#Singleton
#Provides
private Transformer provideTransformer(final HeaderDeserializer headerDeserializer) {
final SimpleModule simpleModule = new SimpleModule();
simpleModule.addDeserializer(Object.class, headerDeserializer);
mapper.registerModule(simpleModule);
}
#Singleton
#Provides
private HeaderDeserializer provideHeaderDeserializer(final ObjectMapper objectMapper) {
return new HeaderDeserializer(objectMapper);
}
#Singleton
#Provides
private ObjectMapper provideObjectMapper() {
final ObjectMapper mapper = new ObjectMapper()
// Tell object mapper how to handle joda-time.
.registerModule(new JodaModule())
// include non-null values only
.setSerializationInclusion(Include.NON_NULL)
// ensures that timezone is preserved
.disable(DeserializationFeature.ADJUST_DATES_TO_CONTEXT_TIME_ZONE);
return mapper;
}
My HeaderDeserializer looks something like this:
public class HeaderDeserializer<T> extends StdDeserializer<T> {
private static final long serialVersionUID = 1L;
private final ObjectMapper mapper;
public HeaderDeserializer(final ObjectMapper mapper) {
this(null, mapper);
}
public HeaderDeserializer(final Class<?> vc, final ObjectMapper mapper) {
super(vc);
this.mapper = mapper;
}
#Override
public T deserialize(final JsonParser jp, final DeserializationContext ctx) {
Object value = null;
try {
JsonNode node = this.mapper.readTree(jp);
JsonNode header = node.get("header");
if (node.has("header")) {
String targetClass = header.get("type").textValue();
removeHeaderFromJsonDoc(node);
value = this.mapper.readValue(jp, Class.forName(targetClass));
}
} catch (final IOException e) {
throw new UncheckedIOException(e);
} catch (final ClassNotFoundException e) {
// do somehting
}
return (T) value;
}
private void removeHeaderFromJsonDoc(final JsonNode document) {
final Iterator<Entry<String, JsonNode>> itr = document.fields();
while (itr.hasNext()) {
final Entry<String, JsonNode> childNodeEntry = itr.next();
if (childNodeEntry.getKey().equals("header")) {
itr.remove();
}
}
}
}
And my main deserializer which will use the custom deserializer defined above looks like:
public final Clothing deserialize(
final String stringValue,
final Class<? extends Clothing> clazz) {
try {
return this.objectMapper.readValue(stringValue, clazz);
} catch (final IOException e) {
throw new IllegalArgumentException();
}
}
this.objectMapper.readValue(stringValue, clazz);
Class type of 'clazz' in this readValue method should match class type passed in simpleModule.addDeserializer.
It is not going inside your deserializer because you are adding deserializer to SimpleModule for 'Object' class and reading value for different class passed to 'Clothing deserialize',
I am trying to create a rest end point and using Swagger as UI representation. The pojo which I'm using it has a variable annotated with #JsonIgnore as shown below.
#JsonIgnore
private Map<String, Object> property = new HashMap<String, Object>();
Now, when I'm providing JSON (with property value) to this end point and trying to read its value it is coming out as null (due to #JsonIgnore).
pojoObj.getProperties(); //null
Is there any way if I can get property value without removing the #JsonIgnore annotation?
This can be achieved by utilizing Jackson's Mixin feature, where you create another class that cancels the ignore annotation. You can then "attach" the mixin to the ObjectMapper at run time:
This is the POJO I used:
public class Bean
{
// always deserialized
public String name;
// ignored (unless...)
#JsonIgnore
public Map<String, Object> properties = new HashMap<String, Object>();
}
This is the "other" class. It is just another POJO with the same property name
public class DoNotIgnore
{
#JsonIgnore(false)
public Map<String, Object> properties;
}
a Jackson Module is used to tie the bean to the mixin:
#SuppressWarnings("serial")
public class DoNotIgnoreModule extends SimpleModule
{
public DoNotIgnoreModule() {
super("DoNotIgnoreModule");
}
#Override
public void setupModule(SetupContext context)
{
context.setMixInAnnotations(Bean.class, DoNotIgnore.class);
}
}
Tying it all together:
public static void main(String[] args)
{
String json = "{\"name\": \"MyName\","
+"\"properties\": {\"key1\": \"val1\", \"key2\": \"val2\", \"key3\": \"val3\"}"
+ "}";
try {
ObjectMapper mapper = new ObjectMapper();
// decide at run time whether to ignore properties or not
if ("do-not-ignore".equals(args[0])) {
mapper.registerModule(new DoNotIgnoreModule());
}
Bean bean = mapper.readValue(json, Bean.class);
System.out.println(" Name: " + bean.name + ", properties " + bean.properties);
} catch (IOException e) {
e.printStackTrace();
}
}
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.
I have a Java class in a servlet that uses GSON to render posted JSON Strings into a Java object. The beauty of the approach is, that GSON filters out all JSON elements that don't match a class property, so I never end up with JSON content that I don't want to process. The servlet's doPost (simplified) looks like this:
protected void doPost(HttpServletRequest request, HttpServletResponse response) {
PrintWriter out = null;
try {
InputStream in = request.getInputStream();
Demo d = Demo.load(in);
in.close();
response.setContentType("text/plain");
response.setStatus(HttpServletResponse.SC_OK);
out = response.getWriter();
out.println(d.toJson);
} catch (Exception e) {
e.printStackTrace();
out.println(e.getMessage());
}
out.close();
}
The Demo class (and that's the one I need to recreate in common.js or node.js looks like this:
#JsonIgnoreProperties(ignoreUnknown = true)
public class Demo implements Serializable {
public static Demo load(InputStream in) {
Demo result = null;
try {
Gson gson = new GsonBuilder().create();
result = gson.fromJson(new InputStreamReader(in), Demo.class);
} catch (Exception e) {
result = null;
}
return result;
}
#TypeDiscriminator
#JsonProperty("_id")
private String id = UUID.randomUUID().toString();
private Date created = new Date();
private String color;
private String name;
private String taste;
public String getColor() {
return this.color;
}
public String getName() {
return this.name;
}
public String getTaste() {
return this.taste;
}
public Date getCreated() {
return this.created;
}
public String getId() {
return this.id;
}
public void setName(String name) {
this.name = name;
}
public void setTaste(String taste) {
this.taste = taste;
}
public void setColor(String color) {
this.color = color;
}
public String toJson() {
GsonBuilder gb = new GsonBuilder();
gb.setPrettyPrinting();
gb.disableHtmlEscaping();
Gson gson = gb.create();
return gson.toJson(this);
}
}
Obviously I stripped out all the processing logic and the servlet just echos the JSON back, which is not what the app does, but serves to illustrate the point. I can throw pretty any String in a HTTP Post at that example and I only get valid Demo objects.
How would I do something like this in node.js?
Node.js is Javascript so has built in support for json. You can use JSON.parse to convert from string to json and wrap in try catch block.
To only include select properties there is no built in feature in node that I know of unless you are using Mongodb with mongoose, but you could do following: Have a "class" that is an object containing all properties that you want and delete those from parsed json object that are not in that "class" object.
var class = {x: null, y:null};
for(var prop in object){
if (!class.hasOwnProperty (prop)) {
delete object [prop]
}
It would be best to use this class as object and expose parseJSON function to encapsulate this functionality