We have written a Springboot Rest Service, it internally uses Jackson for Serialisation / deserialisation of Json input / output of Rest APIs.
We do not want type conversion of primitives to / from String for API input / output.
We have disabled String to Primitive conversion using
spring.jackson.mapper.allow-coercion-of-scalars=false
But Primitive to String conversion is still being allowed.
e.g.
"name": 123,
from API is still deserialised to "123", Java data type of name is String here.
We have gone through Customize the Jackson ObjectMapper section of Spring Docs and does not look like there is anything in those enums that can be used.
Is there a way to achieve this without writing a custom ObjectMapper / Deserializer?
We did not find any config property that achieves this, finally went with the solution posted by Michał Ziober.
package xyz;
import com.fasterxml.jackson.databind.deser.std.StringDeserializer;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.core.JsonToken;
import java.io.IOException;
public class StrictStringDeserializer extends StringDeserializer {
#Override
public String deserialize(JsonParser p, DeserializationContext ctxt) throws IOException {
JsonToken token = p.currentToken();
if (token.isBoolean()
|| token.isNumeric()
|| !token.toString().equalsIgnoreCase("VALUE_STRING")) {
ctxt.reportInputMismatch(String.class, "%s is not a `String` value!", token.toString());
return null;
}
return super.deserialize(p, ctxt);
}
}
POJO Class
public class XyzAbc {
// ...
#JsonDeserialize(using = StrictStringDeserializer.class)
private String name;
// ...
}
Related
Situation
I'm migrating a kotlin spring data neo4j application from spring-data-neo4j version 5.2.0.RELEASE to version 6.0.11.
The original application has several Repository interfaces with custom queries which take some DTO as a parameter, and use the various DTO fields to construct the query. All those types of queries currently fail with
org.springframework.core.convert.ConverterNotFoundException: No converter found capable of converting from type [MyDTO] to type [org.neo4j.driver.Value]
The reference documentation for spring-data-neo4j v6 only provides examples where parameters passed to custom query methods of a #Repository interface are of the same type as the #Node class associated with that repository. The documentation does not explicitly state that only parameters of the Node class are allowed.
Question
Is there any way to pass an arbitrary DTO (not being a #Node class) to a custom query method in a #Repository interface in spring-data-neo4j v6 like it was possible in v5?
Code samples
Example node entity
#Node
data class MyEntity(
#Id
val attr1: String,
val attr2: String,
val attr3: String
)
Example DTO
data class MyDTO(
val field1: String,
val field2: String
)
Example Repository interface
#Repository
interface MyRepository : PagingAndSortingRepository<MyEntity, String> {
// ConverterNotFoundException is thrown when this method is called
#Query("MATCH (e:MyEntity {attr1: {0}.field1}) " +
"CREATE (e)-[l:LINK]->(n:OtherEntity {attr2: {0}.field2))")
fun doSomethingWithDto(dto: MyDTO)
}
Solutions tried so far
Annotate DTO as if it were a Node entity
Based on the following found in the reference docs https://docs.spring.io/spring-data/neo4j/docs/current/reference/html/#custom-queries.parameters
Mapped entities (everything with a #Node) passed as parameter to a
function that is annotated with a custom query will be turned into a
nested map.
#Node
data class MyDTO(
#Id
val field1: String,
val field2: String
)
Replace {0} with $0 in custom query
Based on the following found in the reference docs https://docs.spring.io/spring-data/neo4j/docs/current/reference/html/#custom-queries.parameters
You do this exactly the same way as in a standard Cypher query issued
in the Neo4j Browser or the Cypher-Shell, with the $ syntax (from
Neo4j 4.0 on upwards, the old {foo} syntax for Cypher parameters has
been removed from the database).
...
[In the given listing] we are referring to the parameter by its name.
You can also use $0 etc. instead.
#Repository
interface MyRepository : PagingAndSortingRepository<MyEntity, String> {
// ConverterNotFoundException is thrown when this method is called
#Query("MATCH (e:MyEntity {attr1: $0.field1}) " +
"CREATE (e)-[l:LINK]->(n:OtherEntity {attr2: $0.field2))")
fun doSomethingWithDto(dto: MyDTO)
}
Details
spring-boot-starter: v2.4.10
spring-data-neo4j: v6.0.12
neo4j-java-driver: v4.1.4
Neo4j server version: v3.5.29
RTFM Custom conversions ...
Found the solution myself. Hopefully someone else may benefit from this as well.
Solution
Create a custom converter
import mypackage.model.*
import com.fasterxml.jackson.core.type.TypeReference
import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import org.neo4j.driver.Value
import org.neo4j.driver.Values
import org.springframework.core.convert.TypeDescriptor
import org.springframework.core.convert.converter.GenericConverter
import org.springframework.core.convert.converter.GenericConverter.ConvertiblePair
import java.util.HashSet
class DtoToNeo4jValueConverter : GenericConverter {
override fun getConvertibleTypes(): Set<ConvertiblePair>? {
val convertiblePairs: MutableSet<ConvertiblePair> = HashSet()
convertiblePairs.add(ConvertiblePair(MyDTO::class.java, Value::class.java))
return convertiblePairs
}
override fun convert(source: Any?, sourceType: TypeDescriptor, targetType: TypeDescriptor?): Any? {
return if (MyDTO::class.java.isAssignableFrom(sourceType.type)) {
// generic way of converting an object into a map
val dataclassAsMap = jacksonObjectMapper().convertValue(source as MyDTO, object :
TypeReference<Map<String, Any>>() {})
Values.value(dataclassAsMap)
} else null
}
}
Register custom converter in config
import org.springframework.context.annotation.Bean
import org.springframework.context.annotation.Configuration
import org.springframework.data.neo4j.core.convert.Neo4jConversions
import org.springframework.core.convert.converter.GenericConverter
import java.util.*
#Configuration
class MyNeo4jConfig {
#Bean
override fun neo4jConversions(): Neo4jConversions? {
val additionalConverters: Set<GenericConverter?> = Collections.singleton(DtoToNeo4jValueConverter())
return Neo4jConversions(additionalConverters)
}
}
It's ridiculous that the framework would force you to write a custom converter for this. I made a #Transient object in my overridden User class for a limited set of update-able user profile fields, and I'm encountering the same error. I guess I will just have to break up the object into its component String fields in the method params to get around this problem. What a mess.
#Query("MATCH (u:User) WHERE u.username = :#{#username} SET u.firstName = :#{#up.firstName},u.lastName = :#{#up.firstName},u.intro = :#{#up.intro} RETURN u")
Mono<User> update(#Param("username") String username,#Param("up") UserProfile up);
No converter found capable of converting from type [...UserProfile] to type [org.neo4j.driver.Value]
I have some fields in a model that I only want to be returned when the logged in user has the role ROLE_ADMIN. I can use #JsonIgnore but that hides it for everyone. How can I make it hide dynamically?
You should use Jackson Json Views technology to acheive it - it allows to choose a different set of fields to be serialized programatically. It is also supported by Spring
Consider you have a class Model with two properties: commonField which should be available for everyone and secretField which should be available only for certain users. You should create an hierarchy of views (any classes would work) and specify which field is available in which view using #JsonView annotation
package com.stackoverflow.jsonview;
import com.fasterxml.jackson.annotation.JsonView;
public class Model {
public static class Public {}
public static class Secret extends Public {}
#JsonView(Public.class)
private String commonField;
#JsonView(Secret.class)
private String secretField;
public Model() {
}
public Model(String commonField, String secretField) {
this.commonField = commonField;
this.secretField = secretField;
}
public String getCommonField() {
return commonField;
}
public void setCommonField(String commonField) {
this.commonField = commonField;
}
public String getSecretField() {
return secretField;
}
public void setSecretField(String secretField) {
this.secretField = secretField;
}
}
Now you can specify the view you want to use in concrete ObjectMapper
package com.stackoverflow.jsonview;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import org.junit.Test;
import static org.junit.Assert.*;
/**
*/
public class ModelTest {
#Test
public void testSecretField() throws JsonProcessingException {
Model model = new Model("commonField","secretField");
assertEquals("{\"commonField\":\"commonField\",\"secretField\":\"secretField\"}", new ObjectMapper().writerWithView(Model.Secret.class).writeValueAsString(model));
assertEquals("{\"commonField\":\"commonField\"}", new ObjectMapper().writerWithView(Model.Public.class).writeValueAsString(model));
}
}
I am not sure if you can use declaratie approach to make spring choose the right view based on user role out of the box, so probably you will have to write some code like this:
#RequestMapping("/data")
public String getData(HttpServletRequest request) {
Model model = service.getModel();
ObjectMapper objectMapper = new ObjectMapper();
objectMapper = request.isUserInRole("ROLE_ADMIN") ? objectMapper.writerWithView(Model.Secret.class) : objectMapper.writerWithView(Model.Public.class);
return objectMapper.writeValueAsString(model);
}
I solved this after literally a full month of trying various things. I'm working with Spring 4.3.1 and boot, with data being returned in Hal using a pagedrepository.
extend RepositoryRestMvcConfiguration as MyRepositoryRestMvcConfiguration and add #Configuration to the class, make sure your starter class has #EnableWebMvc
add this to MyRepositoryRestMvcConfiguration- extend TypeConstrainedMappingJackson2HttpMessageConverter as MyResourceSupportHttpMessageConverter
add this to MyRepositoryRestMvcConfiguration
#Override
#Bean
public TypeConstrainedMappingJackson2HttpMessageConverter halJacksonHttpMessageConverter() {
ArrayList<MediaType> mediaTypes = new ArrayList<MediaType>();
mediaTypes.add(MediaTypes.HAL_JSON);
if (config().useHalAsDefaultJsonMediaType()) {
mediaTypes.add(MediaType.APPLICATION_JSON);
}
int order = config().useHalAsDefaultJsonMediaType() ? Ordered.LOWEST_PRECEDENCE - 10
: Ordered.LOWEST_PRECEDENCE - 1;
TypeConstrainedMappingJackson2HttpMessageConverter converter = new MyResourceSupportHttpMessageConverter(
order);
converter.setObjectMapper(halObjectMapper());
converter.setSupportedMediaTypes(mediaTypes);
converter.getObjectMapper().addMixIn(Object.class, MyFilteringMixin.class);
final FilterProvider myRestrictionFilterProvider = new SimpleFilterProvider()
.addFilter("MyFilteringMixin", new MyPropertyFilter()).setFailOnUnknownId(false);
converter.getObjectMapper().setFilterProvider(myRestrictionFilterProvider);
return converter;
}
Create an empty Mixin
package filters;
import com.fasterxml.jackson.annotation.JsonFilter;
#JsonFilter("MyFilteringMixin")
public class MyFilteringMixin {}
Create an empty Mixin
create class MyPropertyFilter extending SimpleBeanPropertyFilter and override adapt this method
serializeAsField(Object, JsonGenerator, SerializerProvider, PropertyWriter)you need to call either super.serializeAsField(pPojo, pJgen, pProvider, pWriter) or pWriter.serializeAsOmittedField(pPojo, pJgen, pProvider) depending on whether you wish to include or discard this particular field.
I added an annotation to the particular fields I wanted to alter and interrogated that annotation when deciding which of these two to call. I injected the security role and stored permitted roles in the annotation.
This alters what Hal shares out to the caller, not what Hal is holding in its repository. Thus you can morph it depending on who the caller is.
I'm using HibernateValidator 4.3.1. Validations are performed as intended throughout the entire application.
I have registered some custom editors to perform validation globally such as for ensuring numeric values (double, int etc) in a text-field, for ensuring valid dates regarding the Joda-Time API etc.
In this type of validation, I'm allowing null/empty values by setting the allowEmpty parameter to false as usual to validate it separately especially for displaying separate user friendly error messages when such fields are left blank.
Therefore, in addition to validating with HibernateValidator and custom editors, I'm trying to use the following validation strategy. Again, this kind of validation is only for those fields which are registered for custom editors are when left blank.
The following is the class that implements the org.springframework.validation.Validator interface.
package test;
import org.springframework.stereotype.Component;
import org.springframework.validation.Errors;
import org.springframework.validation.ValidationUtils;
import org.springframework.validation.Validator;
import validatorbeans.TempBean;
#Component
public final class TempValidator implements Validator {
#Override
public boolean supports(Class<?> clazz) {
System.out.println("supports() invoked.");
return TempBean.class.isAssignableFrom(clazz);
}
#Override
public void validate(Object target, Errors errors) {
TempBean tempBean = (TempBean) target;
System.out.println("startDate = " + tempBean.getStartDate() + " validate() invoked.");
System.out.println("doubleValue = " + tempBean.getDoubleValue() + " validate() invoked.");
System.out.println("stringValue = " + tempBean.getStringValue() + " validate() invoked.");
ValidationUtils.rejectIfEmptyOrWhitespace(errors, "startDate", "java.util.date.nullOrEmpty.error");
ValidationUtils.rejectIfEmptyOrWhitespace(errors, "doubleValue", "java.lang.double.nullOrEmpty.error");
}
}
The class is designated with the #Component annotation so that it can be auto-wired to a specific Spring controller class. The debugging statements display exactly based on the input provided by a user.
The following is the controller class.
package controller;
import customizeValidation.CustomizeValidation;
import java.util.Map;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.validation.Valid;
import javax.validation.groups.Default;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.validation.BindingResult;
import org.springframework.validation.DataBinder;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import test.TempValidator;
import validatorbeans.TempBean;
#Controller
public final class TempController {
#Autowired
private TempService tempService;
private TempValidator tempValidator;
public TempValidator getTempValidator() {
return tempValidator;
}
#Autowired
public void setTempValidator(TempValidator tempValidator) {
this.tempValidator = tempValidator;
}
#RequestMapping(method = {RequestMethod.GET}, value = {"admin_side/Temp"})
public String showForm(#ModelAttribute("tempBean") #Valid TempBean tempBean, BindingResult error, Map model, HttpServletRequest request, HttpServletResponse response) {
return "admin_side/Temp";
}
#RequestMapping(method = {RequestMethod.POST}, value = {"admin_side/Temp"})
public String onSubmit(#ModelAttribute("tempBean") #Valid TempBean tempBean, BindingResult errors, Map model, HttpServletRequest request, HttpServletResponse response) {
//tempValidator.supports(TempBean.class);
//tempValidator.validate(tempBean, errors);
DataBinder dataBinder = new DataBinder(tempBean);
dataBinder.setValidator(tempValidator);
dataBinder.validate();
//errors=dataBinder.getBindingResult();
if (CustomizeValidation.isValid(errors, tempBean, TempBean.ValidationGroup.class, Default.class) && !errors.hasErrors()) {
System.out.println("Validated");
}
return "admin_side/Temp";
}
}
I'm invoking the validator from the Spring controller class itself (which I indeed want) by
DataBinder dataBinder = new DataBinder(tempBean);
dataBinder.setValidator(tempValidator);
dataBinder.validate();
The validator is called but the validation which is expected is not performed.
If only I invoke the validator manually using the following statement (which is commented out above),
tempValidator.validate(tempBean, errors);
then validation is performed. So I don't believe my validator is correctly working. Why does it fail to work with DataBinder?
In my application-context.xml file, this bean is simply configured as follows.
<bean id="tempValidator" class="test.TempValidator"/>
This many packages as below including the test package which the TempValidator class is enclosed within are auto-detected.
<context:component-scan base-package="controller spring.databinder validatorbeans validatorcommands test" use-default-filters="false">
<context:include-filter expression="org.springframework.stereotype.Controller" type="annotation"/>
<context:include-filter expression="org.springframework.web.bind.annotation.ControllerAdvice" type="annotation"/>
</context:component-scan>
I have even tried to put
<bean id="validator" class="org.springframework.validation.beanvalidation.LocalValidatorFactoryBean"/>
In my dispatcher-servlet.xml file.
What am I overlooking here?
If I understand well what you try to achieve - distinguish between blank fields and incorrect values entered - you can use MUCH MORE SIMPLER approach:
public class MyBean {
#NotNull
#DateTimeFormat(pattern="dd.MM.yyyy HH:mm")
private DateTime date;
#NotNull
#Max(value=5)
private Integer max;
#NotNull
#Size(max=20)
private String name;
// getters, setters ...
}
Controller mapping:
public void submitForm(#ModelAttribute #Valid MyBean myBean, BindingResult result) {
if (result.hasErrors){
// do something}
else{
// do something else
}
}
Validation messages:
NotNull=Required field.
NotNull.date=Date is required field.
NotNull.max=Max is required field.
Size=Must be between {2} and {1} letters.
Max=Must be lower than {1}.
typeMismatch.java.lang.Integer=Must be number.
typeMismatch.org.joda.time.DateTime=Required format dd.mm.yyyy HH:mm
Spring configuration:
#Configuration
public class BaseValidatorConfig {
#Bean
public LocalValidatorFactoryBean getValidator() {
LocalValidatorFactoryBean lvfb = new LocalValidatorFactoryBean();
lvfb.setValidationMessageSource(getValidationMessageSource());
return lvfb;
}
protected MessageSource getValidationMessageSource() {// return you validation messages ...}
}
I can provide more details and explanation, if needed.
I don't know why the approach as mentioned in the question didn't work. I didn't make it work but walking through this document, I found another approach that worked for me as per my requirements.
I set the validator inside a method which was designated by the #InitBinder annotation.
From docs
The Validator instance invoked when a #Valid method argument is
encountered may be configured in two ways. First, you may call
binder.setValidator(Validator) within a #Controller's #InitBinder
callback. This allows you to configure a Validator instance per
#Controller class:
Specifically, in my requirements, the validation should only be performed while updating or inserting data into the database i.e when an associated submit button for those operations is pressed (there is a common button for both of these tasks (insert and update) in my application whose name is btnSubmit).
The validation should be muted in any other case (for example, when the delete button is pressed). To meet this requirement, I have registered the validator as follows.
#InitBinder
protected void initBinder(WebDataBinder binder, WebRequest webRequest) {
if (webRequest.getParameter("btnSubmit") != null) {
binder.setValidator(new TempValidator());
} else {
binder.setValidator(null);
}
}
In this situation, the validator - TempValidator would only be set when the submit button whose name attribute is btnSubmit is clicked by the client.
There is no need for xml configuration anywhere as well as auto-wiring.
The exemplary controller class now looks like the following.
#Controller
public final class TempController {
#Autowired
private TempService tempService;
#InitBinder
protected void initBinder(WebDataBinder binder, WebRequest webRequest) {
if (webRequest.getParameter("btnSubmit") != null) {
binder.setValidator(new TempValidator());
} else {
binder.setValidator(null);
}
}
//Removed the #Valid annotation before TempBean, since validation is unnecessary on page load.
#RequestMapping(method = {RequestMethod.GET}, value = {"admin_side/Temp"})
public String showForm(#ModelAttribute("tempBean") TempBean tempBean, BindingResult error, Map model, HttpServletRequest request, HttpServletResponse response) {
return "admin_side/Temp";
}
#RequestMapping(method = {RequestMethod.POST}, value = {"admin_side/Temp"})
public String onSubmit(#ModelAttribute("tempBean") #Valid TempBean tempBean, BindingResult errors, Map model, HttpServletRequest request, HttpServletResponse response) {
if (CustomizeValidation.isValid(errors, tempBean, TempBean.ValidationGroup.class, Default.class) && !errors.hasErrors()) {
System.out.println("Validated");
}
return "admin_side/Temp";
}
}
The WebRequest paramenter in the initBinder() method is not meant for handling the entire Http request as obvious. It's just for using general purpose request metadata.
Javadocs about WebRequest.
Generic interface for a web request. Mainly intended for generic web
request interceptors, giving them access to general request metadata,
not for actual handling of the request.
If there is something wrong that I might be following, then kindly clarify it or add another answer.
I am trying to submit a form from Ext JS 4 to a Spring 3 Controller using JSON. I am using Jackson 1.9.8 for the serialization/deserialization using Spring's built-in Jackson JSON support.
I have a status field that is initially null in the Domain object for a new record. When the form is submitted it generates the following json (scaled down to a few fields)
{"id":0,"name":"someName","status":""}
After submitted the following is seen in the server log
"nested exception is org.codehaus.jackson.map.JsonMappingException: Can not construct instance of com.blah.domain.StatusEnum from String value '': value not one of the declared Enum instance names"
So it appears that Jackson is expecting a valid Enum value or no value at all including an empty string. How do I fix this whether it is in Ext JS, Jackson or Spring?
I tried to create my own ObjectMapper such as
public class MyObjectMapper extends Object Mapper {
public MyObjectMapper() {
configure(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);
}
}
and send this as a property to MappingJacksonMappingView but this didn't work. I also tried sending it in to MappingJacksonHttpMessageConverter but that didn't work. Side question: Which one should I be sending in my own ObjectMapper?
Suggestions?
The other thing you could do is create a specialized deserializer (extends org.codehaus.jackson.map.JsonDeserializer) for your particular enum, that has default values for things that don't match. What I've done is to create an abstract deserializer for enums that takes the class it deserializes, and it speeds this process along when I run into the issue.
public abstract class EnumDeserializer<T extends Enum<T>> extends JsonDeserializer<T> {
private Class<T> enumClass;
public EnumDeserializer(final Class<T> iEnumClass) {
super();
enumClass = iEnumClass;
}
#Override
public T deserialize(final JsonParser jp,
final DeserializationContext ctxt) throws IOException, JsonProcessingException {
final String value = jp.getText();
for (final T enumValue : enumClass.getEnumConstants()) {
if (enumValue.name().equals(value)) {
return enumValue;
}
}
return null;
}
}
That's the generic class, basically just takes an enum class, iterates over the values of the enum and checks the next token to match any name. If they do it returns it otherwise return null;
Then If you have an enum MyEnum you'd make a subclass of EnumDeserializer like this:
public class MyEnumDeserializer extends EnumDeserializer<MyEnum> {
public MyEnumDeserializer() {
super(MyEnum.class);
}
}
Then wherever you declare MyEnum:
#JsonDeserialize(using = MyEnumDeserializer.class)
public enum MyEnum {
...
}
I'm not familiar with Spring, but just in case, it may be easier to handle that on the client side:
Ext.define('My.form.Field', {
extend: 'Ext.form.field.Text',
getSubmitValue: function() {
var me = this,
value;
value = me.getRawValue();
if ( value === '' ) {
return ...;
}
}
});
You can also disallow submitting empty fields by setting their allowBlank property to false.
Ended up adding defaults in the EXT JS Model so there is always a value. Was hoping that I didn't have to this but it's not that big of a deal.
I have the same issue. I am reading a JSON stream with some empty strings. I am not in control of the JSON stream, because it is from a foreign service. And I am always getting the same error message. I tried this here:
mapper.getDeserializationConfig().with(DeserializationConfig.Feature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
But without any effect. Looks like a Bug.
I have the following class:
public static class TestSomething {
Integer test;
public TestSomething(Integer test) {
this.test = test;
}
// getter and setter for test
}
Ok, now create a collection of this class and serialize it with Gson:
Collection<TestSomething> tests = Arrays.asList(
new TestSomething(1),
new TestSomething(2),
new TestSomething(3)
);
String json = new Gson().toJson(tests, new TypeToken<Collection<TestSomething>>() {}.getType());
After this, the String json is set to
[{"test":1},{"test":2},{"test":3}]
Which is great.
But now, all of my model classes inherit from a generic type Identifiable<T> which provides just two methods T getId() and void setId(T). So I change the TestSomething-class from above to
public static class TestSomething extends Identifiable<Long> {
// same as above
}
When I try to put this through Gson.toJson(), Gson ends up with the following Exception:
java.lang.UnsupportedOperationException: Expecting parameterized type, got class path.to.TestSomething.
Are you missing the use of TypeToken idiom?
See http://sites.google.com/site/gson/gson-user-guide#TOC-Serializing-and-Deserializing-Gener
at com.google.gson.TypeInfoFactory.getActualType(TypeInfoFactory.java:97)
...
So, what do I have to do to get this work?
I don't know the answer, but I know that generic type resolution is a tricky thing to get right: specifically full type resolution from interface with type parameter T up through to generic parameter declaration (T=Long). In these cases it is not enough to check for Method object's parameters but also resolve generic type parameters. This is most likely what causes issues; it may be a bug in Gson.
Since you are serializing things, perhaps you could just omit any type declarations? Although your TypeToken is correct for the use case, maybe it confuses Gson.
But just in case you could not make Gson work with this, I know that of other JSON libraries Jackson can handle such cases correctly.
Perhaps this issue was resolved in one of the Gson releases newer than what the original questioner was using, because the example in the original question now serializes as expected.
// output:
// [{"test":1},{"test":2},{"test":3}]
import java.util.Arrays;
import java.util.Collection;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
public class Foo
{
public static void main(String[] args)
{
Collection<TestSomething> tests = Arrays.asList(
new TestSomething(1),
new TestSomething(2),
new TestSomething(3));
String json = new Gson().toJson(tests, new TypeToken<Collection<TestSomething>>() {}.getType());
System.out.println(json);
}
}
class TestSomething extends Identifiable<Long>
{
Integer test;
public TestSomething(Integer test)
{
this.test = test;
}
#Override
Long getId()
{
return new Long(test);
}
#Override
void setId(Long t)
{
this.test = (int)(t.longValue());
}
}
abstract class Identifiable<T>
{
abstract T getId();
abstract void setId(T t);
}