I'm using JAVA 1.6 and Jackson 1.9.9 I've got an enum
public enum Event {
FORGOT_PASSWORD("forgot password");
private final String value;
private Event(final String description) {
this.value = description;
}
#JsonValue
final String value() {
return this.value;
}
}
I've added a #JsonValue, this seems to do the job it serializes the object into:
{"event":"forgot password"}
but when I try to deserialize I get a
Caused by: org.codehaus.jackson.map.JsonMappingException: Can not construct instance of com.globalrelay.gas.appsjson.authportal.Event from String value 'forgot password': value not one of declared Enum instance names
What am I missing here?
The serializer / deserializer solution pointed out by #xbakesx is an excellent one if you wish to completely decouple your enum class from its JSON representation.
Alternatively, if you prefer a self-contained solution, an implementation based on #JsonCreator and #JsonValue annotations would be more convenient.
So leveraging on the example by #Stanley the following is a complete self-contained solution (Java 6, Jackson 1.9):
public enum DeviceScheduleFormat {
Weekday,
EvenOdd,
Interval;
private static Map<String, DeviceScheduleFormat> namesMap = new HashMap<String, DeviceScheduleFormat>(3);
static {
namesMap.put("weekday", Weekday);
namesMap.put("even-odd", EvenOdd);
namesMap.put("interval", Interval);
}
#JsonCreator
public static DeviceScheduleFormat forValue(String value) {
return namesMap.get(StringUtils.lowerCase(value));
}
#JsonValue
public String toValue() {
for (Entry<String, DeviceScheduleFormat> entry : namesMap.entrySet()) {
if (entry.getValue() == this)
return entry.getKey();
}
return null; // or fail
}
}
Note that as of this commit in June 2015 (Jackson 2.6.2 and above) you can now simply write:
public enum Event {
#JsonProperty("forgot password")
FORGOT_PASSWORD;
}
The behavior is documented here: https://fasterxml.github.io/jackson-annotations/javadoc/2.11/com/fasterxml/jackson/annotation/JsonProperty.html
Starting with Jackson 2.6 this annotation may also be used to change serialization of Enum like so:
public enum MyEnum {
#JsonProperty("theFirstValue") THE_FIRST_VALUE,
#JsonProperty("another_value") ANOTHER_VALUE;
}
as an alternative to using JsonValue annotation.
You should create a static factory method which takes single argument and annotate it with #JsonCreator (available since Jackson 1.2)
#JsonCreator
public static Event forValue(String value) { ... }
Read more about JsonCreator annotation here.
Actual Answer:
The default deserializer for enums uses .name() to deserialize, so it's not using the #JsonValue. So as #OldCurmudgeon pointed out, you'd need to pass in {"event": "FORGOT_PASSWORD"} to match the .name() value.
An other option (assuming you want the write and read json values to be the same)...
More Info:
There is (yet) another way to manage the serialization and deserialization process with Jackson. You can specify these annotations to use your own custom serializer and deserializer:
#JsonSerialize(using = MySerializer.class)
#JsonDeserialize(using = MyDeserializer.class)
public final class MyClass {
...
}
Then you have to write MySerializer and MyDeserializer which look like this:
MySerializer
public final class MySerializer extends JsonSerializer<MyClass>
{
#Override
public void serialize(final MyClass yourClassHere, final JsonGenerator gen, final SerializerProvider serializer) throws IOException, JsonProcessingException
{
// here you'd write data to the stream with gen.write...() methods
}
}
MyDeserializer
public final class MyDeserializer extends org.codehaus.jackson.map.JsonDeserializer<MyClass>
{
#Override
public MyClass deserialize(final JsonParser parser, final DeserializationContext context) throws IOException, JsonProcessingException
{
// then you'd do something like parser.getInt() or whatever to pull data off the parser
return null;
}
}
Last little bit, particularly for doing this to an enum JsonEnum that serializes with the method getYourValue(), your serializer and deserializer might look like this:
public void serialize(final JsonEnum enumValue, final JsonGenerator gen, final SerializerProvider serializer) throws IOException, JsonProcessingException
{
gen.writeString(enumValue.getYourValue());
}
public JsonEnum deserialize(final JsonParser parser, final DeserializationContext context) throws IOException, JsonProcessingException
{
final String jsonValue = parser.getText();
for (final JsonEnum enumValue : JsonEnum.values())
{
if (enumValue.getYourValue().equals(jsonValue))
{
return enumValue;
}
}
return null;
}
I've found a very nice and concise solution, especially useful when you cannot modify enum classes as it was in my case. Then you should provide a custom ObjectMapper with a certain feature enabled. Those features are available since Jackson 1.6. So you only need to write toString() method in your enum.
public class CustomObjectMapper extends ObjectMapper {
#PostConstruct
public void customConfiguration() {
// Uses Enum.toString() for serialization of an Enum
this.enable(WRITE_ENUMS_USING_TO_STRING);
// Uses Enum.toString() for deserialization of an Enum
this.enable(READ_ENUMS_USING_TO_STRING);
}
}
There are more enum-related features available, see here:
https://github.com/FasterXML/jackson-databind/wiki/Serialization-Features
https://github.com/FasterXML/jackson-databind/wiki/Deserialization-Features
Try this.
public enum Event {
FORGOT_PASSWORD("forgot password");
private final String value;
private Event(final String description) {
this.value = description;
}
private Event() {
this.value = this.name();
}
#JsonValue
final String value() {
return this.value;
}
}
I like the accepted answer. However, I would improve it a little (considering that there is now Java higher than version 6 available).
Example:
public enum Operation {
EQUAL("eq"),
NOT_EQUAL("ne"),
LESS_THAN("lt"),
GREATER_THAN("gt");
private final String value;
Operation(String value) {
this.value = value;
}
#JsonValue
public String getValue() {
return value;
}
#JsonCreator
public static Operation forValue(String value) {
return Arrays.stream(Operation.values())
.filter(op -> op.getValue().equals(value))
.findFirst()
.orElseThrow(); // depending on requirements: can be .orElse(null);
}
}
You can customize the deserialization for any attribute.
Declare your deserialize class using the annotationJsonDeserialize (import com.fasterxml.jackson.databind.annotation.JsonDeserialize) for the attribute that will be processed. If this is an Enum:
#JsonDeserialize(using = MyEnumDeserialize.class)
private MyEnum myEnum;
This way your class will be used to deserialize the attribute. This is a full example:
public class MyEnumDeserialize extends JsonDeserializer<MyEnum> {
#Override
public MyEnum deserialize(JsonParser jsonParser, DeserializationContext deserializationContext) throws IOException {
JsonNode node = jsonParser.getCodec().readTree(jsonParser);
MyEnum type = null;
try{
if(node.get("attr") != null){
type = MyEnum.get(Long.parseLong(node.get("attr").asText()));
if (type != null) {
return type;
}
}
}catch(Exception e){
type = null;
}
return type;
}
}
Here is another example that uses string values instead of a map.
public enum Operator {
EQUAL(new String[]{"=","==","==="}),
NOT_EQUAL(new String[]{"!=","<>"}),
LESS_THAN(new String[]{"<"}),
LESS_THAN_EQUAL(new String[]{"<="}),
GREATER_THAN(new String[]{">"}),
GREATER_THAN_EQUAL(new String[]{">="}),
EXISTS(new String[]{"not null", "exists"}),
NOT_EXISTS(new String[]{"is null", "not exists"}),
MATCH(new String[]{"match"});
private String[] value;
Operator(String[] value) {
this.value = value;
}
#JsonValue
public String toStringOperator(){
return value[0];
}
#JsonCreator
public static Operator fromStringOperator(String stringOperator) {
if(stringOperator != null) {
for(Operator operator : Operator.values()) {
for(String operatorString : operator.value) {
if (stringOperator.equalsIgnoreCase(operatorString)) {
return operator;
}
}
}
}
return null;
}
}
There are various approaches that you can take to accomplish deserialization of a JSON object to an enum. My favorite style is to make an inner class:
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import org.hibernate.validator.constraints.NotEmpty;
import java.util.Arrays;
import java.util.Map;
import java.util.function.Function;
import java.util.stream.Collectors;
import static com.fasterxml.jackson.annotation.JsonFormat.Shape.OBJECT;
#JsonFormat(shape = OBJECT)
public enum FinancialAccountSubAccountType {
MAIN("Main"),
MAIN_DISCOUNT("Main Discount");
private final static Map<String, FinancialAccountSubAccountType> ENUM_NAME_MAP;
static {
ENUM_NAME_MAP = Arrays.stream(FinancialAccountSubAccountType.values())
.collect(Collectors.toMap(
Enum::name,
Function.identity()));
}
private final String displayName;
FinancialAccountSubAccountType(String displayName) {
this.displayName = displayName;
}
#JsonCreator
public static FinancialAccountSubAccountType fromJson(Request request) {
return ENUM_NAME_MAP.get(request.getCode());
}
#JsonProperty("name")
public String getDisplayName() {
return displayName;
}
private static class Request {
#NotEmpty(message = "Financial account sub-account type code is required")
private final String code;
private final String displayName;
#JsonCreator
private Request(#JsonProperty("code") String code,
#JsonProperty("name") String displayName) {
this.code = code;
this.displayName = displayName;
}
public String getCode() {
return code;
}
#JsonProperty("name")
public String getDisplayName() {
return displayName;
}
}
}
In the context of an enum, using #JsonValue now (since 2.0) works for serialization and deserialization.
According to the jackson-annotations javadoc for #JsonValue:
NOTE: when use for Java enums, one additional feature is that value returned by annotated method is also considered to be the value to deserialize from, not just JSON String to serialize as. This is possible since set of Enum values is constant and it is possible to define mapping, but can not be done in general for POJO types; as such, this is not used for POJO deserialization.
So having the Event enum annotated just as above works (for both serialization and deserialization) with jackson 2.0+.
Besides using #JsonSerialize #JsonDeserialize, you can also use SerializationFeature and DeserializationFeature (jackson binding) in the object mapper.
Such as DeserializationFeature.READ_UNKNOWN_ENUM_VALUES_USING_DEFAULT_VALUE, which give default enum type if the one provided is not defined in the enum class.
In my case, this is what resolved:
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
#JsonFormat(shape = JsonFormat.Shape.OBJECT)
public enum PeriodEnum {
DAILY(1),
WEEKLY(2),
;
private final int id;
PeriodEnum(int id) {
this.id = id;
}
public int getId() {
return id;
}
public String getName() {
return this.name();
}
#JsonCreator
public static PeriodEnum fromJson(#JsonProperty("name") String name) {
return valueOf(name);
}
}
Serializes and deserializes the following json:
{
"id": 2,
"name": "WEEKLY"
}
I hope it helps!
Here, 'value' acts as a deserialiser and 'namespace' acts as a serialiser. Hence, you can pass in value "Student Absent" to API while saving, and in DB it will be saved as "STUDENT_ABSENT". On the other hand, while retrieving data in your class, your API will return "Student Absent"
import com.fasterxml.jackson.annotation.JsonProperty;
public enum AttendanceEnums {
STUDENT_PRESENT,
#JsonProperty(value = "Student Absent", namespace = "Student Absent")
STUDENT_ABSENT;
}
I had been looking for a solution to enum serialization and I finally made a solution.
https://github.com/sirgilligan/EnumerationSerialization
https://digerati-illuminatus.blogspot.com/2022/10/java-enum-generic-serializer-and.html
It uses a new annotation and two new classes, EnumerationSerializer and EnumerationDeserializer. You can subclass the EnumerationDeserializer and make a class that sets the enum Class (typical approach) or you can annotate the enum and you don't have to have a subclass of EnumerationDeserializer.
#JsonSerialize(using = EnumerationSerializer.class)
#JsonDeserialize(using = EnumerationDeserializer.class)
#EnumJson(serializeProjection = Projection.NAME, deserializationClass = RGB.class)
enum RGB {
RED,
GREEN,
BLUE
}
Notice how the implementation of ContextualDeserializer pulls the class from the annotation.
https://github.com/sirgilligan/EnumerationSerialization/blob/main/src/main/java/org/example/EnumerationDeserializer.java
There is a lot of good code in this that might give insights.
For your specific question you could do this:
#JsonSerialize(using = EnumerationSerializer.class)
#JsonDeserialize(using = EnumerationDeserializer.class)
#EnumJson(serializeProjection = Projection.NAME, deserializationClass = Event.class)
public enum Event {
FORGOT_PASSWORD("forgot password");
//This annotation is optional because the code looks for value or alias.
#EnumJson(serializeProjection = Projection.VALUE)
private final String value;
private Event(final String description) {
this.value = description;
}
}
Or you could do this:
#JsonSerialize(using = EnumerationSerializer.class)
#JsonDeserialize(using = EnumerationDeserializer.class)
#EnumJson(serializeProjection = Projection.NAME, deserializationClass = Event.class)
public enum Event {
FORGOT_PASSWORD("forgot password");
private final String value;
private Event(final String description) {
this.value = description;
}
}
That's all you have to do.
Then if you have a class that "has a" event you can annotate each occurance to serialize the way you want.
class EventHolder {
#EnumJson(serializeProjection = Projection.NAME)
Event someEvent;
#EnumJson(serializeProjection = Projection.ORDINAL)
Event someOtherEvent;
#EnumJson(serializeProjection = Projection.VALUE)
Event yetAnotherEvent;
}
The simplest way I found is using #JsonFormat.Shape.OBJECT annotation for the enum.
#JsonFormat(shape = JsonFormat.Shape.OBJECT)
public enum MyEnum{
....
}
I did it like this :
// Your JSON
{"event":"forgot password"}
// Your class to map
public class LoggingDto {
#JsonProperty(value = "event")
private FooEnum logType;
}
//Your enum
public enum FooEnum {
DATA_LOG ("Dummy 1"),
DATA2_LOG ("Dummy 2"),
DATA3_LOG ("forgot password"),
DATA4_LOG ("Dummy 4"),
DATA5_LOG ("Dummy 5"),
UNKNOWN ("");
private String fullName;
FooEnum(String fullName) {
this.fullName = fullName;
}
public String getFullName() {
return fullName;
}
#JsonCreator
public static FooEnum getLogTypeFromFullName(String fullName) {
for (FooEnum logType : FooEnum.values()) {
if (logType.fullName.equals(fullName)) {
return logType;
}
}
return UNKNOWN;
}
}
So the value of the property "logType" for class LoggingDto will be DATA3_LOG
This post is old, but if it can help someone, use JsonFormat.Shape.STRING
#JsonFormat(shape = JsonFormat.Shape.STRING)
public enum SomeEnum{
#JsonProperty("SOME_PROPERTY")
someProperty,
...
}
Code results is like this
{"someenum":"SOME_PROPERTY"}
#JsonFormat(shape = JsonFormat.Shape.OBJECT)
public enum LoginOptionType {
PHONE(1, "Phone"), MAIL(2, "mail"), PERSONAL_EMAIL(3, "Personal email");
private static List<LoginOptionType> all;
static {
all = new ArrayList<LoginOptionType>() {
{
add(LoginOptionType.PHONE);
add(LoginOptionType.MAIL);
add(LoginOptionType.PERSONAL_EMAIL);
}
};
}
private final Integer viewValue;
private final String name;
LoginOptionType(Integer viewValue, String name) {
this.viewValue = viewValue;
this.name = name;
}
public Integer getViewValue() {
return viewValue;
}
public String getName() {
return name;
}
public static List<LoginOptionType> getAll() {
return all;
}
}
Response
[
{
"viewValue": 1,
"name": "Phone"
},
{
"viewValue": 2,
"name": "mail"
},
{
"viewValue": 3,
"name": "Personal email"
}
]
I am trying to read a csv file into JavaRDD. In order to do that, I wrote the code below:
SparkConf conf = new SparkConf().setAppName("NameOfApp").setMaster("spark://Ip here:7077");
JavaSparkContext sc = new JavaSparkContext(conf);
JavaRDD<CurrencyPair> rdd_records = sc.textFile(System.getProperty("user.dir") + "/data/data.csv", 2).map(
new Function<String, CurrencyPair>() {
public CurrencyPair call(String line) throws Exception {
String[] fields = line.split(",");
CurrencyPair sd = new CurrencyPair(Integer.parseInt(fields[0].trim()), Double.parseDouble(fields[1].trim()),
Double.parseDouble(fields[2].trim()), Double.parseDouble(fields[3]), new Date(fields[4]));
return sd;
}
}
);
My data file looks like this:
1,0.034968,212285,7457.23,"2019-03-08 18:36:18"
Here, in order to check that if my data loaded correctly or not, I tried to print some of them:
System.out.println("Count: " + rdd_records.count());
List<CurrencyPair> list = rdd_records.top(5);
System.out.println(list.toString());
But I had following error at both system out lines. I tried each of them alone as well rather than printing count and list at the same time.
Caused by: java.lang.ClassCastException: cannot assign instance of java.lang.invoke.SerializedLambda to field org.apache.spark.rdd.MapPartitionsRDD.f of type scala.Function3 in instance of org.apache.spark.rdd.MapPartitionsRDD
My custom object looks like this:
public class CurrencyPair implements Serializable {
private int id;
private double value;
private double baseVolume;
private double quoteVolume;
private Date timeStamp;
public CurrencyPair(int id, double value, double baseVolume, double quoteVolume, Date timeStamp) {
this.id = id;
this.value = value;
this.baseVolume = baseVolume;
this.quoteVolume = quoteVolume;
this.timeStamp = timeStamp;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public double getValue() {
return value;
}
public void setValue(double value) {
this.value = value;
}
public double getBaseVolume() {
return baseVolume;
}
public void setBaseVolume(double baseVolume) {
this.baseVolume = baseVolume;
}
public double getQuoteVolume() {
return quoteVolume;
}
public void setQuoteVolume(double quoteVolume) {
this.quoteVolume = quoteVolume;
}
public Date getTimeStamp() {
return timeStamp;
}
public void setTimeStamp(Date timeStamp) {
this.timeStamp = timeStamp;
}
}
So I could not figured out what is wrong here. What am I doing wrong?
Edit: It works well when I write local instead of my own spark master IP. But I need to run this on my own IP. So what can be wrong with my master node?
The issue is probably the anonymous class definition new Function<String, CurrencyPair>() { which forces Spark to try to serialize the parent class as well. Try a lambda instead:
rdd_records.map(
(Function<String, CurrencyPair>) line -> {
...
Note: You could read the file as a CSV instead and use the dataset API with a bean encoder to skip the manual parsing completely.
I have a custom object :
public class Response
{
#JsonProperty("values")
private List<Value> values;
#JsonFormat(shape=JsonFormat.Shape.ARRAY)
public static class Value {
public Value(long timestamp, float val)
{
this.timestamp = timestamp;
this.val = val;
}
}
}
But when this is being parsed, I get "Can not deserialize instance of Response$Value out of START_ARRAY token".
The json is :
{
"values":[[1552215648,18]]
}
Any idea if I'm missing something here? Or should I have a custom deserializer to perform this?
JsonFormat does the trick but you also need to declare constructor with JsonCreator annotation. Take a look on below example:
import com.fasterxml.jackson.annotation.JsonCreator;
import com.fasterxml.jackson.annotation.JsonFormat;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.databind.ObjectMapper;
import java.io.File;
import java.util.List;
public class JsonApp {
public static void main(String[] args) throws Exception {
File jsonFile = new File("./resource/test.json").getAbsoluteFile();
ObjectMapper mapper = new ObjectMapper();
Response myPojo = mapper.readValue(jsonFile, Response.class);
System.out.println(myPojo);
}
}
class Response {
private List<Value> values;
public List<Value> getValues() {
return values;
}
public void setValues(List<Value> values) {
this.values = values;
}
#Override
public String toString() {
return "Response{" +
"values=" + values +
'}';
}
}
#JsonFormat(shape = JsonFormat.Shape.ARRAY)
class Value {
private long timestamp;
private float val;
#JsonCreator
public Value(#JsonProperty("timestamp") long timestamp, #JsonProperty("val") float val) {
this.timestamp = timestamp;
this.val = val;
}
public long getTimestamp() {
return timestamp;
}
public void setTimestamp(long timestamp) {
this.timestamp = timestamp;
}
public float getVal() {
return val;
}
public void setVal(float val) {
this.val = val;
}
#Override
public String toString() {
return "Value{" +
"timestamp=" + timestamp +
", val=" + val +
'}';
}
}
Above code for below JSON payload:
{
"values": [
[
1552215648,
18
],
[
123,
12.24
]
]
}
Prints:
Response{values=[Value{timestamp=1552215648, val=18.0}, Value{timestamp=123, val=12.24}]}
You should JsonFormat over the variable values. Also since you are having the variable as of type List, you need not add JsonFormat.
public class Response
{
#JsonProperty("values")
#JsonFormat(shape=JsonFormat.Shape.ARRAY)
private List<Value> values;
public static class Value {
private long timestamp;
private float val;
// Getters and Setters
public Value(long timestamp, float val)
{
this.timestamp = timestamp;
this.val = val;
}
}
}
Your JSON input format would be:
{
values: [
{
"timestamp": 589988,
"val": 56.0,
}
]
}
Hope this helps !! I haven't tested the code, so please ignore syntax issues if any.
I know it's been a while, but since I dealt with the same problem (deserializing part of Prometheus REST API response?), and provided answers weren't helping, I would like to share my solution which should work for every similar case.
Apart from #JsonFormat(shape=JsonFormat.Shape.ARRAY) it was necessary for me to add also #JsonPropertyOrder annotation to reflect the order in which values appear in the array. I also needed #JsonCreator annotation on constructor and #JsonProperty before every constructor's argument. Using your class as an example it should look like this:
public class Response
{
private List<Value> values;
#JsonFormat(shape=JsonFormat.Shape.ARRAY)
#JsonPropertyOrder({"timestamp", "val"})
public static class Value {
private long timestamp;
private float val;
#JsonCreator
public Value(#JsonProperty("timestamp") long timestamp,
#JsonProperty("val") float val)
{
this.timestamp = timestamp;
this.val = val;
}
// Getters and Setters
}
}
Only after I used this particular set of annotations my response was deserialised without any errors.
Hope this is gonna help someone! ;)
EDIT: One note: in Prometheus response I got, an array of values of different types was called value and not values, hence it might be necessary to add a #JsonProperty("value") on private List<Value> values; field or change it's name to value if that is the case for anyone ;)
#JsonProperty("value")
private List<Value> values;
I'm trying to create make a method, that returns a json-string filled with sample-data. I have created a data-constructor class but when I when I create a data-object and afterwards print it, it for some reason returns an empty json: "[]"?
What am I missing here? Why doesn't it return the data-object I just created?
Here is my main class:
public class SimulatedDevice {
public static void printObject(Object object) {
Gson gson = new GsonBuilder().setPrettyPrinting().create();
System.out.println(gson.toJson(object));
}
public static class TelemetryDataPoint {
public String CreateTelemetryDataPoint() {
ArrayList<Data.TrendData> trendData = new ArrayList<>();
trendData.add(new Data.TrendData("Building1", "2018-08-28T01:03:02.997301Z", 2, "occupants", "int"));
Data data = new Data("B1", "0", "0", trendData);
printObject(data);
String json = new Gson().toJson(data);
return json;
}
}
}
This is my data constructor:
package com.microsoft.docs.iothub.samples;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import java.sql.Time;
import java.util.ArrayList;
import java.util.List;
public class Data extends ArrayList {
String Building;
String Floor;
String Zone;
ArrayList<TrendData> Trend;
public Data(String Building, String Floor, String Zone, ArrayList<TrendData> Trend) {
this.Building = Building;
this.Floor = Floor;
this.Zone = Zone;
this.Trend = Trend;
}
public static class TrendData {
String PointId;
String Timestamp;
int Value;
String Type;
String Unit;
public TrendData(String PointId, String Timestamp, int Value, String Type, String Unit) {
this.PointId = PointId;
this.Timestamp = Timestamp;
this.Value = Value;
this.Type = Type;
this.Unit = Unit;
}
}
If you remove 'extends ArrayList' from Data declaration it will work fine. I have not debugged it enough to figure out why Gson does not like the base class being ArrayList.
Here is a possible explanation: Trouble with Gson serializing an ArrayList of POJO's
I'm running into a few issues similar to what others have had in the past with Json parsing in Java. This is the first time I try something like this so any help/tips is extremely useful.
I'm trying to parse in data from this site: https://api.bitcoinaverage.com/exchanges/USD
I have tried numerous ways with both Json and Gson. And have tried looking for help here but to no avail.
Here are the classes that are set up (these were auto generated):
Info.java:
public class Info{
private String display_URL;
private String display_name;
private Rates[] rates;
private String source;
private Number volume_btc;
private Number volume_percent;
public String getDisplay_URL(){
return this.display_URL;
}
public void setDisplay_URL(String display_URL){
this.display_URL = display_URL;
}
public String getDisplay_name(){
return this.display_name;
}
public void setDisplay_name(String display_name){
this.display_name = display_name;
}
public Rates[] getRates(){
return this.rates;
}
public void setRates(Rates[] rates){
this.rates = rates;
}
public String getSource(){
return this.source;
}
public void setSource(String source){
this.source = source;
}
public Number getVolume_btc(){
return this.volume_btc;
}
public void setVolume_btc(Number volume_btc){
this.volume_btc = volume_btc;
}
public Number getVolume_percent(){
return this.volume_percent;
}
public void setVolume_percent(Number volume_percent){
this.volume_percent = volume_percent;
}
}
Rates.java:
public class Rates {
private Number ask;
private Number bid;
private Number last;
public Number getAsk(){
return this.ask;
}
public void setAsk(Number ask){
this.ask = ask;
}
public Number getBid(){
return this.bid;
}
public void setBid(Number bid){
this.bid = bid;
}
public Number getLast(){
return this.last;
}
public void setLast(Number last){
this.last = last;
}
}
MainClass.java:
public class MainClass {
public static void main(String[] args) throws Exception {
Gson gson = new Gson();
String json = readUrl("https://api.bitcoinaverage.com/exchanges/USD");
Info page = gson.fromJson(json, Info.class);
System.out.println(page.getDisplay_name());
}
private static String readUrl(String urlString) throws Exception {
BufferedReader reader = null;
try {
URL url = new URL(urlString);
reader = new BufferedReader(new InputStreamReader(url.openStream()));
StringBuffer buffer = new StringBuffer();
int read;
char[] chars = new char[1024];
while ((read = reader.read(chars)) != -1)
buffer.append(chars, 0, read);
return buffer.toString();
} finally {
if (reader != null)
reader.close();
}
}
}
When I try to call a getter, a null is returned.
How do I go about parsing the data properly, and then being able to call an attribute from which ever object I want? For example, if I want an attribute from "anx_hk" or "bitfinex".
This is the first time me posting something here so I hope I'm following the proper guidelines.
I also plan on passing this over to Android once I get the fell for parsing Json better. Thanks for the help! It'll greatly be appreciated.
I'll be honest with you, that's a pretty lame API response. Here it is
{
"anx_hk": {
"display_URL": "https://anxbtc.com/",
"display_name": "ANXBTC",
"rates": {
"ask": 454.26,
"bid": 444.46,
"last": 443.78
},
"source": "bitcoincharts",
"volume_btc": 11.73,
"volume_percent": 0.02
},
...,
"timestamp": "Fri, 04 Apr 2014 04:30:26 -0000",
...
}
There's no JSON array here, so you can get rid of all your array types. This response is a JSON object, which contains a bunch of JSON objects (which share a format) and a JSON name value pair where the name is timestamp.
The common JSON objects have two fields of type double (that's what type your field should be, not Number)
"volume_btc": 11.73,
"volume_percent": 0.02
, three fields of type String
"display_URL": "https://anxbtc.com/",
"display_name": "ANXBTC",
"source": "bitcoincharts",
and one that is a JSON object that contains three more doubles
"rates": {
"ask": 454.26,
"bid": 444.46,
"last": 443.78
}
The actual issue here is that, I'm assuming, the JSON objects in the root JSON object have names that may change or new ones may be added. This is not a good fit for a POJO. Instead you'd want to use a Map<String, Info>, but Gson can't map to that by default. It is not well suited for such deserialization. You'd have to provide your own TypeAdapter.
Instead, I'm going to suggest you use Jackson.
If we put that all together, we get something like
class ApiResponse {
private Map<String, Info> page = new HashMap<>();
private Date timestamp;
public Map<String, Info> getPage() {
return page;
}
#JsonAnySetter
public void setPage(String name, Info value) {
page.put(name, value);
}
public Date getTimestamp() {
return timestamp;
}
public void setTimestamp(Date timestamp) {
this.timestamp = timestamp;
}
}
class Info {
private String display_URL;
private String display_name;
private Rates rates;
private String source;
private Double volume_btc;
private Double volume_percent;
public String getDisplay_URL() {
return this.display_URL;
}
public void setDisplay_URL(String display_URL) {
this.display_URL = display_URL;
}
public String getDisplay_name() {
return this.display_name;
}
public void setDisplay_name(String display_name) {
this.display_name = display_name;
}
public Rates getRates() {
return this.rates;
}
public void setRates(Rates rates) {
this.rates = rates;
}
public String getSource() {
return this.source;
}
public void setSource(String source) {
this.source = source;
}
public Double getVolume_btc() {
return this.volume_btc;
}
public void setVolume_btc(Double volume_btc) {
this.volume_btc = volume_btc;
}
public Double getVolume_percent() {
return this.volume_percent;
}
public void setVolume_percent(Double volume_percent) {
this.volume_percent = volume_percent;
}
}
class Rates {
private Double ask;
private Double bid;
private Double last;
public Number getAsk() {
return this.ask;
}
public void setAsk(Double ask) {
this.ask = ask;
}
public Double getBid() {
return this.bid;
}
public void setBid(Double bid) {
this.bid = bid;
}
public Double getLast() {
return this.last;
}
public void setLast(Double last) {
this.last = last;
}
}
With deserialization code such as
String json = readUrl("https://api.bitcoinaverage.com/exchanges/USD");
ObjectMapper mapper = new ObjectMapper();
ApiResponse response = mapper.readValue(json, ApiResponse.class);
System.out.println(response);
With appropriate toString() methods (mine were auto-generated with Eclipse), you would get something like
ApiResponse [pages={bitkonan=Info [display_URL=https://bitkonan.com/, display_name=BitKonan, rates=Rates [ask=475.0, bid=438.01, last=437.0], source=api, volume_btc=7.24, volume_percent=0.01], vaultofsatoshi=Info [display_URL=https://vaultofsatoshi.com, display_name=Vault of Satoshi, rates=Rates [ask=460.0, bid=460.0, last=460.0], source=api, volume_btc=11.46, volume_percent=0.02], bitstamp=Info [display_URL=https://bitstamp.net/, display_name=Bitstamp, rates=Rates [ask=439.16, bid=436.34, last=436.34], source=api, volume_btc=22186.29, volume_percent=35.19], ...}, timestamp=Fri Apr 04 01:02:43 EDT 2014]
as output.
The api response contains many objects, but seems that you are trying to read them as a single Info object.
You may try to read the response as a Map<String, Info>, and iterate the entries.
Map<String, Info> hashMap = gson.fromJson(body, HashMap.class);
for (Map.Entry entry : hashMap.entrySet()) {
// your code
}