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Refactor the deserialiser to improve readability and simplify logic #80

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158e902
Refactor the deserializer to improve readability
gayal-r Jan 12, 2026
9686a5f
Remove comment to raise pull request for better implementation
gayal-r Jan 12, 2026
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123 changes: 53 additions & 70 deletions java/src/main/java/org/opensky/model/OpenSkyStatesDeserializer.java
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Original file line number Diff line number Diff line change
@@ -1,110 +1,93 @@
package org.opensky.model;

import com.fasterxml.jackson.core.JsonParseException;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.DeserializationContext;
import com.fasterxml.jackson.databind.JsonNode;
import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
import com.fasterxml.jackson.databind.node.ArrayNode;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

/**
* Custom JSON deserializer for OpenSkyStates retrieved from the API.
*
* XXX Because actual state vectors arrive as array we need a custom deserializer like this.
* If anyone comes up with something better, feel free to create a pull request!
*
* @author Markus Fuchs, fuchs@opensky-network.org
*/
public class OpenSkyStatesDeserializer extends StdDeserializer<OpenSkyStates> {
public OpenSkyStatesDeserializer() {
super(OpenSkyStates.class);
}

private Collection<StateVector> deserializeStates(JsonParser jp) throws IOException {
ArrayList<StateVector> result = new ArrayList<>();
private Collection<StateVector> deserializeStates(TreeNode statesRoot) throws JsonParseException {
Iterator<JsonNode> states = ((ArrayNode) statesRoot).elements();
ArrayList<StateVector> stateVectors = new ArrayList<>();

for (JsonToken next = jp.nextToken(); next != null && next != JsonToken.END_ARRAY; next = jp.nextToken()) {
if (next == JsonToken.START_ARRAY) {
continue;
}
if (next == JsonToken.END_OBJECT) {
break;
}
String icao24 = jp.getText();
if ("null".equals(icao24)) {
throw new JsonParseException("Got 'null' icao24", jp.getCurrentLocation());
}
while (states.hasNext()) {
JsonNode vector = states.next();
String icao24 = vector.get(0).asText();
if (vector.get(0).isNull())
throw new JsonParseException(
String.format("Got 'null' icao24, vector payload: %s", vector), JsonLocation.NA
);

StateVector sv = new StateVector(icao24);
sv.setCallsign(jp.nextTextValue());
sv.setOriginCountry(jp.nextTextValue());
sv.setLastPositionUpdate((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));
sv.setLastContact((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));
sv.setLongitude((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));
sv.setLatitude((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));
sv.setBaroAltitude((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));
sv.setOnGround(jp.nextBooleanValue());
sv.setVelocity((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));
sv.setHeading((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));
sv.setVerticalRate((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));

// sensor serials if present
next = jp.nextToken();
if (next == JsonToken.START_ARRAY) {
for (next = jp.nextToken(); next != null && next != JsonToken.END_ARRAY; next = jp.nextToken()) {
sv.addSerial(jp.getIntValue());
}

sv.setCallsign(stringOrNull(vector.get(1)));
sv.setOriginCountry(stringOrNull(vector.get(2)));
sv.setLastPositionUpdate(doubleOrNull(vector.get(3)));
sv.setLastContact(doubleOrNull(vector.get(4)));
sv.setLongitude(doubleOrNull(vector.get(5)));
sv.setLatitude(doubleOrNull(vector.get(6)));
sv.setBaroAltitude(doubleOrNull(vector.get(7)));
sv.setOnGround(vector.get(8).asBoolean());
sv.setVelocity(doubleOrNull(vector.get(9)));
sv.setHeading(doubleOrNull(vector.get(10)));
sv.setVerticalRate(doubleOrNull(vector.get(11)));

Iterator<JsonNode> serials = vector.get(12).elements(); // Array of serials
while (serials.hasNext()) {
JsonNode serial = serials.next();
sv.addSerial(serial.asInt());
}

sv.setGeoAltitude((jp.nextToken() != null && jp.getCurrentToken() != JsonToken.VALUE_NULL ? jp.getDoubleValue() : null));
sv.setSquawk(jp.nextTextValue());
sv.setSpi(jp.nextBooleanValue());
sv.setGeoAltitude(doubleOrNull(vector.get(13)));
sv.setSquawk(stringOrNull(vector.get(14)));
sv.setSpi(vector.get(15).asBoolean());

int psi = jp.nextIntValue(0);
int psi = vector.get(16).asInt(0);
StateVector.PositionSource ps = psi <= StateVector.PositionSource.values().length ?
StateVector.PositionSource.values()[psi] : StateVector.PositionSource.UNKNOWN;

sv.setPositionSource(ps);

// there are additional fields (upward compatibility), consume until end of this state vector array
next = jp.nextToken();
while (next != null && next != JsonToken.END_ARRAY) {
// ignore
next = jp.nextToken();
}
// consume "END_ARRAY" or next "START_ARRAY"
jp.nextToken();

result.add(sv);
stateVectors.add(sv);
}

return result;
return stateVectors;
}

private static Double doubleOrNull(JsonNode node) {
return node.isNumber() ? node.asDouble() : null;
}

private static String stringOrNull(JsonNode node) {
return node.isNull() ? null : node.asText();
}

@Override
public OpenSkyStates deserialize(JsonParser jp, DeserializationContext dc) throws IOException {
if (jp.getCurrentToken() != null && jp.getCurrentToken() != JsonToken.START_OBJECT) {
throw dc.mappingException(OpenSkyStates.class);
}
try {
OpenSkyStates res = new OpenSkyStates();
for (jp.nextToken(); jp.getCurrentToken() != null && jp.getCurrentToken() != JsonToken.END_OBJECT; jp.nextToken()) {
if (jp.getCurrentToken() == JsonToken.FIELD_NAME) {
if ("time".equalsIgnoreCase(jp.getCurrentName())) {
int t = jp.nextIntValue(0);
res.setTime(t);
} else if ("states".equalsIgnoreCase(jp.getCurrentName())) {
jp.nextToken();
res.setStates(deserializeStates(jp));
} else {
// ignore other fields, but consume value
jp.nextToken();
}
} // ignore others
}
JsonNode node = jp.getCodec().readTree(jp);

if (node.get("time") != null && node.get("time").isNumber())
res.setTime(node.get("time").asInt());

if (node.get("states") != null && node.get("states").isArray())
res.setStates(deserializeStates(node.get("states")));

return res;
} catch (JsonParseException jpe) {
throw dc.mappingException(OpenSkyStates.class);
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