Parsing JSON array to java object

Question

I am trying to parse using Jackson mapper to parse big JSON to java object. I have very big JSON but came across this little piece in it and not sure how to parse.<

Answer 1

Create one json pojo mapper class

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import com.fasterxml.jackson.annotation.JsonAnyGetter;
import com.fasterxml.jackson.annotation.JsonAnySetter;
import com.fasterxml.jackson.annotation.JsonIgnore;
import com.fasterxml.jackson.annotation.JsonInclude;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;

@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
"coordinates"
})
public class Example {

@JsonProperty("coordinates")
private List<List<List<Double>>> coordinates = null;
@JsonIgnore
private Map<String, Object> additionalProperties = new HashMap<String, Object>();

@JsonProperty("coordinates")
public List<List<List<Double>>> getCoordinates() {
return coordinates;
}

@JsonProperty("coordinates")
public void setCoordinates(List<List<List<Double>>> coordinates) {
this.coordinates = coordinates;
}

@JsonAnyGetter
public Map<String, Object> getAdditionalProperties() {
return this.additionalProperties;
}

@JsonAnySetter
public void setAdditionalProperty(String name, Object value) {
this.additionalProperties.put(name, value);
}

}

Then convert jsonString to pojo

Gson gson = new GsonBuilder().create();
Example r = gson.fromJson(jsonString, Example.class);

Answer 2

It depends how really big is your JSON. If you can load it to memory, you can use the simplest way: Solution 1:
POJO class:

class CoordinatesContainer {

    private double[][][] coordinates;

    public double[][][] getCoordinates() {
        return coordinates;
    }

    public void setCoordinates(double[][][] coordinates) {
        this.coordinates = coordinates;
    }

    @Override
    public String toString() {
        StringBuilder builder = new StringBuilder(1024);
        for (double[] arrayItem : coordinates[0]) {
            builder.append(Arrays.toString(arrayItem));
            builder.append(", ");
        }
        return builder.toString();
    }
}

Usage:

ObjectMapper mapper = new ObjectMapper();
CoordinatesContainer coordinatesContainer = mapper.readValue(json, CoordinatesContainer.class);
System.out.println(coordinatesContainer);

Above program prints:

[-72.943068, 45.842298], [-72.943075, 45.841859]

Solution 2:
But if your JSON is really big and you are not able to load it to memory, you should consider Jackson Streaming API. In this case you should not create POJO class and try to process each element "node" by "node":

import java.io.File;
import java.io.IOException;
import java.math.BigDecimal;
import java.util.Arrays;

import com.fasterxml.jackson.core.JsonFactory;
import com.fasterxml.jackson.core.JsonParser;
import com.fasterxml.jackson.core.JsonToken;

public class JsonProgram {

    public static void main(String[] args) throws IOException {
        File json = new File("/x/data.json");
        JsonFactory jsonFactory = new JsonFactory();
        JsonParser parser = jsonFactory.createParser(json);
        // Skip all elements to first array
        while (parser.nextToken() != JsonToken.START_ARRAY) {
        }
        parser.nextToken();
        // First level
        while (parser.nextToken() != JsonToken.END_ARRAY) {
            // Skip inner start array element
            parser.nextToken();
            System.out.println();
            System.out.println("NEXT ARRAY NODE");

            BigDecimal first = parser.getDecimalValue();

            // Go to second value
            parser.nextToken();

            BigDecimal second = parser.getDecimalValue();

            // Skip inner end array element
            parser.nextToken();

            // Handle array item
            System.out.println("First: " + first.toString());
            System.out.println("Second: " + second.toString());
        }
    }
}

Above program prints:

NEXT ARRAY NODE
First: -72.943068
Second: 45.842298

NEXT ARRAY NODE
First: -72.943075
Second: 45.841859

In my examples I used Jackson in 2.2.3 version.