Jackson Deserializing an array of objects into an array list

Question

I have the following JSON file to deserialize

{
    "rows":
    [
        {
            "USER_ID": 001,
            "COMMISSION": 0,
            "SWAPS": -1.87,
            "PROFIT": -73.39,
            "COMMENT": "MAM|12345678|10020031"
        },
        {
            "USER_ID": 002,
            "COMMISSION": 0,
            "SWAPS": 0,
            "PROFIT": 12.23,
            "COMMENT": "PAMM|12345678|10229501"
        },
        {
            "USER_ID": 003,
            "COMMISSION": 0,
            "SWAPS": 0,
            "PROFIT": 396.77,
            "COMMENT": "PAMM|12345678|10229501"
        },      
...
]}

I would like to deserialise the JSON file to something like an ArrayList so that I can calculate individual user's total profit by accessing a value of the array.

I have the following class as a wrapper;

Data
@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
        "rows"
})
@Generated("jsonschema2pojo")
public class Rows {

    @JsonProperty("rows")
    private ArrayList<Row> rows = null;

    @JsonProperty("rows")
    public ArrayList<Row> getRows() {
        return rows;
    }

    @JsonProperty("rows")
    public void setRows(ArrayList<Row> rows) {
        this.rows = rows;
    }

I also have the following class to store each attribute.


@JsonInclude(JsonInclude.Include.NON_NULL)
@JsonPropertyOrder({
        "USER_ID",
        "COMMISSION",
        "SWAPS",
        "PROFIT",
        "COMMENT"
})
@Generated("jsonschema2pojo")
public class Row {
    @JsonProperty("USER_ID")
    private int userId;
    @JsonProperty("COMMISSION")
    private float commission;
    @JsonProperty("SWAPS")
    private float swaps;
    @JsonProperty("PROFIT")
    private float profit;
    @JsonProperty("COMMENT")
    private String comment;

    @JsonProperty("USER_ID")
    public int getUserId() {
        return userId;
    }

    @JsonProperty("USER_ID")
    public void setUserId(int userId) {
        this.userId = userId;
    }

    @JsonProperty("COMMISSION")
    public float getCommission() {
        return commission;
    }
//..setter/getter continue..

Finally, I have the following code in my main at the moment. However, it just stores the array of the objects as a whole and I cannot access an individual attribute of the row. The size of the array is just 1 and every data is in it.

 ObjectMapper mapper = new ObjectMapper();
        mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);


ArrayList<Rows> rowsArrayList = mapper.readValue(new File(ClientsRecordsPath), ArrayList.class);

            //json array to array object
            System.out.println("JSON array to Array objects...");
            System.out.println(rowsArrayList.get(0));

Output:

COMMENT=PAMM|123456|10314558}, {USER_ID=001, COMMISSION=0, SWAPS=0, PROFIT=13.57, COMMENT=PAMM|123456|10314558}, {USER_ID=002, COMMISSION=0, SWAPS=0, PROFIT=67.47, COMMENT=PAMM|123456|10314558}, {USER_ID=003, COMMISSION=0, SWAPS=0, PROFIT=202.41, COMMENT=PAMM|123456|10314558}, {USER_ID=004, COMMISSION=0, SWAPS=0, PROFIT=58.96, COMMENT=PAMM|123456|10314558}, {USER_ID=005, COMMISSION=0, SWAPS=0, PROFIT=6095, COMMENT=PAMM|123456|10314560}, {USER_ID=006, COMMISSION=0, ....

How can I store each user's data into an array list and access it individually so that I can calculate the individual's total profit?

Rows rows = mapper.readValue(new File(ClientsRecordsPath), Rows.class); will produce correct result, no? Do you have one entry of 'Rows' object in your JSON file or many? Probably TypeReference may be useful here: fasterxml.github.io/jackson-core/javadoc/2.2.0/com/fasterxml/… — Monsieur Merso
– Monsieur Merso, Commented May 30, 2021 at 11:03

Most Noble Rabbit · Accepted Answer · 2021-05-30 16:57:40Z

2

Note that leading zeroes are not allowed, so this JSON will be invalid. We can use JSONLint to check this.

Also, ObjectMapper throws com.fasterxml.jackson.databind.JsonMappingException: Invalid numeric value: Leading zeroes not allowed.

After removing leading zeroes, you can do:

ObjectMapper mapper = new ObjectMapper();
mapper.configure(DeserializationFeature.ACCEPT_SINGLE_VALUE_AS_ARRAY, true);

Rows rowsArrayList = mapper.readValue(new File(ClientsRecordsPath), Rows.class);

Output:

JSON array to Array objects...
Row(userId=1, commission=0.0, swaps=-1.87, profit=-73.39, comment=MAM|12345678|10020031)
Row(userId=2, commission=0.0, swaps=0.0, profit=12.23, comment=PAMM|12345678|10229501)
Row(userId=3, commission=0.0, swaps=0.0, profit=396.77, comment=PAMM|12345678|10229501)

While that works fine, I suggest to remove the wrapper class if it has no use. We can deserialize straight to a List<Row>:

List<Row> rows = Arrays.asList(mapper.treeToValue(mapper.readTree(new File(ClientsRecordsPath)).get("rows"), Row[].class));
rows.forEach(System.out::println);

Row(userId=1, commission=0.0, swaps=-1.87, profit=-73.39, comment=MAM|12345678|10020031)
Row(userId=2, commission=0.0, swaps=0.0, profit=12.23, comment=PAMM|12345678|10229501)
Row(userId=3, commission=0.0, swaps=0.0, profit=396.77, comment=PAMM|12345678|10229501)

edited May 30, 2021 at 16:57

answered May 30, 2021 at 16:16

Most Noble Rabbit

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1 Comment

Teriyaki Boy Over a year ago

Thank you very much. I thought I would need to create a wrapper class for this JSON structure... but It looks like I don't.

maneesh54321 · Accepted Answer · 2021-05-30 11:07:49Z

0

The code for parsing the json file will be:

Rows rows = mapper.readValue(new File(ClientsRecordsPath), Rows.class);

as the root of json is represented by Rows class, not ArrayList

answered May 30, 2021 at 11:07

maneesh54321

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