Converting a JSON with array of objects to proper Java object

Question

I have a simple Spring Boot project in which a scheduler periodically consumes a RESTful API and converts the incoming JSON file.

The JSON file is actually an array of Objects with some Keys and Values:

[
{"CoID":1,"CoName":"کشاورزی و دامپروری مگسال","CoNameEnglish":"MagsalAgriculture & Animal Husbandry Co.","CompanySymbol":"MAGS","CoTSESymbol":"زمگسا","GroupID":1,"GroupName":"كشاورزی و دامپروری","IndustryID":1,"IndustryName":"كشاورزی، دامپروری و خدمات وابسته به آن","InstCode":"5054819322815158","TseCIsinCode":"IRO1MAGS0006","TseSIsinCode":"IRO1MAGS0001","MarketID":1,"MarketName":"بورس"},
{"CoID":2,"CoName":"ذغالسنگ نگین طبس","CoNameEnglish":"Negin Tabas Lignite Co.","CompanySymbol":"TBAS","CoTSESymbol":"کطبس","GroupID":2,"GroupName":"استخراج و انبار ذغال سنگ سخت","IndustryID":2,"IndustryName":"استخراج ذغال سنگ","InstCode":"8977369674477111","TseCIsinCode":"IRO1TBAS0004","TseSIsinCode":"IRO1TBAS0001","MarketID":1,"MarketName":"بورس"},{"CoID":3,"CoName":"معدنی و صنعتی چادرملو","CoNameEnglish":"Chadormalu Mining & Industrial Co.","CompanySymbol":"CHML","CoTSESymbol":"کچاد","GroupID":3,"GroupName":"استخراج سنگ معدن های فلزی آهنی","IndustryID":3,"IndustryName":"استخراج كانه های فلزی","InstCode":"18027801615184692","TseCIsinCode":"IRO1CHML0000","TseSIsinCode":"IRO1CHML0001","MarketID":1,"MarketName":"بورس"}
...
]

I have a class called Company with similar fields to one of objects in the array within the JSON file:

@JsonIgnoreProperties(ignoreUnknown = true)
public class Company {

private int CoID;
private String CoName;
private String CoNameEnglish;
private String CompanySymbl;
private String CoTSESymbl;
private int GroupID;
private String GroupName;
private int IndustryID;
private String IndustryName;
private String IndustryCode;
private String TseCIsinCode;
private String TseSIsinCode;
private int MarketID;
private String MarketName;
    // And proper getters, setters and constructor //

I also created a wrapping class called CompanyList:

public class CompanyList {

private ArrayList<Company> companyList;

public ArrayList<Company> getCompanyList() {
    return companyList;
}

public void setCompanyList(ArrayList<Company> companyList) {
    this.companyList = companyList;
}

public CompanyList() {

}

@Override
public String toString() {
    return "CompanyList [companyList=" + companyList + "]";
}

}

I have tried three different ways to fulfill this requirement:

First:

Object[] forNow = restTemplate.getForObject("somewhere", Object[].class);
List<Object> cp= Arrays.asList(forNow);

This one works properly.

Second:

    RestTemplate restTemplate = new RestTemplate();
    ResponseEntity<List<Company>> response = restTemplate.exchange(
      "somewhere",
      HttpMethod.GET,
      null,
      new ParameterizedTypeReference<List<Company>>(){});
    List<Company> companies = response.getBody();

    log.info(companies.toString());

This one is compiled successfully but returns null and 0 in all fields.

Third:

    CompanyList cp = restTemplate.getForObject("somewhere", CompanyList.class);
    log.info(cp.getCompanyList().toString());

This one raises an exception:

Error while extracting response for type [class ir.pisys.rest.CompanyList] and content type [application/json;charset=utf-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize instance of ir.pisys.rest.CompanyList out of START_ARRAY token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of ir.pisys.rest.CompanyList out of START_ARRAY token

So I have some questions here:

1- Is the first approach an optimized one? (Compared to others)

2- How can I fix the two other approaches?

1. You never showed your API function or repository. 2. When your API function successfully returns Object[].class why would you expect it to return CompanyList.class ? — Gonen I
– Gonen I, Commented Sep 10, 2019 at 5:27
@Iman H Please replace your api URLs seems like they are public. Does Company has toString? As the rest API response is array/list(assume from 1) getCompanyList method in the ComapnyList should annotate with @JsonGetter("list") — mallikarjun
– mallikarjun, Commented Sep 10, 2019 at 5:40
@mallikarjun Yes it has toString. I added the noticed annotation but the following exception raises: content type [application/json;charset=utf-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize instance of ir.pisys.rest.CompanyList out of START_ARRAY token; nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize instance of ir.pisys.rest.CompanyList out of START_ARRAY token at [Source: (PushbackInputStream); line: 1, column: 1] — Iman H
– Iman H, Commented Sep 10, 2019 at 5:59
your second approach is wrong. You are missing basic syntax. — Vishwa Ratna
– Vishwa Ratna, Commented Sep 10, 2019 at 6:04

i.bondarenko · Accepted Answer · 2019-09-10 06:38:02Z

1

The second and third approaches should work fine. You need to check your json response structure.

You could use following jsons for tests (they work with your code):

Second approach:

[{"tseCIsinCode":null,"tseSIsinCode":null,"coName":"n1","industryID":0,"coID":0,"coNameEnglish":null,"companySymbl":null,"coTSESymbl":null,"groupID":0,"groupName":null,"industryName":null,"industryCode":null,"marketID":0,"marketName":null},{"tseCIsinCode":null,"tseSIsinCode":null,"coName":"n2","industryID":0,"coID":0,"coNameEnglish":null,"companySymbl":null,"coTSESymbl":null,"groupID":0,"groupName":null,"industryName":null,"industryCode":null,"marketID":0,"marketName":null}]

Third:

{"companyList":[{"coName":"n1","coID":0,"coNameEnglish":null,"companySymbl":null,"coTSESymbl":null,"groupID":0,"groupName":null,"industryID":0,"industryName":null,"industryCode":null,"tseCIsinCode":null,"tseSIsinCode":null,"marketID":0,"marketName":null},{"coName":"n2","coID":0,"coNameEnglish":null,"companySymbl":null,"coTSESymbl":null,"groupID":0,"groupName":null,"industryID":0,"industryName":null,"industryCode":null,"tseCIsinCode":null,"tseSIsinCode":null,"marketID":0,"marketName":null}]}

Update:

Second approach fix: Change your json fields name - "CoName" -> "coName", "CoID" -> "coID" and so on. After that changes it will work pirfectly.

Third approach fix: Wrap your json with "{\"companyList\":[...] And change fields name as for second approach

Second Update If you can't change json from response. You could use mapping in your Company class

@JsonProperty("CoName")
private String CoName;

edited Sep 10, 2019 at 6:38

answered Sep 10, 2019 at 6:06

i.bondarenko

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2 Comments

Iman H Over a year ago

thanks. my JSON structure is as the first one you provided.

i.bondarenko Over a year ago

Glad to help you!

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