How to read JSON array from HttpServletRequest?

Question

I am very new to servlet and I am unable to read JSON array from HttpServletRequest

I am sending below JSON to Java

page: 1
start: 0
limit: 20
sort: [{"property":"fiscalYear","direction":"DESC"}]

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String[] s=request.getParameterValues("sort");
        for(int i=0;i<s.length;i++)
}           System.out.println(s[i]);

actual output

 [{"property":"fiscalYear","direction":"DESC"}]

expected output get values fiscalYear and DESC separately

Use this to generate a domain model class : jsonutils.com then use ObjectMapper to convert the json to an object — Raj
– Raj, Commented Jun 9, 2019 at 9:08

Ryuzaki L · Accepted Answer · 2019-06-09 10:12:23Z

getParameterValues(String name) will return the String array

String[] getParameterValues(String name)

Returns an array of String objects containing all of the values the given request parameter has, or null if the parameter does not exist.

If the parameter has a single value, the array has a length of 1.

getParameter(String name) will return only String

Returns the value of a request parameter as a String, or null if the parameter does not exist. Request parameters are extra information sent with the request. For HTTP servlets, parameters are contained in the query string or posted form data.

You should only use this method when you are sure the parameter has only one value. If the parameter might have more than one value, use getParameterValues(java.lang.String).

Based on this you can go for getParameter which returns JSON representing string

String s=request.getParameter("sort"); // {"property":"fiscalYear","direction":"DESC"}

Now use ObjectMapper to read parse the JSON string

ObjectMapper objectMapper = new ObjectMapper();
JsonNode jsonNode = objectMapper.readTree(s);
String property = jsonNode.get("property").asText();
String direction = jsonNode.get("direction").asText();

If it is Array of JsonObjects //[{"property":"fiscalYear","direction":"DESC"}]

JsonNode jsonNode = objectMapper.readTree(s);
JsonNode node = jsonNode.get(0);
String property = node.get("property").asText();
String direction = node.get("direction").asText();

Govind Sharma · Accepted Answer · 2019-06-10 13:31:11Z

1

protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        String str=request.getParameterValues("sort");
    //  str=" [{\"property\":\"fiscalYear\",\"direction\":\"DESC\"}]";   
      JSONArray array=new JSONArray(str);
      for(int i=0;i<array.length();i++){
              JSONObject json_obj = array.getJSONObject(i);
            System.out.println( json_obj.getString("direction"));

      }
}

OUTPUT

DESC

answered Jun 10, 2019 at 13:31

Govind Sharma

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Comments

Youcef LAIDANI · Accepted Answer · 2019-06-09 09:15:00Z

0

You can create an Object which hold this infor :

public class SortDto {

  private String property;
  private String direction;

  // getters, setters, toString() ..
}

Then create an ObjectMapper like this :

ObjectMapper mapper = new ObjectMapper();
String sortJson = request.getParameter("sort");
// I suppose that sortJson is => {"property":"fiscalYear","direction":"DESC"}
SortDto dto = mapper.readValue(sortJson, SortDto.class);

Then you can just override the toString() method in your class or call dto.getProperty() dto.getDirection() to get the values separately.

Note

I used request.getParameter("sort") which return one String instead of request.getParameterValues("sort") which return an array of values

edited Jun 9, 2019 at 9:15

answered Jun 9, 2019 at 9:02

Youcef LAIDANI

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2 Comments

Anmol Duggal Over a year ago

It is an array [ {"property":"fiscalYear","direction":"DESC"}]

Youcef LAIDANI Over a year ago

@AnmolDuggal even with [ {"property":"fiscalYear","direction":"DESC"}] my solution works fine, I test both of them and both work fine

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