JSON formatting for a Java Server

Question

I am trying to read JSON string using gson into a Java program. In the sample code below - the Java program has 3 object classes. The data in the json string will have a vari

Answer 1

Your JSON-string seems incorrect to me. Let me propose the following:

public static void main(String args[]) {
    String jsonstring = "["
        + "{'TableA':[{'field_A1':'A_11'},{'field_A1':'A_12'}]}"
        + ",{'TableB':[{'field_B1':'B_11','field_B2':'B_12','field_B3':['abc','def','ghi']},"
        + "{'field_B1':'B_21','field_B2':'B_Field22','field_B3':['mno','pqr','xyz']}]}"
        + ",{'TableC':[{'field_C1':'C_11','field_C2':'C_12','field_C3':'C_13'},"
        + "{'field_C1':'C_21','field_C2':'C_22','field_C3':'C_23'},{'field_C1':'C_31','field_C2':'C_32','field_C3':'C_33'}]}"
        + "]";
    jsonstring = jsonstring.replace('\'', '"');

    Gson gson = new Gson();
    JsonParser parser = new JsonParser();
    JsonArray array = parser.parse(jsonstring).getAsJsonArray();

    for (JsonElement jsonElement : array) {
        JsonObject jsonObject = jsonElement.getAsJsonObject();
        Map.Entry table = jsonObject.entrySet().iterator().next();
        String tableName = table.getKey();
        JsonElement rows = table.getValue();
        try {
            Class rowClass = Class.forName("[Lnewpackage." + tableName + ";"); // explanation see below this code snippet
            // rowClass is an array class!
            Object[] parsedRows = gson.fromJson(rows, rowClass);
            // do something with parsedRows
            for (Object x : parsedRows) {
                System.out.println(x);
            }
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }
}

Assuming a "table definition" consists of a property named as the class ob the objects in the table, with the objects as array value of that property.

Explanation of Class.forName("[Lnewpackage." + tableName + ";")

This retrieves the Class instance for the array type of a class located in the package newpackage, e.g. newpackage.TableA[] (note the []). Class.forName("A") returns the instance representing the class A. Class.forName("[LA;") returns the instance representing the "class" of an array of As. Using it as a parameter for fromJson(...) it results in the parsing of a JSON array of A-objects.