Why not write directly from the Sheets API response (this example was extracted from the Java Sheet API quick-start)
public static void main(String... args) throws IOException, GeneralSecurityException {
// Create a new authorized API client service.
final NetHttpTransport HTTP_TRANSPORT = GoogleNetHttpTransport.newTrustedTransport();
final String spreadsheetId = "<SHEET_ID>";
final String range = "<SHEET_RANGE>";
Sheets service = new Sheets.Builder(HTTP_TRANSPORT, JSON_FACTORY, getCredentials(HTTP_TRANSPORT))
.setApplicationName(APPLICATION_NAME)
.build();
ValueRange response = service.spreadsheets().values()
.get(spreadsheetId, range)
.execute();
List<List<Object>> values = response.getValues();
if (values == null || values.isEmpty()) {
System.out.println("No data found.");
} else {
/* Create a new writer */
PrintWriter writer = new PrintWriter("data.csv");
for (List<Object> list : values) {
/* Building the string */
StringBuilder str = new StringBuilder();
str.append(list.get(0).toString() + ",");
str.append(list.get(1).toString() + "\n");
writer.write(str.toString());
}
/* Closing the writer */
writer.close();
}
}
In any case, if you are reading the JSON object correctly, the mechanism would be exactly the same.
Updated
If you want to read directly from JSON, consider using this example (using GSON):
public class SheetResponse {
private String range;
private String majorDimensions;
private List<List<Object>> values;
}
public static void main(String... args) throws IOException, GeneralSecurityException {
// Create a new authorized API client service.
var gson = new Gson();
var reader = new JsonReader(new FileReader("test.json"));
SheetResponse sR = gson.fromJson(reader, SheetResponse.class);
PrintWriter writer = new PrintWriter("data.csv");
for (List<Object> list : sR.values) {
/* Building the string */
StringBuilder str = new StringBuilder();
str.append(list.get(0).toString() + ",");
str.append(list.get(1).toString() + "\n");
writer.write(str.toString());
}
/* Closing the writer */
writer.close();
}
Updated for the general case
public static void main(String... args) throws IOException, GeneralSecurityException {
// Create a new authorized API client service.
var gson = new Gson();
var reader = new JsonReader(new FileReader("test.json"));
SheetResponse sR = gson.fromJson(reader, SheetResponse.class);
PrintWriter writer = new PrintWriter("data.csv");
for (int i = 0; i < sR.values.size(); i++) {
var valueRow = sR.values.get(i);
StringBuilder str = new StringBuilder();
for (int j = 0; j < valueRow.size(); j++) {
if (j == valueRow.size() - 1) {
str.append(valueRow.get(j).toString() + "\n");
} else {
str.append(valueRow.get(j).toString() + ",");
}
}
writer.write(str.toString());
}
/* Closing the writer */
writer.close();
}
Documentation