How to get just the field names from the given string in object format ( not using POJO ) from the following string using regex

String is as follows :

"{
    account_number={
    type=long
    },
    firstname={
    type=text, fields={
    keyword={
    ignore_above=256, type=keyword
            }
        }
    },
    accountnumber={
    type=long
    },
    address={
    type=text, fields={
    keyword={
    ignore_above=256, type=keyword
            }
        }
    },
    gender={
    type=text, fields={
    keyword={
    ignore_above=256, type=keyword
            }
        }
    }
}"

I need to get only the names of these fields, i.e, account_number,firstname,accountnumber,address,gender. Pojo class won't work here since the content inside objects is not fixed. A reg ex may work. Any suggestions ?

Here I have converted ur string into JSON and then retrieved all the keys

import java.util.HashSet;
import java.util.Set;
import java.util.regex.Matcher;
import java.util.regex.Pattern;
import org.json.JSONObject;
public class SOTest {
public static void main(String args[]) {
Set<String> keywords = new HashSet<String>();
final String regex = "[a-z]\\w*";
String string = "{\n"
+ "    account_number={\n"
+ "    type=long\n"
+ "    },\n"
+ "    firstname={\n"
+ "    type=text, fields={\n"
+ "    keyword={\n"
+ "    ignore_above=256, type=keyword\n"
+ "            }\n"
+ "        }\n"
+ "    },\n"
+ "    accountnumber={\n"
+ "    type=long\n"
+ "    },\n"
+ "    address={\n"
+ "    type=text, fields={\n"
+ "    keyword={\n"
+ "    ignore_above=256, type=keyword\n"
+ "            }\n"
+ "        }\n"
+ "    },\n"
+ "    gender={\n"
+ "    type=text, fields={\n"
+ "    keyword={\n"
+ "    ignore_above=256, type=keyword\n"
+ "            }\n"
+ "        }\n"
+ "    }\n"
+ "}";
final Pattern pattern = Pattern.compile(regex, Pattern.MULTILINE);
final Matcher matcher = pattern.matcher(string);
while(matcher.find()) {
String gp = matcher.group();
keywords.add(gp);
}
for (String keyword : keywords) {
string = string.replace(keyword, "\""+keyword+"\"");
}
string = string.replace("=", ":");
System.out.println(string);
JSONObject jsonObject = new JSONObject(string);
System.out.println(jsonObject.keySet());
}
}

output

[account_number, firstname, accountnumber, address, gender]