A simple example to use Jackson to convert a JSON string to a Map.

  String json = "{name:\"mkyong\"}";
 
  Map<String,String> map = new HashMap<String,String>();
  ObjectMapper mapper = new ObjectMapper();
 
  map = mapper.readValue(json, new TypeReference<HashMap<String,String>>(){});

Problem

When the program is executed, it hits following error message

org.codehaus.jackson.JsonParseException: 
   Unexpected character ('n' (code 110)): was expecting double-quote to start field name
   at [Source: java.io.StringReader@7c87c24a; line: 1, column: 3]

Solution

In JSON specification, it requires the use of double quotes for field names. To enable Jackson to handle the unquoted field name, add JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES in the ObjectMapper configuration.

package com.mkyong.jsonexample;
 
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import org.codehaus.jackson.JsonParseException;
import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.type.TypeReference;
 
public class JsonMapExample {
    public static void main(String[] args) {
 
	String json = "{name:\"mkyong\"}";
 
	Map<String,String> map = new HashMap<String,String>();
	ObjectMapper mapper = new ObjectMapper();
 
	mapper.configure(JsonParser.Feature.ALLOW_UNQUOTED_FIELD_NAMES, true);
 
	try {
 
		map = mapper.readValue(json, 
                         new TypeReference<HashMap<String,String>>(){});	
		System.out.println(map);
 
	} catch (JsonParseException e) {
		e.printStackTrace();
	} catch (JsonMappingException e) {
		e.printStackTrace();
	} catch (IOException e) {
		e.printStackTrace();
	}	
 
  }
}

Output

{name=mkyong}
Note
In JSON, unquoted field names are non-standard, and should be avoided.

References

  1. Wikipedia : JSON
  2. JsonParser.Feature JavaDoc
Tags :
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