Convert HashMap.toString() back to HashMap in Java

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I put a key-value pair in a Java HashMap and converted it to a String using the toString() method.

Is it possible to convert this String representation back to a HashMap object and retrieve the value with its corresponding key?

Thanks

hashmap java
12 Answers

You can make use of Google's "GSON" open-source Java library for this,

Example input (Map.toString) : {name=Bane, id=20}

To Insert again in to HashMap you can use below code:

yourMap = new Gson().fromJson(yourString, HashMap.class);

That's it Enjoy.

(In Jackson Library mapper It will produce exception "expecting double-quote to start field name")

user_113113590

Using ByteStream can convert the String but it can encounter OutOfMemory exception in case of large Strings. Baeldung provides some nice solutions in his pot here : https://www.baeldung.com/java-map-to-string-conversion

Using StringBuilder : 

public String convertWithIteration(Map<Integer, ?> map) {
StringBuilder mapAsString = new StringBuilder("{");
for (Integer key : map.keySet()) {
    mapAsString.append(key + "=" + map.get(key) + ", ");
}
mapAsString.delete(mapAsString.length()-2, mapAsString.length()).append("}");
return mapAsString.toString(); }

Please note that lambdas are only available at language level 8 and above Using Stream : 

public String convertWithStream(Map<Integer, ?> map) {
String mapAsString = map.keySet().stream()
  .map(key -> key + "=" + map.get(key))
  .collect(Collectors.joining(", ", "{", "}"));
return mapAsString; }

Converting String Back to Map using Stream : 

public Map<String, String> convertWithStream(String mapAsString) {
Map<String, String> map = Arrays.stream(mapAsString.split(","))
  .map(entry -> entry.split("="))
  .collect(Collectors.toMap(entry -> entry[0], entry -> entry[1]));
return map; }
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