dQw4w9WyXcQ :
input:
public static void main(String[] args) {
final String key = "some key";
final String value = "some value";
Map<String, String> map1 = new HashMap<String, String>(){{put(key, value);}};
System.out.println(new Gson().toJson(map1) + " " + map1.get(key));
Map<String, String> map2 = new HashMap<>();
map2.put(key, value);
System.out.println(new Gson().toJson(map2) + " " + map2.get(key));
}
output:
null some value
{"some key":"some value"} some value
Process finished with exit code 0
Greg Kopff :
For map1, you have created an anonymous subclass. Assuming your class that contains main() is called ExampleClass, then:
System.out.println(map1.getClass().getName())
prints out:
ExampleClass$1
Whereas printing the class for map2 yields:
java.util.HashMap
As to the exact reason that Gson doesn't serialise it - Gson uses the classname to lookup a converter. If you instead serialise it using:
System.out.println(new Gson().toJson(map1, HashMap.class));
... it works as expected.