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How do I cast a HashMap to a concrete class?

I have a class, lets call it Fruit, and I have a HashMap. I want to be able to initialize a new instance of Fruit, but set to the values in HashMap. So for example:

Map<String, String> map = new HashMap<String, String>();
map.put("name", "Banana");
map.put("color", "Yellow");


Then I want to be initialize a new Fruit instance like so:

Fruit myFruit = new Fruit(map);


or

Fruit myFruit = (Fruit)map;


Is this possible in Java, by means of iterating the Map?

8 Answers
8

The second is not possible because a HashMap is not a Fruit. You could do the first by providing a constructor that takes a Map<String, String> argument.

HashMap

Fruit

Map<String, String>

public Fruit(Map<String, String> map)
this.name = map.get("name");
this.color = map.get("color");



It seems like you can use reflection for this

Fruit f = new Fruit();
Class aClass = f.getClass();
for(Field field : aClass.getFields())
if(map.containsKey(field.getName()))
field.set(f,map.get(field.getName()));




Yes, it's possible. But you'd have to write a constructor for Fruit that knows how to pull values -- and which values -- from the map.

public Fruit(Map params)
this.setColor(map.get("color"));
this.setName(map.get("name"));



You would traverse the map in your constructor and assign the values. If there's an actual library for doing this(almost like a Bean), then I've never heard of it.

Casting of a HashMap to a fruit wouldn't be possible.

The second is not possible but you can create a class that will take a Map as a constructor parameter.

class Fruit

private Map<String, String> fruitMap;

Fruit(Map<String, String> map)






Assuming the keys in map correspond to setter methods in the Fruit class, you could use one of Apache bean's utilities like PropertyUtils.

map

Fruit

final Fruit f = new Fruit();
for(String key : map.keySet())
PropertyUtils.setProperty(fruit, key, map.get(key));



For very complicated cases of this you might want to take a look at Dozer. We use Dozer to map very large Maps to very large objects.

I have fixed Anni's solution, now it supports inheritance, and static and final fields.
By the way, I have not checked for type mismatches.

public static void populateBean(Object bean, Map<String, Object> properties) throws Exception
Class<?> clazz = bean.getClass();
while(clazz != null)
for (Field field : clazz.getDeclaredFields())
int modifiers = field.getModifiers();
if (!Modifier.isStatic(modifier) && !Modifier.isFinal(modifier))
if (map.containsKey(field.getName()))
field.accessible(true);
field.set(bean, map.get(field.getName()));



clazz = clazz.getSuperclass();




By the way Apache BeanUtils DynaBeans almost does what you want, as far as I remember it supports Java Beans Introspection.

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