Use reflection to populate fields

[Yan Hu]

Hi:
Thanks for clicking in. I have a question on how to use reflection to populate the public fields in an object.
For example:

 
class Foo{
  private String name;
  private int age;
  public void setAge(int age){ this.age=age;}
  public void setName(String name){this.name=name;} 
} 

If I have tons of such fileds in an object that I will have to fill data in, is there any way not to manully populate them by using reflection? Thank you very much.

[Ernest Friedman-Hill]

Hi,

I don't see any public fields here, and I see setXXX methods for all the private fields. What's the problem, exactly?

[Stan James]

I'm guessing you get name value pairs like "age,21" from a flat file or database query where column name == field name?

Look at the javaDoc for Class.getMethods(). You could look for a method called "setAge", try to cast your value to the type expected by the method and invoke it.

I would probably only do this in a persistence framework or a boundary between Java and something not-Java like XML. For regular hand-made Java objects I'd call the setAge() method the usual way.

[Cay Horstmann]

Let's say, for the sake of the argument, that your properties for a given object are inserted in a map. Maybe your read them from a configuration file and built up a map like this:
Map<String, Object> props = new HashMap<String, Object>();
props.put("name", "Harry Hacker");
props.put("age", 45); // autoboxing

Use this code outline:

BeanInfo info = Introspector.getBeanInfo(obj.getClass());
for (PropertyDescriptor descriptor : info.getPropertyDescriptors())
{
   String name = descriptor.getName();
   // the decapitalized name, like "age" or "name" in your example
   Method setter = descriptor.getWriteMethod();
   if (props.containsKey(name) && setter != null)
      setter.invoke(obj, props.get(name)); // varargs
}

Cheers,

Cay