Java反射：在不知道对象类型的情况下将其转换为另一个对象

Question

I am using reflections to map an ResultSet to a Field in bean.

field = clazz.getDeclaredField(str);
field.setAccessible(true);
Object resultSetObject = rs.getObject(str);
Class fieldType = field.getType();
field.set(clazzInst, fieldType.cast(resultSetObject));

The problem is resultSetObject is of type Integer and fieldType is of Long and I cannot cast Intger to Long and getting ClassCastException .

Answer 1

You are essentially asking to duplicate the type knowledge that is available at compile-time with which the compiler generates the correct conversion. The runtime doesn't have this knowledge, so you will have to provide it by building a matrix of types and coding all the conversions you want, explicitly.

You can define this as a matrix indexed by type along both axes (from-type and to-type) or more likely as a Map whose key is a ConversionType object each instance of which defines fromType , toType and a convert() method.

Answer 2

Whether you have

Object ref = new String("object of type string");

or

String ref = new String("still object of type string");

the object referenced will be of type String . Doing

Object obj = (Object) new String("still a string");

does not change that the referenced object is a String . In your case, you'll probably need a conversion strategy to convert between types.

Answer 3

您还有另一个选择，将long转换为string，然后转换为整数。