How to parse a String variable into any data type in Java?

Question

I want to build a method that can convert a String value to a given Field object data type through Java Reflection.

Here is my code:

String value = ...;

Class<? extends MyObject> clazz = getClazz();

Field f = clazz.getDeclaredField("fieldName");
boolean fieldIsAccessible = f.isAccessible();
if (!fieldIsAccessible) {
   f.setAccessible(true);
}

f.getType().cast(value);

if (!fieldIsAccessible) {
    f.setAccessible(false);
}

When I run this code at firs attempt, I receive this exception java.lang.ClassCastException.

I want to convert value to class java.math.BigDecimal.

What is my code missing ?

EDIT: View the solution I came up with.

Answer 1

You could make this work for classes that have a string constructor like this: f.getType().getConstructor( String.class ).newInstance( value );

Answer 2

In Java, there is no universal method for converting a String into an instance of an arbitrary class. Many classes simply don't support such a conversion. And there's no standard interface for those that do support it.

Your best bet is to look for a constructor that accepts a String as its sole argument. Of course, not every class provides such a constructor, and there's no guarantee that the semantics would be what you'd expect.

Answer 3

There is a Github project (MIT Licensed) called type-parser which does converting a string value to the desired data type

Here is the project description from GitHub

This is a light weight library that does nothing but parse a string to a given type. Supports all applicable java classes, such as Integer, File, Enum, Float etc., including generic Collection types/interfaces such as List, Set, Map, arrays and even custom made types. Also possible to register your own parsers.