com.fasterxml.jackson.core.type.TypeReference Maven / Gradle / Ivy

package com.fasterxml.jackson.core.type;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * This generic abstract class is used for obtaining full generics type information
 * by sub-classing; it must be converted to {@link ResolvedType} implementation
 * (implemented by JavaType from "databind" bundle) to be used.
 * Class is based on ideas from
 * http://gafter.blogspot.com/2006/12/super-type-tokens.html,
 * Additional idea (from a suggestion made in comments of the article)
 * is to require bogus implementation of Comparable
 * (any such generic interface would do, as long as it forces a method
 * with generic type to be implemented).
 * to ensure that a Type argument is indeed given.
 *
 * Usage is by sub-classing: here is one way to instantiate reference
 * to generic type List<Integer>:
 *
 *  TypeReference ref = new TypeReference<List<Integer>>() { };
 *
 * which can be passed to methods that accept TypeReference, or resolved
 * using TypeFactory to obtain {@link ResolvedType}.
 */
public abstract class TypeReference
    implements Comparable>
{
    protected final Type _type;
    
    protected TypeReference()
    {
        Type superClass = getClass().getGenericSuperclass();
        if (superClass instanceof Class) { // sanity check, should never happen
            throw new IllegalArgumentException("Internal error: TypeReference constructed without actual type information");
        }
        /* 22-Dec-2008, tatu: Not sure if this case is safe -- I suspect
         *   it is possible to make it fail?
         *   But let's deal with specific
         *   case when we know an actual use case, and thereby suitable
         *   workarounds for valid case(s) and/or error to throw
         *   on invalid one(s).
         */
        _type = ((ParameterizedType) superClass).getActualTypeArguments()[0];
    }

    public Type getType() { return _type; }
    
    /**
     * The only reason we define this method (and require implementation
     * of Comparable) is to prevent constructing a
     * reference without type information.
     */
//  @Override
    public int compareTo(TypeReference o) {
        // just need an implementation, not a good one... hence:
        return 0;
    }
}