com.ebuddy.cassandra.TypeReference.java Source code

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Here is the source code for com.ebuddy.cassandra.TypeReference.java

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/*
 * Copyright 2013 eBuddy B.V.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *        http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */

package com.ebuddy.cassandra;

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.
 *
 * This class is a copy of com.fasterxml.jackson.core.type.TypeReference in jackson,
 * which is turn is based on ideas from
 * <a href="http://gafter.blogspot.com/2006/12/super-type-tokens.html"
 * >http://gafter.blogspot.com/2006/12/super-type-tokens.html</a>,
 * Additional idea (from a suggestion made in comments of the article)
 * is to require bogus implementation of {@code 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.
 *<p>
 * Usage is by sub-classing: here is one way to instantiate reference
 * to generic type {@code List&lt;Integer>}:
 *<pre>
 *  TypeReference ref = new TypeReference&lt;List&lt;Integer>>() { };
 *</pre>
 * which can be passed to methods that accept TypeReference.
 */
public abstract class TypeReference<T> implements Comparable<TypeReference<T>> {
    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 {@code Comparable}) is to prevent constructing a
     * reference without type information.
     */
    @Override
    public int compareTo(TypeReference<T> o) {
        // just need an implementation, not a good one... hence:
        return 0;
    }
}