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* Licensed to the Apache Software Foundation (ASF) under one
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* distributed with this work for additional information
* regarding copyright ownership. The ASF licenses this file
* to you 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 org.apache.wink.common.internal.type;
import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
/**
* This class is used to pass full generics type information, and
* avoid problems with type erasure (that basically removes most
* usable type references from runtime Class objects).
* It 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</code>
* (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<Integer></code>:
*<pre>
* TypeReference ref = new TypeReference<List<Integer>>() { };
*</pre>
* which can be passed to methods that accept TypeReference.
*/
public abstract class TypeReference<T> implements Comparable<TypeReference<T>> {
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 specifc
* case when we know an actual use case, and thereby suitable
* work arounds 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</code>) is to prevent constructing a
* reference without type information.
*/
public int compareTo(TypeReference<T> o) {
// just need an implementation, not a good one... hence:
return 0;
}
}