001/*
002 * Licensed to the Apache Software Foundation (ASF) under one or more
003 * contributor license agreements.  See the NOTICE file distributed with
004 * this work for additional information regarding copyright ownership.
005 * The ASF licenses this file to You under the Apache License, Version 2.0
006 * (the "License"); you may not use this file except in compliance with
007 * the License.  You may obtain a copy of the License at
008 *
009 *      http://www.apache.org/licenses/LICENSE-2.0
010 *
011 * Unless required by applicable law or agreed to in writing, software
012 * distributed under the License is distributed on an "AS IS" BASIS,
013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014 * See the License for the specific language governing permissions and
015 * limitations under the License.
016 */
017package org.apache.commons.lang3.reflect;
018
019import java.lang.reflect.Type;
020import java.lang.reflect.TypeVariable;
021
022import org.apache.commons.lang3.Validate;
023
024/**
025 * <p>Type literal comparable to {@code javax.enterprise.util.TypeLiteral},
026 * made generally available outside the JEE context. Allows the passing around of
027 * a "token" that represents a type in a typesafe manner, as opposed to
028 * passing the (non-parameterized) {@link Type} object itself. Consider:</p>
029 * <p>
030 * You might see such a typesafe API as:
031 * <pre>
032 * class Typesafe {
033 *   &lt;T&gt; T obtain(Class&lt;T&gt; type, ...);
034 * }
035 * </pre>
036 * Consumed in the manner of:
037 * <pre>
038 * Foo foo = typesafe.obtain(Foo.class, ...);
039 * </pre>
040 * Yet, you run into problems when you want to do this with a parameterized type:
041 * <pre>
042 * List&lt;String&gt; listOfString = typesafe.obtain(List.class, ...); // could only give us a raw List
043 * </pre>
044 * {@code java.lang.reflect.Type} might provide some value:
045 * <pre>
046 * Type listOfStringType = ...; // firstly, how to obtain this? Doable, but not straightforward.
047 * List&lt;String&gt; listOfString = (List&lt;String&gt;) typesafe.obtain(listOfStringType, ...); // nongeneric Type would necessitate a cast
048 * </pre>
049 * The "type literal" concept was introduced to provide an alternative, i.e.:
050 * <pre>
051 * class Typesafe {
052 *   &lt;T&gt; T obtain(TypeLiteral&lt;T&gt; type, ...);
053 * }
054 * </pre>
055 * Consuming code looks like:
056 * <pre>
057 * List&lt;String&gt; listOfString = typesafe.obtain(new TypeLiteral&lt;List&lt;String&gt;&gt;() {}, ...);
058 * </pre>
059 * <p>
060 * This has the effect of "jumping up" a level to tie a {@code java.lang.reflect.Type}
061 * to a type variable while simultaneously making it short work to obtain a
062 * {@code Type} instance for any given type, inline.
063 * </p>
064 * <p>Additionally {@link TypeLiteral} implements the {@link Typed} interface which
065 * is a generalization of this concept, and which may be implemented in custom classes.
066 * It is suggested that APIs be defined in terms of the interface, in the following manner:
067 * </p>
068 * <pre>
069 *   &lt;T&gt; T obtain(Typed&lt;T&gt; typed, ...);
070 * </pre>
071 *
072 * @since 3.2
073 */
074public abstract class TypeLiteral<T> implements Typed<T> {
075
076    @SuppressWarnings("rawtypes")
077    private static final TypeVariable<Class<TypeLiteral>> T = TypeLiteral.class.getTypeParameters()[0];
078
079    /**
080     * Represented type.
081     */
082    public final Type value;
083
084    private final String toString;
085
086    /**
087     * The default constructor.
088     */
089    protected TypeLiteral() {
090        this.value =
091            Validate.notNull(TypeUtils.getTypeArguments(getClass(), TypeLiteral.class).get(T),
092                "%s does not assign type parameter %s", getClass(), TypeUtils.toLongString(T));
093
094        this.toString = String.format("%s<%s>", TypeLiteral.class.getSimpleName(), TypeUtils.toString(value));
095    }
096
097    @Override
098    public final boolean equals(final Object obj) {
099        if (obj == this) {
100            return true;
101        }
102        if (obj instanceof TypeLiteral == false) {
103            return false;
104        }
105        final TypeLiteral<?> other = (TypeLiteral<?>) obj;
106        return TypeUtils.equals(value, other.value);
107    }
108
109    @Override 
110    public int hashCode() {
111        return 37 << 4 | value.hashCode();
112    }
113
114    @Override
115    public String toString() {
116        return toString;
117    }
118
119    @Override
120    public Type getType() {
121        return value;
122    }
123}