Java Reflection Generic Type from Class getGenericFirstClass(Type type)

Description

get Generic First Class

License

Apache License

Parameter

Parameter	Description
type	The type that has the generic type. (NotNull)

Return

The first generic type for the specified type. (NullAllowed: e.g. not found)

Declaration

public static Class<?> getGenericFirstClass(Type type) 

Method Source Code

//package com.java2s;
/*/* w  w  w .j av a2  s .co m*/
 * Copyright 2015-2016 the original author or authors.
 *
 * 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.
 */

import java.lang.reflect.Array;
import java.lang.reflect.GenericArrayType;

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

import java.lang.reflect.WildcardType;

public class Main {
    protected static final Type[] EMPTY_TYPES = new Type[0];

    /**
     * @param type The type that has the generic type. (NotNull)
     * @return The first generic type for the specified type. (NullAllowed: e.g. not found)
     */
    public static Class<?> getGenericFirstClass(Type type) {
        return findGenericClass(type, 0);
    }

    protected static Class<?> findGenericClass(Type type, int index) {
        return getRawClass(getGenericParameterType(type, index));
    }

    public static Class<?> getRawClass(final Type type) {
        if (Class.class.isInstance(type)) {
            return Class.class.cast(type);
        }
        if (ParameterizedType.class.isInstance(type)) {
            final ParameterizedType parameterizedType = ParameterizedType.class
                    .cast(type);
            return getRawClass(parameterizedType.getRawType());
        }
        if (WildcardType.class.isInstance(type)) {
            final WildcardType wildcardType = WildcardType.class.cast(type);
            final Type[] types = wildcardType.getUpperBounds();
            return getRawClass(types[0]);
        }
        if (GenericArrayType.class.isInstance(type)) {
            final GenericArrayType genericArrayType = GenericArrayType.class
                    .cast(type);
            final Class<?> rawClass = getRawClass(genericArrayType
                    .getGenericComponentType());
            return Array.newInstance(rawClass, 0).getClass();
        }
        return null;
    }

    public static Type getGenericParameterType(final Type type,
            final int index) {
        if (!ParameterizedType.class.isInstance(type)) {
            return null;
        }
        final Type[] genericParameter = getGenericParameterTypes(type);
        if (genericParameter.length == 0 || genericParameter.length < index) {
            return null;
        }
        return genericParameter[index];
    }

    public static Type[] getGenericParameterTypes(final Type type) {
        if (ParameterizedType.class.isInstance(type)) {
            return ParameterizedType.class.cast(type)
                    .getActualTypeArguments();
        }
        if (GenericArrayType.class.isInstance(type)) {
            return getGenericParameterTypes(GenericArrayType.class.cast(
                    type).getGenericComponentType());
        }
        return EMPTY_TYPES;
    }
}

Related

1. getGenericClass(Object source, ParameterizedType type)
2. getGenericClass(Type type)
3. getGenericClassByIndex(Type genericType, int index)
4. getGenericClassType(Class clazz, Class filterClass)
5. getGenericDeclaringType(Class baseClass, Class declaringClass)
6. getGenericInterface(final Class sourceClass, final Class genericInterface)
7. getGenericInterfaceParamType(Class cls, Class rawType)
8. getGenericInterfacesActualTypes(Collection types, Class aClass)
9. getGenericParameter(Class clazz, int index)