Java Reflection Generic Type from Field getGenericReturnType(Method method, Field field, boolean isAllowNull)

Description

Returns the generic type parameter of a return value by a field or method.

License

Open Source License

Parameter

Parameter	Description
method	method or null if field
field	field or null if method
isAllowNull	whether null is allowed as a return value or expected Object.class

Return

generic type parameter

Declaration

public static Class getGenericReturnType(Method method, Field field, boolean isAllowNull) 

Method Source Code

//package com.java2s;
/**************************************************************************************
 * Copyright (C) 2008 EsperTech, Inc. All rights reserved.                            *
 * http://esper.codehaus.org                                                          *
 * http://www.espertech.com                                                           *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the GPL license       *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/

import java.lang.reflect.*;

public class Main {
    /**//from   w w  w.j  av  a  2  s  .  com
     * Returns the generic type parameter of a return value by a field or method.
     * @param method method or null if field
     * @param field field or null if method
     * @param isAllowNull whether null is allowed as a return value or expected Object.class
     * @return generic type parameter
     */
    public static Class getGenericReturnType(Method method, Field field, boolean isAllowNull) {
        if (method == null) {
            return getGenericFieldType(field, isAllowNull);
        } else {
            return getGenericReturnType(method, isAllowNull);
        }
    }

    /**
     * Returns the generic type parameter of a return value by a method.
     * @param method method or null if field
     * @param isAllowNull whether null is allowed as a return value or expected Object.class
     * @return generic type parameter
     */
    public static Class getGenericReturnType(Method method, boolean isAllowNull) {
        Type t = method.getGenericReturnType();
        Class result = getGenericType(t, 0);
        if (!isAllowNull && result == null) {
            return Object.class;
        }
        return result;
    }

    /**
     * Returns the generic type parameter of a return value by a field.
     * @param field field or null if method
     * @param isAllowNull whether null is allowed as a return value or expected Object.class
     * @return generic type parameter
     */
    public static Class getGenericFieldType(Field field, boolean isAllowNull) {
        Type t = field.getGenericType();
        Class result = getGenericType(t, 0);
        if (!isAllowNull && result == null) {
            return Object.class;
        }
        return result;
    }

    public static Class getGenericType(Type t, int index) {
        if (t == null) {
            return null;
        }
        if (!(t instanceof ParameterizedType)) {
            return null;
        }
        ParameterizedType ptype = (ParameterizedType) t;
        if ((ptype.getActualTypeArguments() == null) || (ptype.getActualTypeArguments().length < (index + 1))) {
            return Object.class;
        }
        Type typeParam = ptype.getActualTypeArguments()[index];
        if (!(typeParam instanceof Class)) {
            return Object.class;
        }
        return (Class) typeParam;
    }
}

Related

1. getGenericMultivalueType(final Field p)
2. getGenericParameterClass(Field field)
3. getGenericParameterClass(Field field)
4. getGenericParameters(Field f)
5. getGenericParametersInternal(Type genericFieldType)
6. getGenericsTypeFromCollectionField(Field field)
7. getGenericType(Field field)
8. getGenericType(Field field)
9. getGenericType(Field field)