GenericsUtils.java

/* --------------------------------------
 * CREATED ON 2007-11-23 15:26:58
 *
 * MSN ardenemily@msn.com
 * QQ 83058327（太阳里的雪）
 * MOBILE 13590309275
 * BLOG http://www.caojianghua.com
 *
 * ALL RIGHTS RESERVED BY ZHENUU CO,.LTD.
 * --------------------------------------
 */
package com.jrails.commons.utils;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

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

/**
 * 泛型工具处理类
 *
 * @author <a href="mailto:arden.emily@gmail.com">arden</a>
 */
public class GenericsUtils {

    private static final Log log = LogFactory.getLog(GenericsUtils.class);

    private GenericsUtils() {

    }

    /**
     * 通过反射,获得定义Class时声明的父类的范型参数的类型. 如public BookManager extends GenricManager<Book>
     *
     * @param clazz The class to introspect
     * @return the first generic declaration, or <code>Object.class</code> if
     *         cannot be determined
     */
    @SuppressWarnings("unchecked")
    public static Class getSuperClassGenricType(Class clazz) {
        return getSuperClassGenricType(clazz, 0);
    }

    /**
     * 通过反射,获得定义Class时声明的父类的范型参数的类型. 如public BookManager extends GenricManager<Book>
     *
     * @param clazz clazz The class to introspect
     * @param index the Index of the generic ddeclaration,start from 0.
     * @return the index generic declaration, or <code>Object.class</code> if
     *         cannot be determined
     */
    @SuppressWarnings("unchecked")
    public static Class getSuperClassGenricType(Class clazz, int index) {

        Type genType = clazz.getGenericSuperclass();

        if (!(genType instanceof ParameterizedType)) {
            log.warn(clazz.getSimpleName() + "'s superclass not ParameterizedType");
            return Object.class;
        }

        Type[] params = ((ParameterizedType) genType).getActualTypeArguments();

        if (index >= params.length || index < 0) {
            log.warn("Index: " + index + ", Size of " + clazz.getSimpleName() + "'s Parameterized Type: " + params.length);
            return Object.class;
        }
        if (!(params[index] instanceof Class)) {
            log.warn(clazz.getSimpleName() + " not set the actual class on superclass generic parameter");
            return Object.class;
        }
        return (Class) params[index];
    }
}