实用工具类 && CollectionUtils

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.commons.collections.CollectionUtils;
import org.apache.commons.lang.StringUtils;

import com.ibatis.common.beans.Probe;
import com.ibatis.common.beans.ProbeFactory;

/**
 * <pre>
 * 
 * </pre>
 *
 * @author liuhongbo
 * @version $Id: YHDCollectionUtils.java, v 0.1 2013-12-4 上午09:50:53 liuhongbo Exp $
 */
public class YHDCollectionUtils {
	
	private YHDCollectionUtils(){}
	
	private static final Probe PROBE = ProbeFactory.getProbe();
	@SuppressWarnings("rawtypes")
	public static final Collection NULL_COLLECTION = new NullCollection();
		
	@SuppressWarnings("unchecked")
	public static final <T> Collection<T> nullCollection() {
		return (List<T>) NULL_COLLECTION;
	}
	
	/**
	 * @author liuhongbo
	 * <pre>
	 * 批量获取map中的值
	 * </pre>
	 *
	 * @param <K>
	 * @param <V>
	 * @param keys
	 * @param source
	 * @return
	 */
    public static <K,V> List<V> getAllFormMap(List<K> keys,Map<K,V> source) {
    	List<V> values = Collections.emptyList();
    	if (keys != null && !keys.isEmpty() && source != null && !source.isEmpty()) {
    		values = new ArrayList<V>();
        	for (K k : keys) {
        		values.add(source.get(k));
    		}
    	}
    	return values;
    }
    
    /**
     * @author liuhongbo
     * <pre>
     * 从List中获取valueProp组成一个新的list
     * </pre>
     *
     * @param <E>
     * @param list
     * @param valueProp
     * @return
     */
    public static <E,K> List<K> getValueList(List<E> list, String valueProp) {
    	List<K> valueList = Collections.emptyList();
    	if (CollectionUtils.isNotEmpty(list)) {
    		list.removeAll(nullCollection());
    		valueList = new ArrayList<K>(list.size());
    		for (E e : list) {
    			@SuppressWarnings("unchecked")
				K value = (K)PROBE.getObject(e, valueProp);
    			valueList.add(value);
			}
    	} 
        return valueList;
    }
    
    /**
     * @author liuhongbo
     * <pre>
     * 用list生成一个map,keyProp 为指定的key,valueProp 为指定是value
     * </pre>
     *
     * @param <K>
     * @param <V>
     * @param <E>
     * @param list
     * @param keyProp
     * @param valueProp
     * @return
     */
	@SuppressWarnings("unchecked")
	public static <K,V,E> Map<K,V> listforMap(List<E> list, String keyProp, String valueProp) {
        Map<K,V> map = Collections.emptyMap();
        if (CollectionUtils.isNotEmpty(list)) {
        	list.removeAll(nullCollection());
        	map = new HashMap<K, V>(list.size());
        	for (E object : list) {
    			K key = (K)PROBE.getObject(object, keyProp);
                Object value = null;
                if (StringUtils.isEmpty(valueProp)) {
                    value = object;
                } else {
                    value = PROBE.getObject(object, valueProp);
                }
                map.put(key, (V)value);
			}
        }
        return map;
    }
	
	/**
	 * @author liuhongbo
	 * <pre>
	 * list 生成一个Map<K,List<V>>
	 * </pre>
	 *
	 * @param <K>
	 * @param <V>
	 * @param <E>
	 * @param list
	 * @param keyProp
	 * @param valueProp
	 * @return
	 */
	@SuppressWarnings("unchecked")
	public static <K,V,E> Map<K,List<V>> listforListMap(List<E> list, String keyProp,
            String valueProp) {
        Map<K, List<V>> map = Collections.emptyMap();
        if (CollectionUtils.isNotEmpty(list)) {
        	list.removeAll(nullCollection());
        	map = new HashMap<K, List<V>>(list.size());
        	V value = null;
        	for (E object : list) {
        		K key = (K)PROBE.getObject(object, keyProp);
        		if (StringUtils.isEmpty(valueProp)) {
        			value = (V)object;
        		} else {
        			value = (V)PROBE.getObject(object, valueProp);
        		}
        		List<V> values = map.get(key);
        		if (values == null) {
        			values = new ArrayList<V>();
        		}
        		values.add(value);
        		map.put(key, values);
			}
        }
        return map;
	}
}