Java的map自定义工具类MapUtils

public class MapUtil {
	public static final char UNDERLINE = '_';

	/**
	 * 下划线方式转驼峰
	 * @param <T>
	 */
	public static <T> Map<String, T> underlineToCamel(Map<String, T> param) {
		if (param == null) {
			return null;
		}
		Map<String, T> retMap = new HashMap<String, T>();
		Set<String> list = param.keySet();
		for (String string : list) {
			String str = string.toLowerCase();
			int len = str.length();
			StringBuilder sb = new StringBuilder(len);
			for (int i = 0; i < len; i++) {
				char c = str.charAt(i);
				if (c == UNDERLINE) {
					if (++i < len) {
						sb.append(Character.toUpperCase(str.charAt(i)));
					}
				} else {
					sb.append(c);
				}
			}
			String key = sb.toString();
			retMap.put(key, param.get(string));
		}

		return retMap;
	}

	/**
	 * map转javabean
	 * @param <T>
	 */
	public static <T> T convertMap(Class type, Map map)
			throws IntrospectionException, IllegalAccessException,
			InstantiationException, InvocationTargetException {
		BeanInfo beanInfo = Introspector.getBeanInfo(type); // 获取类属性
		T obj = (T) type.newInstance(); // 创建 JavaBean 对象

		// 给 JavaBean 对象的属性赋值
		PropertyDescriptor[] propertyDescriptors = beanInfo
				.getPropertyDescriptors();
		for (int i = 0; i < propertyDescriptors.length; i++) {
			PropertyDescriptor descriptor = propertyDescriptors[i];
			String propertyName = descriptor.getName();

			if (map.containsKey(propertyName)) {
				// 下面一句可以 try 起来，这样当一个属性赋值失败的时候就不会影响其他属性赋值。
				Object value = map.get(propertyName);

				Object[] args = new Object[1];
				args[0] = value;

				descriptor.getWriteMethod().invoke(obj, args);
			}
		}
		return obj;
	}

	public static Map<String, String> sumMapForString(Map<String, String> a,
			Map<String, String> b) {
		/**
		 * @Return java.util.Map<java.lang.String,java.lang.String>
		 * @Description 将两个Map<String, String>拼接成一个
		 * @param a
		 * @param b
		*/
		Map<String, String> res = new HashMap<String, String>();
		for (Map.Entry<String, String> aMap : a.entrySet()) {
			res.put(aMap.getKey(), aMap.getValue());
		}
		for (Map.Entry<String, String> bMap : b.entrySet()) {
			if (res.containsKey(bMap.getKey())) {
				String key = bMap.getKey();
				int aValue = Integer.valueOf(res.get(key));
				int bValue = Integer.valueOf(bMap.getValue());
				int temp = aValue + bValue;
				res.put(key, temp + "");
			} else {
				res.put(bMap.getKey(), bMap.getValue());
			}
		}
		return b;
	}

	public static Map<String, Integer> sumMapForInteger(Map<String, Integer> a,
			Map<String, Integer> b) {
		/**
		 * @Return java.util.Map<java.lang.String,java.lang.Integer>
		 * @Description 将两个Map<String, Integer>拼接成一个
		 * @param a
		 * @param b
		*/
		Map<String, Integer> res = new HashMap<String, Integer>();
		for (Map.Entry<String, Integer> aMap : a.entrySet()) {
			res.put(aMap.getKey(), aMap.getValue());
		}
		for (Map.Entry<String, Integer> bMap : b.entrySet()) {
			if (res.containsKey(bMap.getKey())) {
				String key = bMap.getKey();
				int aValue = res.get(key);
				int bValue = bMap.getValue();
				int temp = aValue + bValue;
				res.put(key, temp);
			} else {
				res.put(bMap.getKey(), bMap.getValue());
			}
		}
		return res;
	}

	/**
	 * Map<String, Object>转换成Map<String, String>
	 * 
	 * @param map
	 * @return
	 */
	public static Map<String, String> objectToString(Map<String, Object> map) {
		Map<String, String> res = new HashMap<String, String>();
		for (Map.Entry<String, Object> iterable : map.entrySet()) {
			if(!(iterable.getValue() ==null)){
				res.put(iterable.getKey(), iterable.getValue().toString());
			}else {
				res.put(iterable.getKey(), "");
			}
			
		}
		return res;
	}

	/**
	 * 将Map中的value取出存入List
	 * 
	 * @param map
	 * @return
	 */
	public static List<String> mapToList(Map<String, String> map) {
		List<String> list = new ArrayList<>();
		for (Map.Entry<String, String> string : map.entrySet()) {
			list.add(string.getValue());
		}
		return list;
	}
	
	
	
	/**
	 * MODULE   : sortMapByValue      
	 * ABSTRACT : 将map的值从大到小排序         
	 * @author  : BJ
	 * @param   ：HashMap<String, Integer> 
	 * @return  ：TreeMap<String, Integer>
	 * @note    : 将map的值从大到小排序
	 */
	public static TreeMap<String, Integer> sortMapByValue(HashMap<String, Integer> map){
        Comparator<String> comparator = new ValueComparator(map);
        //TreeMap is a map sorted by its keys. 
        //The comparator is used to sort the TreeMap by keys. 
        TreeMap<String, Integer> result = new TreeMap<String, Integer>(comparator);
        result.putAll(map);
        return result;
    }
	
	
	
}


class ValueComparator implements Comparator<String>{

    HashMap<String, Integer> map = new HashMap<String, Integer>();

    public ValueComparator(HashMap<String, Integer> map){
        this.map.putAll(map);
    }

    @Override
    public int compare(String s1, String s2) {
        if(map.get(s1) >= map.get(s2)){
            return -1;
        }else{
            return 1;
        }   
    }
}