java:Set,Map排序输出到Writer

    /**
     * 对{@link Map}中元素以key排序后，每行以{key}={value}形式输出到{@link Writer}<br>
     * map为空或null时则不向writer写入任何内容
     * @param map
     * @param writer 为null抛出{@link IllegalArgumentException}
     * @throws IOException
     */
    public static  void storeSortedMap(Map<String,String> map,Writer writer)  throws IOException {
        if(null==writer)
            throw new IllegalArgumentException("the arugment 'writer' must not be null ");
        TreeMap<String, String> sortedMap = new TreeMap<String,String>();
        if(null!=map)
            sortedMap.putAll(map);
        BufferedWriter bw=(writer instanceof BufferedWriter)?(BufferedWriter)writer
                : new BufferedWriter(writer);
        for (Entry<String,String> e:sortedMap.entrySet()) {
            bw.write(e.getKey() + "=" + e.getValue());
            bw.newLine();
        }
        bw.flush();
    }
    /**
     * 对 {@link Collection}中元素排序后(去除重复)，元素分行输出到{@link Writer}<br>
     * collection为空或null时则不向writer写入任何内容
     * @param collection
     * @param writer 为null抛出{@link IllegalArgumentException}
     * @throws IOException
     */
    public static  void storeSortedSet(Collection<String> collection,Writer writer)  throws IOException {
        if(null==writer)
            throw new IllegalArgumentException("the arugment 'writer' must not be null ");
        TreeSet<String> sortedSet = new TreeSet<String>();
        if(null!=collection)
            sortedSet.addAll(collection);
        BufferedWriter bw=(writer instanceof BufferedWriter)?(BufferedWriter)writer
                : new BufferedWriter(writer);
        for (String e:sortedSet) {          
            bw.write(e);
            bw.newLine();
        }
        bw.flush();
    }

Map<String,String> map;
//....
storeSortedMap(map,new FileWriter(new File("c:\\id.txt")));
Set<String,String> set;
//....
storeSortedSet(set,new FileWriter(new File("c:\\trainval.txt")));