java:Set,Map排序输出到Writer

一般来说java.util.Set,java.util.Map输出的内容的顺序并不是按key的顺序排列的，但是java.util.TreeMap,java.util.TreeSet的实现却可以让Map/Set中元素内容以key的顺序排序，所以利用这个特性，可以将Map/Set转为TreeMap,TreeSet然后实现排序输出。
以下是实现的代码片段：

    /** * 对{@link Map}中元素以key排序后，每行以{key}={value}形式输出到{@link Writer}
 * 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 map,Writer writer)  throws IOException {
        if(null==writer)
            throw new IllegalArgumentException("the arugment 'writer' must not be null ");
        TreeMap sortedMap = new TreeMap();
        if(null!=map)
            sortedMap.putAll(map);
        BufferedWriter bw=(writer instanceof BufferedWriter)?(BufferedWriter)writer
                : new BufferedWriter(writer);
        for (Entry 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}
 * 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 collection,Writer writer)  throws IOException {
        if(null==writer)
            throw new IllegalArgumentException("the arugment 'writer' must not be null ");
        TreeSet sortedSet = new TreeSet();
        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();
    }

调用示例如下：

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

生成结果已经是排序的了