java中 Set与Map排序输出到Writer详解及实例

 /**   * 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")));