java中 Set与Map排序输出到Writer详解及实例

 java中 Set与Map排序输出到Writer详解及实例

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：

   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();  }    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();  }