java:Set,Map排序输出到Writer

﹏ヽ暗。殇╰゛Y 2022-09-30 06:30 121阅读 0赞

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}<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();
        }

调用示例如下：

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")));

生成结果已经是排序的了  
![这里写图片描述][SouthEast]

![这里写图片描述][SouthEast 1]

[SouthEast]: /images/20220708/cc62c7080fc24e16ae39eb7a5818f012.png
[SouthEast 1]: /images/20220708/1cfcc17558a046469d4a6c4e6f70d19f.png