java中 Set與Map排序輸出到Writer詳解及實(shí)例
一般來說java.util.Set,java.util.Map輸出的內(nèi)容的順序并不是按key的順序排列的，但是java.util.TreeMap,java.util.TreeSet的實(shí)現(xiàn)卻可以讓Map/Set中元素內(nèi)容以key的順序排序，所以利用這個(gè)特性，可以將Map/Set轉(zhuǎn)為TreeMap,TreeSet然后實(shí)現(xiàn)排序輸出。
以下是實(shí)現(xiàn)的代碼片段：
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/** * 對(duì){@link Map}中元素以key排序后，每行以{key}={value}形式輸出到{@link Writer}<br> * map為空或null時(shí)則不向writer寫入任何內(nèi)容 * @param map * @param writer 為null拋出{@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(); } /** * 對(duì) {@link Collection}中元素排序后(去除重復(fù))，元素分行輸出到{@link Writer}<br> * collection為空或null時(shí)則不向writer寫入任何內(nèi)容 * @param collection * @param writer 為null拋出{@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(); } |
調(diào)用示例如下：
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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"))); |
生成結(jié)果已經(jīng)是排序的了
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