Java8 对Map的转换封装

1、Map 与 List 的转换
2、Map 的排序
3、参考文章：
http://www.mkyong.com/java8/java-8-convert-list-to-map/
http://www.mkyong.com/tutorials/java-8-tutorials/

    @Test    public void testToMapSort() {        Map<String, Integer> unsortMap = new HashMap<>();        unsortMap.put("z", 10);        unsortMap.put("b", 5);        unsortMap.put("a", 6);        unsortMap.put("c", 20);        unsortMap.put("d", 1);        unsortMap.put("e", 7);        unsortMap.put("y", 8);        unsortMap.put("n", 99);        unsortMap.put("g", 50);        unsortMap.put("m", 2);        unsortMap.put("f", 9);        System.out.println("Original...");        System.out.println(unsortMap);        // sort by keys, a,b,c..., and return a new LinkedHashMap        // toMap() will returns HashMap by default, we need LinkedHashMap to keep the order.        Map<String, Integer> result = unsortMap.entrySet().stream()                .sorted(Map.Entry.comparingByKey())                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));        // Not Recommend, but it works.        //Alternative way to sort a Map by keys, and put it into the "result" map        Map<String, Integer> result2 = new LinkedHashMap<>();        unsortMap.entrySet().stream()                .sorted(Map.Entry.comparingByKey())                .forEachOrdered(x -> result2.put(x.getKey(), x.getValue()));        System.out.println("Sorted...");        System.out.println(result);        System.out.println(result2);    }    @Test    public void testToMapSort2() {        Map<String, Integer> unsortMap = new HashMap<>();        unsortMap.put("z", 10);        unsortMap.put("b", 5);        unsortMap.put("a", 6);        unsortMap.put("c", 20);        unsortMap.put("d", 1);        unsortMap.put("e", 7);        unsortMap.put("y", 8);        unsortMap.put("n", 99);        unsortMap.put("g", 50);        unsortMap.put("m", 2);        unsortMap.put("f", 9);        System.out.println("Original...");        System.out.println(unsortMap);        //sort by values, and reserve it, 10,9,8,7,6...        Map<String, Integer> result = unsortMap.entrySet().stream()                .sorted(Map.Entry.comparingByValue(Comparator.reverseOrder()))                .collect(Collectors.toMap(Map.Entry::getKey, Map.Entry::getValue,                        (oldValue, newValue) -> oldValue, LinkedHashMap::new));        //Alternative way        Map<String, Integer> result2 = new LinkedHashMap<>();        unsortMap.entrySet().stream()                .sorted(Map.Entry.<String, Integer>comparingByValue().reversed())                .forEachOrdered(x -> result2.put(x.getKey(), x.getValue()));        System.out.println("Sorted...");        System.out.println(result);        System.out.println(result2);    }    @Test    public void testMap2List() {        Map<Integer, String> map = new HashMap<>();        map.put(10, "apple");        map.put(20, "orange");        map.put(30, "banana");        map.put(40, "watermelon");        map.put(50, "dragonfruit");        System.out.println("\n1. Export Map Key to List...");        List<Integer> result = new ArrayList(map.keySet());        result.forEach(System.out::println);        System.out.println("\n2. Export Map Value to List...");        List<String> result2 = new ArrayList(map.values());        result2.forEach(System.out::println);    }    @Test    public void testConvertMapToList() {        Map<Integer, String> map = new HashMap<>();        map.put(10, "apple");        map.put(20, "orange");        map.put(30, "banana");        map.put(40, "watermelon");        map.put(50, "dragonfruit");        // split a map into 2 List        List<Integer> resultSortedKey = new ArrayList<>();        List<String> resultValues = map.entrySet().stream()                //sort a Map by key and stored in resultSortedKey                .sorted(Map.Entry.<Integer, String>comparingByKey().reversed())                .peek(e -> resultSortedKey.add(e.getKey()))                .map(x -> x.getValue())                // filter banana and return it to resultValues                .filter(x -> !"banana".equalsIgnoreCase(x))                .collect(Collectors.toList());        resultSortedKey.forEach(System.out::println);        resultValues.forEach(System.out::println);    }    //统计字符的出现次数    @Test    public void testFrequency() {        List<String> list = new ArrayList<String>();        list.add("a");        list.add("b");        list.add("c");        list.add("d");        list.add("b");        list.add("c");        list.add("a");        list.add("a");        list.add("a");        System.out.println("\nExample 1 - Count 'a' with frequency");        System.out.println("a : " + Collections.frequency(list, "a"));        System.out.println("\nExample 2 - Count all with frequency");        Set<String> uniqueSet = new HashSet<String>(list);        System.out.println("==========>" + uniqueSet);        for (String temp : uniqueSet) {            System.out.println(temp + ": " + Collections.frequency(list, temp));        }    }