java 根据其值对地图进行排序。资料来源：http：//stackoverflow.com/a/2581754/1057348

Posted 2021-05-08

	// Java 6 and lower:
	public static <K, V extends Comparable<? super V>> Map<K, V> sortByValue(Map<K, V> map) {
		List<Map.Entry<K, V>> list = new LinkedList<Map.Entry<K, V>>(map.entrySet());
		Collections.sort(list, new Comparator<Map.Entry<K, V>>() {
			public int compare(Map.Entry<K, V> o1, Map.Entry<K, V> o2) {
				return (o1.getValue()).compareTo(o2.getValue());
			}
		});

		Map<K, V> result = new LinkedHashMap<K, V>();
		for (Map.Entry<K, V> entry : list) {
			result.put(entry.getKey(), entry.getValue());
		}
		return result;
	}
	
	// Java 7:
	public static <K, V extends Comparable<? super V>> Map<K, V> 
    sortByValue( Map<K, V> map ) {
    List<Map.Entry<K, V>> list =
        new LinkedList<>( map.entrySet() );
    Collections.sort( list, new Comparator<Map.Entry<K, V>>()
    {
        @Override
        public int compare( Map.Entry<K, V> o1, Map.Entry<K, V> o2 )
        {
            return (o1.getValue()).compareTo( o2.getValue() );
        }
    } );

    Map<K, V> result = new LinkedHashMap<>();
    for (Map.Entry<K, V> entry : list)
    {
        result.put( entry.getKey(), entry.getValue() );
    }
    return result;
}

// Java 8:
public static <K, V extends Comparable<? super V>> Map<K, V> 
    sortByValue( Map<K, V> map )
{
      Map<K,V> result = new LinkedHashMap<>();
     Stream <Entry<K,V>> st = map.entrySet().stream();

     st.sorted(Comparator.comparing(e -> e.getValue()))
          .forEach(e ->result.put(e.getKey(),e.getValue()));

     return result;
}

// Unit-Test:
public class MapUtilTest
{
    @Test
    public void testSortByValue()
    {
        Random random = new Random(System.currentTimeMillis());
        Map<String, Integer> testMap = new HashMap<String, Integer>(1000);
        for(int i = 0 ; i < 1000 ; ++i) {
            testMap.put( "SomeString" + random.nextInt(), random.nextInt());
        }

        testMap = MapUtil.sortByValue( testMap );
        Assert.assertEquals( 1000, testMap.size() );

        Integer previous = null;
        for(Map.Entry<String, Integer> entry : testMap.entrySet()) {
            Assert.assertNotNull( entry.getValue() );
            if (previous != null) {
                Assert.assertTrue( entry.getValue() >= previous );
            }
            previous = entry.getValue();
        }
    }
}