Guava Maps 用法示例

Guava Maps 用法

不定期更新

1. 初始化

    @Test
    public void test_init(){
    	Map<String,String> map = Maps.newHashMap();
    }
   

2. 将List转为Map，这个特性主要针对的场景是有一组对象，它们在某个属性上分别有独一无二的值，而我们希望能够按照这个属性值查找对象

    List<Person> personList = Lists.newArrayList();
    @Before
    public void before(){
        for(int i=0;i<10;i++){
            String temp = String.valueOf(i);
            Person p = new Person(Long.valueOf(i),temp,temp);
            personList.add(p);
        }
    }
    @Test
    public void test_list2map(){
        ImmutableMap<Long,Person> map = Maps.uniqueIndex(personList, new Function<Person, Long>() {
            @Override
            public Long apply(Person input) {
                return input.getId();
            }
        });
        System.out.println(map);
    }
   

   output:

    {0=Person{id=0, name='0', value='0'}, 1=Person{id=1, name='1', value='1'}, 2=Person{id=2, name='2', value='2'}, 3=Person{id=3, name='3', value='3'}, 4=Person{id=4, name='4', value='4'}, 5=Person{id=5, name='5', value='5'}, 6=Person{id=6, name='6', value='6'}, 7=Person{id=7, name='7', value='7'}, 8=Person{id=8, name='8', value='8'}, 9=Person{id=9, name='9', value='9'}}
   

3. 将Properties转化为Map

    @Test
    public void test_properties2map(){
        Properties prop = new Properties();
        prop.put("a","a1");
        prop.put("b","b1");
        ImmutableMap<String,String> map = Maps.fromProperties(prop);
        System.out.println(map);
    }
   

4. 根据key来过滤map

    @Test
    public void test_filter_by_key(){
        Map<String,String> map = Maps.newHashMap();
        map.put("a1","b1");
        map.put("c1","d1");
        map.put("c2","d2");
        map.put("a2","b2");
        Map<String,String> result = Maps.filterKeys(map, new Predicate<String>() {
            @Override
            public boolean apply(String input) {
                return input.contains("1");
            }
        });
        System.out.println(result);
    }
   

如果和java8的lambda一起使用，就会更加简洁

	@Test
    public void test_filter_by_key(){
        Map<String,String> map = Maps.newHashMap();
        map.put("a1","b1");
        map.put("c1","d1");
        map.put("c2","d2");
        map.put("a2","b2");

        Map<String,String> result = Maps.filterKeys(map,a->a.contains("1"));
        System.out.println(result);
    }

5. 根据value来过滤map

    @Test
    public void test_filter_by_value(){
        Map<String,String> map = Maps.newHashMap();
        map.put("a1","b1");
        map.put("c1","d1");
        map.put("c2","d2");
        map.put("a2","b2");
        System.out.println(Maps.filterValues(map,a->a.contains("1")));
    }
   

6. 根据key+value来过滤，其实就是Entry的方式

    @Test
    public void test_filter_by_entry(){
        Map<String,String> map = Maps.newHashMap();
        map.put("a1","b1");
        map.put("c1","d1");
        map.put("c2","d2");
        map.put("a2","b2");
        System.out.println(Maps.filterEntries(map,a->a.getKey().contains("1") && a.getValue().contains("b")));
    }