public IdChain get(IdChain key) {
        return mapping.get(key);
    }
@Test
    public void test() {
        IdChain key = new IdChain(10005L, 10006L, 10005L, 10007L, 10008L);
        Assert.assertTrue(key.equals(src));
        Assert.assertEquals(src, key);
        IdChain val = fileMapping.get(key);
        Assert.assertNotNull(val);
        Assert.assertEquals(dest, val);

        Long l1 = new Long(10005L);
        Long l2 = new Long(10005L);
        Assert.assertFalse(l1 == l2);
        Assert.assertTrue(l1.equals(l2));

        Long l3 = new Long(1L);
        Long l4 = new Long(1L);
        Assert.assertFalse(l3 == l4);
        Assert.assertTrue(l3.equals(l4));
    }