@Test public void test4() { SimpleObj2 so2 = new SimpleObj2(); so2.setId(334); User user = new User(); user.setId(2434L); user.setName("Pengtao"); so2.setUser(user); Book book = new Book(); book.setId(23424); book.setPrice(3.4); book.setSell(true); book.setText("cccccccc"); book.setTitle("ddddd"); so2.setBook(book); String jsonStr = Json.toJson(so2); SimpleObj2 temp = Json.toObject(jsonStr, SimpleObj2.class); Assert.assertThat(temp.getBook().getPrice(), is(3.4)); Assert.assertThat(temp.getBook().getTitle(), nullValue()); Assert.assertThat(temp.getId(), is(334)); }