Jackson ObjectMapper：如何从序列化中省略（忽略）特定类型的字段？

Question

如何告诉 Jackson ObjectMapper 从序列化中忽略特定类型（类）的字段（在我的 Object.class的情况下）？

约束条件：

• 不控制源类-它是第三方类。
• 被序列化的类类型是未知的-我猜它取消了MixIn的资格。
• 此类字段的名称预先未知

为了提供帮助，下面是一个单元测试，期望从序列化中忽略字段对象列表和对象字段，但它的方法是不正确的，它是按名称而不是按类型过滤它们。

public static class FavoriteShows {
    public Simpsons favorite = new Simpsons();
    public BigBangTheory preferred = new BigBangTheory();
}

public static class Simpsons {
    public String title = "The Simpsons";

    public List<Object> objectsList = List.of("homer", "simpson");
    public Object objectField = new HashMap() {{
        put("mr", "burns");
        put("ned", "flanders");
    }};
}

public static class BigBangTheory {
    public String title = "The Big Bang Theory";

    public List<Object> objectsList = List.of("sheldon", "cooper");
    public Object objectField = new HashMap() {{
        put("leonard", "hofstadter");
        put("Raj", "koothrappali");
    }};
}

public abstract static class MyMixIn {
    @JsonIgnore
    private Object objectField;
    @JsonIgnore
    private Object objectsList;
}

@Test
public void test() throws JsonProcessingException {
    // GIVEN
    // Right solution must work for any (MixIn(s) is out of questions) Jackson annotated class
    // without its modification.
    final ObjectMapper mapper = new ObjectMapper()
            .addMixIn(Simpsons.class, MyMixIn.class)
            .addMixIn(BigBangTheory.class, MyMixIn.class);

    // WHEN
    String actual = mapper.writeValueAsString(new FavoriteShows());
    System.out.println(actual);

    // THEN
    // Expected: {"favorite":{"title":"The Simpsons"},"preferred":{"title":"The Big Bang Theory"}}
    assertThat(actual).isEqualTo("{\"favorite\":{\"title\":\"The Simpsons\"},\"preferred\":{\"title\":\"The Big Bang Theory\"}}");

}

Answer 1

如果你正在使用mixins，你应该能够用@ JsonIgnoreType注释，让它忽略这个类。参考文件全局忽略Jackson中的类

Answer 2

其中一种方法是使用自定义AnnotationINSPECTOR。

class A {

    int three = 3;
    int four = 4;
    B b = new B();

    // setters + getters
}

class B {

    int one = 1;
    int two = 2;

    // setters + getters
}

要忽略类型为B的所有字段：

ObjectMapper mapper = new ObjectMapper();
mapper.setAnnotationIntrospector(new JacksonAnnotationIntrospector() {
    @Override
    protected boolean _isIgnorable(Annotated a) {
        return super._isIgnorable(a)
                 // Ignore B.class
                 || a.getRawType() == B.class
                 // Ignore List<B>
                 || a.getType() == TypeFactory.defaultInstance()
                       .constructCollectionLikeType(List.class, B.class);
    }
});

String json = mapper.writeValueAsString(new A());