在杰克逊中序列化时如何在运行时忽略字段

Question

我有一个包含很多布尔字段的 bean。我只想将那些具有真实值的字段添加到 json 以保存一些有效负载。这是一项功能，应基于客户的需求，因此必须以动态方式完成。我不认为注释会起作用，因为它们是静态的东西。对此有什么想法吗？

Answer 1

类似Jackson's JSON Views?

在 Spring 的问题跟踪器中有 an issue open for that。

Answer 2

除了杰克逊的观点，你还可以写一个custom Jackson filter，它会过滤掉所有布尔字段的负值。

这是一个例子：

public class JacksonFilterBoolean {
    @JsonFilter("boolean-filter")
    public static class Test {
        public final Boolean f1;
        public final boolean f2;
        public final boolean f3;
        public final Boolean fNull = null;
        public final String f4 = "string";

        public Test(Boolean f1, boolean f2, boolean f3) {
            this.f1 = f1;
            this.f2 = f2;
            this.f3 = f3;
        }
    }

    public static class BooleanPropertyFilter extends SimpleBeanPropertyFilter {
        @Override
        protected boolean include(BeanPropertyWriter writer) {
            return true;
        }

        @Override
        protected boolean include(PropertyWriter writer) {
            return true;
        }

        @Override
        public void serializeAsField(Object pojo, JsonGenerator jgen,
                                     SerializerProvider provider, PropertyWriter writer)
                throws Exception {
            if (writer instanceof BeanPropertyWriter) {
                BeanPropertyWriter bWriter = (BeanPropertyWriter) writer;
                Class<?> type = bWriter.getType().getRawClass();
                if (type == Boolean.class || type == boolean.class) {
                    Object o = bWriter.get(pojo);
                    if (o != null && !(boolean) o) {
                        return;
                    }
                }
            }
            super.serializeAsField(pojo, jgen, provider, writer);
        }
    }

    public static void main(String[] args) throws JsonProcessingException {
        Test t = new Test(true, false, true);
        ObjectMapper mapper = new ObjectMapper();
        mapper.setFilters(new SimpleFilterProvider().addFilter("boolean-filter",
                new BooleanPropertyFilter()));
        System.out.println(mapper.writerWithDefaultPrettyPrinter().writeValueAsString(t));
    }

}

输出：

{
  "f1" : true,
  "f3" : true,
  "fNull" : null,
  "f4" : "string"
}