Jackson检测重复的JSON POJO属性和Map键

Question

我正在尝试捕获重复的POJO属性或传递给我的WebService的Map键。

例如，如果field1出现两次或者map键1出现两次，我想抛出一个错误:

{
  "field1" : 1,
  "field1" : 2,
  "map" : {
    "1" : {
      "fieldA" : "null",
      "fieldB" : "2"
    },
    "1" : {
      "fieldX" : "null",
      "fieldY" : "2"
    }
  }
}

- DarVar

Answer 1

可以使用 JsonParser.Feature.STRICT_DUPLICATE_DETECTION

ObjectMapper mapper = new ObjectMapper();
mapper.enable(JsonParser.Feature.STRICT_DUPLICATE_DETECTION);
MyPOJO result = mapper.readValue(json, MyPOJO.class);

结果为：

com.fasterxml.jackson.core.JsonParseException: Duplicate field 'field1'

如何使用Jackson验证重复属性？关于DeserializationFeature.FAIL_ON_READING_DUP_TREE_KEY的帖子。

- varren

Answer 2

请查看这个讨论：http://jackson-users.ning.com/forum/topics/detecting-duplicate-field 以下是该讨论中给出的Map类示例代码：

public class JacksonDuplicates {

    private static final String JSON = "{\n" +
            "  \"field1\" : 1,\n" +
            "  \"field1\" : 2,\n" +
            "  \"map\" : {\n" +
            "    \"1\" : {\n" +
            "      \"fieldA\" : \"null\",\n" +
            "      \"fieldB\" : \"2\"\n" +
            "    },\n" +
            "    \"1\" : {\n" +
            "      \"fieldX\" : \"null\",\n" +
            "      \"fieldY\" : \"2\"\n" +
            "    }\n" +
            "  }\n" +
            "}";

    private static class SingleKeyHashMap<K, V> extends HashMap<K, V> {
        @Override
        public V put(K key, V value) {
            if (containsKey(key)) {
                throw new IllegalArgumentException("duplicate key " + key);
            }
            return super.put(key, value);
        }
    }

    public static void main(String[] args) throws IOException {
        SimpleModule module = new SimpleModule();
        module.addAbstractTypeMapping(Map.class, SingleKeyHashMap.class);
        ObjectMapper mapper = new ObjectMapper();
        mapper.registerModule(module);

        mapper.readValue(JSON, Map.class);

    }
}

输出：

Exception in thread "main" java.lang.IllegalArgumentException: duplicate key field1
    at jackson.JacksonDuplicates$SingleKeyHashMap.put(JacksonDuplicates.java:38)
    at com.fasterxml.jackson.databind.deser.std.MapDeserializer._readAndBindStringMap(MapDeserializer.java:434)
    at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:312)
    at com.fasterxml.jackson.databind.deser.std.MapDeserializer.deserialize(MapDeserializer.java:26)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:2993)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:2098)
    at jackson.JacksonDuplicates.main(JacksonDuplicates.java:50)

- Alexey Gavrilov

---

如何在JAX-RS应用程序中进行配置？ - DarVar

根据您的使用情况，有几种方法可以实现这一点。例如，此维基页面描述了如何为给定的MIME类型配置对象映射器。 - Alexey Gavrilov

我想我找到了一个解决方案。 http://jackson-users.ning.com/forum/topics/configuring-custom-modules-when-using-jaxrs-provider - DarVar

这个技术上可行，但是算是一个hack。varren的回答才是“正确”的。 - Cannoliopsida