Question

我是Jackson Streaming API的新手。

我想动态地从以下JSON对象中读取值数组。

{
    "jsonAry": [
        {
            "key1": "val1",
            "key2": "val2"
        },
        {
            "key3": "val3",
            "key4": "val4"
        }
    ]
}

Answer 1

阅读this article后，您可以通过以下方式对其进行反序列化：

ObjectMapper mapper = new ObjectMapper();
JsonFactory f = new JsonFactory();
JsonParser jp = f.createParser(JSON);
//Skip all tokens before start array token.
while (jp.nextToken() != JsonToken.START_ARRAY) {
}
MapType mapType = mapper.getTypeFactory().constructMapType(Map.class, String.class, String.class);
while (jp.nextToken() != JsonToken.END_ARRAY) {
    Map<String, String> map = mapper.readValue(jp, mapType);
    System.out.println(map);
}

下一个选项是使用JsonNode：

ObjectMapper mapper = new ObjectMapper();
JsonNode rootNode = mapper.readTree(JSON);
JsonNode arrayNode = rootNode.get("jsonAry");
Iterator<JsonNode> jsonNodeIterator = arrayNode.elements();
while (jsonNodeIterator.hasNext()) {
    JsonNode itemNode = jsonNodeIterator.next();
    Iterator<String> fieldNames = itemNode.fieldNames();
    while (fieldNames.hasNext()) {
        String field = fieldNames.next();
        System.out.println(field + " = " + itemNode.get(field));
    }
}

如果您的JSON不大，可以将其反序列化为POJO。例如：

class JsonRoot {

    @JsonProperty("jsonAry")
    private List<JsonEntity> entities;

    public List<JsonEntity> getEntities() {
        return entities;
    }

    public void setEntities(List<JsonEntity> entities) {
        this.entities = entities;
    }

    @Override
    public String toString() {
        return "JsonRoot{" +
                "entities=" + entities +
                '}';
    }
}

class JsonEntity {

    private Map<String, String> values = new LinkedHashMap<String, String>();

    public Map<String, String> getValues() {
        return values;
    }

    @JsonAnySetter
    public void setValues(String key, String value) {
        values.put(key, value);
    }

    @Override
    public String toString() {
        return "JsonEntity{" +
                "values=" + values +
                '}';
    }
}

反序列化看起来像这样：

ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.readValue(JSON, JsonRoot.class));

如何使用Jackson Streaming API动态地从Json读取值数组？

1 个答案: