Jayway JsonPath與Jackson一起使用

Question

我一直在使用JsonPath 。 但是，在昨天的一個問題中，我發現默認的JsonSmartJsonProvider在解析時未報告無效文檔錯誤，我修改了設置以使用Jackson

public JsonPathExtractor(String document) throws DocumentFormatException
{
    try
    {
        Configuration.setDefaults(new Configuration.Defaults() 
        {
              private final JsonProvider jsonProvider = new JacksonJsonProvider();
                private final MappingProvider mappingProvider = new JacksonMappingProvider();

            @Override
            public JsonProvider jsonProvider() 
            {
                return jsonProvider;
            }

            @Override
            public MappingProvider mappingProvider() 
            {
                return mappingProvider;
            }

            @Override
            public Set<Option> options() 
            {
                return EnumSet.noneOf(Option.class);
            }
            });

        // Get an object representation of the JSON to allow values to be extracted
        this.document = Configuration.defaultConfiguration().jsonProvider().parse(document);
    }
    catch(Exception e)
    {
        throw new DocumentFormatException("Invalid JSON document", e);
    }
}

但是，我看到了行為上的差異，因為如果我得到的路徑包含幾個字段，則在使用JsonSmartJsonProvider時它們不會被引用。
JSON范例

{
  "firstName": "John",
  "lastName": "Smith",
  "isAlive": true,
  "age": 25,
  "height_cm": 167.6,
  "address": {
    "streetAddress": "21 2nd Street",
    "city": "New York",
    "state": "NY",
    "postalCode": "10021-3100"
  },
  "phoneNumbers": [
    {
      "type": "home",
      "number": "212 555-1234"
    },
    {
      "type": "office",
      "number": "646 555-4567"
    }
  ],
  "children": [],
  "spouse": null
}

致電：

Object obj = JsonPath.read(document, "$.phoneNumbers"); 

當使用JacksonMappingProvider我得到

[{type=home, number=212 555-1234}, {type=office, number=646 555-4567}] 

當使用JsonSmartJsonProvider我得到：

[{"type":"home","number":"212 555-1234"},{"type":"office","number":"646 555-4567"}]  

如果我想讓傑克遜以同樣的方式行事，還有其他可以配置的東西嗎？

Answer 1

Jackson處理這些值的方式與打印它們的方式之間是有區別的。

使用JsonSmartJsonProvider此行...

JsonPath.read(parse, "$.phoneNumbers");

...返回一個JSONArray和toString()方法-當您“打印” JSONArray實例時就足夠聰明，以至於知道它正在處理JSON，因此它將狀態打印為JSON字符串。 例如：

[{"type":"home","number":"212 555-1234"},{"type":"office","number":"646 555-4567"}]

但是，當您使用JacksonJsonProvider此行...

JsonPath.read(parse, "$.phoneNumbers");

...返回LinkedHashMap的List ，以及當您“打印”該實例不支持JSON時調用的toString()實現，因此將打印以下內容：

[{type=home, number=212 555-1234}, {type=office, number=646 555-4567}]

如果要在使用JacksonJsonProvider時打印JSON，則必須使用支持JSON的內容進行打印。 這是一個例子：

String payload = "{\n" +
        "  \"firstName\": \"John\",\n" +
        "  \"lastName\": \"Smith\",\n" +
        "  \"isAlive\": true,\n" +
        "  \"age\": 25,\n" +
        "  \"height_cm\": 167.6,\n" +
        "  \"address\": {\n" +
        "    \"streetAddress\": \"21 2nd Street\",\n" +
        "    \"city\": \"New York\",\n" +
        "    \"state\": \"NY\",\n" +
        "    \"postalCode\": \"10021-3100\"\n" +
        "  },\n" +
        "  \"phoneNumbers\": [\n" +
        "    {\n" +
        "      \"type\": \"home\",\n" +
        "      \"number\": \"212 555-1234\"\n" +
        "    },\n" +
        "    {\n" +
        "      \"type\": \"office\",\n" +
        "      \"number\": \"646 555-4567\"\n" +
        "    }\n" +
        "  ],\n" +
        "  \"children\": [],\n" +
        "  \"spouse\": null\n" +
        "}";

// this is a simpler way of declaring and using the JacksonJsonProvider
ObjectMapper objectMapper = new ObjectMapper();

Configuration conf = Configuration.builder()
        .jsonProvider(new JacksonJsonProvider(objectMapper))
        .build();

Object obj = JsonPath.using(conf).parse(payload).read("$.phoneNumbers");

// prints out:
//      [{type=home, number=212 555-1234}, {type=office, number=646 555-4567}]
System.out.println(obj);

// prints out:
//      [{"type":"home","number":"212 555-1234"},{"type":"office","number":"646 555-4567"}]
System.out.println(objectMapper.writer().writeValueAsString(obj));