将ZonedDateTime类型转换为Gson

Question

我有一个返回对象数组的REST服务，我实现了Jersy RESTful客户端来执行它，但是我在将ZonedDateTime类型转换为JSON时遇到了问题，因此出现了这个错误。

 Caused by: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 231 path $[0].lastmodifieddate

我该如何解决这个问题？

实体中的lastmodifieddate列

 @Column(name = "lastmodifieddate")
 private ZonedDateTime lastmodifieddate;

 //getter and setter

rest service

@RequestMapping(value = "/getScoreFactor",
        method = RequestMethod.GET,
        produces = MediaType.APPLICATION_JSON_VALUE)
@Timed
public List<Scorefactor> getScoreFactor() throws JSONException {
    return scoreService.getScoreFactor();
}   

Jersey RESTful客户端

  try {

        Client client = Client.create();
        WebResource webResource = client
           .resource("http://localhost:8080/adap/api/getScoreFactor");
        ClientResponse response = webResource.accept("application/json")
                   .get(ClientResponse.class);

        String output =  response.getEntity(String.class);

        System.out.println("output--"+output);
        Type listType =  new TypeToken<List<Scorefactor>>() {}.getType();

        List<Scorefactor> scorefactors = new Gson().fromJson(output,listType);

        System.out.println(scorefactors);

    } catch (Exception e) {

        e.printStackTrace();

}    

- Ali-Alrabi

---

可能是Java 8 LocalDateTime使用Gson反序列化的重复问题。 - andersschuller

Answer 1

public static final Gson GSON = new GsonBuilder()
    .registerTypeAdapter(ZonedDateTime.class, new TypeAdapter<ZonedDateTime>() {
        @Override
        public void write(JsonWriter out, ZonedDateTime value) throws IOException {
            out.value(value.toString());
        }

        @Override
        public ZonedDateTime read(JsonReader in) throws IOException {
            return ZonedDateTime.parse(in.nextString());
        }
    })
    .enableComplexMapKeySerialization()
    .create();

- pomo

Answer 2

我已经修复了它，这是更新后的代码。

Client client = Client.create();
        WebResource webResource = client
           .resource("http://localhost:8080/adap/api/getScoreFactor");
        ClientResponse response = webResource.accept("application/json")
                   .get(ClientResponse.class);

        String output =  response.getEntity(String.class);

        Gson gson = new GsonBuilder().registerTypeAdapter(ZonedDateTime.class, new JsonDeserializer<ZonedDateTime>() {
            @Override
            public ZonedDateTime deserialize(JsonElement json, Type type, JsonDeserializationContext jsonDeserializationContext) throws JsonParseException {
                return ZonedDateTime.parse(json.getAsJsonPrimitive().getAsString());
            }
            }).create();

        Type listType =  new TypeToken<List<Scorefactor>>() {}.getType();

        List<Scorefactor> scorefactors = gson.fromJson(output,listType);

- Ali-Alrabi

Answer 3

至少有两种方法可以实现这一点：

1) 使用JsonDeserializer的Gson

在您的代码中进行小更改：

Type listType =  new TypeToken<List<Scorefactor>>() {}.getType();
List<Scorefactor> scorefactors = new GsonBuilder()
            .registerTypeAdapter(ZonedDateTime.class, GsonHelper.ZDT_DESERIALIZER)
            .create()
            .fromJson(output, listType);

助手类

class GsonHelper {

    public static final JsonDeserializer<ZonedDateTime> ZDT_DESERIALIZER = new JsonDeserializer<ZonedDateTime>() {
        @Override
        public ZonedDateTime deserialize(final JsonElement json, final Type typeOfT, final JsonDeserializationContext context) throws JsonParseException {
            JsonPrimitive jsonPrimitive = json.getAsJsonPrimitive();
            try {

                // if provided as String - '2011-12-03T10:15:30+01:00[Europe/Paris]'
                if(jsonPrimitive.isString()){
                    return ZonedDateTime.parse(jsonPrimitive.getAsString(), DateTimeFormatter.ISO_ZONED_DATE_TIME);
                }

                // if provided as Long
                if(jsonPrimitive.isNumber()){
                    return ZonedDateTime.ofInstant(Instant.ofEpochMilli(jsonPrimitive.getAsLong()), ZoneId.systemDefault());
                }

            } catch(RuntimeException e){
                throw new JsonParseException("Unable to parse ZonedDateTime", e);
            }
            throw new JsonParseException("Unable to parse ZonedDateTime");
        }
    };

}

2) 使用MessageBodyReader和XMLAdapter

客户端实现的更改：

ClientConfig config = new DefaultClientConfig();
config.getFeatures().put(JSONConfiguration.FEATURE_POJO_MAPPING, Boolean.TRUE);
Client client = Client.create(config);

List<Scorefactor> result = client.resource("http://localhost:8080/adap/api/getScoreFactor"")
                .accept("application/json")
                .get(ClientResponse.class)
                .getEntity(new GenericType<List<Scorefactor>>(){});

System.out.println(result);

您可能需要导入jersey-json来实现此功能。

<dependency>
    <groupId>com.sun.jersey</groupId>
    <artifactId>jersey-bundle</artifactId>
    <version>1.19.1</version>
</dependency>
<dependency>
    <groupId>com.sun.jersey</groupId>
    <artifactId>jersey-json</artifactId>
    <version>1.19.1</version>
</dependency>

顺便问一下，为什么你使用1.*版本？

您的得分因素。

@XmlRootElement
@XmlAccessorType(XmlAccessType.FIELD)
public class Scorefactor implements Serializable {

    @Column(name = "lastmodifieddate")
    @XmlElement(name = "lastmodifieddate")
    @XmlJavaTypeAdapter(ZonedDateTimeToStringXmlAdapter.class)
    private ZonedDateTime lastmodifieddate;

    //...

ZonedDateTime从/到字符串（推荐）

public class ZonedDateTimeToStringXmlAdapter extends XmlAdapter<String, ZonedDateTime> {

    @Override
    public ZonedDateTime unmarshal(final String v) throws DateTimeParseException {
        return ZonedDateTime.parse(v);
    }

    @Override
    public String marshal(final ZonedDateTime v) throws Exception {
        return v.toString();
    }

}

从 Long 转换为 ZonedDateTime

public class ZonedDateTimeToLongXmlAdapter extends XmlAdapter<Long, ZonedDateTime> {

    @Override
    public ZonedDateTime unmarshal(final Long v) throws DateTimeParseException {
        return ZonedDateTime.ofInstant(Instant.ofEpochMilli(v.longValue()), ZoneId.systemDefault()); 
    }

    @Override
    public Long marshal(final ZonedDateTime v) throws Exception {
        return Long.valueOf(v.toInstant().toEpochMilli());
    }

}

您也可以构建自己的MessageBodyReader/MessageBodyWriter，或使用其他实现，如Moxy。

我建议使用Jersey 2.*。

希望这些对您有所帮助。祝您拥有愉快的一天。

- zyexal

Answer 4

你发布的解决方案不起作用，因为ZonedDateTime的Json序列化不是一个Json原语，而是一个包含多个元素的Json对象。它需要进行一些开发，这里是一个完整的解决方案：

public Gson gson() {
    return new GsonBuilder().registerTypeAdapter(ZonedDateTime.class, new JsonDeserializer<ZonedDateTime>() {
        @Override
        public ZonedDateTime deserialize(JsonElement json, Type type,
                JsonDeserializationContext jsonDeserializationContext) throws JsonParseException {

            JsonObject jsonObj = json.getAsJsonObject();

            JsonObject dateTime = jsonObj.getAsJsonObject("dateTime");
            JsonObject date = dateTime.getAsJsonObject("date");
            int year = date.get("year").getAsInt();
            int month = date.get("month").getAsInt();
            int day = date.get("day").getAsInt();

            JsonObject time = dateTime.getAsJsonObject("time");
            int hour = time.get("hour").getAsInt();
            int minute = time.get("minute").getAsInt();
            int second = time.get("second").getAsInt();
            int nano = time.get("nano").getAsInt();

            JsonObject zone = jsonObj.getAsJsonObject("zone");
            String id = zone.get("id").getAsString();

            return ZonedDateTime.of(year, month, day, hour, minute, second, nano, ZoneId.of(id));
        }
    }).create();
}

- Quang Vien

---

这个解决方案对我有效。但是，你知道为什么gson无法正确反序列化ZonedDateTime吗？ - Sami

因为ZonedDateTime的JSON序列化是包含超过一个元素的JSON对象。因此在重写的反序列化方法中，我们需要正确地读取JSON对象，例如JsonObject jsonObj = json.getAsJsonObject()。在原始解决方案中，它是json.getAsJsonPrimitive()。 - Quang Vien