Question

我以JSON

接收数据

{
"status": "INVALID_DATA",
"errors":{ "invalid_id": "Id isn't available",
           ...
           "wrong_address": "Address error msg"
         }
}

键及其结构中的数量“错误”对我来说是未知的。我正在尝试用类

来映射它

@JsonIgnoreProperties(ignoreUnknown = true)
public class StatusErrors
{
    private String status;
    private HashMap<String, String> errors = new HashMap<String, String>();

    public String getStatus() {
        return status;
    }

    public void setStatus(String status) {
        this.status = status;
    }

    public HashMap<String, String> getErrors() {
        return errors;
    }

    public void setErrors(HashMap<String, String> errors) {
        this.errors = errors;
    }
}

如果我有“错误”，它可以正常工作，但是当服务器说“OK”并且没有错误时它会发送给我

{
"status": "OK",
"errors":[]
}

（不要问我是谁写的服务器）因此映射器崩溃了。我正在尝试编写一个自定义的JsonDeserializer（通用方式）

public abstract class ExcludeEmptyArrayDeserializer<T> extends JsonDeserializer<T> {

    private final Class<T> clazz;

    protected ExcludeEmptyArrayDeserializer(Class<T> clazz) {
        this.clazz = clazz;
    }

    @Override
    public T deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException {
        ObjectCodec oc = jp.getCodec();
        JsonNode node = oc.readTree(jp);

        if(node.has("errors")) {
            if (node.get("errors").isArray() && !node.get("errors").getElements().hasNext())
                ((ObjectNode)node).remove("errors");
        }

        ObjectMapper objectMapper = new ObjectMapper();
        return objectMapper.readValue(node, clazz);   // doesn't work
        //return oc.treeToValue(node, clazz);   // doesn't work too
    }
}

public class StatusErrorsDeserializer extends ExcludeEmptyArrayDeserializer<StatusErrors> {
    public StatusErrorsDeserializer() {
        super(StatusErrors.class);
    }
}

结果使用代码有一个视图

    SimpleModule module = new SimpleModule("", Version.unknownVersion());
    module.addDeserializer(StatusErrors.class, new StatusErrorsDeserializer());

    ObjectMapper mapper = new ObjectMapper().setVisibility(JsonMethod.FIELD, JsonAutoDetect.Visibility.ANY).withModule(module); 
    MappingJacksonHttpMessageConverter messageConverter = new MappingJacksonHttpMessageConverter();
    messageConverter.setObjectMapper(mapper);

    getRestTemplate().getMessageConverters().clear();
    getRestTemplate().getMessageConverters().add(messageConverter);

“错误”节点已正确删除，但此解决方案仍无效。我想我在JsonDeserializer.deserialize方法中犯了一个错误，但是没有想到。

BTW StatusErrors类可以是来自服务器的其他复杂消息的基类。

Answer 1

最简单的解决方案是将错误变量声明更改为Object：

@JsonIgnoreProperties(ignoreUnknown = true)
class StatusErrors {
    private String status;
    private Object errors;
    public Map<String, String> getErrorsMap() {
        if (this.errors instanceof Map) {
            return (Map)this.errors;
        }
        return null;
    }
....

您不需要任何序列化程序和反序列化程序：

ObjectMapper objectMapper = new ObjectMapper();

StatusErrors result1 = objectMapper.readValue(JSON1, StatusErrors.class);
System.out.println(result1);
System.out.println(result1.getErrors().getClass());
System.out.println(result1.getErrorsMap());
StatusErrors result2 = objectMapper.readValue(JSON2, StatusErrors.class);
System.out.println(result2);

上面的代码将打印：

StatusErrors(status=INVALID_DATA, errors={invalid_id=Id isn't available, wrong_address=Address error msg})
class java.util.LinkedHashMap
{invalid_id=Id isn't available, wrong_address=Address error msg}
StatusErrors(status=OK, errors=[])

杰克逊中的自定义JSON反序列化，不包括invalide数组

1 个答案: