杰克逊反序列化 - 包含ArrayList< T> [英] Jackson deserialization - with contained ArrayList<T>
问题描述
美好的一天,
我目前正在尝试使用Jackson(使用Jersey)来使用生成JSON(用.NET编写)的REST服务。 JSON由可能的错误消息和对象数组组成。下面是Jersey的日志记录过滤器返回的JSON示例:
I am currently integration attempting to consume a REST service that produces JSON (written in .NET) using Jackson (with Jersey). The JSON consists of a possible error message and an array of objects. Below is a sample of the JSON returned as produced by Jersey's logging filter:
{
"error":null,
"object":"[{\"Id\":16,\"Class\":\"ReportType\",\"ClassID\":\"4\",\"ListItemParent_ID\":4,\"Item\":\"Pothole\",\"Description\":\"Pothole\",\"Sequence\":1,\"LastEditDate\":null,\"LastEditor\":null,\"ItemStatus\":\"Active\",\"ItemColor\":\"#00AF64\"}]"
}
我有两个类代表类型(外部ListResponse):
I have two classes to represent the type (the outer ListResponse):
public class ListResponse {
public String error;
public ArrayList<ListItem> object;
public ListResponse() {
}
}
和(内部ListItem):
and (the inner ListItem):
public class ListItem {
@JsonProperty("Id")
public int id;
@JsonProperty("Class")
public String classType;
@JsonProperty("ClassID")
public String classId;
@JsonProperty("ListItemParent_ID")
public int parentId;
@JsonProperty("Item")
public String item;
@JsonProperty("Description")
public String description;
@JsonAnySetter
public void handleUnknown(String key, Object value) {}
public ListItem() {
}
}
调用并返回JSON的类如下所示:
The class that invokes and returns the JSON looks like this:
public class CitizenPlusService {
private Client client = null;
private WebResource service = null;
public CitizenPlusService() {
initializeService("http://localhost:59105/PlusService/");
}
private void initializeService(String baseURI) {
// Use the default client configuration.
ClientConfig clientConfig = new DefaultClientConfig();
clientConfig.getClasses().add(JacksonJsonProvider.class);
client = Client.create(clientConfig);
// Add a logging filter to track communication between server and client.
client.addFilter(new LoggingFilter());
// Add the base URI
service = client.resource(UriBuilder.fromUri(baseURI).build());
}
public ListResponse getListItems(String id) throws Exception
{
ListResponse response = service.path("GetListItems").path(id).accept(MediaType.APPLICATION_JSON_TYPE, MediaType.APPLICATION_XML_TYPE).get(ListResponse.class);
return response;
}
}
这里重要的调用是getListItems方法。在测试工具中运行代码,产生以下结果:
The important call here is the getListItems method. Running the code in a test harness, produces the following:
org.codehaus.jackson.map.JsonMappingException: Can not deserialize instance of java.util.ArrayList out of VALUE_STRING token
at [Source: java.io.StringReader@49497eb8; line: 1, column: 14] (through reference chain: citizenplus.types.ListResponse["object"])
请协助。
问候,
Carl-Peter Meyer
Regards, Carl-Peter Meyer
推荐答案
你的问题是'object'属性值是一个String而不是一个数组!该字符串包含一个JSON数组,但Jackson期望一个原生数组(没有包装引号)。
Your problem is that the 'object' property value is a String and not an array! The string contains a JSON array but Jackson expects a native array (without the wrapping quotes).
我有同样的问题,我创建了一个自定义反序列化器,它将反序列化一个字符串值到所需类型的泛型集合:
I had the same problem and I created a custom deserializer, which will deserialize a string value to a generic collection of the desired type:
public class JsonCollectionDeserializer extends StdDeserializer<Object> implements ContextualDeserializer {
private final BeanProperty property;
/**
* Default constructor needed by Jackson to be able to call 'createContextual'.
* Beware, that the object created here will cause a NPE when used for deserializing!
*/
public JsonCollectionDeserializer() {
super(Collection.class);
this.property = null;
}
/**
* Constructor for the actual object to be used for deserializing.
*
* @param property this is the property/field which is to be serialized
*/
private JsonCollectionDeserializer(BeanProperty property) {
super(property.getType());
this.property = property;
}
@Override
public JsonDeserializer<?> createContextual(DeserializationContext ctxt, BeanProperty property) throws JsonMappingException {
return new JsonCollectionDeserializer(property);
}
@Override
public Object deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
switch (jp.getCurrentToken()) {
case VALUE_STRING:
// value is a string but we want it to be something else: unescape the string and convert it
return JacksonUtil.MAPPER.readValue(StringUtil.unescapeXml(jp.getText()), property.getType());
default:
// continue as normal: find the correct deserializer for the type and call it
return ctxt.findContextualValueDeserializer(property.getType(), property).deserialize(jp, ctxt);
}
}
}
请注意,此解串器也会如果值实际上是一个数组而不是字符串,则工作,因为它会相应地委托实际的反序列化。
Note that this deserializer will also work if the value actually is an array and not a string, because it delegates the actual deserialization accordingly.
在您的示例中,您现在必须注释您的集合字段,如此:
In your example you would now have to annotate your collection field like so:
public class ListResponse {
public String error;
@JsonDeserialize(using = JsonCollectionDeserializer.class)
public ArrayList<ListItem> object;
public ListResponse() {}
}
应该是它。
注意:JacksonUtil和StringUtil是自定义类,但您可以轻松替换它们。例如,使用 new ObjectMapper()
和 org.apache.commons.lang3.StringEscapeUtils
。
Note: JacksonUtil and StringUtil are custom classes, but you can easily replace them. For example by using new ObjectMapper()
and org.apache.commons.lang3.StringEscapeUtils
.
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