如何将java.lang.String的空白JSON字符串值反序列化为null? [英] How to deserialize a blank JSON string value to null for java.lang.String?
问题描述
我正在尝试使用简单的JSON来反序列化到java对象。但是,我为 java.lang.String
属性值获取空 String 值。在其他属性中,空值正在转换为 null 值(这就是我想要的)。
I am trying a simple JSON to de-serialize in to java object. I am however, getting empty String values for java.lang.String
property values. In rest of the properties, blank values are converting to null values(which is what I want).
我的JSON和相关的Java类是下面列出。
My JSON and related Java class are listed below.
JSON字符串:
{
"eventId" : 1,
"title" : "sample event",
"location" : ""
}
EventBean class POJO:
EventBean class POJO:
public class EventBean {
public Long eventId;
public String title;
public String location;
}
我的主类代码:
ObjectMapper mapper = new ObjectMapper();
mapper.disable(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES);
mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);
try {
File file = new File(JsonTest.class.getClassLoader().getResource("event.txt").getFile());
JsonNode root = mapper.readTree(file);
// find out the applicationId
EventBean e = mapper.treeToValue(root, EventBean.class);
System.out.println("It is " + e.location);
}
我原本期待打印它是空的。相反,我得到它是。显然, Jackson 在转换为我的 String 对象类型时,并未将空字符串值视为NULL。
I was expecting print "It is null". Instead, I am getting "It is ". Obviously, Jackson is not treating blank String values as NULL while converting to my String object type.
我读到了预期的地方。但是,对于 java.lang.String ,我也想避免这种情况。有一个简单的方法吗?
I read somewhere that it is expected. However, this is something I want to avoid for java.lang.String too. Is there a simple way?
推荐答案
杰克逊会为其他对象提供null,但对于String,它会给出空字符串。
Jackson will give you null for other objects, but for String it will give empty String.
但您可以使用自定义 JsonDeserializer
来执行此操作:
But you can use a Custom JsonDeserializer
to do this:
class CustomDeserializer extends JsonDeserializer<String> {
@Override
public String deserialize(JsonParser jsonParser, DeserializationContext context) throws IOException, JsonProcessingException {
JsonNode node = jsonParser.readValueAsTree();
if (node.asText().isEmpty()) {
return null;
}
return node.toString();
}
}
在课堂上你必须使用它对于位置字段:
In class you have to use it for location field:
class EventBean {
public Long eventId;
public String title;
@JsonDeserialize(using = CustomDeserializer.class)
public String location;
}
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