Jackson 在反序列化时抛出 JsonMappingException；需要单字符串构造函数? [英] Jackson throws JsonMappingException on deserialize; demands single-String constructor?

问题描述

另一个问题，但它与这个问题有关:使用 Jackson 反序列化 JSON - 为什么 JsonMappingException 没有合适的构造函数"?

Another question, but it relates to this one: Deserializing JSON with Jackson - Why JsonMappingException "No suitable constructor"?

这次我遇到了一个不同的错误，即 Jackson 反序列化器抱怨我的类 ProtocolContainer 中没有单字符串构造函数/工厂方法".

This time I am getting a different error, namely that the Jackson deserializer complains that I do not have a "single-String constructor/factory method" in my class ProtocolContainer.

但是，如果我添加一个单字符串构造函数，如下所示:

However, if I add a single-String constructor, like this:

public ProtocolContainer(String json) {}

异常确实消失了，但是我期望的 ProtocolContainer 全是空的"，即它的所有属性都处于初始状态，而不是根据 JSON 字符串填充.

the exception does indeed disappear, but the ProtocolContainer that I expected to be there is all "empty", i.e. all its properties are in their initial state, and not populated according to the JSON-string.

这是为什么?

我很确定您不应该需要单字符串构造函数，如果这样做，您就不必在该构造函数中填充属性，对吗?

I'm pretty sure you shouldn't need a single-String constructor, and if you do that you should not have to populate the properties in that constructor, right?

=)

推荐答案

哦，所以我在发布这个问题后再次找到了答案(尽管我在发布之前尝试了很多东西).

Oh, so once again I found out the answer AFTER I posted this question (even though I tried a lot of things before posting).

我为解决这个问题所做的是使用 @JsonCreator 注释.我只是注释了我的静态 Create 方法，如下所示:

What I did to solve this was to use the @JsonCreator annotation. I simply annotated my static Create method, like this:

@JsonCreator
public static ProtocolContainer Create(String jsonString)
{

    ProtocolContainer pc = null;
    try {
        pc = mapper.readValue(jsonString, ProtocolContainer.class);
    } catch (JsonParseException|JsonMappingException|IOException e) {
        // handle
    }

    return pc;
}

然后问题就解决了.

这篇关于Jackson 在反序列化时抛出 JsonMappingException；需要单字符串构造函数?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！