使用Jackson ObjectMapper和Java 8可选值 [英] Using Jackson ObjectMapper with Java 8 Optional values

问题描述

我试图使用Jackson将类值写入JSON，其中包含Optional作为字段：

I was trying to use Jackson to write a class value to JSON that has Optional as fields:

public class Test {
    Optional<String> field = Optional.of("hello, world!");

    public Optional<String> getField() {
        return field;
    }

    public static void main(String[] args) throws JsonProcessingException {
        ObjectMapper mapper = new ObjectMapper();
        System.out.println(mapper.writeValueAsString(new Test()));
    }
}

执行时，此类生成以下输出：

When executed, this class generates the following output:

{"field":{"present":true}}

我理解当前/不存在的字段被包含在内并且在阅读JSON数据时可以解决它，但是我无法解决实际的内容可选的永远不会写入输出。 :(

I understand the present/not present field being included and could work around it when reading the JSON data, however I can't get around the fact that the actual content of the optional is never written to the output. :(

除了不使用ObjectMapper之外，这里有任何变通方法吗？

Any workarounds here except not using ObjectMapper at all?

推荐答案

您可以使用 jackson-datatype-jdk8 ，其描述如下：

You could use jackson-datatype-jdk8 which is described as:

支持新的JDK8特定类型，例如Optional

Support for new JDK8-specific types, such as Optional

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