从JSON反序列化Java枚举 [英] Deserialize java enum from JSON

问题描述

我们使用Jackson 1.9.1对与Java对象之间的JSON请求响应字符串进行序列化和反序列化。原始Java类型，集合类型和自定义对象都可以（反）序列化而不会出现问题。但是，尝试将JSON字符串反序列化为Java枚举时遇到问题。
JSON字符串的序列化方式如下：

We use Jackson 1.9.1 to serialize and deserialize JSON request response strings to/from Java objects. Primitive Java types, collection types, and custom objects are (de)serialized without issues. However, I have a problem trying to deserialize JSON string into java enum. JSON string is serialized like so:

"wt":{"wt":100.5,"unit":{"LBS":3}}

wt的Java类型如下：

Java type for wt is like so:

public class Weight {

    protected double weight;
    protected Unit unit;
}

我指的是这，此，以及此因此，提出了重量单位的枚举，如下所示：

I referred to this, this, and this on SO and came up with enum for weight units like so:

public enum Unit {

    KG("kg"),
    GM("gm"),
    LBS("lbs"),
    OZ("oz");

    private String value;  
    private WeightMeasurementUnit(String value) { this.value = value; }

    @JsonValue
    public String getValue() { return this.value; }

    @JsonCreator
    public static Unit create(String val) {
        Unit[] units = Unit.values();
        for (Unit unit : units) {
            if (unit.getValue().equals(val)) {
                return unit;
            }
        }
        return LBS;
    }
}

问题是，当我尝试反序列化时提到JSON，我得到这个错误，说：无法识别的字段 LBS（类abcdWeight），未标记为可忽略异常stacktrace如下：

The problem is, when ever I try to deserialize above mentioned JSON I get this error saying: "Unrecognized field "LBS" (Class a.b.c.d.Weight), not marked as ignorable" Exception stacktrace is like so:

Caused by: org.codehaus.jackson.map.exc.UnrecognizedPropertyException: Unrecognized field "LBS" (Class a.b.c.d.Weight), not marked as ignorable
 at [Source: java.io.ByteArrayInputStream@20172017; line: 1, column: 464] (through reference chain: a.b.c.d.MyRequest["blah"]->a.b.c.d.AnotherType["wt"]->a.b.c.d.Weight["LBS"])
    at org.codehaus.jackson.map.exc.UnrecognizedPropertyException.from(UnrecognizedPropertyException.java:53)
    at org.codehaus.jackson.map.deser.StdDeserializationContext.unknownFieldException(StdDeserializationContext.java:267)
    at org.codehaus.jackson.map.deser.std.StdDeserializer.reportUnknownProperty(StdDeserializer.java:673)
    at org.codehaus.jackson.map.deser.std.StdDeserializer.handleUnknownProperty(StdDeserializer.java:659)
    at org.codehaus.jackson.map.deser.BeanDeserializer.handleUnknownProperty(BeanDeserializer.java:1365)

。 ..

我的问题是：
枚举的序列化JSON字符串是否正确？
为使枚举正确反序列化，我还应该包括（或注释）什么？

My questions are: Is the serialized JSON string for enum seem correct ? What else should I include (or annotate) for the enum to be properly deserialized ?

推荐答案

我假设在枚举单位代码块中，您的意思是 Unit 而不是 WeightMeasurementUnit 。

I am assuming that in the public enum Unit code block, you mean Unit instead of WeightMeasurementUnit.

体重类的体重只有 和 unit ，因此，如果您传递 { wt：100.5， unit： lbs} ，它应该起作用，因为单位只是一个没有价值的单位。因此，反序列化程序无法将 { LBS：3} 解析为 Unit 。 3 的用途是什么？

The Weight class has only a weight and a unit, so if you pass {"wt":100.5,"unit":"lbs"}, it should work, because a unit is just a unit without value. So there is no way for the deserializer to parse {"LBS":3} as a Unit. What is the 3 for?

另一个问题是您的值是 lbs，而您传递的是 LBS 。因此，要么需要标准化，要么需要使用 unit.getValue（）。equalsIgnoreCase（val）

Another problem is that your value is "lbs" whereas you are passing "LBS". So either you need to standardise or you need to use unit.getValue().equalsIgnoreCase(val)

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