带有变量 JsonProperty 的 Jackson 泛型(与泛型一起使用) [英] Jackson Generics with variable JsonProperty (usage with generics)

问题描述

我有这样的课程:

public class Data<U> {

    @JsonProperty("difficulties")
    private U[] data;

    // ... geter setter constructor
}

而且我不想再创建 10 个类似的类，因为我只需要更改一行代码(在这种情况下为 @JsonProperty("difficulties")).属性值取决于类型.可以在一个班级里写吗?

And I don't want to create 10 more similar classes just because I need to change only one line of code (@JsonProperty("difficulties") in this case). The property value depends on Type. Is it possible to write it in one class?

推荐答案

基于 Jackson - 在没有注释的情况下在运行时修改属性 作者 Michał Ziober 在这里我能够更改默认字段名称值通过覆盖 PropertyNamingStrategy:

Based on response of Jackson - Modify an attribute at runtime without annotation by Michał Ziober here I was able to change default field name values by overriding PropertyNamingStrategy:

这些是我收到的 JSON 示例(简化版):

These are my received JSON examples (simplified):

{"status": "OK","error": null,"data": {
    "difficulties": [{"value":"easy"},{"value":"medium"}]
}}

{"status": "ok", "error": null, "data": {
    "countries": [{"code": "AT"},{"code": "BE"}]
}}

查看第二行中数据对象包含困难的区别或国家/地区(或基于上下文的许多其他名称).

see the difference in second line where data object contains either difficulties or countries (or many other names based on context).

基于JSON响应的响应类:

Response class based on JSON response:

public class Response<T>{
    private String status;
    private String error;
    private Data<T> data;
    // Getters Setters Constructors
}

基于JSON响应的数据类:

Data class based on JSON response:

public class Data<T> {
    // property name, that will be changed
    @JsonProperty(DataNamingStrategy.DATA_FIELD)
    private T[] data;
    // Getters Setters Constructors
}

这是命名策略，将默认值更改为运行时指定值

And this is Naming strategy, that changes default value to runtime specified value

public class DataNamingStrategy extends PropertyNamingStrategy{

    // used by other classes (this will be default field name that should be changed)
    public static final String DATA_FIELD = "variable:data";
    private String fieldName;

    public DataNamingStrategy(String fieldName) {
        this.fieldName = fieldName;
    }

    // use this to change field name (format "variable":"value") not needed in my case
    @Override
    public String nameForField(MapperConfig<?> config, AnnotatedField field,
            String defaultName) {
        return (defaultName.equals(DATA_FIELD))?
            fieldName :
            super.nameForField(config, field, defaultName);
    }

    // use this to change setter method field name (JSON -> Object with format "variable":{})
    @Override
    public String nameForSetterMethod(MapperConfig<?> config,
            AnnotatedMethod method, String defaultName) {
        return (defaultName.equals(DATA_FIELD))?
            fieldName :
            super.nameForGetterMethod(config, method, defaultName);
    }

    // use this to change getter method field name (Object -> JSON with format "variable":{})
    // should be same as nameForSetterMethod
    @Override
    public String nameForGetterMethod(MapperConfig<?> config,
            AnnotatedMethod method, String defaultName) {
        return nameForSetterMethod(config, method, defaultName);
    }
}

用法应该是这样的:

ObjectMapper mapper = new ObjectMapper();
mapper.setPropertyNamingStrategy(new DataNamingStrategy(tableName));
JavaType type = mapper.getTypeFactory().constructParametricType(Response.class, dataClass);
Response<U> u = mapper.readValue(result, type);

其中 result 是 Json as String，tableName 是将在 JSON 中使用的字符串而不是默认值，dataClass 是 dataClass 的类code>U(例如 Difficulty.class).

Where result is Json as String, tableName is String that will be used in JSON instead of default value and dataClass is class for U (for example Difficulty.class).

PropertyNamingStrategy 的更好用法应该是 Map 而不是一个 String.但我只需要更改一个特定值.

Better usage of PropertyNamingStrategy should be Map instead of one String. But I just needed to change one particular value.

也看看PropertyNamingStrategy 文档 或再次访问 Michał Ziober 的回答

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