如何在映射的映射中使用jackson键序列化器

Question

class MainContainer {
    private final Map<String, Object> entries;
}

class Item {
    // a lot of attributes
}

class ItemMapKeySerializer extends JsonSerializer<Item> {
     // serialize an item into something simple for map keys
}

class IntermediateContainer {
     private final Map<Item, ... > someMapping;
}

MainContainer.add("test", new IntermediateContainer(Map.of(new Item(), ...)));

 entries: {
    "test": {
        someMapping: {
            "my nice item 1": {
            ...
            }             
        }
    }
}

MainContainer.add("test", Map.of(new Item(), ...));

 entries: {
    "test": {
        Item@12D23: {  // This kind of fieldname is not desired
        ...
        }             
    }
}

Answer 1

应该将“toString（）”方法添加到项中。例如，我检查了以下示例：

public static class Item {
    private String val1;
    private int val2;

    public Item(String val1, int val2) {
        this.val1 = val1;
        this.val2 = val2;
    }

    @Override
    public boolean equals(Object obj) {
        return obj instanceof Item && toString().equals(obj.toString());
    }

    @Override
    public int hashCode() {
        return toString().hashCode();
    }

    @Override
    public String toString() {
        return "val1=" + val1 + ",val2=" + val2;
    }
}

这为简单映射wiht项（“AAA”，123)提供了这样的JSON字符串，指向“super！”：

{"val1=AAA,val2=123":"Super!"}

您甚至可以更进一步，使用Item.ToString中的ObjectMapper.WriteValueAsString为键文本生成Item的JSON表示。