杰克逊地图序列化模块 [英] Jackson Modules for Map Serialization

问题描述

我有一个包含Map（带非String键）和其他一些字段的Class。

I have a Class that contains a Map (with non String key) and some other fields.

public class MyClass() {
    private Map<KeyObject, OtherObject> map;
    private String someField;

    public MyClass(Map<KeyObject, OtherObject> map, String someField) {
        this.map = map;
        this.someField = someField;
    }

    // Getters & Setters
}

我想使用Jackson序列化和反序列化这个类。
我看到了不同的方法，并决定尝试使用 jackson模块。

I would like to serialize and deserialize this class using Jackson. I saw a different ways of doing that and decided to try using jackson modules.

我跟着这篇文章并扩展了JsonDeserializer和JsonSerializer。问题是这些类应该键入，所以它应该看起来像

I followed this post and extended JsonDeserializer and JsonSerializer. The problem is that those classes should be typed, so it should look like

public class keyDeserializer extends JsonDeserializer<Map<KeyObject, OtherObject>> {
...
}

KeySerializer的相同内容。

The same for the KeySerializer.

然后添加到模块：

module.addSerializer(new keySerializer());
module.addDeserializer(Map.class, new keyDeserializer());

但这显然是错误的，因为我得到了一个例外：

But this is wrong apparently since I'm getting an exception:

keySerializer does not define valid handledType() -- must either register with method that takes type argument  or make serializer extend 'org.codehaus.jackson.map.ser.std.SerializerBase'

我可以将我的序列化器和反序列化器输入 MyClass ，但后来我不得不手动解析所有这些，这是不合理的。

I could have my serializer and deserializer to be typed to MyClass, but then I had to manually parse all of it, which is not reasonable.

更新：

我设法通过使用注释绕过了代码中的模块创建

I managed to bypass the module creation in the code by using annotations

@JsonDeserialize(using = keyDeserializer.class)
@JsonSerialize(using = keySerializer.class)
private Map<KeyObject, OtherObject> map;

但是我必须自己从toString（）输出序列化/反序列化整个地图结构。所以尝试了不同的注释：

But then I have to serialize/deserialize the whole map structure on my own from the toString() output. So tried a different annotation:

@JsonDeserialize(keyUsing = MyKeyDeserializer.class)
private Map<KeyObject, OtherObject> map;

MyKeyDeserializer扩展 org.codehaus.jackson.map.KeyDeserializer 并覆盖方法

Where MyKeyDeserializer extends org.codehaus.jackson.map.KeyDeserializer and overriding the method

public Object deserializeKey(String key, DeserializationContext ctxt) throws IOException, JsonProcessingException {...}

然后再次从我的密钥类的toString（）输出反序列化我的密钥。

Then manually deserializing my key but again from the toString() output of my key class.

这不是最佳的（这种对toString（）方法的依赖）。有更好的方法吗？

This is not optimal (this dependency on the toString() method). Is there a better way?

推荐答案

结束使用此序列化程序：

Ended up using this serializer:

public class MapKeySerializer extends SerializerBase<Object> {
    private static final SerializerBase<Object> DEFAULT = new StdKeySerializer();
    private static final ObjectMapper mapper = new ObjectMapper();

    protected MapKeySerializer() {
    super(Object.class);
    }

    @Override
    public JsonNode getSchema(SerializerProvider provider, Type typeHint) throws JsonMappingException {
    return DEFAULT.getSchema(provider, typeHint);
    }

    @Override
    public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonGenerationException {
    if (null == value) {
        throw new JsonGenerationException("Could not serialize object to json, input object to serialize is null");
    }
    StringWriter writer = new StringWriter();
    mapper.writeValue(writer, value);
    jgen.writeFieldName(writer.toString());
    }
}

此解串器：

public class MapKeyDeserializer extends KeyDeserializer {

    private static final ObjectMapper mapper = new ObjectMapper();

    @Override
    public Object deserializeKey(String key, DeserializationContext ctxt) throws IOException, JsonProcessingException {
    return mapper.readValue(key, MyObject.class);
    }
}

注释我的地图：

@JsonDeserialize(keyUsing = MapKeyDeserializer.class)
@JsonSerialize(keyUsing = MapKeySerializer.class)
private Map<KeyObject, OtherObject> map;

这是对我有用的解决方案，希望这有助于其他人。

This is the solution that worked for me, hope this helps other.

这篇关于杰克逊地图序列化模块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！