如何使用Jackson和Spring Boot提供自定义解串器 [英] How to provide a custom deserializer with Jackson and Spring Boot

问题描述

我有以下三个应用程序:

I have the following three applications:

项目1持有

Project 1 holds

• 业务逻辑(Spring Cloud功能)
• 接口 IDemoEntity
• Business logic (Spring Cloud Function)
• An interface IDemoEntity

项目2

• 特定于AWS的处理程序
• IDemoEntity 的一种实现，带有DynamoDB特定的注释
• 该项目基于Spring Boot
• AWS-specific handler
• One implementation of IDemoEntity, with DynamoDB-specific annotations
• The project is based on Spring Boot

项目3

• IDemoEntity 的一个实现，带有CosmosDB批注
• 天蓝色特定的处理程序
• One implementation of IDemoEntity, with CosmosDB annotation
• Azure-specific handler

项目1的类如下:

public interface IDemoEntity {
    String getName();
    void setName(String name);
}

@Component
public class StoreFunction implements Consumer<Message<IDemoEntity>> {

    @Override
    public void accept(Message<IDemoEntity> t) {

        System.out.println("Stored entity " + t.getPayload().getName());
        return;
    }
}

对于项目2，IDemoEntity的实现如下所示:

For project 2, the implementation of IDemoEntity looks like this:

@DynamoDBTable(tableName = "DemoEntity")
public class DynamoDemoEntity implements IDemoEntity {

    private String name;
    @Override
    @DynamoDBHashKey
    public String getName() {

        return name;
    }

    @Override
    public void setName(String name) {

        this.name = name;
    }    
}

对于项目3， IDemoEntity 的实现与 DynamoDemoEntity 相似，但带有CosmosDB批注.

For project 3, the implementation of IDemoEntity would look similar to DynamoDemoEntity, but with CosmosDB annotations.

结构可能看起来有点复杂，但是其构想如下:

The structure might look a bit complicated, but the idea is the following:

1. 一次实施业务逻辑和数据模型(在项目1中)(利用Spring Cloud Function)
2. 仅针对每个平台实施一个包装项目(我从项目2中的AWS Lambda开始，但针对Azure的项目3看起来很相似)，以及特定于平台的内容(例如实体实现，需要特定于DB的东西)注释)
3. 使用项目1作为依赖项编译特定于平台的项目(例如，AWS Lambda的项目2)

我已经尝试过了，安装程序基本上可以正常工作了. 但是，有一个大问题:

I've tried it, and the setup works basically. However, there is one big problem:

调用上面的 StoreFunction 时，Jackson抛出以下异常:

When calling the StoreFunction above, Jackson throws the following exception:

Caused by: com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `de.margul.awstutorials.springcloudfunction.logic.IDemoEntity` (no Creators, like default construct, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
 at [Source: (String)"{"name": "Detlef"}"; line: 1, column: 1]
    at com.fasterxml.jackson.databind.exc.InvalidDefinitionException.from(InvalidDefinitionException.java:67)
    at com.fasterxml.jackson.databind.DeserializationContext.reportBadDefinition(DeserializationContext.java:1452)
    at com.fasterxml.jackson.databind.DeserializationContext.handleMissingInstantiator(DeserializationContext.java:1028)
    at com.fasterxml.jackson.databind.deser.AbstractDeserializer.deserialize(AbstractDeserializer.java:265)
    at com.fasterxml.jackson.databind.ObjectMapper._readMapAndClose(ObjectMapper.java:4013)
    at com.fasterxml.jackson.databind.ObjectMapper.readValue(ObjectMapper.java:3004)
    at de.margul.awstutorials.springcloudfunction.aws.handler.RestSpringBootApiGatewayRequestHandler.deserializeBody(RestSpringBootApiGatewayRequestHandler.java:57)
    ... 3 more

这是有道理的，因为杰克逊不知道，如果IDemoEntity它将对接收到的JSON反序列化到哪个实现.

That makes sense, because Jackson does not know, to which implementation if IDemoEntity it shall deserialize the received JSON.

现在最简单的方法是将@JsonDeserialize(as = DynamoDemoEntity.class)放置在IDemoEntity上.

The easiest way now would be to place a @JsonDeserialize(as = DynamoDemoEntity.class) on IDemoEntity.

但是，这将破坏我的完整结构:项目1将不包含任何信息，它是与哪个平台特定的项目一起编译的.

However, that would break my complete structure: Project 1 shall have no information, which platform-specific project it is compiled with.

有什么想法，我如何提供自定义解串器(例如Spring bean)，而又不对项目1进行平台特定的修改?

Any ideas, how I could provide a custom deserializer (e. g. as Spring bean), but without making platform-specific modifications in project 1?

推荐答案

首先，您需要创建自定义DynamoDemoEntityDeserializer，如下所示:

Firstly, you need to create your custom DynamoDemoEntityDeserializer like below:

class DynamoDemoEntityDeserializer extends JsonDeserializer<DynamoDemoEntity> {
    @Override
    public DynamoDemoEntity deserialize(JsonParser p, DeserializationContext ctxt)
                throws IOException, JsonProcessingException {
       // return DynamoDemoEntity instance;
    }
}

然后您可以创建com.fasterxml.jackson.databind.Module的bean，如下所示:

Then you can create bean of com.fasterxml.jackson.databind.Module like below:

@Bean
public Module dynamoDemoEntityDeserializer() {
    SimpleModule module = new SimpleModule();
    module.addDeserializer(IDemoEntity.class, new DynamoDemoEntityDeserializer());
    return module;
}

任何类型为com.fasterxml.jackson.databind.Module的bean都会自动注册到自动配置的Jackson2ObjectMapperBuilder中，并应用于它创建的任何ObjectMapper实例.当您向应用程序中添加新功能时，这提供了一种用于贡献自定义模块的全局机制.

Any beans of type com.fasterxml.jackson.databind.Module are automatically registered with the auto-configured Jackson2ObjectMapperBuilder and are applied to any ObjectMapper instances that it creates. This provides a global mechanism for contributing custom modules when you add new features to your application.

来源:如何自定义杰克逊对象映射器

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