java - 扩展 Jackson 自定义序列化器

Question

鉴于 MyClass2 扩展了 MyClass1 并且只是向 MyClass1 添加了两个属性，我为这两个类编写了两个 Jackson 自定义序列化程序，如下所示:

public class MyClass1Serializer extends JsonSerializer<MyClass1> {

    @Override
    public void serialize(MyClass1 myClass1, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {

        jsonGenerator.writeStartObject();
        jsonGenerator.writeStringField("ApplicationName", myClass1.getApplicationName());
        jsonGenerator.writeStringField("UserName", myClass1.getUserName());
    }       
}

和

public class MyClass2Serializer extends JsonSerializer<MyClass2> {

    @Override
    public void serialize(MyClass2 myClass2, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {

        jsonGenerator.writeStartObject();
        jsonGenerator.writeStringField("ApplicationName", myClass2.getApplicationName());       
        jsonGenerator.writeStringField("ErrorMessage", myClass2.getErrorMessage());
        jsonGenerator.writeStringField("ResultCode", myClass2.getResultCode());
        jsonGenerator.writeStringField("UserName", myClass2.getUserName());
    }       
}

效果很好，并给出以下输出:

{"ApplicationName":"FakeApp","UserName":"Joe the Schmoe"}

{"ApplicationName":"AnotherApp","ErrorMessage":"呃哦!","ResultCode":"Errrrrm，不好...","UserName":"John Doe"}

嗯，对我来说，两个序列化方法中似乎存在代码重复，我可以从第一个序列化器中子类化第二个序列化器吗？嗯嗯...

嗯，好吧，我尝试过这个:

public class MyClass1Serializer<T extends MyClass1> extends JsonSerializer<MyClass1> {

    @Override
    public void serialize(MyClass1 myClass1, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {

        jsonGenerator.writeStartObject();
        jsonGenerator.writeStringField("ApplicationName", myClass1.getApplicationName());
        jsonGenerator.writeStringField("UserName", myClass1.getUserName());
    }       
}

和

public class MyClass2Serializer extends MyClass1Serializer<MyClass2> {

    public void serialize(MyClass2 myClass2, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {

        super.serialize(myClass2, jsonGenerator, serializerProvider);
        jsonGenerator.writeStringField("ErrorMessage", myClass2.getErrorMessage());
        jsonGenerator.writeStringField("ResultCode", myClass2.getResultCode());
    }       
}

它编译并运行，但给我这个输出:

{"ApplicationName":"FakeApp","UserName":"Joe the Schmoe"}

{"ApplicationName":"AnotherApp","UserName":"John Doe"}

我很清楚，MyClass2Serializer 现在完全被忽略，Jackson 找到了 MyClass1Serializer 并将其用于 MyClass2。 (因为它不直接子类 JsonSerializer？)

对于这种简单的情况来说，没什么大不了的，但是我在工作中的真实类结构确实可以通过将自定义序列化器“链接”在一起而不是从头开始每个序列化器而受益。

为了以防万一，我通过类上的注释告诉 Jackson 哪个序列化器用于哪个类:

@JsonSerialize(using=MyClass1Serializer.class)
public class MyClass1 {

future 可能的问题:假设子类化自定义序列化器是可能的，子类化自定义反序列化器也可以工作吗？指向一些示例代码或教程的指针会很棒!

Answer 1

有趣的事情:我试图复制这个问题，但它似乎有效:

import java.io.*;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.annotation.*;

public class Test
{
    public static void main(String[] args) {
        MyClass1 myc1 = new MyClass1("app1", "user1");
        MyClass1 myc2 = new MyClass2("app2", "user2", "err2", "rc2");

        try {
            System.out.println(new ObjectMapper().writeValueAsString(myc1));
            System.out.println(new ObjectMapper().writeValueAsString(myc2));
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    @JsonSerialize(using = MyClass1Serializer.class)
    public static class MyClass1 {
        protected String applicationName;
        protected String userName;

        public MyClass1() {}

        public MyClass1(String applicationName, String userName) {
            this.applicationName = applicationName;
            this.userName = userName;
        }

        public String getApplicationName() { return applicationName; }
        public String getUserName()        { return userName; }
    }

    @JsonSerialize(using = MyClass2Serializer.class)
    public static class MyClass2 extends MyClass1 {
        protected String errorMessage;
        protected String resultCode;

        public MyClass2() {}

        public MyClass2(String applicationName, String userName, String errorMessage, String resultCode) {
            super(applicationName, userName);
            this.errorMessage = errorMessage;
            this.resultCode = resultCode;
        }

        public String getErrorMessage() { return errorMessage; }
        public String getResultCode()   { return resultCode; }
    }

    public static class MyClass1Serializer<T extends MyClass1> extends JsonSerializer<T> {
        @Override
        public void serialize(MyClass1 myClass1, JsonGenerator jsonGenerator, SerializerProvider serializerProvider)
                throws IOException
        {
            jsonGenerator.writeStartObject();
            jsonGenerator.writeStringField("ApplicationName", myClass1.getApplicationName());
            jsonGenerator.writeStringField("UserName", myClass1.getUserName());
            //jsonGenerator.writeEndObject();
        }
    }

    public static class MyClass2Serializer extends MyClass1Serializer<MyClass2> {
        @Override
        public void serialize(MyClass2 myClass2, JsonGenerator jsonGenerator, SerializerProvider serializerProvider)
                throws IOException
        {
            super.serialize(myClass2, jsonGenerator, serializerProvider);
            jsonGenerator.writeStringField("ErrorMessage", myClass2.getErrorMessage());
            jsonGenerator.writeStringField("ResultCode", myClass2.getResultCode());
            //jsonGenerator.writeEndObject();
        }
    }
}

输出:

{"ApplicationName":"app1","UserName":"user1"}
{"ApplicationName":"app2","UserName":"user2","ErrorMessage":"err2","ResultCode":"rc2"}