Java 扩展jackson自定义序列化程序

考虑到MyClass2扩展了MyClass1并向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());
    }       
}

---

未来可能出现的问题：假设自定义序列化器的子类化是可能的，那么自定义反序列化器的子类化也可以工作吗？一个指向一些示例代码或教程的指针就太棒了

有趣的是：我试图复制这个问题，但似乎奏效了：

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();
        }
    }
}

---

我试图复制这个问题，但我从jackson那里得到了运行时异常：“类MyClassSerializer没有默认（无参数）构造函数”。顺便问一下，您是否在主类中为序列化程序使用非静态的内部类？这就是我开始的地方，我也犯了这个错误。您可以使它们成为静态类，也可以将它们移到主类之外（我就是这么做的）。我忘了把内部类做得很奇怪！我复制/窃取了你的代码，一行接一行，是的，它是有效的。不知道第一次我发生了什么。哦，好吧。。。

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());
    }       
}

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());
    }       
}

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

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();
        }
    }
}

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