fasterxml使用toString进行序列化，使用String构造函数进行反序列化

Question

我有一个POJO，看起来像这样:

public class Thing
{
   private final int x;
   private final int y;
   private final int z;
   public Thing(String strThing)
   {
       // parse strThing which is in some arbitrary format to set x, y and z
   }
   @Override
   public String toString()
   {
       // return a string representation of thing
       // (same format as that parsed by the constructor)
   }
   @Override
   public boolean equals(Object obj) ...
   @Override
   public int hashCode() ...
}

，我想使用它作为一个映射(例如HashMap<Thing, SomeOtherPOJO>)的键，当序列化到json时，使用toString()表示的Thing作为键，当反序列化时，使用String构造函数。是否可以使用jackson数据绑定注释之类的简单方法?解决这个问题的最好方法是什么?

Answer 1

通过实验(我认为文档可以更清楚一点)，我发现我可以在String构造器上使用JsonCreator注释，在toString()方法上使用JsonValue来实现我想要的:

public class Thing
{
   private final int x;
   private final int y;
   private final int z;
   @JsonCreator
   public Thing(String strThing)
   {
       // parse strThing which is in some arbitrary format to set x, y and z
   }
   @Override
   @JsonValue
   public String toString()
   {
       // return a string representation of thing
       // (same format as that parsed by the constructor)
   }
   @Override
   public boolean equals(Object obj) ...
   @Override
   public int hashCode() ...
}

Answer 2

你可以创建一个新的类来扩展JsonSerializer并覆盖它的serialize方法。将您应该在toString()方法中编写的实现写入JsonGenerator的writeString()方法中，如图所示。你必须在你的项目中使用jackson-core-asl.jar和jackson-mapper-asl.jar。下面是JsonThingSerializer.java类

import java.io.IOException;
import org.codehaus.jackson.JsonGenerator;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.map.JsonSerializer;
import org.codehaus.jackson.map.SerializerProvider;

public class JsonThingSerializer extends JsonSerializer<Thing>{ //note use of generics
@Override
public void serialize(Thing myThing, JsonGenerator gen,
        SerializerProvider provider) throws IOException,
        JsonProcessingException {
    gen.writeString("I want this way.. which I was thinking to implement inside toString() method "+" "+myThing.getX()+" "+myThing.getY()+" "+myThing.getZ());
}
}

在你的Thing.java中使用下面的注释

import org.codehaus.jackson.annotate.JsonAutoDetect;
import org.codehaus.jackson.map.annotate.JsonSerialize;
@JsonAutoDetect
@JsonSerialize(using=JsonThingSerializer.class)
public class Thing
{
   private final int x;
   private final int y;
   private final int z;
   public Thing(String strThing)
   {
       // parse strThing which is in some arbitrary format to set x, y and z
       //insert your own implementation to get x, y and z
       x=y=z=10;
   }
   @Override
   public String toString()
   {
       //no need to override this for json serialization.. mapper will not use it
   }
   @Override
   public boolean equals(Object obj){
     //you can have your own implementation
   }
   @Override
   public int hashCode() {
     //you can have your own implementation
    }
public int getX() {
    return x;
}
public int getY() {
    return y;
}
public int getZ() {
    return z;
}
}

你可以使用下面的代码来测试你的代码。

import java.io.IOException;
import org.codehaus.jackson.JsonGenerationException;
import org.codehaus.jackson.map.JsonMappingException;
import org.codehaus.jackson.map.ObjectMapper;
public class TestJsonSerialization {
    public static void main(String[] args) {
        Thing thing =new Thing("your strThing which is in some arbitrary format to set x, y and z");
        ObjectMapper mapper =new ObjectMapper();
        try {
            String thingString = mapper.writeValueAsString(thing);
            System.out.println(thingString);
        } catch (JsonGenerationException e) {
            e.printStackTrace();
        } catch (JsonMappingException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Blow为输出:

"我想这样……"我想在toString()方法中实现10 10 10"