获取同一对象的不同JSON表示形式 [英] Get different JSON representations of the same object

问题描述

给出一个用Jackson序列化为JSON字符串的java对象. 是否可以控制序列化过程以从同一对象生成不同的JSON输出?

Given a java object which is serialised into a JSON string with Jackson. Is it possible to control the serialisation process to generate different JSON outputs from the same object?

压缩:

{
  "a":"123",
  "s":"100"
}

或正常:

{
  "altitude":"123",
  "speed":"100"
}

我要达到的目标是拥有一个长的JSON格式(可用于调试)(易于阅读)，并具有一个压缩的格式(可提供最小的占用空间).

The goal I want to achieve with this to have a long JSON format which is good for debugging (human-readable) and have a compressed format which is providing the smallest footprint.

推荐答案

您可以通过多种方式进行操作.这取决于您的要求.我建议您实施自己的财产命名策略.参见以下示例:

You can do it in many ways. It depends from your requirements. I suggest to implement your own property naming strategy. See below example:

class CompressedPropertyNamingStrategy extends PropertyNamingStrategyBase {

    private static final long serialVersionUID = 1L;

    @Override
    public String translate(String name) {
        return String.valueOf(name.charAt(0));
    }
}

您可以通过以下方式使用它:

You can use it in this way:

ObjectMapper mapper = new ObjectMapper();
mapper.setPropertyNamingStrategy(new CompressedPropertyNamingStrategy());
String json = mapper.writeValueAsString(new Pojo());

如果您不想压缩属性名称，只需删除第2行.

If you do not want to compress property names, just remove line number 2.

编辑1
在@aumand注释之后，我想告诉您，该解决方案不适用于包含以同一字母开头的许多属性的实体.我们必须编写很多复杂的解决方案.例如:

EDIT 1
After @aumand comment I want to inform, that this solution will not work for entities which contain many properties which starts from the same letter. We have to write much sophisticated solution. For example:

class CompressedPropertyNamingStrategy extends PropertyNamingStrategyBase {

    private static final long serialVersionUID = 1L;

    private final int length;

    public CompressedPropertyNamingStrategy(int length) {
        this.length = length;
    }

    @Override
    public String translate(String name) {
        if (name.length() < length) {
            return name;
        }

        return name.substring(0, length);
    }
}

编辑2
如果您确实希望在序列化过程中控制属性名称，则应实现自己的注释.例如:

Edit 2
If you really want to have control on property names during serialization process, you should implement your own annotation. For example:

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target(value = { ElementType.METHOD, ElementType.FIELD })
@Retention(value = RetentionPolicy.RUNTIME)
public @interface CompressedName {
    String value();
}

在这种情况下，您的命名策略可能如下所示:

Your naming strategy in this case could look like this:

class CompressedPropertyNamingStrategy extends PropertyNamingStrategy {

    private static final long serialVersionUID = 1L;

    @Override
    public String nameForGetterMethod(MapperConfig<?> config, AnnotatedMethod method,
            String defaultName) {
        CompressedName compressedProperty = method.getAnnotation(CompressedName.class);
        if (compressedProperty != null) {
            return compressedProperty.value();
        }

        // Implement default value: first letter, or something else
        return defaultName;
    }
}

现在，您必须在实体方法中添加注释:

Now, you have to add annotation to your entity methods:

class Entity {

    private long altitude = 123;
    private int speed = 100;

    @CompressedName("a")
    public long getAltitude() {
        return altitude;
    }

    public void setAltitude(long altitude) {
        this.altitude = altitude;
    }

    @CompressedName("sp")
    public int getSpeed() {
        return speed;
    }

    public void setSpeed(int speed) {
        this.speed = speed;
    }
}

在这种情况下，JSON可能如下所示:

In this scenario example JSON could look like this:

{"a":123,"sp":100}

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