如何将jackson json null字符串序列化为空字符串 [英] How to serialize in jackson json null string to empty string

问题描述

我需要jackson json（1.8）将java NULL字符串序列化为空字符串。你怎么做呢？
非常感谢任何帮助或建议。

I need jackson json (1.8) to serialize a java NULL string to an empty string. How do you do it? Any help or suggestion is greatly appreciated.

谢谢

推荐答案

请参阅自定义序列化程序的文档;有一个这样的例子，适合我。

See the docs on Custom Serializers; there's an example of exactly this, works for me.

如果文档移动，请让我粘贴相关答案：

In case the docs move let me paste the relevant answer:

将空值转换为其他值

（如空字符串）

如果你想要输出一些其他JSON值而不是null（主要是
，因为其他一些处理工具更喜欢其他常量值 -
经常是空字符串），事情有点棘手，因为名义类型可能是
任何东西;虽然您可以为 Object.class 注册序列化程序，但除非没有更多特定的序列化程序可供使用，否则不会使用
。

If you want to output some other JSON value instead of null (mainly because some other processing tools prefer other constant values -- often empty String), things are bit trickier as nominal type may be anything; and while you could register serializer for Object.class, it would not be used unless there wasn't more specific serializer to use.

但是有一个特定的null serializer概念，您可以使用
如下：

But there is specific concept of "null serializer" that you can use as follows:

// Configuration of ObjectMapper:
{
    // First: need a custom serializer provider
   StdSerializerProvider sp = new StdSerializerProvider();
   sp.setNullValueSerializer(new NullSerializer());
   // And then configure mapper to use it
   ObjectMapper m = new ObjectMapper();
   m.setSerializerProvider(sp);
}

// serialization as done using regular ObjectMapper.writeValue()

// and NullSerializer can be something as simple as:
public class NullSerializer extends JsonSerializer<Object>
{
   public void serialize(Object value, JsonGenerator jgen,
SerializerProvider provider)
       throws IOException, JsonProcessingException
   {
       // any JSON value you want...
       jgen.writeString("");
   }
}

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