java - 让 Jackson 在任何地方都使用自定义反序列化器(对于不是我的类型)

Question

我正在尝试设置 Jackson JSON 自定义反序列化器以将 JSON 值转换为 Long 对象。我按照本网站上的说明进行操作:http://wiki.fasterxml.com/JacksonHowToCustomDeserializers设置自定义解串器。

但是，要启动自定义反序列化器，我必须每次都进行注释例如

public class TestBean {
    Long value;

    @JsonDeserialize(using=LongJsonDeserializer.class)
    public void setValue(Long value) {
       this.value = value;
     }
 }

有没有办法告诉 Jackson 始终使用自定义反序列化器反序列化所有 Long 属性，而不必使用 @JsonDeserialize(using=LongJsonDeserializer.class) 注释每次？

Answer 1

LongJsonDeserializer deserializer = new LongJsonDeserializer();

SimpleModule module =
  new SimpleModule("LongDeserializerModule",
      new Version(1, 0, 0, null, null, null));
module.addDeserializer(Long.class, deserializer);

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(module);

---

这是一个完整的演示应用程序。这适用于 Jackson 的最新版本，也可能适用于回溯到 1.7 的 Jackson 版本。

import java.io.IOException;

import org.codehaus.jackson.JsonParser;
import org.codehaus.jackson.JsonProcessingException;
import org.codehaus.jackson.Version;
import org.codehaus.jackson.map.DeserializationContext;
import org.codehaus.jackson.map.JsonDeserializer;
import org.codehaus.jackson.map.ObjectMapper;
import org.codehaus.jackson.map.module.SimpleModule;

public class Foo
{
  public static void main(String[] args) throws Exception
  {
    TestBean bean = new TestBean();
    bean.value = 42L;

    ObjectMapper mapper = new ObjectMapper();

    String beanJson = mapper.writeValueAsString(bean);
    System.out.println(beanJson);
    // output: {"value":42}

    TestBean beanCopy1 = mapper.readValue(beanJson, TestBean.class);
    System.out.println(beanCopy1.value);
    // output: 42

    SimpleModule module =
      new SimpleModule("LongDeserializerModule",
          new Version(1, 0, 0, null));
    module.addDeserializer(Long.class, new LongJsonDeserializer());

    mapper = new ObjectMapper();
    mapper.registerModule(module);

    TestBean beanCopy2 = mapper.readValue(beanJson, TestBean.class);
    System.out.println(beanCopy2.value);
    // output: 126
  }
}

class TestBean
{
  Long value;
  public Long getValue() {return value;}
  public void setValue(Long value) {this.value = value;}
}

class LongJsonDeserializer extends JsonDeserializer<Long>
{
  @Override
  public Long deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException
  {
    Long value = jp.getLongValue();
    return value * 3;
  }
}