有没有办法使用杰克逊 JSON 处理器进行自定义字段级序列化？例如，我想上课
public class Person {
public String name;
public int age;
public int favoriteNumber;
}
序列化为以下 JSON：
{ "name": "Joe", "age": 25, "favoriteNumber": "123" }
请注意，age=25 被编码为数字，而 favoriteNumber=123 被编码为字符串。开箱即用的杰克逊编组int到一个数字。在这种情况下，我希望将 favoriteNumber 编码为字符串。
您可以按如下方式实现自定义序列化程序：
public class Person {
public String name;
public int age;
@JsonSerialize(using = IntToStringSerializer.class, as=String.class)
public int favoriteNumber:
}
public class IntToStringSerializer extends JsonSerializer<Integer> {
@Override
public void serialize(Integer tmpInt,
JsonGenerator jsonGenerator,
SerializerProvider serializerProvider)
throws IOException, JsonProcessingException {
jsonGenerator.writeObject(tmpInt.toString());
}
}
Java 应该为您处理从int到的自动装箱Integer。
Jackson-databind (至少 2.1.3) 提供了特殊的ToStringSerializer( com.fasterxml.jackson.databind.ser.std.ToStringSerializer)
例子：
public class Person {
public String name;
public int age;
@JsonSerialize(using = ToStringSerializer.class)
public int favoriteNumber:
}
为该字段添加一个带@JsonProperty注释的 getter，它返回 a ：StringfavoriteNumber
public class Person {
public String name;
public int age;
private int favoriteNumber;
public Person(String name, int age, int favoriteNumber) {
this.name = name;
this.age = age;
this.favoriteNumber = favoriteNumber;
}
@JsonProperty
public String getFavoriteNumber() {
return String.valueOf(favoriteNumber);
}
public static void main(String... args) throws Exception {
Person p = new Person("Joe", 25, 123);
ObjectMapper mapper = new ObjectMapper();
System.out.println(mapper.writeValueAsString(p));
// {"name":"Joe","age":25,"favoriteNumber":"123"}
}
}
jackson-annotations 提供@JsonFormat了无需编写自定义序列化程序即可处理大量自定义的功能。
例如，STRING为数字类型的字段请求形状会将数值输出为字符串
public class Person {
public String name;
public int age;
@JsonFormat(shape = JsonFormat.Shape.STRING)
public int favoriteNumber;
}
将产生所需的输出
{"name":"Joe","age":25,"favoriteNumber":"123"}
如果你不想用注释污染你的模型并且想要执行一些自定义操作，你可以使用 mixins。
ObjectMapper mapper = new ObjectMapper();
SimpleModule simpleModule = new SimpleModule();
simpleModule.setMixInAnnotation(Person.class, PersonMixin.class);
mapper.registerModule(simpleModule);
覆盖年龄：
public abstract class PersonMixin {
@JsonSerialize(using = PersonAgeSerializer.class)
public String age;
}
随年龄做任何你想做的事：
public class PersonAgeSerializer extends JsonSerializer<Integer> {
@Override
public void serialize(Integer integer, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeString(String.valueOf(integer * 52) + " months");
}
}
在@JsonView的帮助下，我们可以决定要序列化的模型类的字段满足最低标准（我们必须定义标准），就像我们可以拥有一个具有 10 个属性的核心类，但只能序列化 5 个客户需要的属性只要
通过简单地创建以下类来定义我们的视图：
public class Views
{
static class Android{};
static class IOS{};
static class Web{};
}
带视图的注释模型类：
public class Demo
{
public Demo()
{
}
@JsonView(Views.IOS.class)
private String iosField;
@JsonView(Views.Android.class)
private String androidField;
@JsonView(Views.Web.class)
private String webField;
// getters/setters
...
..
}
现在我们必须通过简单地从 spring 扩展 HttpMessageConverter 类来编写自定义 json 转换器：
public class CustomJacksonConverter implements HttpMessageConverter<Object>
{
public CustomJacksonConverter()
{
super();
//this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView(Views.ClientView.class));
this.delegate.getObjectMapper().configure(MapperFeature.DEFAULT_VIEW_INCLUSION, true);
this.delegate.getObjectMapper().setSerializationInclusion(Include.NON_NULL);
}
// a real message converter that will respond to methods and do the actual work
private MappingJackson2HttpMessageConverter delegate = new MappingJackson2HttpMessageConverter();
@Override
public boolean canRead(Class<?> clazz, MediaType mediaType) {
return delegate.canRead(clazz, mediaType);
}
@Override
public boolean canWrite(Class<?> clazz, MediaType mediaType) {
return delegate.canWrite(clazz, mediaType);
}
@Override
public List<MediaType> getSupportedMediaTypes() {
return delegate.getSupportedMediaTypes();
}
@Override
public Object read(Class<? extends Object> clazz,
HttpInputMessage inputMessage) throws IOException,
HttpMessageNotReadableException {
return delegate.read(clazz, inputMessage);
}
@Override
public void write(Object obj, MediaType contentType, HttpOutputMessage outputMessage) throws IOException, HttpMessageNotWritableException
{
synchronized(this)
{
String userAgent = ((ServletRequestAttributes) RequestContextHolder.getRequestAttributes()).getRequest().getHeader("userAgent");
if ( userAgent != null )
{
switch (userAgent)
{
case "IOS" :
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView(Views.IOS.class));
break;
case "Android" :
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView(Views.Android.class));
break;
case "Web" :
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView( Views.Web.class));
break;
default:
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView( null ));
break;
}
}
else
{
// reset to default view
this.delegate.getObjectMapper().setConfig(this.delegate.getObjectMapper().getSerializationConfig().withView( null ));
}
delegate.write(obj, contentType, outputMessage);
}
}
}
现在需要告诉spring使用这个自定义的json转换，只需将它放在dispatcher-servlet.xml中
<mvc:annotation-driven>
<mvc:message-converters register-defaults="true">
<bean id="jsonConverter" class="com.mactores.org.CustomJacksonConverter" >
</bean>
</mvc:message-converters>
</mvc:annotation-driven>
这就是您能够决定要序列化哪些字段的方式。
您可以在 mixin 中内联创建自定义序列化程序。然后用它注释一个字段。请参阅下面的示例，该示例将“ - something else ”附加到 lang 字段。这有点骇人听闻- 如果您的序列化程序需要诸如存储库之类的东西或 spring 注入的任何东西，这将是一个问题。可能最好使用自定义反序列化器/序列化器而不是 mixin。
package com.test;
import com.fasterxml.jackson.annotation.JsonAutoDetect;
import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
import com.fasterxml.jackson.annotation.JsonProperty;
import com.fasterxml.jackson.annotation.JsonPropertyOrder;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import com.fasterxml.jackson.databind.annotation.JsonSerialize;
import com.test.Argument;
import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
//Serialize only fields explicitly mentioned by this mixin.
@JsonAutoDetect(
fieldVisibility = Visibility.NONE,
setterVisibility = Visibility.NONE,
getterVisibility = Visibility.NONE,
isGetterVisibility = Visibility.NONE,
creatorVisibility = Visibility.NONE
)
@JsonPropertyOrder({"lang", "name", "value"})
public abstract class V2ArgumentMixin {
@JsonProperty("name")
private String name;
@JsonSerialize(using = LangCustomSerializer.class, as=String.class)
@JsonProperty("lang")
private String lang;
@JsonProperty("value")
private Object value;
public static class LangCustomSerializer extends JsonSerializer<String> {
@Override
public void serialize(String value,
JsonGenerator jsonGenerator,
SerializerProvider serializerProvider)
throws IOException, JsonProcessingException {
jsonGenerator.writeObject(value.toString() + " - something else");
}
}
}