自定義傑克遜對象映射器

Question

我有一個用例，我需要維護兩組JSON輸出，一個帶有JSON屬性的漂亮名稱，另一個沒有。所以我決定自定義我的ObjectMapper，以便它忽略字段上的@JsonProperty（「漂亮名稱」）註釋並使用字段屬性名稱。在這種情況下，需要以下JSON輸出

{"result":{"data":[{"totalUsers":12345,"totalBooks":883}]}} 

漂亮的名字想喜歡的JSON輸出如下

{"result":{"data":[{"Total Users":12345,"Total Books":883}]}} 

我ObjectMapper配置代碼看起來像

ObjectMapper mapper = new ObjectMapper(); 
mapper.setSerializationInclusion(Include.NON_EMPTY); 
mapper.setSerializationInclusion(Include.NON_NULL); 
mapper.configure(MapperFeature.USE_WRAPPER_NAME_AS_PROPERTY_NAME, true); 
mapper.configure(SerializationFeature.WRAP_ROOT_VALUE, true); 
mapper.configure(MapperFeature.USE_ANNOTATIONS, false); 
mapper.setVisibility(PropertyAccessor.FIELD, Visibility.NONE) 
     .setVisibility(PropertyAccessor.GETTER, Visibility.ANY); 

我已經看過還有一些其他的答案對我來說不起作用。我得到一個NPE。請看下面的堆棧跟蹤

java.lang.NullPointerException 
at com.fasterxml.jackson.databind.introspect.POJOPropertiesCollector._renameWithWrappers(POJOPropertiesCollector.java:728) 
at com.fasterxml.jackson.databind.introspect.POJOPropertiesCollector.collect(POJOPropertiesCollector.java:264) 
at com.fasterxml.jackson.databind.introspect.BasicClassIntrospector.collectProperties(BasicClassIntrospector.java:142) 
at com.fasterxml.jackson.databind.introspect.BasicClassIntrospector.forSerialization(BasicClassIntrospector.java:68) 
at com.fasterxml.jackson.databind.introspect.BasicClassIntrospector.forSerialization(BasicClassIntrospector.java:11) 
at com.fasterxml.jackson.databind.SerializationConfig.introspect(SerializationConfig.java:490) 
at com.fasterxml.jackson.databind.ser.BeanSerializerFactory.createSerializer(BeanSerializerFactory.java:131) 
at com.fasterxml.jackson.databind.ser.SerializerFactory.createSerializer(SerializerFactory.java:53) 
at com.fasterxml.jackson.databind.SerializerProvider._createUntypedSerializer(SerializerProvider.java:935) 
at com.fasterxml.jackson.databind.SerializerProvider._createAndCacheUntypedSerializer(SerializerProvider.java:892) 
at com.fasterxml.jackson.databind.SerializerProvider.findValueSerializer(SerializerProvider.java:429) 
at com.fasterxml.jackson.databind.SerializerProvider.findTypedValueSerializer(SerializerProvider.java:520) 
at com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.serializeValue(DefaultSerializerProvider.java:99) 
at com.fasterxml.jackson.databind.ObjectWriter.writeValue(ObjectWriter.java:457) 
at com.fasterxml.jackson.jaxrs.json.JacksonJsonProvider.writeTo(JacksonJsonProvider.java:583) 
at org.apache.cxf.jaxrs.utils.JAXRSUtils.writeMessageBody(JAXRSUtils.java:1173) 
at org.apache.cxf.jaxrs.interceptor.JAXRSOutInterceptor.serializeMessage(JAXRSOutInterceptor.java:259) 
at org.apache.cxf.jaxrs.interceptor.JAXRSOutInterceptor.processResponse(JAXRSOutInterceptor.java:155) 
at org.apache.cxf.jaxrs.interceptor.JAXRSOutInterceptor.handleMessage(JAXRSOutInterceptor.java:86) 
at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:271) 
at org.apache.cxf.interceptor.OutgoingChainInterceptor.handleMessage(OutgoingChainInterceptor.java:77) 
at org.apache.cxf.phase.PhaseInterceptorChain.doIntercept(PhaseInterceptorChain.java:271) 
at org.apache.cxf.transport.ChainInitiationObserver.onMessage(ChainInitiationObserver.java:121) 
at org.apache.cxf.transport.http.AbstractHTTPDestination.invoke(AbstractHTTPDestination.java:238) 
at org.apache.cxf.transport.servlet.ServletController.invokeDestination(ServletController.java:222) 
at org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:163) 
at org.apache.cxf.transport.servlet.ServletController.invoke(ServletController.java:137) 
at org.apache.cxf.transport.servlet.CXFNonSpringServlet.invoke(CXFNonSpringServlet.java:158) 
at org.apache.cxf.transport.servlet.AbstractHTTPServlet.handleRequest(AbstractHTTPServlet.java:239) 
at org.apache.cxf.transport.servlet.AbstractHTTPServlet.doGet(AbstractHTTPServlet.java:164) 

的問題是在這行代碼在

com.fasterxml.jackson.databind.introspect.POJOPropertiesCollector._renameWithWrappers(POJOPropertiesCollector.java:728) 

其中_annotationIntrospector爲空

PropertyName wrapperName = _annotationIntrospector.findWrapperName(member); 

不太疼我應該怎麼做才能acheieve我目標。有什麼建議？謝謝。

Answer 1

小例子，以示對你的使用情況與混入的解決方案：

class Data { 
    int totalUsers; 
    int totalBooks; 
} 

...

class DataMixin { 
    @JsonProperty("Total Users") 
    int totalUsers; 
    @JsonProperty("Total Books") 
    int totalBooks; 
} 

...

傑克遜2.0 - 2.4（在2.5棄用）

ObjectMapper mapper = new ObjectMapper(); 
if (pretty) { 
    mapper.addMixInAnnotations(Data.class, DataMixin.class); 
} 

傑克遜2.5+

ObjectMapper mapper = new ObjectMapper(); 
if (pretty) { 
    mapper.addMixin(Data.class, DataMixin.class); 
}