如何配置java jackson不要在空bean上抛出NPE异常？

Question

我试图看看我怎么能说服杰克逊什么也不做,而不是在空豆上抛出异常.你可以在这里看到完整的代码.

org.codehaus.jackson.map.JsonMappingException: No serializer found for class java.lang.Exception and no properties discovered to create BeanSerializer (to avoid
exception, disable SerializationConfig.Feature.FAIL_ON_EMPTY_BEANS) )
    at org.codehaus.jackson.map.ser.impl.UnknownSerializer.failForEmpty(UnknownSerializer.java:52)
    at org.codehaus.jackson.map.ser.impl.UnknownSerializer.serialize(UnknownSerializer.java:25)
    at org.codehaus.jackson.map.ser.StdSerializerProvider._serializeValue(StdSerializerProvider.java:610)
    at org.codehaus.jackson.map.ser.StdSerializerProvider.serializeValue(StdSerializerProvider.java:256)

Answer 1

您需要关闭序列化功能FAIL_ON_EMPTY_BEANS.您可以通过在ObjectMapper上设置以下内容来实现:

import org.codehaus.jackson.map.SerializationConfig.Feature;

ObjectMapper mapper = new ObjectMapper();
mapper.disable(Feature.FAIL_ON_EMPTY_BEANS);

要在JAX-RS中配置自定义ObjectMapper设置,您需要创建一个Provider或一个ContextResolver.您可以使用其中一个.这些允许您的JAX-RS框架查找您希望使用的ObjectMapper,而不是使用默认配置.这些将在您的应用程序启动时进行扫描并在您的框架中注册.

这是一个例子Provider:

@Named
@Provider
public class MyJacksonJsonProvider extends JacksonJsonProvider
{
    @Override
    public void writeTo(Object value, Class<?> type, Type genericType, Annotation[] annotations, 
            MediaType mediaType, MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) 
            throws IOException 
    {
        ObjectMapper mapper = locateMapper(type, mediaType);

        mapper.disable(Feature.FAIL_ON_EMPTY_BEANS);

        super.writeTo(value, type, genericType, annotations, mediaType, httpHeaders, entityStream);
    }
}

以下是如何Provider使用a 执行相同操作的示例ContextResolver:

@Provider
@Produces(MediaType.APPLICATION_JSON)
public class ObjectMapperResolver implements ContextResolver<ObjectMapper> 
{
    private final ObjectMapper mapper;

    public ObjectMapperResolver() 
    {
        mapper = new ObjectMapper();
        mapper.disable(Feature.FAIL_ON_EMPTY_BEANS);
    }

    @Override
    public ObjectMapper getContext(Class<?> type) 
    {
        return mapper;
    }
}