spring-boot处理jackson的null值

说明

接口返回的json对象内的字段可能包含null值，前端可能还需要再对null做处理，判断、显示等

方案

除对象外，字段不会再返回null值

全局对返回null的处理

后端可使用注解@JacksonAllowNull允许字段返回null

类型	默认返回值	默认处理
String	""	无
Boolean	false	无
Integer,Float,Double,BigDecimal	0	无
Long	0	无
Array,List,Set	[]	无
Date	null	FORMAT('yyyy-MM-dd HH:mm:ss'), timeZone(GMT+8)

内容

JacksonAllowNull

/**
 
 
 
  
 
  
不处理null的数据
 
  
 
  
 
 
  
@author miaoyj
 
  
@version 1.0.0-SNAPSHOT
 
  
@since 2020-07-09
 */
 @Retention(RetentionPolicy.RUNTIME)
 @Target(ElementType.FIELD)
 public @interface JacksonAllowNull {
 }

JacksonHttpMessageConverter

@Component
 public class JacksonHttpMessageConverter extends MappingJackson2HttpMessageConverter {
 
 
/**
 
 
 
  
 
  
构造函数
 
  
 
  
 
 
  
@author miaoyj
 
  
@since 2020-09-09
 */
 public JacksonHttpMessageConverter() {
 ObjectMapper objectMapper = getObjectMapper();
 // 日期格式化
 objectMapper.setDateFormat(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss"));
 // 时区设置
 objectMapper.setTimeZone(TimeZone.getTimeZone("GMT+8"));
 objectMapper.setSerializerFactory(objectMapper.getSerializerFactory()
 .withSerializerModifier(new MyBeanSerializerModifier()));
 
 
 
 
//解决 /instances/%5Bobject%20Object%5D/actuator/metrics
 //https://github.com/codecentric/spring-boot-admin/issues/1517
 objectMapper.addMixIn(InstanceId.class, InstanceIdMixin.class);
 String[] pwdConstructor = new String[]{".*password$"};
 objectMapper.registerModule(new AdminServerModule(pwdConstructor));
 //解决domain.values.Registration cannot deserialize from Object
 SimpleModule simpleModule = new SimpleModule();
 simpleModule.addSerializer(Registration.class, ToStringSerializer.instance);
 simpleModule.addDeserializer(Registration.class, new RegistrationDeserializer());
 objectMapper.registerModule(simpleModule);
 }
 
 
/**
 
 
 
  
{@inheritDoc}
 
  
 
 
  
 
  
类型只支持application/json
 
  
 
  
 
 
  
@author miaoyj
 
  
@since 2020-09-09
 */
 @Override
 public List getSupportedMediaTypes() {
 return CollUtil.newArrayList(MediaType.APPLICATION_JSON, MediaType.TEXT_PLAIN);
 }
 
 
 
 
/**
 
 
 
  
{@inheritDoc}
 
  
 
 
  
 
  
JSON输出只处理Wrapper的包装类
 
  
 
  
 
  
不注释会导致springBootAdmin显示失败
 
  
 
  
 
 
  
@author miaoyj
 
  
@since 2020-09-09
 */
 // @Override
 // public boolean canWrite(Class clazz, MediaType mediaType) {
 // return ResultWrapper.class.isAssignableFrom(clazz);
 // }
 
 
 
 
private class MyBeanSerializerModifier extends BeanSerializerModifier {
 @Override
 public List changeProperties(SerializationConfig config, BeanDescription beanDesc, List beanProperties) {
 for (Object beanProperty : beanProperties) {
 BeanPropertyWriter writer = (BeanPropertyWriter) beanProperty;
 /过滤允许为null的注解/
 if (ObjectUtil.isNull(writer.getAnnotation(JacksonAllowNull.class))) {
 if (isArrayType(writer)) {
 writer.assignNullSerializer(new NullArrayJsonSerializer());
 } else if (isNumberType(writer)) {
 writer.assignNullSerializer(new NullNumberJsonSerializer());
 } else if (isBooleanType(writer)) {
 writer.assignNullSerializer(new NullBooleanJsonSerializer());
 } else if (isStringType(writer)) {
 writer.assignNullSerializer(new NullStringJsonSerializer());
 }
 }
 /* 防止Long精度丢失 */
 // if(isLongType(writer)){
 // writer.assignSerializer(new ToStringSerializer());
 // }
 }
 return beanProperties;
 }
 
 
private boolean isArrayType(BeanPropertyWriter writer) {
 Class clazz = writer.getType().getRawClass();
 return clazz.isArray() || Collection.class.isAssignableFrom(clazz);
 }
 
 
private boolean isStringType(BeanPropertyWriter writer) {
 Class clazz = writer.getType().getRawClass();
 return CharSequence.class.isAssignableFrom(clazz) || Character.class.isAssignableFrom(clazz);
 }
 
 
private boolean isNumberType(BeanPropertyWriter writer) {
 Class clazz = writer.getType().getRawClass();
 return Number.class.isAssignableFrom(clazz);
 }
 
 
private boolean isLongType(BeanPropertyWriter writer) {
 Class clazz = writer.getType().getRawClass();
 return Long.class.isAssignableFrom(clazz);
 }
 
 
private boolean isBooleanType(BeanPropertyWriter writer) {
 Class clazz = writer.getType().getRawClass();
 return clazz.equals(Boolean.class);
 }
 }
 
 
private class NullArrayJsonSerializer extends JsonSerializer