springboot项目中jackson-序列化-处理 NULL教程
在项目中有事需要对值为NULL的对象中Field不做序列化输入配置方式如下:
[配置类型]:
源码包中的枚举类:
public static enum Include { ALWAYS, NON_NULL, NON_ABSENT, NON_EMPTY, NON_DEFAULT, USE_DEFAULTS; private Include() { } }
Include.Include.ALWAYS 默认
Include.NON_DEFAULT 属性为默认值不序列化
Include.NON_EMPTY 属性为 空(“”) 或者为 NULL 都不序列化
Include.NON_NULL 属性为NULL 不序列化
方式一:全局配置,处理所有整个应用的实体对象
#对日期类型的转换配置 spring.jackson.date-format=yyyy-MM-dd HH:mm:ss # 配置 参数如下 always non_absent non_default non_empty non_null use_defaults spring.jackson.default-property-inclusion=non_null
方式二:在需要序列的话的实体类上加注解 ->[配置类型]所列
@JsonInclude(Include.NON_NULL)
方式三:配置类型
3.1自定义序列化实现类,可以作用在类上 自定义json序列化需要实现StdSerializer<T>或者JsonSerializer<T>
@JsonSerialize(using = ClientObjectSerialize.class) public class CreditBorrowerRepaymentRequestDto{ }
实现类:对字段类型转换,以及对值为null字段的过滤
public class ClientObjectSerialize extends JsonSerializer<CreditBorrowerRepaymentRequestDto>{ @Override public void serialize(CreditBorrowerRepaymentRequestDto dto, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException, JsonProcessingException { jsonGenerator.writeStartObject(); try { Field[] fields = dto.getClass().getDeclaredFields(); for (Field field : fields) { field.setAccessible(true); if(null == field.get(dto)){ continue; } jsonGenerator.writeFieldName(field.getName()); jsonGenerator.writeObject(field.get(dto)); } } catch (Exception e) { e.printStackTrace(); } jsonGenerator.writeEndObject(); } }
3.2自定义序列化实现类,可以作用在实体对象字段上,对NULL值的处理,或者转换
@JsonSerialize(using = ClientStringSerialize.class) private String name; @JsonSerialize(using = ClientDtaeSerialize.class) private Date date; public class ClientStringSerialize extends JsonSerializer<String> { @Override public void serialize(String string, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException { if(string == null){ jsonGenerator.writeString(string + "[NULL]"); }else{ jsonGenerator.writeString(string); } } } public class ClientDtaeSerialize extends JsonSerializer<Date> { @Override public void serialize(Date createDate, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException { jsonGenerator.writeString(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(createDate)); } }
实践总结:
一当全局配置了NULL字段过滤的配置,但有的实体对象需要序列化出NULL的字段值,如何处理?
答:
1. 直接在对象上增加 @JsonInclude(JsonInclude.Include.ALWAYS) 类上的注解优先级比较高,会覆盖全局的配置
2.用自定义的类序列化注解(同上)
二直接在字段上加自定义序列化类会覆盖全局配置吗?
答:不会,有默认的 public class NullSerializer extends StdSerializer<Object> 来处理,当值不为Null的时候才会执行自定义字段上的序列化注解实现类
补充知识:SpringBoot中Jackson返回null处理,字符串类型转空串,数组集合转[],对象转{}
SpringBoot返回Json数据中null值处理,将字符串类型null值转换为"",将集合数组类型null值转换为[],将原始数据类型null值转换为0,将布尔类型null值转换为false,将实体对象null值转换为{}。
1.自定义null值序列化处理器
import com.fasterxml.jackson.core.JsonGenerator; import com.fasterxml.jackson.databind.JsonSerializer; import com.fasterxml.jackson.databind.SerializerProvider; import java.io.IOException; /** * 自定义null值序列化处理器 */ public class CustomizeNullJsonSerializer { /** * 处理数组集合类型的null值 */ public static class NullArrayJsonSerializer extends JsonSerializer<Object> { @Override public void serialize(Object value, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException { jsonGenerator.writeStartArray(); jsonGenerator.writeEndArray(); } } /** * 处理字符串类型的null值 */ public static class NullStringJsonSerializer extends JsonSerializer<Object> { @Override public void serialize(Object value, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException { jsonGenerator.writeString(""); } } /** * 处理数值类型的null值 */ public static class NullNumberJsonSerializer extends JsonSerializer<Object> { @Override public void serialize(Object value, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException { jsonGenerator.writeNumber(0); } } /** * 处理boolean类型的null值 */ public static class NullBooleanJsonSerializer extends JsonSerializer<Object> { @Override public void serialize(Object value, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException { jsonGenerator.writeBoolean(false); } } /** * 处理实体对象类型的null值 */ public static class NullObjectJsonSerializer extends JsonSerializer<Object> { @Override public void serialize(Object value, JsonGenerator jsonGenerator, SerializerProvider serializerProvider) throws IOException { jsonGenerator.writeStartObject(); jsonGenerator.writeEndObject(); } } }
2.序列化程序修改器
import com.fasterxml.jackson.databind.BeanDescription; import com.fasterxml.jackson.databind.SerializationConfig; import com.fasterxml.jackson.databind.ser.BeanPropertyWriter; import com.fasterxml.jackson.databind.ser.BeanSerializerModifier; import java.util.Collection; import java.util.List; /** * <pre> * 此modifier主要做的事情为: * 1.当序列化类型为数组集合时,当值为null时,序列化成[] * 2.String类型值序列化为"" * * </pre> */ public class MyBeanSerializerModifier extends BeanSerializerModifier { @Override public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc, List<BeanPropertyWriter> beanProperties) { // 循环所有的beanPropertyWriter for (int i = 0; i < beanProperties.size(); i++) { BeanPropertyWriter writer = beanProperties.get(i); // 判断字段的类型,如果是数组或集合则注册nullSerializer if (isArrayType(writer)) { // 给writer注册一个自己的nullSerializer writer.assignNullSerializer(new CustomizeNullJsonSerializer.NullArrayJsonSerializer()); } if (isStringType(writer)) { writer.assignNullSerializer(new CustomizeNullJsonSerializer.NullStringJsonSerializer()); } } return beanProperties; } /** * 是否是数组 */ private boolean isArrayType(BeanPropertyWriter writer) { Class<?> clazz = writer.getType().getRawClass(); return clazz.isArray() || Collection.class.isAssignableFrom(clazz); } /** * 是否是String */ private boolean isStringType(BeanPropertyWriter writer) { Class<?> clazz = writer.getType().getRawClass(); return CharSequence.class.isAssignableFrom(clazz) || Character.class.isAssignableFrom(clazz); } /** * 是否是数值类型 */ private boolean isNumberType(BeanPropertyWriter writer) { Class<?> clazz = writer.getType().getRawClass(); return Number.class.isAssignableFrom(clazz); } /** * 是否是boolean */ private boolean isBooleanType(BeanPropertyWriter writer) { Class<?> clazz = writer.getType().getRawClass(); return clazz.equals(Boolean.class); } }
3.配置Jackson实体
import com.fasterxml.jackson.databind.ObjectMapper; import com.fasterxml.jackson.databind.SerializerProvider; import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.Primary; import org.springframework.http.converter.json.Jackson2ObjectMapperBuilder; /** * 配置Jackson实体 */ @Configuration public class JacksonConfig { @Bean @Primary @ConditionalOnMissingBean(ObjectMapper.class) public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) { ObjectMapper objectMapper = builder.createXmlMapper(false).build(); /** 为objectMapper注册一个带有SerializerModifier的Factory */ objectMapper.setSerializerFactory(objectMapper.getSerializerFactory() .withSerializerModifier(new MyBeanSerializerModifier())); SerializerProvider serializerProvider = objectMapper.getSerializerProvider(); serializerProvider.setNullValueSerializer(new CustomizeNullJsonSerializer .NullObjectJsonSerializer()); return objectMapper; } }
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