springboot專案中jackson-序列化-處理 NULL教程
阿新 • • 發佈：2020-10-09
在專案中有事需要對值為NULL的物件中Field不做序列化輸入配置方式如下：
[配置型別]：
原始碼包中的列舉類：
public static enum Include {
ALWAYS,NON_NULL,NON_ABSENT,NON_EMPTY,NON_DEFAULT,USE_DEFAULTS;
private Include() {
}
}
Include.Include.ALWAYS 預設
Include.NON_DEFAULT 屬性為預設值不序列化
Include.NON_EMPTY 屬性為 空（“”） 或者為 NULL 都不序列化
Include.NON_NULL 屬性為NULL 不序列化
方式一：全域性配置，處理所有整個應用的實體物件
#對日期型別的轉換配置 spring.jackson.date-format=yyyy-MM-dd HH:mm:ss # 配置 引數如下 always non_absent non_default non_empty non_null use_defaults spring.jackson.default-property-inclusion=non_null
方式二：在需要序列的話的實體類上加註解 ->[配置型別]所列
@JsonInclude(Include.NON_NULL)
方式三：配置型別
3.1自定義序列化實現類，可以作用在類上 自定義json序列化需要實現StdSerializer<T>或者JsonSerializer<T>
@JsonSerialize(using = ClientObjectSerialize.class)
public class CreditBorrowerRepaymentRequestDto{
}
實現類：對欄位型別轉換，以及對值為null欄位的過濾
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自定義序列化實現類，可以作用在實體物件欄位上，對NULL值的處理，或者轉換
@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,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,SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeString(new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(createDate));
}
}
實踐總結：
一當全域性配置了NULL欄位過濾的配置，但有的實體物件需要序列化出NULL的欄位值，如何處理？
答：
1. 直接在物件上增加 @JsonInclude(JsonInclude.Include.ALWAYS) 類上的註解優先順序比較高，會覆蓋全域性的配置
2.用自定義的類序列化註解（同上）
二直接在欄位上加自定義序列化類會覆蓋全域性配置嗎？
答：不會，有預設的 public class NullSerializer extends StdSerializer<Object> 來處理，當值不為Null的時候才會執行自定義欄位上的序列化註解實現類
補充知識：SpringBoot中Jackson返回null處理,字串型別轉空串,陣列集合轉[],物件轉{}
SpringBoot返回Json資料中null值處理，將字串型別null值轉換為""，將集合陣列型別null值轉換為[]，將原始資料型別null值轉換為0，將布林型別null值轉換為false，將實體物件null值轉換為{}。
1.自定義null值序列化處理器
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
import java.io.IOException;
/**
* 自定義null值序列化處理器
*/
public class CustomizeNullJsonSerializer {
/**
* 處理陣列集合型別的null值
*/
public static class NullArrayJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value,SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeStartArray();
jsonGenerator.writeEndArray();
}
}
/**
* 處理字串型別的null值
*/
public static class NullStringJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value,SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeString("");
}
}
/**
* 處理數值型別的null值
*/
public static class NullNumberJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value,SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeNumber(0);
}
}
/**
* 處理boolean型別的null值
*/
public static class NullBooleanJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value,SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeBoolean(false);
}
}
/**
* 處理實體物件型別的null值
*/
public static class NullObjectJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value,SerializerProvider serializerProvider) throws IOException {
jsonGenerator.writeStartObject();
jsonGenerator.writeEndObject();
}
}
}
2.序列化程式修改器
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主要做的事情為：
* 1.當序列化型別為陣列集合時，當值為null時，序列化成[]
* 2.String型別值序列化為""
*
* </pre>
*/
public class MyBeanSerializerModifier extends BeanSerializerModifier {
@Override
public List<BeanPropertyWriter> changeProperties(SerializationConfig config,BeanDescription beanDesc,List<BeanPropertyWriter> beanProperties) {
// 迴圈所有的beanPropertyWriter
for (int i = 0; i < beanProperties.size(); i++) {
BeanPropertyWriter writer = beanProperties.get(i);
// 判斷欄位的型別，如果是陣列或集合則註冊nullSerializer
if (isArrayType(writer)) {
// 給writer註冊一個自己的nullSerializer
writer.assignNullSerializer(new CustomizeNullJsonSerializer.NullArrayJsonSerializer());
}
if (isStringType(writer)) {
writer.assignNullSerializer(new CustomizeNullJsonSerializer.NullStringJsonSerializer());
}
}
return beanProperties;
}
/**
* 是否是陣列
*/
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);
}
/**
* 是否是數值型別
*/
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實體
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實體
*/
@Configuration
public class JacksonConfig {
@Bean
@Primary
@ConditionalOnMissingBean(ObjectMapper.class)
public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder) {
ObjectMapper objectMapper = builder.createXmlMapper(false).build();
/** 為objectMapper註冊一個帶有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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