springboot项目中jackson

springboot项目中jackson

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或者JsonSerializer

@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{

@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 {

@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 {

@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

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

@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

@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

@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

@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

@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;

/**

*

* 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""

*

*

*/

public class MyBeanSerializerModifier extends BeanSerializerModifier {

@Override

public List changeProperties(SerializationConfig config,

BeanDescription beanDesc,

List 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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