How to solve the serialization and deserialization problems of Json in SpringBoot-javaTutorial-php.cn

Control json serialization/deserialization

1. Usage of @JsonIgnoreProperties

@JsonIgnoreProperties(value = { "prop1","prop2" })

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is used to modify the Pojo class and ignore the specified properties during serialization and deserialization. One or more attributes can be ignored.

@JsonIgnoreProperties(ignoreUnknown = true)

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is used to modify the Pojo class and ignore those attributes that cannot be set during deserialization, including those that cannot be set in the constructor and have no corresponding setter methods.

2. @JsonProperty annotation

If the name of the json field is inconsistent with the property name of the Pojo, you can use @JsonProperty to annotate the getter() or setter() method. This annotation sets the json corresponding In addition, @JsonProperty is often used to annotate the formal parameters of the constructor. At this time, the constructor should be annotated with @JsonCreator.

3. @JsonCreator annotation

If the Pojo class definition has Parameter constructor, but if no parameterless constructor is provided, an error will be reported during deserialization. There are two methods:

Method 1: Add a parameterless constructor
Method 2: Add the @JsonCreator annotation to this parameterized constructor, and the parameters need to be annotated with @JsonProperty.

4. @JsonSetter and @JsonGetter annotations

If the name of the json field is inconsistent with the property name of the Pojo, you can use @JsonGetter to annotate the getter() and @JsonSetter to annotate the setter() method. These two Each annotation can specify a property name. Both annotations can be replaced with @JsonProperty.

5. @JsonAnySetter annotation

Generally, the object property names are determined, such as the Car object , there are named attributes such as brand/price, but sometimes we also need to set some extended attributes for the Car object. The names of these extended attributes are not yet determined. Map are usually used to store the K/ of these extended attributes. V. To deserialize these attributes in the json data into the Map of the class, you need to add a K/V setter method to the class, and this setter method must be annotated with @JsonAnySetter.

public class Car {
    public String brand;
    private Map<String, String> properties;
 
    @JsonAnySetter
    public void add(String key, String value) {
        properties.put(key, value);
    }
}

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Once the class is added with @JsonAnySetter, the following json data can be deserialized into the Map:

{
"brand":"Benz",
"attr2":"val2",
"attr1":"val1"
}

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6. The @JsonAnyGetter annotation

corresponds to the @JsonAnySetter annotation. If you want to convert the class To serialize the Map K/V attributes into json, you need to add a @JsonAnyGetter method to the class. This method can directly return the KV map.

public class Car {
    public String brand;
    private Map<String, String> properties;
 
    @JsonAnyGetter
    public Map<String, String> getProperties() {
        return properties;
    }
}

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The serialized json is:

{
"brand":"Benz",
"attr2":"val2",
"attr1":"val1"
}

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7. @JsonFormat annotation

Usually clear the time format used for serialization of Date/Time properties.

public class Event {
    public String name;
 
    @JsonFormat(
      shape = JsonFormat.Shape.STRING, pattern = "dd-MM-yyyy hh:mm:ss")
    public Date eventDate;
}

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8.@JsonSerialize and @JsonDeserialize annotation

@JsonSerialize annotation You can set a special serialization function for class attributes. The @JsonDeserialize annotation is used to customize the deserialization function for json attributes

SpringBoot serialization rules

Include.Include.ALWAYS Default
Include.NON_DEFAULT The attribute is the default value and is not serialized
Include.NON_EMPTY If the attribute is empty ("") or NULL, it will not be serialized.
Include.NON_NULL If the attribute is NULL, it will not be serialized.

1. Global settings

/**
 * 〈返回json空值去掉null和""〉 〈功能详细描述〉
 * 
 * @author gogym
 * @version 2017年10月13日
 * @see JacksonConfig
 * @since
 */
@Configuration
public class JacksonConfig
{
    @Bean
    @Primary
    @ConditionalOnMissingBean(ObjectMapper.class)
    public ObjectMapper jacksonObjectMapper(Jackson2ObjectMapperBuilder builder)
    {
        ObjectMapper objectMapper = builder.createXmlMapper(false).build();
        // 通过该方法对mapper对象进行设置，所有序列化的对象都将按改规则进行系列化
        // 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，则返回的json是没有这个字段的。这样对移动端会更省流量
        // Include.NON_NULL 属性为NULL 不序列化,就是为null的字段不参加序列化
        //objectMapper.setSerializationInclusion(Include.NON_EMPTY);
        objectMapper.setSerializationInclusion(JsonInclude.Include.NON_EMPTY);
        return objectMapper;
    }
}

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spring.jackson.default-property-inclusion=non_null
spring:
  jackson:
    default-property-inclusion: non_null

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2. Local settings

on the entity class or field that needs to be set Add annotation

@JsonInclude(Include.NON_NULL)

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3. Customize local serialization

(1), customize a serialization tool class, you need to implement StdSerializer or JsonSerializer

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();
 }
}

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(2) Use annotations to act on entity classes

@JsonSerialize(using = ClientObjectSerialize.class)
public class CreditBorrowerRepaymentRequestDto{
}

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(3) Can act on entity object fields, process NULL values, or convert

@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));
 }
}

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4. Customization Global null conversion serialization

SpringBoot returns null value processing in Json data, converts string type null value to "", converts collection array type null value to [], converts original data type null value to 0, convert the Boolean type null value to false, and convert the entity object null value to {}.

(1)Custom null value serialization processor

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();
  }
 }
}

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(2)Serializer modifier

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 class="brush:php;toolbar:false">
 * 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); } }

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(3)Configure Jackson entity

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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