SpringBoot中Jackson返回null處理,字符串類型轉空串,數組集合轉[],對象轉{}

SpringBoot返回Json數據中null值處理，將字符串類型null值轉換爲""，將集合數組類型null值轉換爲[]，將原始數據類型null值轉換爲0，將布爾類型null值轉換爲false，將實體對象null值轉換爲{}。

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 {

    /**
     * 處理數組集合類型的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();
        }
    }

    /**
     * 處理字符串類型的null值
     */
    public static class NullStringJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator, 
        					  SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeString("");
        }
    }

    /**
     * 處理數值類型的null值
     */
    public static class NullNumberJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator, 
                              SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeNumber(0);
        }
    }

    /**
     * 處理boolean類型的null值
     */
    public static class NullBooleanJsonSerializer extends JsonSerializer<Object> {
        @Override
        public void serialize(Object value, JsonGenerator jsonGenerator, 
                              SerializerProvider serializerProvider) throws IOException {
            jsonGenerator.writeBoolean(false);
        }
    }

    /**
     * 處理實體對象類型的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主要做的事情爲：
 * 1.當序列化類型爲數組集合時，當值爲null時，序列化成[]
 * 2.String類型值序列化爲""
 *
 * </pre>
 */
public class MyBeanSerializerModifier extends BeanSerializerModifier {

    @Override
    public List<BeanPropertyWriter> changeProperties(SerializationConfig config, 
                                                     BeanDescription beanDesc,
                                                     List<BeanPropertyWriter> beanProperties) {
        // 循環所有的beanPropertyWriter
        for (int i = 0; i < beanProperties.size(); i++) {
            BeanPropertyWriter writer = beanProperties.get(i);
            // 判斷字段的類型，如果是數組或集合則註冊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;
    }

    /**
     * 是否是數組
     */
    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);
    }

    /**
     * 是否是數值類型
     */
    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();
        /** 爲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;
    }
}

本文參考:
jackson自定義序列化中null值的處理
SpringBoot Jackson 將null轉字符串"" ，List、Array轉[]，Int轉0
springboot返回前端對象null轉爲空字符串