jackson提供了一些注解来定义序列化的规则，但是针对array、list、set没有相对应的注解，所以需要我们自己来实现
1.实体上
@JsonInclude(Include.NON_NULL)
将该标记放在属性上，如果该属性为NULL则不参与序列化
如果放在类上边,那对这个类的全部属性起作用
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
2.代码上
ObjectMapper mapper = new ObjectMapper();
mapper.setSerializationInclusion(Include.NON_NULL);
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
Include.NON_NULL 属性为NULL 不序列化
注意：只对VO起作用，Map List不起作用
package com.yunli.riverchief.map.model;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.databind.*;
import com.fasterxml.jackson.databind.ser.BeanPropertyWriter;
import com.fasterxml.jackson.databind.ser.BeanSerializerModifier;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Primary;
import java.io.IOException;
import java.math.BigDecimal;
import java.time.LocalDate;
import java.time.LocalDateTime;
import java.util.Date;
import java.util.List;
import java.util.Set;
/**
* @Author ：feiyang
* @Date ：Created in 8:54 PM 2019/6/24
*/
@Configuration
public class JacksonConfig {
@Bean
@Primary
public ObjectMapper jacksonObjectMapper() {
ObjectMapper objectMapper = new ObjectMapper();
// 为mapper注册一个带有SerializerModifier的Factory
objectMapper.setSerializerFactory(objectMapper.getSerializerFactory().withSerializerModifier(new YlBeanSerializerModifier()));
objectMapper.configure(SerializationFeature.WRITE_DATES_AS_TIMESTAMPS, false);
objectMapper.configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false);
objectMapper.configure(SerializationFeature.FAIL_ON_EMPTY_BEANS, false);
objectMapper.configure(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT, true);
/*
long类型前端精度丢失问题（超过53位二进制数），
建议在需要转换的字段上加注解 @JsonFormat(shape = JsonFormat.Shape.STRING)
不做整体数值转换，防止无需转换的long类型也转为string
*/
return objectMapper;
}
/**
* Description: 此modifier主要做的事情为：
* 当序列化类型为array，list、set时，当值为空时，序列化成[]
* 为date,localdate,localdatetime 时，当值为空时，序列化成0
* 为数值类型时，当值为空时，序列化成0
* 为字符类型时，当值为空时，序列化成“”
* @author feiyang
* @date 2019/6/24
*/
public class YlBeanSerializerModifier extends BeanSerializerModifier {
private JsonSerializer<Object> arrayJsonSerializer = new ArrayJsonSerializer();
private JsonSerializer<Object> strJsonSerializer = new StrJsonSerializer();
private JsonSerializer<Object> dateJsonSerializer = new DateJsonSerializer();
private JsonSerializer<Object> numberJsonSerializer = new NumJsonSerializer();
@Override
public List<BeanPropertyWriter> changeProperties(SerializationConfig config, BeanDescription beanDesc,
List<BeanPropertyWriter> beanProperties) {
// 循环所有的beanPropertyWriter
for (BeanPropertyWriter writer : beanProperties) {
// 判断字段的类型，如果是array，list，set则注册nullSerializer
if (isArrayType(writer)) {
//给writer注册一个自己的nullSerializer
writer.assignNullSerializer(arrayJsonSerializer);
} else if (isDate(writer)) {
writer.assignNullSerializer(dateJsonSerializer);
} else if (isNumber(writer)) {
writer.assignNullSerializer(numberJsonSerializer);
} else if (isStr(writer)) {
writer.assignNullSerializer(strJsonSerializer);
}
}
return beanProperties;
}
/**
* 判断数组类型
* @param writer
* @return
*/
boolean isArrayType(BeanPropertyWriter writer) {
Class<?> clazz = writer.getType().getRawClass();
return clazz.isArray() || clazz.equals(List.class) || clazz.equals(Set.class);
}
/**
* 判断日期类型
* @param writer
* @return
*/
boolean isDate(BeanPropertyWriter writer) {
Class<?> clazz = writer.getType().getRawClass();
return clazz.equals(Date.class) || clazz.equals(LocalDateTime.class) || clazz.equals(LocalDate.class);
}
/**
* 判断数字类型
* @param writer
* @return
*/
boolean isNumber(BeanPropertyWriter writer) {
Class<?> clazz = writer.getType().getRawClass();
return clazz.equals(Short.class) || clazz.equals(Integer.class)
|| clazz.equals(Long.class) || clazz.equals(BigDecimal.class)
|| clazz.equals(Double.class) || clazz.equals(Float.class);
}
/**
* 判断字符类型
* @param writer
* @return
*/
boolean isStr(BeanPropertyWriter writer) {
Class<?> clazz = writer.getType().getRawClass();
return clazz.equals(String.class) || clazz.equals(Character.class)
|| clazz.equals(StringBuilder.class) || clazz.equals(StringBuffer.class);
}
}
/**
* 数组以及集合序列化实现类
*/
public class ArrayJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
if (value == null) {
jgen.writeStartArray();
jgen.writeEndArray();
} else {
jgen.writeObject(value);
}
}
}
/**
* 日期序列化实现类
*/
public class DateJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
if (value == null) {
jgen.writeNumber(0);
} else {
jgen.writeObject(value);
}
}
}
/**
* 字符串序列化实现类
*/
public class StrJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
if (value == null) {
jgen.writeString("");
} else {
jgen.writeObject(value);
}
}
}
/**
* 数字序列化实现类
*/
public class NumJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider) throws IOException {
if (value == null) {
jgen.writeNumber(0);
} else {
jgen.writeObject(value);
}
}
}
}