Spring JPA的实体属性类型转换器并反序列化工具类详解

{"key": "颜色", "value": "深白色", "key_id": 1, "value_id": 3}

private Map<String,Object> test;

import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonMappingException;
import com.fasterxml.jackson.databind.ObjectMapper;
import com.lin.missyou.exception.http.ServerErrorException;
import org.springframework.beans.factory.annotation.Autowired;
import javax.persistence.AttributeConverter;
import javax.persistence.Convert;
import javax.persistence.Converter;
import java.util.HashMap;
import java.util.Map;
// 第一个泛型类型就是  entity字段的类型 
// json没有类型，对应在JAVA中就是String类型
// 第二个泛型类型就是  数据库字段的类型
@Converter
public class MapAndJson implements AttributeConverter<Map<String, Object>, String> {
    /*
    ObjectMapper类是Jackson库的主要类，它提供一些功能将数据集或对象转换的实现。
    它将使用JsonParser和JsonGenerator实例来实现JSON的实际读/写。
    */
    @Autowired
    private ObjectMapper mapper;
    @Override
    public String convertToDatabaseColumn(Map<String, Object> map) {
        try {
            return mapper.writeValueAsString(map);
        } catch (Exception e) {
            e.printStackTrace();
            throw new ServerErrorException(99999);
        }
    }
    @Override
    @SuppressWarnings("unchecked")
    public Map<String, Object> convertToEntityAttribute(String s) {
        try {
        	if (s == null) return null;
            return mapper.readValue(s, HashMap.class);
        } catch (Exception e) {
            e.printStackTrace();
            throw new ServerErrorException(9999);
        }
    }
}

@Convert(converter = MapAndJson.class)
private Map<String,Object> test;

[{"key": "颜色", "value": "深白色", "key_id": 1, "value_id": 3}, {"key": "尺寸", "value": "4.3英寸", "key_id": 2, "value_id": 7}]

@Getter
@Setter
public class Spec {
    private Long keyId;
    private String key;
    private Long valueId;
    private String value;
}

//反序列化工具类
@Component
public class GenericAndJson {
    private static ObjectMapper mapper;
//将ObjectMapper注入到方法里，再通过方法赋值到成员变量上
    @Autowired
    public void setMapper(ObjectMapper mapper) {
        GenericAndJson.mapper = mapper;
    }
    public static <T> String objectToJson(T o) {
        try {
            return GenericAndJson.mapper.writeValueAsString(o);
        } catch (Exception e) {
            e.printStackTrace();
            throw new ServerErrorException(99999);
        }
    }
    public static <T> T jsonToObject(String s, TypeReference<T> typeReference) {
        if (s == null) return null;
        try {
            return GenericAndJson.mapper.readValue(s, typeReference);
        } catch (Exception e) {
            e.printStackTrace();
            throw new ServerErrorException(9999);
        }
    }
}

private String specs;
public List<Spec> getSpecs() {
    if (specs == null) return Collections.emptyList();
    return GenericAndJson.jsonToObject(this.specs, new TypeReference<List<Spec>>() {});
}
public void setSpecs(List<Spec> specs) {
    if (specs.isEmpty()) return;
    this.specs = GenericAndJson.objectToJson(specs);
}