一、背景：

后台系统配置越来越多的出现需要进行日志记录的功能，且当前已有日志记录不可复用，需要统一日志记录格式，提高日志记录开发效率。

二、预期效果展示：

新建动作：

修改动作：

删除动作：

三、数据存储：

注：可以选择其他存储方式，这里只简单举个例子

`biz_id` bigint(20) NOT NULL DEFAULT 0 COMMENT '业务id',
`biz_type` tinyint(4) NOT NULL DEFAULT 0 COMMENT '业务类型',
`operator_id` varchar(128) NOT NULL DEFAULT '' COMMENT '操作人',
`operate_content` text COMMENT '操作内容',
`change_before` text COMMENT '修改前',
`change_after` text COMMENT '修改后',
`create_time` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP COMMENT '创建时间'

四、原理简述：

日志构建关注两个对象，一个是修改前，修改后：

      修改前：null + 修改后：X = 新建

修改前：Y + 修改后：X = 更新

修改前：Y + 修改后：null = 删除

修改内容判断依据传入的两个对象，对两个对象的每个属性进行逐一对比，如果发生变化则是需要进行日志记录字段；关注的属性使用注解进行标注。

五、具体实现：

注解：

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface LogField {

    String name() default "";

    String valueFun() default "";

    boolean spliceValue() default true;
}

name: name值表示该字段如果被修改，应在日志中记录的字段名；默认取字段名

valueFun: 表示获取改变字段内容的获取方法；默认取字段值，若valueFun方法不存在，则取默认值

spliceValue: 日志是否需要拼接变更内容，默认拼接

注解处理：

@Service
@Slf4j
public class OperateLogService {
    @Resource
    private CommonOperateLogService commonOperateLogService;

    enum ActionEnum{
        ADD("新建"),
        UPDATE("修改"),
        DELETE("删除");

        ActionEnum(String desc) {
            this.desc = desc;
        }
        public String desc;
    }

    private int insertLog(CommonOperatorLog commonOperatorLog){
        String result = commonOperateLogService.insertLog(JSON.toJSONString(commonOperatorLog));
        Response response = JSON.parseObject(result, Response.class);
        return Objects.isNull(response) || ApiResponse.Status.fail.equals(response.getStatus()) ? 0 : (int) response.getContent();
    }

    public PageOutput<CommonOperatorLog> queryList(Long bizId, Integer bizType, Integer pageNum, Integer pageSize){
        String result = commonOperateLogService.queryLog(bizId, bizType, pageNum, pageSize);
        PageOutput pageOutput = JSON.parseObject(result, new TypeReference<PageOutput<CommonOperatorLog>>() {});
        return pageOutput;
    }

    public <T> void saveLog(String operatorId,Long bizId, Integer bizType, T target, T original){
        if(StringUtils.isBlank(operatorId) || (Objects.isNull(target) && Objects.isNull(original))){
            throw new IllegalArgumentException();
        }
        if(Objects.nonNull(target) && Objects.nonNull(original) && !target.getClass().isAssignableFrom(original.getClass())){
            throw new IllegalArgumentException();
        }
        ActionEnum action = getAction(target, original);
        List<Triple<String, String, LogField>> changeInfos = getChangeInfoList(target, original);
        List<String> changeInfoList = new ArrayList<>();
        if(CollectionUtils.isEmpty(changeInfos) && !ActionEnum.UPDATE.equals(action)){
            changeInfoList.add(0, action.desc);
        }else if (CollectionUtils.isEmpty(changeInfos)){
            return;
        }else {
            changeInfoList = changeInfos.stream().map(i -> i.getRight().spliceValue() ?
                            action.desc + StringUtils.joinWith("为:", i.getLeft(), i.getMiddle()) :
                            action.desc + StringUtils.join("了", i.getLeft()))
                    .collect(Collectors.toList());
        }

        String operateContext = StringUtils.join(changeInfoList, "\n");
        operateContext = operateContext.replaceAll("\"","")
                .replaceAll("\\[","").replaceAll("\\]","");
        CommonOperatorLog operatorLog = new CommonOperatorLog();
        operatorLog.setBizId(bizId);
        operatorLog.setBizType(bizType);
        operatorLog.setOperateContent(operateContext);
        operatorLog.setOperatorId(operatorId);
        operatorLog.setChangeBefore(JSON.toJSONString(original));
        operatorLog.setChangeAfter(JSON.toJSONString(target));
        this.insertLog(operatorLog);
    }

    private ActionEnum getAction(Object target, Object original){
        ActionEnum action = ActionEnum.ADD;
        if(Objects.nonNull(target) && Objects.nonNull(original)){
            action = ActionEnum.UPDATE;
        }else if(Objects.nonNull(target)){
            action = ActionEnum.ADD;
        }else if (Objects.nonNull(original)){
            action = ActionEnum.DELETE;
        }
        return action;
    }


    private<T> List<Triple<String, String, LogField>> getChangeInfoList(T target, T original){
        if(Objects.isNull(target) || Objects.isNull(original)){
            return new ArrayList<>();
        }        
        List<Pair<Field, Object>> targetFields = allFields(target);
        List<Pair<Field, Object>> originalFields = allFields(original);
        if(targetFields.size() != originalFields.size()){
            //理论上不可能执行到这
            throw new IllegalArgumentException();
        }

        List<Triple<String, String, LogField>> result = new ArrayList<>();
        for (int i = 0; i < targetFields.size(); i++) {
            Pair<Field, Object> targetField = targetFields.get(i);
            Pair<Field, Object> originalField = originalFields.get(i);
            ReflectionUtils.makeAccessible(targetField.getKey());
            ReflectionUtils.makeAccessible(originalField.getKey());
            Object targetValue = ReflectionUtils.getField(targetField.getKey(), targetField.getValue());
            Object originalValue = ReflectionUtils.getField(originalField.getKey(), originalField.getValue());
               if(targetValue != originalValue && (Objects.isNull(targetValue) ||
                        (!targetValue.equals(originalValue) &&
                        compareTo(Pair.of(targetField.getKey(), targetValue), Pair.of(originalField.getKey(), originalValue)) &&
                        !JSON.toJSONString(targetValue).equals(JSON.toJSONString(originalValue))))){
                result.add(Triple.of(getFieldName(targetField.getKey()), getFieldValue(targetField.getKey(), targetField.getValue()), targetField.getKey().getAnnotation(LogField.class)));
            }
        }
        return result;
    }

    private boolean compareTo(Pair<Field, Object> targetField, Pair<Field, Object> originalField){
        Field field = targetField.getKey();
        Object targetValue = targetField.getValue();
        Object originalValue = originalField.getValue();
        boolean canCompare = Arrays.stream(field.getType().getInterfaces()).anyMatch(i -> Comparable.class.getName().equals(i.getName()));
        if(canCompare && Objects.nonNull(targetValue) && Objects.nonNull(originalValue)){
            Method compareTo = ReflectionUtils.findMethod(field.getType(), "compareTo", field.getType());
            if(Objects.isNull(compareTo)){
                return true;
            }
            Object compared = ReflectionUtils.invokeMethod(compareTo, targetValue, originalValue);
            return (int)compared != 0 ;
        }
        return true;
    }

    private <T> List<Pair<Field, Object>> allFields(T obj){
        List<Triple<Field, Object, Boolean>> targetField = findField(obj);
        List<Triple<Field, Object, Boolean>> allField = Lists.newArrayList(targetField);
        List<Triple<Field, Object, Boolean>> needRemove = new ArrayList<>();
        for (int i = 0; i < allField.size(); i++) {
            Triple<Field, Object, Boolean> fieldObjectDes = allField.get(i);
            if(!fieldObjectDes.getRight()){
                ReflectionUtils.makeAccessible(fieldObjectDes.getLeft());
                Object fieldV = ReflectionUtils.getField(fieldObjectDes.getLeft(), fieldObjectDes.getMiddle());
                List<Triple<Field, Object, Boolean>> fieldList = findField(fieldV);
                if(CollectionUtils.isNotEmpty(fieldList)){
                    allField.addAll(fieldList);
                    needRemove.add(fieldObjectDes);
                }
            }
        }

        if(CollectionUtils.isNotEmpty(needRemove)){
            allField.removeAll(needRemove);
        }
        return allField.stream().map(i->Pair.of(i.getLeft(), i.getMiddle())).collect(Collectors.toList());
    }

    private <T> List<Triple<Field, Object, Boolean>> findField(T obj){
        Class<?> objClass = obj.getClass();
        Field[] declaredFields = objClass.getDeclaredFields();
        List<Field> allFields = Lists.newArrayList(declaredFields);
        if(Objects.nonNull(objClass.getSuperclass())){
            Field[] superClassFields = objClass.getSuperclass().getDeclaredFields();
            allFields.addAll(Arrays.asList(superClassFields));
        }
        List<Triple<Field, Object, Boolean>> result = new ArrayList<>();
        for (Field declaredField : allFields) {
            LogField annotation = declaredField.getAnnotation(LogField.class);
            if(Objects.nonNull(annotation)){
                result.add(Triple.of(declaredField, obj, declaredField.getType().getPackage().getName().startsWith("java")));
            }
        }
        return result;
    }


    private String getFieldName(Field field){
        LogField annotation = field.getAnnotation(LogField.class);
        String name = annotation.name();
        if(StringUtils.isBlank(name)){
            name = field.getName();
        }
        return name;
    }

    private <T> String getFieldValue(Field field, T targetObj){
        LogField annotation = field.getAnnotation(LogField.class);
        if(!annotation.spliceValue()){
            return "";
        }
        String valueFun = annotation.valueFun();
        if(StringUtils.isBlank(valueFun)){
            Object fieldValue = ReflectionUtils.getField(field, targetObj);
            return getStrValue(fieldValue);
        }else {
            Method valueMethod = ReflectionUtils.findMethod(targetObj.getClass(), valueFun);
            if(Objects.isNull(valueMethod)){
                Object fieldValue = ReflectionUtils.getField(field, targetObj);
                return getStrValue(fieldValue);
            }else {
                ReflectionUtils.makeAccessible(valueMethod);
                Object invokeMethodRes = ReflectionUtils.invokeMethod(valueMethod, targetObj);
                return getStrValue(invokeMethodRes);
            }
        }
    }

    private String getStrValue(Object fieldValue){
        List<String> emptyStr = ImmutableList.of("\"\"", "{}","[]");
        String value = Objects.isNull(fieldValue) ? "无" : JSON.toJSONString(fieldValue);
        return emptyStr.contains(value) ? "无" : value;
    }
}

六、使用示例：

1、使用的日志记录对象（这个对象只为日志服务）

public class SubsidyRateLog {

    @LogField(name = "补贴率名称")
    private String name;

    @LogField(name = "适用城市", valueFun = "getCityNames")
    private List<Integer> cityIds;

    private List<String> cityNames;
}

name是直接展示字段，所以修改值即name本身的值；cityIds 是我们关心比较字段，当它值不一样时进行 字段value 值获取，这个值是展示在前端的，所以可以根据需要进行格式定义，默认是将取到的值进行toJSON；当前例子中获取的是getCityNames方法返回的值；

2、无专用日志对象（大多数时候我们有自己的实体对象，但不包含具体日志描述字段），需要进行继承

public class SubsidyRate {

    @LogField(name = "补贴率名称")
    private String name;

    @LogField(name = "适用城市", valueFun = "getCityNames")
    private List<Integer> cityIds;
}

@Data
public class SubsidyRateLog extends SubsidyRate{
    
    private List<String> cityNames;
}

此方式适用于兼容现有对象，而不去破坏现有对象的完整性

3、对象包含子对象（比较复杂的大对象，如Task中的券信息）

public class SubsidyRateLog {

    @LogField(name = "补贴率名称")
    private String name;

    @LogField
    private Address address;
}

public class Address {
    @LogField(name = "省份")
    private String province;
    @LogField(name = "城市")
    private String city;
}

此情况下会将所有信息平铺，如果 Address 中 没有LogField 注解，那么会直接使用将获取address值，如果存在注解，那么将忽略address本身，只关注注解字段。