1. 需求：對資料庫id統一生成

2. 實現方案：通過mybatis攔截器，攔截sql，對要插入的資料重置id

3. 上程式碼：

/**
 * @author yangxj
 * @date 2020-08-10 15:57
 * <p>
 * 自定義id生成器
 */
@Component
@Intercepts(@Signature(type = Executor.class, method = "update", args = {MappedStatement.class, Object.class}))
public class IDGeneratorPlugin implements
 
 Interceptor {
    // 實體主鍵欄位
    private final static String ID_FIELD = "id";

    @Override
    @SuppressWarnings("unchecked")
    public Object intercept(Invocation invocation) throws Throwable {
        MappedStatement mappedStatement = (MappedStatement) invocation.getArgs()[0];
        Object param 
 
= invocation.getArgs()[1];
        SqlCommandType sqlCommandType = mappedStatement.getSqlCommandType();
        
        // 非插入型別跳過
        if (!sqlCommandType.equals(SqlCommandType.INSERT)) { 
           return invocation.proceed();
        }
        // 引數型別 map or entity
        // 注: mybatis在處理多引數，以及引數型別為集合時，會將引數轉map型別處理
 

        if (param instanceof Map) {
            Map paramMap = (Map)param;
            // 是否為批量插入操作
            Optional batchParam = paramMap.values().stream().filter(paramValues -> paramValues instanceof List).findFirst();
            if (batchParam.isPresent()) {
                for (Object o : (List) batchParam.get()) {
                    restId(o); // 設定id
                }
            } else {
                paramMap.put(ID_FIELD, IdUtil.fastSimpleUUID()); // 設定id
            }
        } else {
            restId(param);
        }
        return invocation.proceed();
    }

    private void restId(Object param) {
        try {
            Field id = param.getClass().getDeclaredField(ID_FIELD);
            id.setAccessible(true);
            //TODO  id生成邏輯自實現
            if (Objects.isNull(id.get(param))) {
                id.set(param, IdUtil.fastSimpleUUID());
            }
        } catch (Exception e) {
        }
    }

    @Override
    public Object plugin(Object target) {
        return target instanceof Executor ? (Plugin.wrap(target, this)) : target;
    }

    @Override
    public void setProperties(Properties properties) {

    }
}

4. over