【对线面试官】 Java 泛型

一时失言乱红尘 2021-09-04 07:50 372阅读 0赞

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public interface JpaRepository<T, ID> extends PagingAndSortingRepository<T, ID>, QueryByExampleExecutor<T> { 
    
    	List<T> findAll();
    
    	List<T> findAll(Sort sort);
    
    	List<T> findAllById(Iterable<ID> ids);
    
    	<S extends T> List<S> saveAll(Iterable<S> entities);
    
    	void flush();
    
    	<S extends T> S saveAndFlush(S entity);
    
    	void deleteInBatch(Iterable<T> entities);
    
    	void deleteAllInBatch();
    
    	T getOne(ID id);
    
    	@Override
    	<S extends T> List<S> findAll(Example<S> example);
    
    	@Override
    	<S extends T> List<S> findAll(Example<S> example, Sort sort);
    }

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// 传入 需要group by 和 sum 的字段名
    public cacheMap(List<String> groupByKeys, List<String> sumValues) { 
      this.groupByKeys = groupByKeys;
      this.sumValues = sumValues;
    }
    
    private void excute(T e) { 
      
      // 从pojo 取出需要group by 的字段 list
      List<Object> key = buildPrimaryKey(e);
      
      // primaryMap 是存储结果的Map
      T value = primaryMap.get(key);
      
      // 如果从存储结果找到有相应记录
      if (value != null) { 
        for (String elem : sumValues) { 
          // 反射获取对应的字段，做累加处理
          Field field = getDeclaredField(elem, e);
          if (field.get(e) instanceof Integer) { 
            field.set(value, (Integer) field.get(e) + (Integer) field.get(value));
          } else if (field.get(e) instanceof Long) { 
            field.set(value, (Long) field.get(e) + (Long) field.get(value));
          } else { 
            throw new RuntimeException("类型异常,请处理异常");
          }
        }
        
        // 处理时间记录
        Field field = getDeclaredField("updated", value);
        if (null != field) { 
          field.set(value, DateTimeUtils.getCurrentTime());
        }
      } else { 
        // group by 字段 第一次进来
        try { 
          primaryMap.put(key, Tclone(e));
          createdMap.put(key, DateTimeUtils.getCurrentTime());
        }catch (Exception ex) { 
          log.info("first put value error {}" , e);
        }
      }
    }

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