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项目中有段代码逻辑是个双重for循环，发现数据量大的时候，直接导致数据接口响应超时，这里记录下不断优化的过程，算是抛砖引玉吧~
Talk is cheap,show me your code！

1、数据准备

Order

@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class Order {private Integer orderId;private String orderName;
}

OrderDetail

@Data
@AllArgsConstructor
@NoArgsConstructor
@Builder
public class OrderDetail {private Integer orderDetailId;private Integer orderId;private String orderNums;private String orderAddress;
}

造测试数据

public static List<Order> getOrderTestList() {List<Order> orders = new ArrayList<>();for (int i = 1; i <= 50000; i++) {Order order = new Order();order.setOrderName(UUID.randomUUID().toString());order.setOrderId(i);orders.add(order);}return orders;}public static List<OrderDetail> getOrderDetailTestList() {List<OrderDetail> orderDetails = new ArrayList<>();for (int i = 30000; i >= 1; i--) {OrderDetail orderDetail = new OrderDetail();orderDetail.setOrderAddress(UUID.randomUUID().toString());orderDetail.setOrderId(i);orderDetail.setOrderDetailId(i);orderDetails.add(orderDetail);}return orderDetails;}

2、原始双重for循环

@Testvoid test3() {List<Order> orderTestList = getOrderTestList();List<OrderDetail> orderDetailTestList = getOrderDetailTestList();StopWatch stopWatch = new StopWatch();stopWatch.start();// 直接使用双重for循环查询条件for (Order order : orderTestList) {int orderId = order.getOrderId();for (OrderDetail orderDetail : orderDetailTestList) {if(orderId == orderDetail.getOrderId() ){System.out.println("模拟数据orderAddress 业务处理......" + orderDetail.getOrderAddress());}}}stopWatch.stop();System.out.println("最终耗时" + stopWatch.getTotalTimeMillis());}

执行结果

3、直接使用双重for循环查询条件，增加break条件

	@Testvoid test3() {List<Order> orderTestList = getOrderTestList();List<OrderDetail> orderDetailTestList = getOrderDetailTestList();StopWatch stopWatch = new StopWatch();stopWatch.start();// 直接使用双重for循环查询条件，增加break条件for (Order order : orderTestList) {int orderId = order.getOrderId();for (OrderDetail orderDetail : orderDetailTestList) {if(orderId == orderDetail.getOrderId() ){System.out.println("模拟数据orderAddress 业务处理......" + orderDetail.getOrderAddress());break;}}}stopWatch.stop();System.out.println("最终耗时" + stopWatch.getTotalTimeMillis());}

执行结果

4、使用迭代器来删除内层循环中已使用或判断过的元素，减少循环次数

	@Testvoid test3() {List<Order> orderTestList = getOrderTestList();List<OrderDetail> orderDetailTestList = getOrderDetailTestList();StopWatch stopWatch = new StopWatch();stopWatch.start();// 使用迭代器来删除内层循环中已使用或判断过的元素，减少循环次数for (Order order : orderTestList) {ListIterator<OrderDetail> orderDetailListIterator = orderDetailTestList.listIterator();int orderId = order.getOrderId();while (orderDetailListIterator.hasNext()) {OrderDetail nextOrderDetail = orderDetailListIterator.next();if(orderId == nextOrderDetail.getOrderId() ){System.out.println("模拟数据orderAddress 业务处理......" + nextOrderDetail.getOrderAddress());orderDetailListIterator.remove();}}}stopWatch.stop();System.out.println("最终耗时" + stopWatch.getTotalTimeMillis());}

执行结果

5、把要筛选的信息写成map集合，遍历List时用map.get(key)来实现检索

	@Testvoid test3() {List<Order> orderTestList = getOrderTestList();List<OrderDetail> orderDetailTestList = getOrderDetailTestList();StopWatch stopWatch = new StopWatch();stopWatch.start();//使用stream() 记得一定要判空Map<Integer, String> orderAddressMap =orderDetailTestList.stream().collect(Collectors.toMap(OrderDetail::getOrderId, OrderDetail::getOrderAddress));for (Order order : orderTestList) {int orderId = order.getOrderId();String orderAddress = orderAddressMap.get(orderId);if (StringUtils.hasLength(orderAddress)) {System.out.println("模拟数据orderAddress 业务处理......" + orderAddress);}}if (StringUtils.hasLength(orderAddress)) {System.out.println("模拟数据orderAddress 业务处理......" + orderAddress);}stopWatch.stop();System.out.println("最终耗时" + stopWatch.getTotalTimeMillis());}

测试结果

6、总结

可以看出，通过迭代删除或者利用map集合特性均能够有效提升查询效率。