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<font color=#999AAA >提示：本文仅供学习交流，请勿用于非法活动！<hr style=" border:solid; width:100px; height:1px;" color=#000000 size=1">

前言

<font color=#999AAA >本文大概内容：例如：随着MongoDB的广泛应用，电商用到MongoDB也越来越多。本文主要是在将购物车模块切换到MongoDB框架前，如何快速将Mysql中购物车大批量订单拷贝到MongoDB数据库中？</font>

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一、原来代码

<font color=#999AAA >如下，我们将拷贝100万条数据到MongoDB中。

public void copyCartToMongo() { List<Cart> carts = cartMapper.selectAll(); if(carts.size() >0 ){ cartMongoService.saveCartList(carts); } }

二、改进后代码

public void copyCartToMongoByThread() { // 1.我们先将批量查询及拷贝的数据分批 EntityWrapper<Cart> wrapper = SQLHelper.buildEmptyWrapper(Cart.class); long count = cartMapper.selectCount(SQLHelper.build(Cart.class).geEntityWrapper()); int preCount = 100; int operateCount = 0; int num = operateCount = (int)count / preCount; if(count % preCount == 0){ operateCount = num; }else { operateCount = num + 1; } for(int i=0;i<operateCount;i++){ logger.info("保存或更新第"+(i+1)*preCount+"条数据"); Page<Cart> page = new Page<>(i,preCount); List<Cart> cartList = cartMapper.selectPage(page, wrapper); // 2.通过多线程、线程池（其他替换即可） this.copyCartToMongoThread(cartList); } }

<font color=#999AAA >上述代码中有以下三种方式实现：</font>

1.使用new Thread方式

<font color=#999AAA >代码如下：

public void copyCartToMongoThread(List<Cart> cartList){ final CountDownLatch latch = new CountDownLatch(cartList.size()); try{ for(Cart cart:cartList){ Thread thread = new Thread(() -> { cartMongoService.saveCart(cart); latch.countDown(); }); thread.start(); } latch.await(); } catch (Exception e) { e.printStackTrace(); } }

2.使用Runnable接口

<font color=#999AAA >代码如下：

public void copyCartToMongoThread(List<Cart> cartList){ final CountDownLatch latch = new CountDownLatch(cartList.size()); try { for (Cart cart:cartList){ new Thread(new Runnable() { @Override public void run() { cartMongoService.saveCart(cart); latch.countDown(); } }).start(); } latch.await(); } catch (InterruptedException e) { e.printStackTrace(); } }

3.使用线程池

<font color=#999AAA >代码如下：

public void copyCartToMongoThreadPool(List<Cart> cartList){ final CountDownLatch latch = new CountDownLatch(cartList.size()); // 配置线程池个数 ExecutorService executorService = Executors.newFixedThreadPool(1); try{ for(Cart cart:cartList){ executorService.submit(new Runnable() { @Override public void run() { try{ cartMongoService.saveCart(cart); // 一直阻塞当前线程，直到计数器值为0，保证并发 latch.await(); } catch (Exception e) { e.printStackTrace(); } } }); latch.countDown(); } } catch (Exception e) { e.printStackTrace(); } }

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