Java 多线程并发编程提高数据处理效率的详细过程

public ResponseData updateHostDept() {
		// ...
		List<Map> hostMapList = monGoTemplate.find(query, Map.class, "host");
        // split the hostMapList for the following multi-threads task
        // return the number of logical CPUs
        int processorsNum = Runtime.getRuntime().availableProcessors();
        // set the threadNum as 2*(the number of logical CPUs) for handling IO Tasks,
        // if Computing Tasks set the threadNum as (the number of logical  CPUs) + 1
        int threadNum = processorsNum * 2;  
        // the number of each group data 
        int eachGroupNum = hostMapList.size() / threadNum; 
        List<List<Map>> groupList = new ArrayList<>();
        for (int i = 0; i < threadNum; i++) {
            int start = i * eachGroupNum;
            if (i == threadNum - 1) {
                int end = mapList.size();
                groupList.add(hostMapList.subList(start, end));
            } else {
                int end = (i+1) * eachGroupNum;
                groupList.add(hostMapList.subList(start, end));
            }
        }
        // update data by using multi-threads asynchronously
        ExecutorService executorService = Executors.newFixedThreadPool(threadNum/2);
        CountDownLatch countDownLatch = new CountDownLatch(threadNum);
        for (List<Map> group : groupList) {
            executorService.execute(()->{
                try {
                    for (Map map : group) {
                    	// update the data in mongoDB
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                	// let counter minus one 
                    countDownLatch.countDown();  
                }
            });
        }
        try {
        	// main thread donnot execute until all child threads finish
            countDownLatch.await();  
        } catch (Exception e) {
            e.printStackTrace();
        }
        // remember to shutdown the threadPool
        executorService.shutdown();  
        return ResponseData.success();
}

public ResponseData updateHostDept() {
		// ...
		List<Map> hostMapList = mongoTemplate.find(query, Map.class, "host");
        // split the hostMapList for the following multi-threads task
        // return the number of logical CPUs
        int processorsNum = Runtime.getRuntime().availableProcessors();
        // set the threadNum as 2*(the number of logical CPUs) for handling IO Tasks,
        // if Computing Tasks set the threadNum as (the number of logical  CPUs) + 1
        int threadNum = processorsNum * 2;  
        // the number of each group data 
        int eachGroupNum = hostMapList.size() / threadNum; 
        List<List<Map>> groupList = new ArrayList<>();
        for (int i = 0; i < threadNum; i++) {
            int start = i * eachGroupNum;
            if (i == threadNum - 1) {
                int end = mapList.size();
                groupList.add(hostMapList.subList(start, end));
            } else {
                int end = (i+1) * eachGroupNum;
                groupList.add(hostMapList.subList(start, end));
            }
        }
        // update data by using multi-threads asynchronously
        ThreadPoolExecutor executor = new ThreadPoolExecutor(5, 8, 30L, TimeUnit.SECONDS, 
                new ArrayBlockingQueue<>(100));
        CountDownLatch countDownLatch = new CountDownLatch(threadNum);
        for (List<Map> group : groupList) {
            executor.execute(()->{
                try {
                    for (Map map : group) {
                    	// update the data in mongodb
                    }
                } catch (Exception e) {
                    e.printStackTrace();
                } finally {
                	// let counter minus one 
                    countDownLatch.countDown();  
                }
            });
        }
        try {
        	// main thread donnot execute until all child threads finish
            countDownLatch.await();  
        } catch (Exception e) {
            e.printStackTrace();
        }
        // remember to shutdown the threadPool
        executor.shutdown();  
        return ResponseData.success();
}