Java多线程导致CPU占用100%解决及线程池正确关闭方式

private AtomicLong threadNum = new AtomicLong(0);

public void init() throws Exception {
	ExecutorService executor = Executors.newFixedThreadPool(15);

	Integer total = accountMapper.selectCount(new QueryWrapper<>());
	Integer pageSize = 10000;  // 页大小
	Integer pageCount = (total + pageSize -1) / pageSize; // 总页数

	for (Integer start = 1; start <= pageCount; start++) {

		List<Account> list = accountMapper.selectPage(new Page<>(start, pageSize), query).getRecords();

		//等待线程任务完成，设置30，可令运行线程数为15，等待队列线程数为15
		while (threadNum.get() >= 30){
			Thread.sleep(5000);
		}

		//开启1个线程+1
		threadNum.incrementAndGet();
	
		executor.submit(() -> {

			try {
				// 处理业务
				dealMessage(list);
				// 任务完成 -1
				threadNum.decrementAndGet();
			} catch (Exception e) {
				e.printStackTrace();
			}

		});

	}
        executor.shutdown();
        executor.awaitTermination(1, TimeUnit.DAYS);

}

public static void main(String[] args) {
    final List<String> tableNames = new ArrayList<>();
    tableNames.add("a");
    tableNames.add("b");
    tableNames.add("c");
    tableNames.add("d");
    tableNames.add("e");
    tableNames.add("f");

    final Semaphore semaphore = new Semaphore(2);
    final ExecutorService fixedThread = Executors.newCachedThreadPool();
    for (final String tableName : tableNames) {
        //阻塞，获取令牌
        try {
            semaphore.acquire();
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        //do
        fixedThread.execute(() -> {  //can throw ex log
            final ExecutorService executorService = Executors.newCachedThreadPool();
            try {
                executorService.submit(() -> { //can't throw ex log
                    //int i = 1/0;
                    System.out.println("tableName2:" + tableName);
                });
                //int i = 1/0;
                System.out.println("tableName:" + tableName);
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                executorService.shutdown();
                try {
                    executorService.awaitTermination(1, TimeUnit.DAYS);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                semaphore.release();
                System.out.println("semaphore.release");
            }
        });
    }
    // 记得关闭线程池
    fixedThread.shutdown();
    try {
        fixedThread.awaitTermination(1, TimeUnit.DAYS);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
    System.out.println("主线程...");
}