Multi-threaded query results, add List collection

Problem description

The List collection created by the new ArrayList<>() method, adding data to the collection in the case of multi-threading, the data will be missing, because the List created in this way is not thread-safe.

Solution

Process the List collection in the following ways:

Collections.synchronizedList(new ArrayListspan><>());

After calling the add() method, it is actually thread-safe, because the synchronized keyword is added, as follows:

But the iterator() method is not added, as follows:

So be careful when using it.