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Spring boot app and what approach to use to download bulk data

I have spring boot application with basic REST API.
My question is what shall we use to download some bulk data? What is preferable way how to download bulk data without memory leak? Let's suppose we have 10 million records.
Here are some approaches but not sure:
download with PipedInputStream when data are written with PipedOutputStream in separated thread. Is it fine or it is not good choice?
download with ByteArrayOutputStream when data are written into temp file in separated thread and after finish it is ready to download. We can mark this operation with some flags for end user eg. DOWNLOAD_ACTIVE, DOWNLOAD_DONE. The user is just initiating download with result flag DOWNLOAD_ACTIVE and trying to ping server for response flag DOWNLOAD_DONE. When it is done then the user is going to send request to download data.
Summary 2)
1. initiate request to download data - ACTIVE state
2. ping server and server returns current state - ACTIVE or DONE
3. if final state is DONE then user initiate final request to download data
Thanks

You can use the second approach. Which can prepare data in the background and once it's ready you can download it.
Send a request to prepare data. The server responds with a UUID.
Server starts preparing files in the background. The server has a Map that has the key with a new UUID and value as status ACTIVE.
Client saved UUID and checks the server after a certain interval by passing the UUID.
Once the server finishes the task it will update the Map for the given UUID value as status DONE.
As the status is DONE next request will provide the status DONE and UI and send another request to download the file.
The above approach will only work if you don't refresh the page. As page refresh will clear the UUID and you have to proceed again.
To achieve this after refresh/cross-logins then you need to use a database table instead of Map. Store the username along with other information and inform the user once it's ready.

Google Drive setup push notifications

We want to receive notifications from google when we do anychange(Add,Edit OR Delete) on google drive folder for these purpose we have integrated google watch api in our spring boot application.
code snippet :
public Channel setUpWatch() throws IOException, GeneralSecurityException {
Channel channel = new Channel();
channel.setAddress("https://somedomain.com/notifications");
channel.setType("web_hook");
channel.setId(UUID.randomUUID().toString());
channel.setKind("api#channel");
StartPageToken pageToken =
driveServiceProvider.getDriveService().changes().getStartPageToken().execute();
System.out.println(pageToken.getStartPageToken());
Channel changesChannel = driveServiceProvider.getDriveService().changes()
.watch(pageToken.getStartPageToken(), channel).execute();
System.out.println(changesChannel.getExpiration());return
return changesChannel;
}
After running this code we are getting 200 in response, but we are not receiving any push notification from google when we do any operation in google drive. We are getting empty changeList
We are checking this code on local with no domain registration
Is there any other way to get the edit, add or deleted files list from google drive?
We do not want any notification on any domain or address. Whenever we trigger the api and if any file(s) is changed, we want that file(s) details like drive url, file name.

It seems that you are passing the current token to the changeList api.
This will return no results.
Actually, the solution is to find the changes since last token till the current token using a loop. So, store the last token somewhere and iterate till last token to current and pass the iterative value to chageList api to get the files changed.
Hope that works.

Push-notification channel will not send you requests for files inside a folder inside of a folder, just because you set up a watch on the folder itself.
To request push notifications, you need to set up a notification channel for each resource you want to watch.
If you preform a watch on a folder you will get a notification if for example the name of the folder is changed.
If you want to know if there are changes to a file then you will need to set up the watch for each of the files.

How to create Ajax request that gets information as the servlet runs?

I have a form that creates an account and a servlet that handles the request.
However, the process to create this account is a long process and I want to create something like a status bar or a progress bar. Heres the POST:
$.post("createAccount.jsp", function(data) { $("#status").text(data);
});
And the servlet would continuously print data like "creating x..." then "creating y" as the servlet runs. Is there a way to accomplish this or maybe another way to tackle this issue?
Thanks

Http works on a request-response model. You send a request, and server responds back. After that Server doesn't know who are you?!
It's like Server is a post-office that doesn't know your address. You
go to it and get your letters.It doesn't come to your home for
delivering letters.
If you want constant notifications from server, You can either use Web Sockets(Stack Overflow also uses Web Sockets) or use `AJAX Polling' mechanisms,
which sends an AJAX request to the server and waits for server to
respond. On retrieval of response,it generates another AJAX request
and keep on doing the same until server stops generating new data.
Read this for an explanation of AJAX Polling techniques

You could have your account creation servlet update a database or context attribute as it creates the account.
You could have a separate AJAX request to a different servlet that sends back to the webpage the most recent development found in the database or context attribute. You would then poll your server with that AJAX request every so many fractions of a second(or relevant time interval depending on how long of a task it is to create an account) to get all the updates.

To get database updates using servlets or jsp

What I want is to get database updates.
i.e If any changes occur to the database or a new record is inserted it should notify to the user.
Up to know what I implemented is using jQuery as shown below
$(document).ready(function() {
var updateInterval = setInterval(function() {
$('#chat').load('Db.jsp?elect=<%=emesg%>');
},1000);
});
It worked fine for me, but my teacher told to me that it's not a good way to do recommended using comet or long polling technology.
Can anyone give me examples for getting database updates using comet or long polling
in servlets/jsp? I'm using Tomcat as server.

Just taking a shot in the dark since I don't know your exact environment... You could have the database trigger fire a call to a servlet each time a row is committed which would then run some code that looked like the following:
Get the script sessions that are active for the page that we want to update. This eliminates the need to check every reverse ajax script session that is running on the site. Once we have the script sessions we can use the second code block to take some data and update a table on the client side. All that the second code section does is send javascript to the client to be executed via the reverse ajax connection that is open.
String page = ServerContextFactory.get().getContextPath() + "/reverseajax/clock.html";
Browser.withPage(page, new Runnable() {
public void run() {
Util.setValue("clockDisplay", output);
}
});
// Creates a new Person bean.
Person person = new Person(true);
// Creates a multi-dimensional array, containing a row and the rows column data.
String[][] data = {
{person.getId(), person.getName(), person.getAddress(), person.getAge()+"", person.isSuperhero()+""}
};
// Call DWR's util which adds rows into a table. peopleTable is the id of the tbody and
// data conta
ins the row/column data.
Util.addRows("peopleTable", data);
Note that both of the above sections of code are pulled straight from the documentation examples # http://directwebremoting.org/dwr-demo/. These are only simple examples of how reverse ajax can sent data to the client, but your exact situation seems to be more dependent on how you receive the notification than how you update the client screen.
Without some type of database notification to the java code I think you will have to poll the system at set intervals. You could make the system a little more efficient even when polling by verifying that there are reverse ajax script sessions active for the page before polling the database for info.

Accessing data to display as search results in Android app

I am developing an Android app which takes the current location of the user and displays a list of restaurants close to his/her location. The restaurants' data is available to me (i.e I do have the lat/long of each restaurant I want to display in the search results). I can't use Google Places API, because I need to show only those restaurants that are available in our database(in our website). My question is how do I access my database(or even an URL),which is on a computer, to extract the restaurants' data and display as search results in my android app?
I am actually making a Seamless ( http://bit.ly/Jp7pUN ) type application for my company.
I am a complete newbie to android app development. So, pardon me if this is really a very broad or a stupid question. Please just tell me what topics I need to study to implement this. I would study and do it myself.
Thanks.

You will need:
a Sqlite database to store the restaurants and their longitude/latitude
a MapView to display the map (Don't forget to register your Google Maps API key)
a map overlay to show the markers on the map
GPS access to get the user's location (needs the appropriate Android permission)
a simple search algorithm that retrieves a result set of restaurants within x distance of the user's location
EDIT
If your database is stored on a server, you will need a way to query the server, preferably using an HTTP-based protocol such as REST. It is useful (but not required) to cache the restaurant locations on the Android device (using Sqlite), in case the user is offline (The good news: Since you can use Java both on Android and the server, 90% of your data access layer you will only need to write once).
For the data transfer from server to the Android client, JSON is a popular format.

To acces database on your computer (not SQLite on Android) you should use url for your database server changing localhost to: 10.0.2.2. But in case your database will be on the Internet - you should create maybe some REST API to get the data you need. Then use HttpClient to fetch the data from server.
Everything that you need is in Developer Guide: MapView
And for retrieving current location I advice using MyLocationOverlay
For example (url to server):
//public static final String SERVER_ADDRESS = "http://10.0.2.2:3000"; // for localhost server
public static final String SERVER_ADDRESS = "http://railsserver.herokuapp.com"; //for remote server
Accessing data on your server - this depends on that how you implement (and using what thechnology) your server (REST API?, WebService?, Plain HTML?) and what will be the format of the response from server (JSON? XML?, etc.)
I suggest using JSON because it is easy to parse using included classes in Android SDK:
String json = execute(new HttpGet(Constants.SERVER_URL + "/fetchData"));
JSONObject responseJSON = new JSONObject(json);
if(responseJSON.has("auth_error")) {
throw new IOException("fetchData_error");
}