Develop Reference

How can i check in front-end if user input is valid based on my ANTLR grammar in back-end?

I've written some logic using the ANTLR parser, in Java, in the back-end of our software (frontend in Angular 2+). I've linked some front-end inputs to this back-end logic which works fine, but it would very easy for a user to make some typo and get some server internal errors.
I'm looking for a way to check if the user's input is valid before he sends his request to the server, and potentially make suggestions based on my grammar file. I've seen many examples using ANTLR with JS / TS. But I really don't want to rewrite everything from Java -> JS and, even more important, might not want all the logic to be available in front end.
Any ideas how i could generate some useful files based on my grammar file that would, at least, just check validity ?
Thanks in advance

You could create an endpoint on your backend that validates an input then create a custom async validator in Angular to call that endpoint.
Rough idea might be...
form.component.ts
this.form = this._formBuilder.group({
input: ['', [Validators.required, AntlrValidator.checkGrammarValidity]]
});
antlr.validator.ts
export class AntlrValidator{
static checkGrammarValidity(control: AbstractControl) => {
const input = control.value;
// Your async http request to server to validate input.
this.antlrService.checkGrammarValidity(input).map(res => {
return res ? null : { validGrammar: true };
})
}
}
https://alligator.io/angular/async-validators/

Java database application Freezing when loading lots of records

I need some advice from you more experienced coders with an issue I am having.
I created a Java SE application which deals with data stored locally on a MySQL server.
It works fine where there are small number or records but when i start to pull large number of records , it sometimes freezes the app for a few seconds until it gets all the data.
I used a DAO pattern and made sure to close the connection each time I am done with it.
I used prepared statement 99% of the time
(the only times i didn't used it are not connected to the parts of the program that freeze up)
I tried to load records in small batches, that cuts down on freezing a bit but its still quite a problem for me.
I checked the log in NetBeans when the application freezes up and didn't see any errors, only the stuff like some system.out.println i put in the various loops and functions processing the data. I just see the NetBeans output log with the system.out.println text scrolling up as the app works in the back ground while the GUI is frozen.
I want to know if there is anything I can do to stop the freezing or at least reduce it ?
I had been thinking of using an API like c3p0 but I wanted to ask your opinions first.
Here is a sample of my code from the GUI part
fx_trade_model ftm = new fx_trade_model();
ArrayList all2 = ftm.loadall_B(t);
and here is the load all_B function from the fx trade model class which extends my DAO class :
public ArrayList loadall_B(int x) throws SQLException {
ArrayList g = new ArrayList();
connect = Get_Conn();
statement = connect.createStatement();
resultSet = statement.executeQuery("select * from fx_trade limit "+ x +" ");
//preparedStatement.setInt(1, x);
while (resultSet.next()) {
fx_trade t = new fx_trade();
t.id = resultSet.getInt("id");
t.BS = resultSet.getString("BS");
t.account_id = resultSet.getInt("Account_id");
t.comm = resultSet.getDouble("comm");
t.fr = resultSet.getString("fr");
t.to = resultSet.getString("to");
t.price = resultSet.getDouble("price");
t.amount = resultSet.getInt("amount");
t.settle_date = resultSet.getDate("Settle_Date");
t.trade_date = resultSet.getDate("Trade_Date");
t.note = resultSet.getString("note");
//get qty in stock
t.qty = get_qty(t.id);
g.add(t);
}
connect.close();
return g;
}

What you're seeing here is the database taking lot of time (?) to resolve your query because you're loading lot of records. This call is a synchronized call, so the application will wait until the database could generate a proper response with all the results.
What do to for these cases?
Usually, you execute this slow work in another thread, and show to the user a nice Loading message/gif/animation/etc. After the background thread finishes its work, it retrieves the data back to the main thread and continue with the current work to do.

You could eliminate the freezing by creating a new thread to load the data. If you want the user to wait for the data, you could provide a progress bar or spinner to show it is loading. Otherwise, you could let the user interact with the UI while the data loads in the background.

Google Drive script doesn't work,

I found online google drive script that sends an email with the changes on the prices of Amazon products that I insert.
This is the file
I couldn't make it work for 100%.. It work sometimes only for some of the products, and I cant find the reason.
Please help me to understand what is wrong.
Also, I wanted to know if I could modify the script so it will send me an alert twice a day and not only once, as it is now.

Configuring Email Notification Intervals
The email notifications are configured as Google Apps Scripts triggers invoking the priceEmail function. They're randomly assigned when you initialize the spreadsheet (refer to the Start_Tracking implementation).
To configure email notifications manually – e.g. adding a second daily email – open the Copy of Amazon Price Tracker by ctrlq.org script associated with the spreadsheet (via the spreadsheet Tools > Script editor... menu command). Then proceed to opening the triggers dialog (Resources > Current project's triggers menu command) and add a new time-driven trigger for the priceEmail hook.
Script Errors
By default, the priceEmail function handles all errors silently. There's not much clue to what would cause the script to not work 100% of the time. If you'd like to be notified of the errors, either remove the exception handling in the current implementation or update the priceEmail body.
I'd advice making the following modifications (again via the spreadsheet Tools > Script editor... menu command):
function priceEmail() {
var sheet, data, page, table="";
sheet = SpreadsheetApp.getActiveSheet();
data = sheet.getRange(2, 2, 21, 2).getValues(); // Note that the script will only look at the first 20 rows.
try {
for (i in data) {
if (data[i][0] !== "") {
page = UrlFetchApp.fetch(
"http://ctrlq.org/aws/lookup/", {
"method": "post", "payload": {"url":data[i][0]}
}).getContentText();
table = table + tableRow(page);
}
}
} catch (e) {
Logger.log(e.toString());
// Following line inserted to include any error messages in your daily email(s).
table += "<tr><td><strong>Error:</strong></td><td>" + e + " (url: \"" + data[i][0] + "\")</td></tr>";
}
// ...

Temporary URLs that expire after download

I'd like to create a launcher for a Java game I'm developing that will require the user to log in before the game itself can be downloaded. My idea was to have the launcher send the credentials to my webserver, and the webserver would output the location of a temporary file given the credentials were correct. However, this would be a bit tricky/inefficient, given:
The server would need to copy the game file every time someone updates, and
The webserver wouldn't know when the file was finished downloading.
Perhaps the launcher could send a request to a separate script to delete a file of the given temporary name? The problem with that is that the launcher could easily be decompiled and modified to not send the request, defeating the purpose of creating a new file.
Any suggestions as to this idea and its issues?

I would use a database, like this:
urlgenerator.php
<?php
// generate code
$code = uniqid();
// save code to database
db_save($code);
// write link
echo 'Download';
download.php
<?php
// get code from url
$single_use_code = $_GET['code'];
// check if the code is in the db
if(db_get_code($single_use_code)) {
// remove code from database as it is single use only
db_remove($single_use_code);
// start download
start_download();
} else {
// the code is not valid
die('BAD code');
}

Try something like this:
// Define a random key
$key = 'kgjiowtjiohgjiut09ig90im09yig90mi903i490ti209tgwgt';
$secondsValid = 300;
if($_GET['action'] == 'download')
{
$time = $_GET['time'];
if(time() - $time > $secondsValid)
die('Code has expired, please try again');
if($_GET['validation'] != md5($time.$key))
die('Invalid validation code');
DownloadFile();
die;
}
elseif(CredentialsAreCorrect())
{
$time = time();
header('Location: '.$_SERVER['REQUEST_URI'].'?action=download&time='.$time.'&validation='.md5($time.$key));
die;
}
else
die('Invalid credentials');
This is an easy way to give a validated user a timebombed URL (valid for 5 minutes in this case) without any nasty copying/symlinking/whatever involved, no databases, just using basic facilities that cannot be hacked as long as the key is secure. Just make sure your key has enough entropy (40+ random keypresses should do it) so no rainbow table or brute force attack is feasible.

Simple workaround: on a unix system, you can remove a file while it's in use without affecting currently-open file handles on that file. so
user requests download
script makes a symlink in the documentroot somewhere that points at wherever the file is really stored (somewhere outside of the document root)
URL to the symlink is send out as a parameter to the user.
User clicks on the donwload link, e.g. http://example.com?get=path/of/symlink
The download script fopen()'s the symlink and starts dishing out the file's contents
script REMOVES the symlink after it's been fopen()'d
Now the symlink is gone and can't be reused anymore, but the download script will still be sending data to the user because it opened the symlink/file before it was removed.

Detect mobile devices from user agent string [closed]

Closed. This question does not meet Stack Overflow guidelines. It is not currently accepting answers.
We don’t allow questions seeking recommendations for books, tools, software libraries, and more. You can edit the question so it can be answered with facts and citations.
Closed 4 years ago.
Improve this question
I am looking for a way to analyze user agent strings to determine whether they were generated by mobile devices. This needs to be java-based and usable in large batch log file analysis on hadoop for generating statistics (i.e., a web service wouldn't be appropriate).
I have seen WURFL, but given that I just need a binary mobile/not mobile response, the license fee seems prohibitive.
So far I have been using UADetector, which is almost exactly what I need. However, I have encountered some limitations with it. In my testing, I have found many user agent strings that provide enough information to determine that the user agent is from a mobile device, but are reported as UNKNOWN by UADetector.
For example, poorly-standardized Android apps can send the UA string "Android". This is enough to know that it came from a mobile device, but UADetector reports this UserAgentType as UNKNOWN rather than MOBILE_BROWSER.
Apache Mobile Filter's Lite Device Detection does the right thing, but I need something I can use from Java.
Can anyone recommend a better solution?

I'm the founder and maintainer of the MobileESP project, a free open source cross-platform library for detecting mobile devices. It's still very much alive! :-)
www.mobileesp.org
MobileESP only gives binary "is mobile" responses. You can detect by platform like iOS, Android or Windows Phone, or by device category, like "iPhone Tier" smartphones vs. tablet. Be sure to take a quick review of the API page.
As you may know, useragent strings vary widely. If the browser shipped on the device, the manufacturer may customize it. For example, HTC often customizes the native Android browser's useragent string.
Google provides recommendations on how the OEM should customize the useragent. If the device should be considered a phone, then Google recommends including the word "mobile" element in the string. But if the device should be considered a tablet, then the string should not contain "mobile." Adherence to this recommendation varies widely, of course.
Third party browsers like Opera or Maxthon can put whatever they want to in the useragent string -- and do! Certain "new" browsers which shall remain nameless have been doing very poor jobs of putting the correct information in their useragent strings for each platform (e.g., Android vs. iOS versions). There's not much you can do unless you get a lot of traffic from these browsers and wish to invest in tracking their exact useragent values per platform and software rev.
Anyway, MobileESP was created with the vision of doing the detection on a page-by-page basis when the page is served. I purposefully wrote the code to be very easy to read and customize, too.
To do the batch processing, you might do something like this:
1.) In the constructor, comment out the initDeviceScan() method. You won't need this for bulk processing.
2.) Pass the UserAgent and an empty string in to the constructor (UAgentInfo()).
3.) Then run whatever detect methods you're interested in. Be thoughtful about the order in which you do them to save time, based on a scan of your users.
For example, if most of your users are on iPhone and that's one of the detection criteria you're interested in, then run that check first. If this example, you certainly wouldn't run the BlackBerry method first!
My contact info is in the source code and on the web site. Send me a note if you have any questions or run into any bugs. Definitely look around the MobileESP.org web site for some tips.
Best wishes on your project, Aniket!
Anthony

Another thread suggests using the following library:
https://github.com/ahand/mobileesp/blob/master/Java/UAgentInfo.java
which seems OK.

How to read the Apache Mobile Filter value in JSP (for Tomcat)?
Before in the httpd.conf file where you have to configure mod_jk you muse add this:
JkEnvVar AMF_IS_MOBILE undefined
The Java code is:
request.getAttribute("AMF_IS_MOBILE")
from: http://wiki.apachemobilefilter.org

51Degrees has a free open source Java API that allows you to run offline processing. You can access it from the GitHub Repository here. https://github.com/51Degrees/Java-Device-Detection.
As part of the API there is an offline processing example (code also shown below) this takes a CSV file of User-Agents and returns the required properties into an Output file. The following example just uses 3 of the properties within the data set, for a full list you can look at the dictionary here https://51degrees.com/resources/property-dictionary
// output file in current working directory
public String outputFilePath = "batch-processing-example-results.csv";
// pattern detection matching provider
private final Provider provider;
/**
* Initialises the device detection Provider with the included Lite data
* file. For more data see:
* <a href="https://51degrees.com/compare-data-options">compare data options
* </a>
*
* #throws IOException if there was a problem reading from the data file.
*/
public OfflineProcessingExample() throws IOException {
provider = new Provider(StreamFactory.create(
Shared.getLitePatternV32(), false));
}
/**
* Reads a CSV file containing User-Agents and adds the IsMobile,
* PlatformName and PlatformVersion information for the first 20 lines.
* For a full list of properties and the files they are available in please
* see: <a href="https://51degrees.com/resources/property-dictionary">
* Property Dictionary</a>
*
* #param inputFileName the CSV file to read from.
* #param outputFilename where to save the file with extra entries.
* #throws IOException if there was a problem reading from the data file.
*/
public void processCsv(String inputFileName, String outputFilename)
throws IOException {
BufferedReader bufferedReader =
new BufferedReader(new FileReader(inputFileName));
try {
FileWriter fileWriter = new FileWriter(outputFilename);
try {
// it's more efficient over the long haul to create a match
// once and reuse it in multiple matches
Match match = provider.createMatch();
// there are 20k lines in supplied file, we'll just do a couple
// of them!
for (int i = 0; i < 20; i++) {
// read next line
String userAgentString = bufferedReader.readLine();
// ask the provider to match the UA using match we created
provider.match(userAgentString, match);
// get some property values from the match
Values isMobile = match.getValues("IsMobile");
Values platformName = match.getValues("PlatformName");
Values platformVersion = match.getValues("PlatformVersion");
// write result to file
fileWriter.append("\"")
.append(userAgentString)
.append("\", ")
.append(getValueForDisplay(isMobile))
.append(", ")
.append(getValueForDisplay(platformName))
.append(", ")
.append(getValueForDisplay(platformVersion))
.append('\n')
.flush();
}
} finally {
fileWriter.close();
}
} finally {
bufferedReader.close();
}
}
/**
* Match values may be null. A helper method to get something displayable
* #param values a Values to render
* #return a non-null String
*/
protected String getValueForDisplay(Values values) {
return values == null ? "N/A": values.toString();
}
/**
* Closes the {#link fiftyone.mobile.detection.Dataset} by releasing data
* file readers and freeing the data file from locks. This method should
* only be used when the {#code Dataset} is no longer required, i.e. when
* device detection functionality is no longer required, or the data file
* needs to be freed.
*
* #throws IOException if there was a problem accessing the data file.
*/
#Override
public void close() throws IOException {
provider.dataSet.close();
}
/**
* Instantiates this class and starts
* {#link #processCsv(java.lang.String, java.lang.String)} with default
* parameters.
*
* #param args command line arguments.
* #throws IOException if there was a problem accessing the data file.
*/
public static void main(String[] args) throws IOException {
System.out.println("Starting Offline Processing Example");
OfflineProcessingExample offlineProcessingExample =
new OfflineProcessingExample();
try {
offlineProcessingExample.processCsv(Shared.getGoodUserAgentsFile(),
offlineProcessingExample.outputFilePath);
System.out.println("Output written to " +
offlineProcessingExample.outputFilePath);
} finally {
offlineProcessingExample.close();
}
}
Hope this helps.
Disclosure: I work at 51Degrees.

To detect iPhone, Android and other mobile devices in Java user-agent can be used. If you are using Spring you can customize the below code as per your need.
#Override
public ModelAndView redirectToAppstore(HttpServletRequest request) {
String userAgent = request.getHeader("user-agent").toLowerCase();
String iphoneStoreUrl = "IPONE_STORE_URL";
String androidStoreUrl = "ANDROID_STORE_URL";
if (userAgent.contains("iphone"))
return new ModelAndView("redirect:" + iphoneStoreUrl);
else if (userAgent.contains("android"))
return new ModelAndView("redirect:" + androidStoreUrl);
return new ModelAndView("redirect:/");
}