Programming for Dynamic String Patterns

[Steve Dyke]

In my java web app I have a part number validator class.
The purpose is to insure that a particular video monitor is assembled to the correct aircraft seat.
A bar code reader is used for the following steps.
Process is the seat assembly serial number is scanned, creating an indented bill list.
Then the part number on the monitor is scanned. The app looks for the part number in the indented bill.
If it exists the user is prompted to scan the serial number of the monitor.
This will cause a validation label to be printed out which is attached to seat assembly.

All was well when the monitors presented 1D barcodes, one for the part number and one for the serial number.
Then the monitors started having a QR code. I adjusted my app to break the code down using identifiers. Example QR Code: PNR RD-FD2802-01/SER J248628/CAG SZ437
However, the latest monitors have a QR code that has no identifiers. Example QR code: 00-5120-02-F,134009,090618,3FGZ1

Is there some way to use a pattern solution so I do not have to do hard code changes to try and manage this.  

[Nicolas Beney]

Hi Steve,

Your description is pretty succint so I am not sure I understand you problem fully but did you already consider having a list of regexps with named capture groups coming from your configuration?

Based on the example you gave this could be something like this:

PNR (?<PART>[^/]+)/SER (?<SERIAL>[^/]+)/CAG [^/]+
(?<PART>[^,]+),(?<SERIAL>[^,]+),[^,]+,[^,]+

Your program would try them sequenatially until it finds one that matches.

Hope this helps.

[Stephan van Hulst]

You could write a plugin mechanism that allows you just drop JARs on the classpath and it will recognize new kinds of codes.

First write a model and a service provider interface (SPI):

package aircraft.seat.monitor;

public final class MonitorCode {

  private final String partNumber;

  private final String serialNumber;

  ...

}

package aircraft.seat.monitor.scanning;

import java.awt.*;
import java.util.*;

import aircraft.seat.monitor.*

public interface MonitorCodeScanner {

  Optional<MonitorCode> tryScanMonitorCode(Image image);

}

package aircraft.seat.monitor.scanning.spi;

import java.util.function.*;

import aircraft.seat.monitor.scanning.*;

public interface MonitorCodeScannerProvider {

  MonitorCodeScanner provideScanner(MonitorCodeScanOption... scanOptions);

}

Now, in a separate library, you implement your SPI:

package aircraft.seat.monitor.scanning.qr;

import aircraft.seat.monitor.scanning.*;
import aircraft.seat.monitor.scanning.spi.*;

public final class QrMonitorCodeWithIdScannerProvider implements MonitorCodeScannerProvider {

  @Override
  public MonitorCodeScanner provideScanner(MonitorCodeScanOption... scanOptions) {
    return new QrMonitorCodeWithIdScanner(scanOptions);
  }
}

If you're on Java 9+, add a module-info.java to the root package of your plugin:

import aircraft.seat.monitor.scanning.spi.*;
import aircraft.seat.monitor.scanning.qr.*;

module aircraft.seat.monitor.scanning.qr {

  requires java.desktop;

  requires aircraft.seat.monitor;

  provides MonitorCodeScannerProvider with QrMonitorCodeWithIdScannerProvider;

}

If you're on Java 8-, add a META-INF/services/aircraft.seat.monitor.scanning.spi.MonitorCodeScannerProvider file (without extension) to the root package of your plugin:
aircraft.seat.monitor.scanning.qr.QrMonitorCodeWithIdScannerProvider
Now, as long as the plugin JAR is on the module path of your main application (or on the class path if you're on Java 8-) you can load it like this:

package aircraft.seat.monitor.scanning;

import java.awt.*;
import java.util.*;

import aircraft.seat.monitor.*;
import aircraft.seat.monitor.scanning.spi.*;

import static java.util.stream.Collectors.toList;

final class MonitorCodeScannerGroup {

  private final Collection<MonitorCodeScanner> scanners;

  private MonitorCodeScannerGroup(Collection<MonitorCodeScanner> scanners) {
    this.scanners = scanners;
  }

  static MonitorCodeScannerGroup load(MonitorCodeScanOption... scanOptions) {
    return new MonitorCodeScannerGroup(
      ServiceLoader.load(MonitorCodeScannerProvider.class).stream()
        .map(ServiceLoader.Provider::get)
        .map(provider -> provider.provideScanner(scanOptions))
        .collect(toList())
    );
  }

  Optional<MonitorCode> tryScanMonitorCode(Image image) {
    return scanners.stream()
      .map(scanner -> scanner.tryScanMonitorCode(image))
      .flatMap(Optional::stream)
      .findFirst();
  }
}

You can use it like this:

var scanners = MonitorCodeScannerGroup.load();

...

scanners.tryScanMonitorCode(image).ifPresent(monitorCode -> {
  // do something with the code
});