Let’s create a Java app which watches a folder for file changes and automatically compares new PDFs.
The idea is that any time two PDFs are added to the folder, we will run a simple comparison of the two PDFs using i-net PDFC, create a report of the comparison and store it in a “reports” folder, and move the source PDFs to a source archive folder.
To start with, we will use Oracle’s own WatchDir example which already handles Java’s Watch Service API to watch a directory for changes. The only modification we will make is to pass in a listener to handle the WatchEvents generated when the directory’s files change:
...
interface WatchEventListener {
void directoryChanged(WatchEvent<Path> event);
}
private WatchEventListener listener;
...
WatchDir(Path dir, boolean recursive,
WatchEventListener listener) throws IOException {
this.listener = listener;
...
}
Additionally, we need to make sure our WatchDir calls this listener when it receives events instead of simply logging the events as the default WatchDir implementation does:
void processEvents() {
for (;;) {
...
// print out event
System.out.format("%s: %s\n", event.kind().name(), child);
// send event to listeners
this.listener.directoryChanged( ev );
...
}
}
Using our WatchDir is now relatively straightforward using the i-net PDFC API. First, we set up our paths based on arguments passed into our tool:
public static void main(String[] args) throws Exception {
String sourceFolder = "";
String archiveFolder = "sourceArchive";
String reportsFolder = "reports";
for (int i=0; i<args.length-1; i+=2) {
if ("-s".equals( args[i] )) {
sourceFolder = args[i+1];
} else if ("-a".equals( args[i] )) {
archiveFolder = args[i+1];
} else if ("-r".equals( args[i] )) {
reportsFolder = args[i+1];
}
}
Path sourcePath = Paths.get( sourceFolder );
Path archivePath = Paths.get( archiveFolder );
Path reportsPath = Paths.get( reportsFolder );
if (!Files.exists( sourcePath )) {
Files.createDirectories( sourcePath );
}
if (!Files.exists( archivePath )) {
Files.createDirectories( archivePath );
}
if (!Files.exists( reportsPath )) {
Files.createDirectories( reportsPath );
}
...
Next, we set up our WatchDir listener to listen for two separate ENTRY_CREATE events of PDF files. Once the second PDF is detected, we launch the PDFC comparison with a DifferencesPDFPresenter which creates our comparison report in the target folder. Finally, we move the source files to the archive folder.
private static Path firstPdfPath;
...
System.out.println("watching for new files at "+sourcePath.toAbsolutePath().toString());
WatchDir.WatchEventListener listener = ev -> {
Path path = ev.context().toAbsolutePath();
try {
String fileName = path.getFileName().toString().toLowerCase();
if (ev.kind() == StandardWatchEventKinds.ENTRY_CREATE &&
fileName.endsWith( ".pdf" )) {
if (firstPdfPath == null) {
firstPdfPath = path;
} else {
PDFComparer comparer = new PDFComparer();
String datetime = DateTimeFormatter.ofPattern( "yyyy-MM-dd" ).format( LocalDateTime.now() );
File subfolder= new File(reportsPath.toFile(), "ComparisonReports-"+datetime);
comparer.addPresenter( new DifferencesPDFPresenter( subfolder ) );
ResultModel result = comparer.compare( firstPdfPath.toFile(), path.toFile() );
System.out.println("Compared "+firstPdfPath.toString()+" to "+path.toString()+".");
System.out.println("Differences found: "+result.getDifferencesCount( false ));
Files.move( firstPdfPath, archivePath.resolve( firstPdfPath.getFileName() ) );
Files.move( path, archivePath.resolve( path.getFileName() ) );
}
}
} catch (IOException ex) {
ex.printStackTrace();
}
};
WatchDir watcher = new WatchDir( sourcePath, false, listener);
watcher.processEvents();
Note that to successfully run this sample, you will need to…
- include
PDFC.jarin your classpath - have the plugins
pdfcparserplugin.zipandreporting.zipin yourpluginsfolder, located in your working directory. - have at least a trial license in your i-net PDFC configuration
The entire sample can be found on the PDFC samples GitHub.