IText keep pfm file open in Ubuntu - tomcat7

Question

We have a web app running on Tomcat/Ubuntu and using iText7.1.8 to generate pdf documents (Invoices). We noticed that our Tomcat crashed many times and then after investigations found that it was iText the problem. Here is the exception
SEVERE: Socket accept failed
org.apache.tomcat.jni.Error: 24: Too many open files
at org.apache.tomcat.jni.Socket.accept(Native Method)
at org.apache.tomcat.util.net.AprEndpoint$Acceptor.run(AprEndpoint.java:992)
at java.lang.Thread.run(Thread.java:745)
When we run this command: sudo ls -l /proc/Tomcat-PID/fd we notice that most of the files opened are with extension .pfm (ex: /usr/share/fonts/type1/gsfonts/n022004l.pfm) and never released. This number continue to increase till reaches the max number of opened files.
Here is the code in Java used to generate the pdf.
public static File convertToPDF(File pdfFile,URL webURL){
InputStream htmlStream=null;
FileOutputStream pdfStream=null;
try {
htmlStream=webURL.openStream();
pdfStream=new FileOutputStream(pdfFile);
ConverterProperties properties = new ConverterProperties();
properties.setFontProvider(new DefaultFontProvider(true, true, true));
HtmlConverter.convertToPdf(htmlStream, pdfStream,properties);
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}finally{
try {
if(htmlStream!= null){
htmlStream.close();
}
if(pdfStream!= null){
pdfStream.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
return pdfFile;
}
Should we use a singleton to avoid multi instance, of this process which generates pdf, and the multiple files opened?
Environment:
Ubuntu 14.04
Tomcat 7.0.52
Java 1.7.0_80-b15
itext 7.1.8
Thank you

Answer 1

Fixed issue.
Use a singleton to get converter properties:
private static ConverterProperties properties;
private static DefaultFontProvider defaultFontProvider;
...
defaultFontProvider= new DefaultFontProvider(true, true, true);
properties.setFontProvider(defaultFontProvider);