First approach for implementing PDF Exporter

Remove code that produces NPE

src/main/java/org/jabref/logic/exporter/ExportFormat.java

@@ -314,12 +314,6 @@ public void performExport(final BibDatabaseContext databaseContext, final String
 
     }
 
-    @Override
-    public void performExport(final BibDatabaseContext databaseContext, Path file, final Charset encoding,
-            List<BibEntry> entries) throws Exception {
-        performExport(databaseContext, file.getFileName().toString(), encoding, entries);
-    }
-
     /**
      * See if there is a name formatter file bundled with this export format. If so, read
      * all the name formatters so they can be used by the filter layouts.

src/main/java/org/jabref/logic/exporter/ExportFormats.java

@@ -61,6 +61,7 @@ public static void initAllExports(Map<String, ExportFormat> customFormats,
         ExportFormats.putFormat(new OpenDocumentSpreadsheetCreator());
         ExportFormats.putFormat(new MSBibExportFormat());
         ExportFormats.putFormat(new ModsExportFormat());
+        ExportFormats.putFormat(new PdfFileExporter());
 
         // Now add custom export formats
         for (IExportFormat format : customFormats.values()) {

src/main/java/org/jabref/logic/exporter/IExportFormat.java

@@ -1,7 +1,6 @@
 package org.jabref.logic.exporter;
 
 import java.nio.charset.Charset;
-import java.nio.file.Path;
 import java.util.List;
 
 import org.jabref.model.database.BibDatabaseContext;
@@ -38,18 +37,4 @@ public interface IExportFormat {
     void performExport(BibDatabaseContext databaseContext, String file, Charset encoding, List<BibEntry> entries)
             throws Exception;
 
-    /**
-     * Perform the Export.
-     * Gets the path as a java.nio.path instead of a string.
-     *
-     * @param databaseContext the database to export from.
-     * @param file  the Path to the file to write to.The path should be an java.nio.Path
-     * @param encoding  The encoding to use.
-     * @param entries  A list containing all entries that
-     * should be exported. The list of entries must be non null
-     * @throws Exception
-     */
-    void performExport(BibDatabaseContext databaseContext, Path file, Charset encoding, List<BibEntry> entries)
-            throws Exception;
-
 }

src/main/java/org/jabref/logic/exporter/PdfFileExporter.java

@@ -0,0 +1,39 @@
+package org.jabref.logic.exporter;
+
+import java.nio.charset.Charset;
+import java.util.List;
+import org.jabref.logic.TypedBibEntry;
+import org.jabref.model.database.BibDatabaseContext;
+import org.jabref.model.entry.BibEntry;
+import org.jabref.model.entry.ParsedFileField;
+
+public class PdfFileExporter extends ExportFormat {
+
+    public PdfFileExporter() {
+        super("PDF files", "PDF", null, null, ".pdf");
+    }
+    @Override
+    public void performExport(final BibDatabaseContext databaseContext, String file, final Charset encoding,
+            List<BibEntry> entries) throws Exception {
+
+        for (BibEntry entry : entries) {
+            TypedBibEntry typedEntry = new TypedBibEntry(entry, databaseContext);
+
+            List<ParsedFileField> files = typedEntry.getFiles();
+            for (ParsedFileField fileEntry : files) {
+                String fileName = fileEntry.getLink();
+
+                //    databaseContext.getFileDirectories(preferences)
+                //   Optional<File> oldFile = FileUtil.expandFilename(fileName,
+                //         databaseContext.getFileDirectories(Globals.prefs.getFileDirectoryPreferences()));
+
+                System.out.println("Export pdfs");
+                //  FileUtil.copyFile(oldFile.get().toPath(), file, false);
+
+            }
+
+        }
+
+    }
+
+}