Added ISBN integrity checker

CHANGELOG.md

@@ -14,6 +14,7 @@ We refer to [GitHub issues](https://github.com/JabRef/jabref/issues) by using `#
 ### Changed
 - [#1026](https://github.com/JabRef/jabref/issues/1026) JabRef does no longer delete user comments outside of BibTeX entries and strings
 - [#1249](https://github.com/JabRef/jabref/issues/1249) Date layout formatter added
+- Added ISBN integrity checker
 
 ### Fixed
 - Fixed [#1264](https://github.com/JabRef/jabref/issues/1264): S with caron does not render correctly

src/main/java/net/sf/jabref/logic/integrity/ISBNChecker.java

@@ -0,0 +1,37 @@
+package net.sf.jabref.logic.integrity;
+
+import java.util.Collections;
+import java.util.List;
+
+import net.sf.jabref.logic.integrity.IntegrityCheck.Checker;
+import net.sf.jabref.logic.l10n.Localization;
+import net.sf.jabref.logic.util.ISBN;
+import net.sf.jabref.model.entry.BibEntry;
+
+
+public class ISBNChecker implements Checker {
+
+
+    @Override
+    public List<IntegrityMessage> check(BibEntry entry) {
+        if (!entry.hasField("isbn")) {
+            return Collections.emptyList();
+        }
+
+        // Check that the ISBN is on the correct form
+        ISBN isbn = new ISBN(entry.getFieldOptional("isbn").get());
+
+        if (!isbn.isValidFormat()) {
+            return Collections.singletonList(
+                    new IntegrityMessage(Localization.lang("incorrect format"), entry, "isbn"));
+        }
+
+        if (!isbn.isValidChecksum()) {
+            return Collections
+                    .singletonList(new IntegrityMessage(Localization.lang("incorrect control digit"), entry, "isbn"));
+        }
+
+        return Collections.emptyList();
+    }
+
+}

src/main/java/net/sf/jabref/logic/integrity/IntegrityCheck.java

@@ -68,6 +68,7 @@ private List<IntegrityMessage> checkBibtexEntry(BibEntry entry) {
         result.addAll(new HTMLCharacterChecker().check(entry));
         result.addAll(new BooktitleChecker().check(entry));
         result.addAll(new ISSNChecker().check(entry));
+        result.addAll(new ISBNChecker().check(entry));
 
         return result;
     }

src/main/java/net/sf/jabref/logic/util/ISBN.java

@@ -0,0 +1,76 @@
+package net.sf.jabref.logic.util;
+
+import java.util.Objects;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+public class ISBN {
+
+    private static final Pattern ISBN_PATTERN = Pattern.compile("^(\\d{9}[\\dxX]|\\d{13})$");
+
+    private final String isbnString;
+
+
+    public ISBN(String isbnString) {
+        this.isbnString = Objects.requireNonNull(isbnString).trim().replace("-", "");
+    }
+
+    public boolean isValidFormat() {
+        Matcher isbnMatcher = ISBN_PATTERN.matcher(isbnString);
+        if (isbnMatcher.matches()) {
+            return true;
+        }
+        return false;
+    }
+
+    public boolean isValidChecksum() {
+        boolean valid;
+        if (isbnString.length() == 10) {
+            valid = isbn10check();
+        } else {
+            // length is either 10 or 13 based on regexp so will be 13 here
+            valid = isbn13check();
+        }
+        return valid;
+    }
+
+    public boolean isIsbn10() {
+        return isbn10check();
+    }
+
+    public boolean isIsbn13() {
+        return isbn13check();
+    }
+
+    // Check that the control digit is correct, see e.g. https://en.wikipedia.org/wiki/International_Standard_Book_Number#Check_digits
+    private boolean isbn10check() {
+        if ((isbnString == null) || (isbnString.length() != 10)) {
+            return false;
+        }
+
+        int sum = 0;
+        for (int pos = 0; pos <= 8; pos++) {
+            sum += (isbnString.charAt(pos) - '0') * ((10 - pos));
+        }
+        char control = isbnString.charAt(9);
+        if ((control == 'x') || (control == 'X')) {
+            control = '9' + 1;
+        }
+        sum += (control - '0');
+        return (sum % 11) == 0;
+    }
+
+    // Check that the control digit is correct, see e.g. https://en.wikipedia.org/wiki/International_Standard_Book_Number#Check_digits
+    private boolean isbn13check() {
+        if ((isbnString == null) || (isbnString.length() != 13)) {
+            return false;
+        }
+
+        int sum = 0;
+        for (int pos = 0; pos <= 12; pos++) {
+            sum += (isbnString.charAt(pos) - '0') * ((pos % 2) == 0 ? 1 : 3);
+        }
+        return (sum % 10) == 0;
+    }
+
+}

src/test/java/net/sf/jabref/logic/integrity/IntegrityCheckTest.java

@@ -196,14 +196,23 @@ public void testHTMLCharacterChecks() {
 
     @Test
     public void testISSNChecks() {
-        assertCorrect(createContext("issn", "0020-7217"));
         assertCorrect(createContext("issn", "0020-7217"));
         assertCorrect(createContext("issn", "1687-6180"));
         assertCorrect(createContext("issn", "2434-561x"));
         assertWrong(createContext("issn", "Some other stuff"));
         assertWrong(createContext("issn", "0020-7218"));
     }
 
+    @Test
+    public void testISBNChecks() {
+        assertCorrect(createContext("isbn", "0-201-53082-1"));
+        assertCorrect(createContext("isbn", "0-9752298-0-X"));
+        assertCorrect(createContext("isbn", "978-0-306-40615-7"));
+        assertWrong(createContext("isbn", "Some other stuff"));
+        assertWrong(createContext("isbn", "0-201-53082-2"));
+        assertWrong(createContext("isbn", "978-0-306-40615-8"));
+    }
+
     private BibDatabaseContext createContext(String field, String value, String type) {
         BibEntry entry = new BibEntry();
         entry.setField(field, value);