Fixed the DOI connection Error by Automatically Removing all Special Characters at the end of DOI

CHANGELOG.md

@@ -44,6 +44,9 @@ Note that this project **does not** adhere to [Semantic Versioning](http://semve
 
 ### Fixed
 
+- We fixed an issue where an invalid DOI should not show "Connection error" [#8127](https://github.com/JabRef/jabref/issues/8127)
+- We fixed an issue where an invalid DOI should not show "Connection error" [#8127](https://github.com/JabRef/jabref/issues/8127)
+- We fixed an issue where an exception ocurred when a linked online file was edited in the entry editor [#8008](https://github.com/JabRef/jabref/issues/8008)
 - We fixed an issue where an exception occurred when a linked online file was edited in the entry editor [#8008](https://github.com/JabRef/jabref/issues/8008)
 - We fixed an issue when checking for a new version when JabRef is used behind a corporate proxy. [#7884](https://github.com/JabRef/jabref/issues/7884)
 - We fixed some icons that were drawn in the wrong color when JabRef used a custom theme. [#7853](https://github.com/JabRef/jabref/issues/7853)

src/main/java/org/jabref/model/entry/identifier/DOI.java

@@ -106,6 +106,9 @@ public DOI(String doi) {
         // Remove whitespace
         String trimmedDoi = doi.trim();
 
+        // Remove non-valid special character at the end
+        trimmedDoi = removeScharDOI(trimmedDoi);
+
         // HTTP URL decoding
         if (doi.matches(HTTP_EXP) || doi.matches(SHORT_DOI_HTTP_EXP)) {
             try {
@@ -141,6 +144,32 @@ public DOI(String doi) {
         }
     }
 
+    /**
+     * Removes all special characters at the end of the DOI string
+     *
+     * @param doiStr the DOI/Short DOI string
+     * @return an DOI string with the special character at the end removed
+     */
+    public static String removeScharDOI(String doiStr) {
+        char[] lcharDoi = doiStr.toCharArray();
+        int i = lcharDoi.length - 1;
+        // valid DOI characters are a-z(97-122), A-Z(65-90), 0-9(48-57), -(45), .(46), _(95), ;(59), ( (40), ) (41), /(47)
+        for (; i >= 0; i--) {
+            if ((lcharDoi[i] >= 45 && lcharDoi[i] <= 47) ||
+                    (lcharDoi[i] >= 48 && lcharDoi[i] <= 57) ||
+                    (lcharDoi[i] >= 65 && lcharDoi[i] <= 90) ||
+                    (lcharDoi[i] >= 97 && lcharDoi[i] <= 122) ||
+                    lcharDoi[i] == 95 ||
+                    lcharDoi[i] == 59 ||
+                    lcharDoi[i] == 40 ||
+                    lcharDoi[i] == 41
+            ) {
+                break;
+            }
+        }
+        return doiStr.substring(0, i + 1);
+    }
+
     /**
      * Creates an Optional&lt;DOI> from various schemes including URL, URN, and plain DOIs.
      * <p>

src/test/java/org/jabref/model/entry/identifier/DOITest.java

@@ -272,4 +272,21 @@ public void rejectMissingDivider() {
     public void rejectMissingDividerInShortDoi() {
         assertThrows(IllegalArgumentException.class, () -> new DOI("10gf4gqc end"));
     }
+
+    private static Stream<Arguments> testECharData() {
+        return Stream.of(
+                // Arguments.of("10.1006/jmbi.1998.2354", new DOI("10.1006/jmbi.1998.2354").getDOI()),
+                Arguments.of(DOI.removeScharDOI("10.1007/978-3-319-47590-5_8?"), "10.1007/978-3-319-47590-5_8"),
+                Arguments.of(DOI.removeScharDOI("10.1007/978-3-319-47590-5_8?$"), "10.1007/978-3-319-47590-5_8"),
+                Arguments.of(DOI.removeScharDOI("10.1007/978-3-319-47590-5_8"), "10.1007/978-3-319-47590-5_8"),
+                Arguments.of(DOI.removeScharDOI("10.1007/978-3-319-47590-?%"), "10.1007/978-3-319-47590-"),
+                Arguments.of(DOI.removeScharDOI("10.1007/*?"), "10.1007/")
+        );
+    }
+
+    @ParameterizedTest
+    @MethodSource("testECharData")
+    public void testEquals2(String expected, String input) {
+        assertEquals(expected, input);
+    }
 }