Refine error message in URLUtil::create

jablib/src/main/java/org/jabref/logic/util/URLUtil.java

@@ -97,7 +97,25 @@ public static boolean isURL(String url) {
      * @throws MalformedURLException if the URL is malformed and cannot be converted to a {@link URL}.
      */
     public static URL create(String url) throws MalformedURLException {
-        return createUri(url).toURL();
+        try {
+            if (url == null || url.trim().isEmpty()) {
+                throw new MalformedURLException("Provided URL is null or empty.");
+            }
+            URI parsedUri = new URI(url.trim());
+            if (!parsedUri.isAbsolute()) {
+                throw new MalformedURLException("URI is not absolute: " + url);
+            }
+            if (parsedUri.getScheme() == null || parsedUri.getHost() == null) {
+                throw new MalformedURLException("URI must include both scheme and host: " + url);
+            }
+            return parsedUri.toURL();
+        } catch (URISyntaxException e) {
+            throw new MalformedURLException("Invalid  URI syntax: " + url + " | Error: " + e.getMessage());
+        } catch (IllegalArgumentException e) {
+            throw new MalformedURLException("Illegal argument in URI construction: " + url + " | Error: " + e.getMessage());
+        } catch (NullPointerException e) {
+            throw new MalformedURLException("Null value encountered during URI parsing: " + url);
+        }
     }
 
     /**

jablib/src/test/java/org/jabref/logic/net/URLUtilTest.java

@@ -1,14 +1,15 @@
 package org.jabref.logic.net;
 
+import java.net.MalformedURLException;
 import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.URL;
 
 import org.jabref.logic.util.URLUtil;
 
 import org.junit.jupiter.api.Test;
 
-import static org.junit.jupiter.api.Assertions.assertEquals;
-import static org.junit.jupiter.api.Assertions.assertFalse;
-import static org.junit.jupiter.api.Assertions.assertTrue;
+import static org.junit.jupiter.api.Assertions.*;
 
 class URLUtilTest {
 
@@ -87,4 +88,64 @@ void createUriShouldHandlePipeCharacter() {
         URI uri = URLUtil.createUri(input);
         assertEquals("http://example.com/test%7Cfile", uri.toString());
     }
+
+    // valid absolute URL
+    @Test
+    public void testValidUrl() {
+        String input = "http://example.com";
+
+        try {
+            URL result = URLUtil.create(input);
+            assertNotNull(result, "URL should not be null");
+            assertEquals(input, result.toString(), "Returned URL should match input");
+        } catch (MalformedURLException e) {
+            fail("Exception " + e.getMessage());
+        }
+    }
+
+
+    // null input
+    @Test
+    public void testNullUrl() {
+        MalformedURLException exception = assertThrows(MalformedURLException.class, () -> {
+            URLUtil.create(null);
+        });
+        assertTrue(exception.getMessage().contains("null or empty"), "Error message should indicate null or empty input");
+    }
+
+    //empty string input
+    @Test
+    public void testEmptyUrl() {
+        MalformedURLException exception = assertThrows(MalformedURLException.class, () -> {
+            URLUtil.create("   ");
+        });
+        assertTrue(exception.getMessage().contains("null or empty"), "Error message ");
+    }
+
+    // URI without scheme
+    @Test
+    public void testUriMissingScheme() {
+        MalformedURLException exception = assertThrows(MalformedURLException.class, () -> {
+            URLUtil.create("www.example.com");
+        });
+        assertTrue(exception.getMessage().contains("not absolute"), "URI is not absolute");
+    }
+
+    // URI with scheme but missing host
+    @Test
+    public void testUriMissingHost() {
+        MalformedURLException exception = assertThrows(MalformedURLException.class, () -> {
+            URLUtil.create("mailto:[email protected]");
+        });
+        assertTrue(exception.getMessage().contains("must include both scheme and host"), "Error message should mention scheme and host");
+    }
+
+    // malformed syntax
+    @Test
+    public void testMalformedSyntax() {
+        MalformedURLException exception = assertThrows(MalformedURLException.class, () -> {
+            URLUtil.create("http://[invalid-url]");
+        });
+        assertTrue(exception.getMessage().contains("Invalid  URI syntax"), " URI syntax error");
+    }
 }