refactor(api): replace regex string literals with Pattern instances for improved performance and readability (#5680)

# Description of Changes

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Please provide a summary of the changes, including:

- What was changed
- Why the change was made
- Any challenges encountered

Closes #(issue_number)
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---

## Checklist

### General

- [ ] I have read the [Contribution
Guidelines](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/CONTRIBUTING.md)
- [ ] I have read the [Stirling-PDF Developer
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md)
(if applicable)
- [ ] I have read the [How to add new languages to
Stirling-PDF](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md)
(if applicable)
- [ ] I have performed a self-review of my own code
- [ ] My changes generate no new warnings

### Documentation

- [ ] I have updated relevant docs on [Stirling-PDF's doc
repo](https://github.com/Stirling-Tools/Stirling-Tools.github.io/blob/main/docs/)
(if functionality has heavily changed)
- [ ] I have read the section [Add New Translation
Tags](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/HowToAddNewLanguage.md#add-new-translation-tags)
(for new translation tags only)

### Translations (if applicable)

- [ ] I ran
[`scripts/counter_translation.py`](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/docs/counter_translation.md)

### UI Changes (if applicable)

- [ ] Screenshots or videos demonstrating the UI changes are attached
(e.g., as comments or direct attachments in the PR)

### Testing (if applicable)

- [ ] I have tested my changes locally. Refer to the [Testing
Guide](https://github.com/Stirling-Tools/Stirling-PDF/blob/main/devGuide/DeveloperGuide.md#6-testing)
for more details.

---------

Signed-off-by: Balázs Szücs <[email protected]>

app/core/src/test/java/stirling/software/SPDF/controller/api/converters/ConvertWebsiteToPdfTest.java

@@ -18,6 +18,7 @@ import java.nio.file.Files;
 import java.nio.file.Path;
 import java.time.Duration;
 import java.util.List;
+import java.util.regex.Pattern;
 
 import org.apache.pdfbox.pdmodel.PDDocument;
 import org.junit.jupiter.api.AfterEach;
@@ -46,6 +47,7 @@ import stirling.software.common.util.WebResponseUtils;
 
 public class ConvertWebsiteToPdfTest {
 
+    private static final Pattern PDF_FILENAME_PATTERN = Pattern.compile("[A-Za-z0-9_]+\\.pdf");
     @Mock private CustomPDFDocumentFactory pdfDocumentFactory;
     @Mock private RuntimePathConfig runtimePathConfig;
 
@@ -142,7 +144,7 @@ public class ConvertWebsiteToPdfTest {
 
         assertTrue(out.endsWith(".pdf"));
         // Only A–Z, a–z, 0–9, underscore and dot allowed
-        assertTrue(out.matches("[A-Za-z0-9_]+\\.pdf"));
+        assertTrue(PDF_FILENAME_PATTERN.matcher(out).matches());
         // no truncation here (source not that long)
         assertTrue(out.length() <= 54);
     }
@@ -159,7 +161,7 @@ public class ConvertWebsiteToPdfTest {
         String out = (String) m.invoke(sut, longUrl);
 
         assertTrue(out.endsWith(".pdf"));
-        assertTrue(out.matches("[A-Za-z0-9_]+\\.pdf"));
+        assertTrue(PDF_FILENAME_PATTERN.matcher(out).matches());
         // safeName limited to 50 -> total max 54 including '.pdf'
         assertTrue(out.length() <= 54, "Filename should be truncated to 50 + '.pdf'");
     }

app/core/src/test/java/stirling/software/SPDF/controller/api/misc/StampControllerTest.java

@@ -5,6 +5,7 @@ import static org.junit.jupiter.api.Assertions.*;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.time.LocalDateTime;
+import java.util.regex.Pattern;
 
 import org.apache.pdfbox.pdmodel.PDDocument;
 import org.apache.pdfbox.pdmodel.PDDocumentInformation;
@@ -26,6 +27,18 @@ import stirling.software.common.util.TempFileManager;
 @ExtendWith(MockitoExtension.class)
 class StampControllerTest {
 
+    private static final Pattern UUID_HEX_PATTERN = Pattern.compile("[0-9a-f]{8}");
+    private static final Pattern DATE_LITERAL_REGEX =
+            Pattern.compile("@date is \\d{4}-\\d{2}-\\d{2}");
+    private static final Pattern DATE_TIME_MIN_PATTERN =
+            Pattern.compile("\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}");
+    private static final Pattern DATE_SLASH_PATTERN = Pattern.compile("\\d{2}/\\d{2}/\\d{4}");
+    private static final Pattern DAY_LABEL_PATTERN = Pattern.compile("Day: \\d{2}");
+    private static final Pattern MONTH_LABEL_PATTERN = Pattern.compile("Month: \\d{2}");
+    private static final Pattern DATE_TIME_FULL_PATTERN =
+            Pattern.compile("\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}:\\d{2}");
+    private static final Pattern TIME_LABEL_PATTERN = Pattern.compile("Time: \\d{2}:\\d{2}:\\d{2}");
+    private static final Pattern DATE_LABEL_PATTERN = Pattern.compile("Date: \\d{4}-\\d{2}-\\d{2}");
     @Mock private CustomPDFDocumentFactory pdfDocumentFactory;
     @Mock private TempFileManager tempFileManager;
 
@@ -173,7 +186,7 @@ class StampControllerTest {
         void testDateReplacement() throws Exception {
             String result = invokeProcessStampText("Date: @date", 1, 1, "test.pdf", null);
             assertTrue(
-                    result.matches("Date: \\d{4}-\\d{2}-\\d{2}"),
+                    DATE_LABEL_PATTERN.matcher(result).matches(),
                     "Date should match YYYY-MM-DD format");
         }
 
@@ -182,7 +195,7 @@ class StampControllerTest {
         void testTimeReplacement() throws Exception {
             String result = invokeProcessStampText("Time: @time", 1, 1, "test.pdf", null);
             assertTrue(
-                    result.matches("Time: \\d{2}:\\d{2}:\\d{2}"),
+                    TIME_LABEL_PATTERN.matcher(result).matches(),
                     "Time should match HH:mm:ss format");
         }
 
@@ -192,7 +205,7 @@ class StampControllerTest {
             String result = invokeProcessStampText("@datetime", 1, 1, "test.pdf", null);
             // DateTime format: YYYY-MM-DD HH:mm:ss
             assertTrue(
-                    result.matches("\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}:\\d{2}"),
+                    DATE_TIME_FULL_PATTERN.matcher(result).matches(),
                     "DateTime should match YYYY-MM-DD HH:mm:ss format");
         }
 
@@ -208,14 +221,15 @@ class StampControllerTest {
         @DisplayName("Should replace @month with zero-padded month")
         void testMonthReplacement() throws Exception {
             String result = invokeProcessStampText("Month: @month", 1, 1, "test.pdf", null);
-            assertTrue(result.matches("Month: \\d{2}"), "Month should be zero-padded");
+            assertTrue(
+                    MONTH_LABEL_PATTERN.matcher(result).matches(), "Month should be zero-padded");
         }
 
         @Test
         @DisplayName("Should replace @day with zero-padded day")
         void testDayReplacement() throws Exception {
             String result = invokeProcessStampText("Day: @day", 1, 1, "test.pdf", null);
-            assertTrue(result.matches("Day: \\d{2}"), "Day should be zero-padded");
+            assertTrue(DAY_LABEL_PATTERN.matcher(result).matches(), "Day should be zero-padded");
         }
     }
 
@@ -228,7 +242,7 @@ class StampControllerTest {
         void testCustomDateFormatSlash() throws Exception {
             String result = invokeProcessStampText("@date{dd/MM/yyyy}", 1, 1, "test.pdf", null);
             assertTrue(
-                    result.matches("\\d{2}/\\d{2}/\\d{4}"),
+                    DATE_SLASH_PATTERN.matcher(result).matches(),
                     "Should match dd/MM/yyyy format: " + result);
         }
 
@@ -238,7 +252,7 @@ class StampControllerTest {
             String result =
                     invokeProcessStampText("@date{yyyy-MM-dd HH:mm}", 1, 1, "test.pdf", null);
             assertTrue(
-                    result.matches("\\d{4}-\\d{2}-\\d{2} \\d{2}:\\d{2}"),
+                    DATE_TIME_MIN_PATTERN.matcher(result).matches(),
                     "Should match yyyy-MM-dd HH:mm format: " + result);
         }
 
@@ -345,7 +359,7 @@ class StampControllerTest {
             // @@date should become @date, and @date should be replaced with actual date
             assertTrue(result.startsWith("@date is "), "Should start with literal @date");
             assertTrue(
-                    result.matches("@date is \\d{4}-\\d{2}-\\d{2}"),
+                    DATE_LITERAL_REGEX.matcher(result).matches(),
                     "Should have date after: " + result);
         }
 
@@ -463,7 +477,9 @@ class StampControllerTest {
         @DisplayName("UUID should contain only hex characters")
         void testUuidFormat() throws Exception {
             String result = invokeProcessStampText("@uuid", 1, 1, "test.pdf", null);
-            assertTrue(result.matches("[0-9a-f]{8}"), "UUID should be 8 hex characters: " + result);
+            assertTrue(
+                    UUID_HEX_PATTERN.matcher(result).matches(),
+                    "UUID should be 8 hex characters: " + result);
         }
     }