java frontend (#5097)

# Description of Changes

<!--
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.

---------

Co-authored-by: Reece <[email protected]>
Co-authored-by: Reece Browne <[email protected]>

app/core/src/main/java/stirling/software/SPDF/controller/web/ReactRoutingController.java

@@ -1,20 +1,61 @@
 package stirling.software.SPDF.controller.web;
 
+import java.io.IOException;
+import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.core.io.ClassPathResource;
+import org.springframework.http.MediaType;
+import org.springframework.http.ResponseEntity;
 import org.springframework.stereotype.Controller;
 import org.springframework.web.bind.annotation.GetMapping;
 
+import jakarta.servlet.http.HttpServletRequest;
+
 @Controller
 public class ReactRoutingController {
 
-    @GetMapping(
-            "/{path:^(?!api|static|robots\\.txt|favicon\\.ico|pipeline|pdfjs|pdfjs-legacy|fonts|images|files|css|js)[^\\.]*$}")
-    public String forwardRootPaths() {
-        return "forward:/index.html";
+    @Value("${server.servlet.context-path:/}")
+    private String contextPath;
+
+    @GetMapping(value = {"/", "/index.html"}, produces = MediaType.TEXT_HTML_VALUE)
+    public ResponseEntity<String> serveIndexHtml(HttpServletRequest request)
+            throws IOException {
+        ClassPathResource resource = new ClassPathResource("static/index.html");
+
+        try (InputStream inputStream = resource.getInputStream()) {
+            String html = new String(inputStream.readAllBytes(), StandardCharsets.UTF_8);
+
+            // Replace %BASE_URL% with the actual context path for base href
+            String baseUrl = contextPath.endsWith("/") ? contextPath : contextPath + "/";
+            html = html.replace("%BASE_URL%", baseUrl);
+            // Also rewrite any existing <base> tag (Vite may have baked one in)
+            html =
+                    html.replaceFirst(
+                            "<base href=\\\"[^\\\"]*\\\"\\s*/?>",
+                            "<base href=\\\"" + baseUrl + "\\\" />");
+
+            // Inject context path as a global variable for API calls
+            String contextPathScript =
+                    "<script>window.STIRLING_PDF_API_BASE_URL = '" + baseUrl + "';</script>";
+            html = html.replace("</head>", contextPathScript + "</head>");
+
+            return ResponseEntity.ok().contentType(MediaType.TEXT_HTML).body(html);
+        }
     }
 
     @GetMapping(
-            "/{path:^(?!api|static|pipeline|pdfjs|pdfjs-legacy|fonts|images|files|css|js)[^\\.]*}/{subpath:^(?!.*\\.).*$}")
-    public String forwardNestedPaths() {
-        return "forward:/index.html";
+            "/{path:^(?!api|static|robots\\.txt|favicon\\.ico|manifest.*\\.json|pipeline|pdfjs|pdfjs-legacy|fonts|images|files|css|js|assets|locales|modern-logo|classic-logo|Login|og_images|samples)[^\\.]*$}")
+    public ResponseEntity<String> forwardRootPaths(HttpServletRequest request)
+            throws IOException {
+        return serveIndexHtml(request);
+    }
+
+    @GetMapping(
+            "/{path:^(?!api|static|pipeline|pdfjs|pdfjs-legacy|fonts|images|files|css|js|assets|locales|modern-logo|classic-logo|Login|og_images|samples)[^\\.]*}/{subpath:^(?!.*\\.).*$}")
+    public ResponseEntity<String> forwardNestedPaths(HttpServletRequest request)
+            throws IOException {
+        return serveIndexHtml(request);
     }
 }