#328 - add doc how to handle reloads on the server in case useHash is false - done (#334)

Author: FrankHossfeld

etc/wiki/06.-Application.md

@@ -56,6 +56,73 @@ Nalu offers the possibility to add a custom alert and confirm dialog. In case it
 
 A custom alert needs to implement the `IsCustomAlertPresenter` and a custom confirm dialog needs to implement the `IsCustomConfirmPresenter`.
 
+## Hash-less Routing
+
+Usually Nalu uses hashes to route. A hash looks something like this: **#/applicationShell/myroute01**. In case you want to use anchors or use Domino-UI v2 as widget library, you might run into trouble.
+For example Domino-UI generates **href="#"** attributes for links. This is correct, but, when clicked will update the hash which wil trigger a - unwanted - routing.
+In case of Domino-UI you can configure the **ElementsFactory**-class to create an a-tag without the href-attribute.
+
+Nalu offers also an alternative. By setting the **useHash**-attribute of the **Applicaiton**-interface to **false**, Nalu will not use a hash. Instead it uses the URI.
+
+This is an example of an URL in case useHash is true:
+
+```
+http://localhost:8080/index.html#/applicationShell/myRoute01"
+```
+
+and this represents the same URI in cae useHash is false:
+
+```
+http://localhost:8080/applicationShell/myRoute01"
+```
+
+This will work with no difference with one exception:
+
+In case of a reload, the hash will be ignored on the server side and the hash-less URI will create a Status 404 because the path is unknown.
+
+To avoid that, you have to implement a filter, that recognize this URIs and redirect after updating the URL. Here is an example (based on Spring Boot v3) how the filter looks like:
+
+```java
+@Component
+@Order(1)
+public class RedirectFilter extends GenericFilterBean {
+
+  // TODO: add here the list of shell names.
+  private final String[] uriStarts = new String[] {"/login", "/application"};
+
+  @Override
+  public void doFilter(
+      ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
+      throws IOException, jakarta.servlet.ServletException {
+    HttpServletRequest request = (HttpServletRequest) servletRequest;
+    HttpServletResponse response = (HttpServletResponse) servletResponse;
+    if (this.isClientUri(request.getRequestURI())) {
+      response.sendRedirect("/index.html?uri=" + request.getRequestURI());
+      return;
+    }
+    filterChain.doFilter(servletRequest, servletResponse);
+  }
+
+  /**
+   * this method recognize path of the clients
+   **/ 
+  private boolean isClientUri(String path) {
+    for (String s : this.uriStarts) {
+      if (path.startsWith(s)) {
+        return true;
+      }
+    }
+    return false;
+  }
+}
+```
+
+The classes need to identify the routes of the clients. The easiest way to do that is look for the shell names at the start of the path.
+In case a route is identified, change the route to something like **index.html?uri=[route]** and redirect the URL. Now the client calls the server
+again. This time with and URL that looks like:  **index.html?uri=[route]**. Now the server works as expected and because of the **uri**-key Nalu 
+will use this as start route.
+
+
 ## Filter Annotation
 Nalu allows you to use filters to stop routings in order to interrupt a route before it is handled. In case a route is interrupted, you can redirect to another route.