improved slightly link generation code

Author: rozagerardo

spring-boot-rest/src/main/java/com/baeldung/web/hateoas/listener/PaginatedResultsRetrievedDiscoverabilityListener.java

@@ -1,5 +1,7 @@
 package com.baeldung.web.hateoas.listener;
 
+import java.util.StringJoiner;
+
 import javax.servlet.http.HttpServletResponse;
 
 import org.springframework.context.ApplicationListener;
@@ -27,32 +29,32 @@ public PaginatedResultsRetrievedDiscoverabilityListener() {
     public final void onApplicationEvent(final PaginatedResultsRetrievedEvent ev) {
         Preconditions.checkNotNull(ev);
 
-        addLinkHeaderOnPagedResourceRetrieval(ev.getUriBuilder(), ev.getResponse(), ev.getClazz(), ev.getPage(), ev.getTotalPages(), ev.getPageSize());
+        addLinkHeaderOnPagedResourceRetrieval(ev.getUriBuilder(), ev.getResponse(), ev.getClazz(), ev.getPage(),
+            ev.getTotalPages(), ev.getPageSize());
     }
 
     // - note: at this point, the URI is transformed into plural (added `s`) in a hardcoded way - this will change in the future
-    final void addLinkHeaderOnPagedResourceRetrieval(final UriComponentsBuilder uriBuilder, final HttpServletResponse response, final Class clazz, final int page, final int totalPages, final int pageSize) {
+    final void addLinkHeaderOnPagedResourceRetrieval(final UriComponentsBuilder uriBuilder,
+        final HttpServletResponse response, final Class clazz, final int page, final int totalPages,
+        final int pageSize) {
         plural(uriBuilder, clazz);
 
-        final StringBuilder linkHeader = new StringBuilder();
+        final StringJoiner linkHeader = new StringJoiner(", ");
         if (hasNextPage(page, totalPages)) {
             final String uriForNextPage = constructNextPageUri(uriBuilder, page, pageSize);
-            linkHeader.append(LinkUtil.createLinkHeader(uriForNextPage, LinkUtil.REL_NEXT));
+            linkHeader.add(LinkUtil.createLinkHeader(uriForNextPage, LinkUtil.REL_NEXT));
         }
         if (hasPreviousPage(page)) {
             final String uriForPrevPage = constructPrevPageUri(uriBuilder, page, pageSize);
-            appendCommaIfNecessary(linkHeader);
-            linkHeader.append(LinkUtil.createLinkHeader(uriForPrevPage, LinkUtil.REL_PREV));
+            linkHeader.add(LinkUtil.createLinkHeader(uriForPrevPage, LinkUtil.REL_PREV));
         }
         if (hasFirstPage(page)) {
             final String uriForFirstPage = constructFirstPageUri(uriBuilder, pageSize);
-            appendCommaIfNecessary(linkHeader);
-            linkHeader.append(LinkUtil.createLinkHeader(uriForFirstPage, LinkUtil.REL_FIRST));
+            linkHeader.add(LinkUtil.createLinkHeader(uriForFirstPage, LinkUtil.REL_FIRST));
         }
         if (hasLastPage(page, totalPages)) {
             final String uriForLastPage = constructLastPageUri(uriBuilder, totalPages, pageSize);
-            appendCommaIfNecessary(linkHeader);
-            linkHeader.append(LinkUtil.createLinkHeader(uriForLastPage, LinkUtil.REL_LAST));
+            linkHeader.add(LinkUtil.createLinkHeader(uriForLastPage, LinkUtil.REL_LAST));
         }
 
         if (linkHeader.length() > 0) {
@@ -61,19 +63,35 @@ final void addLinkHeaderOnPagedResourceRetrieval(final UriComponentsBuilder uriB
     }
 
     final String constructNextPageUri(final UriComponentsBuilder uriBuilder, final int page, final int size) {
-        return uriBuilder.replaceQueryParam(PAGE, page + 1).replaceQueryParam("size", size).build().encode().toUriString();
+        return uriBuilder.replaceQueryParam(PAGE, page + 1)
+            .replaceQueryParam("size", size)
+            .build()
+            .encode()
+            .toUriString();
     }
 
     final String constructPrevPageUri(final UriComponentsBuilder uriBuilder, final int page, final int size) {
-        return uriBuilder.replaceQueryParam(PAGE, page - 1).replaceQueryParam("size", size).build().encode().toUriString();
+        return uriBuilder.replaceQueryParam(PAGE, page - 1)
+            .replaceQueryParam("size", size)
+            .build()
+            .encode()
+            .toUriString();
     }
 
     final String constructFirstPageUri(final UriComponentsBuilder uriBuilder, final int size) {
-        return uriBuilder.replaceQueryParam(PAGE, 0).replaceQueryParam("size", size).build().encode().toUriString();
+        return uriBuilder.replaceQueryParam(PAGE, 0)
+            .replaceQueryParam("size", size)
+            .build()
+            .encode()
+            .toUriString();
     }
 
     final String constructLastPageUri(final UriComponentsBuilder uriBuilder, final int totalPages, final int size) {
-        return uriBuilder.replaceQueryParam(PAGE, totalPages).replaceQueryParam("size", size).build().encode().toUriString();
+        return uriBuilder.replaceQueryParam(PAGE, totalPages)
+            .replaceQueryParam("size", size)
+            .build()
+            .encode()
+            .toUriString();
     }
 
     final boolean hasNextPage(final int page, final int totalPages) {
@@ -92,16 +110,11 @@ final boolean hasLastPage(final int page, final int totalPages) {
         return (totalPages > 1) && hasNextPage(page, totalPages);
     }
 
-    final void appendCommaIfNecessary(final StringBuilder linkHeader) {
-        if (linkHeader.length() > 0) {
-            linkHeader.append(", ");
-        }
-    }
-
     // template
 
     protected void plural(final UriComponentsBuilder uriBuilder, final Class clazz) {
-        final String resourceName = clazz.getSimpleName().toLowerCase() + "s";
+        final String resourceName = clazz.getSimpleName()
+            .toLowerCase() + "s";
         uriBuilder.path("/auth/" + resourceName);
     }