PaginationDiscoverabilityListener.java

@Component
class PaginatedResultsRetrievedEventDiscoverabilityListener implements ApplicationListener< PaginatedResultsRetrievedEvent >{
   
   @Override
   public void onApplicationEvent( PaginatedResultsRetrievedEvent ev ){
      Preconditions.checkNotNull( ev );
      this.addLinkHeaderOnPagedResourceRetrieval( 
       ev.getUriBuilder(), ev.getResponse(), ev.getClazz(), ev.getPage(), ev.getTotalPages(), ev.getPageSize() );
   }
   void addLinkHeaderOnPagedResourceRetrieval( UriComponentsBuilder uriBuilder, HttpServletResponse response, 
    Class clazz, int page, int totalPages, final int pageSize ){
      String resourceName = clazz.getSimpleName().toString().toLowerCase();
      uriBuilder.path( "/admin/" + resourceName );

      StringBuilder linkHeader = new StringBuilder();
      if( this.hasNextPage( page, totalPages ) ){
         String uriForNextPage = this.constructNextPageUri( uriBuilder, page, pageSize );
         linkHeader.append( createLinkHeader( uriForNextPage, REL_NEXT ) );
      }
      if( this.hasPreviousPage( page ) ){
         String uriForPrevPage = this.constructPrevPageUri( uriBuilder, page, pageSize  );
         appendCommaIfNecessary( linkHeader );
         linkHeader.append( createLinkHeader( uriForPrevPage, REL_PREV ) );
      }
      if( this.hasFirstPage( page ) ){
         String uriForFirstPage = this.constructFirstPageUri( uriBuilder, pageSize );
         appendCommaIfNecessary( linkHeader );
         linkHeader.append( createLinkHeader( uriForFirstPage, REL_FIRST ) );
      }
      if( this.hasLastPage( page, totalPages ) ){
         String uriForLastPage = this.constructLastPageUri( uriBuilder, totalPages, pageSize  );
         appendCommaIfNecessary( linkHeader );
         linkHeader.append( createLinkHeader( uriForLastPage, REL_LAST ) );
      }
      response.addHeader( HttpConstants.LINK_HEADER, linkHeader.toString() );
   }
   
   String constructNextPageUri( UriComponentsBuilder uriBuilder, int page, final int size ){
      return uriBuilder.replaceQueryParam( "page", page + 1 ).replaceQueryParam( "size", size ).build().encode().toUriString();
   }
   String constructPrevPageUri( UriComponentsBuilder uriBuilder, int page, final int size ){
      return uriBuilder.replaceQueryParam( "page", page - 1 ).replaceQueryParam( "size", size ).build().encode().toUriString();
   }
   String constructFirstPageUri( UriComponentsBuilder uriBuilder, final int size ){
      return uriBuilder.replaceQueryParam( "page", 0 ).replaceQueryParam( "size", size ).build().encode().toUriString();
   }
   String constructLastPageUri( UriComponentsBuilder uriBuilder, int totalPages, final int size ){
      return uriBuilder.replaceQueryParam( "page", totalPages ).replaceQueryParam( "size", size ).build().encode().toUriString();
   }
   
   boolean hasNextPage( int page, int totalPages ){
      return page < totalPages - 1;
   }
   boolean hasPreviousPage( int page ){
      return page > 0;
   }
   boolean hasFirstPage( int page ){
      return this.hasPreviousPage( page );
   }
   boolean hasLastPage( int page, int totalPages ){
      return totalPages > 1 && this.hasNextPage( page, totalPages );
   }
   
   void appendCommaIfNecessary( final StringBuilder linkHeader ){
      if( linkHeader.length() > 0 ){
         linkHeader.append( ", " );
      }
   }
	
}