import java.io.*; public class AlbumServlet extends PhotoApplicationServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { User user = getCurrentUser(request); if (user == null) { response.sendRedirect(LOGIN_PAGE_URL); return; } PrintWriter out = startWritingPage(response); String albumName = request.getParameter("album"); if (!validateAlbumName(albumName, out)) return; Album album = loadAlbumByName(albumName); if (!validateAlbum(album, out)) return; new AlbumPage(album, request).printPage(out); out.flush(); } private boolean validateAlbum(Album album, PrintWriter out) { boolean valid = true; if (album == null) { new ErrorPage("Could not load album '" + album.getName() + "'").printError(out); valid = false; } return valid; } private boolean validateAlbumName(String albumName, PrintWriter out) { boolean valid = true; if (albumName == null || albumName.equals("")) { new ErrorPage("Missing parameter: album").printError(out); valid = false; } return valid; } private PrintWriter startWritingPage(HttpServletResponse response) { response.setContentType("text/html"); disableCache(response); PrintWriter out = response.getWriter(); return out; } User getCurrentUser(HttpServletRequest request) { return (User) (request.getSession(true).getAttribute(CURRENT_USER_SESSION_ATTRIBUTE)); } private void disableCache(HttpServletResponse response) { response.setHeader("Cache-Control", "no-cache"); //HTTP 1.1 response.setHeader("Pragma", "no-cache"); //HTTP 1.0 // prevents caching at the proxy server response.setHeader("Expires", "Thu, 01 Jan 1970 00:00:00 GMT"); } } class Page { protected void printHead(PrintWriter out, String title) { out.println(""); out.println(""); out.println(""); out.println("" + title + ""); out.println(""); } } class AlbumPage extends Page { private Album album; private HttpServletRequest request; public AlbumPage(Album album, HttpServletRequest request) { this.album = album; this.request = request; } private static final int PICTURES_PER_PAGE = 20; private int getPageNumber() { String pageParameter = request.getParameter("page"); int page; if (pageParameter == null || pageParameter.equals("")) { page = 0; } else { page = Integer.parseInt(pageParameter); } return page; } public void printPage(PrintWriter out) { String title = "Album: " + album.getName(); printHead(out, title); out.println(""); out.println("

" + title + "

"); int end = printPictureTable(out, getPageNumber()); printPreviousAndNextLinks(out, getPageNumber(), end); } private void printPreviousAndNextLinks(PrintWriter out, int pageNumber, int end) { out.println("
"); if (pageNumber > 0) { out.print("<< previous "); } if (end < album.getPictures().size()) { out.print(" next >>"); } out.println("
"); } private int printPictureTable(PrintWriter out, int page) { out.println(""); int start = page * PICTURES_PER_PAGE; int end = start + PICTURES_PER_PAGE; end = Math.min(end, album.getPictures().size()); for (int i = start; i < end; ++i) { Picture picture = (Picture) album.getPictures().get(i); printPicture(out, picture); } out.println("
"); return end; } private void printPicture(PrintWriter out, Picture picture) { out.print(""); out.print(""); out.print(""); out.print(""); out.print(""); out.print(picture.getCaption()); out.print(""); out.println(""); } public void printError(PrintWriter out, String message) { printHead(out, "Error"); out.println("

"); out.print(message); out.print("

"); out.println(""); } } class ErrorPage extends Page { String message; public ErrorPage(String message) { this.message = message; } public void printError(PrintWriter out) { printHead(out, "Error"); out.println("

"); out.print(message); out.print("

"); out.println(""); } }