Template abstrak untuk servlet sumber daya statis
Sebagian didasarkan pada blog ini dari tahun 2007, inilah templat abstrak yang dimodernisasi dan dapat digunakan kembali untuk servlet yang menangani caching dengan benar ETag,, If-None-Matchdan If-Modified-Since(tetapi tidak ada dukungan Gzip dan Range; hanya untuk membuatnya tetap sederhana; Gzip dapat dilakukan dengan filter atau melalui konfigurasi wadah).
public abstract class StaticResourceServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
private static final long ONE_SECOND_IN_MILLIS = TimeUnit.SECONDS.toMillis(1);
private static final String ETAG_HEADER = "W/\"%s-%s\"";
private static final String CONTENT_DISPOSITION_HEADER = "inline;filename=\"%1$s\"; filename*=UTF-8''%1$s";
public static final long DEFAULT_EXPIRE_TIME_IN_MILLIS = TimeUnit.DAYS.toMillis(30);
public static final int DEFAULT_STREAM_BUFFER_SIZE = 102400;
@Override
protected void doHead(HttpServletRequest request, HttpServletResponse response) throws ServletException ,IOException {
doRequest(request, response, true);
}
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doRequest(request, response, false);
}
private void doRequest(HttpServletRequest request, HttpServletResponse response, boolean head) throws IOException {
response.reset();
StaticResource resource;
try {
resource = getStaticResource(request);
}
catch (IllegalArgumentException e) {
response.sendError(HttpServletResponse.SC_BAD_REQUEST);
return;
}
if (resource == null) {
response.sendError(HttpServletResponse.SC_NOT_FOUND);
return;
}
String fileName = URLEncoder.encode(resource.getFileName(), StandardCharsets.UTF_8.name());
boolean notModified = setCacheHeaders(request, response, fileName, resource.getLastModified());
if (notModified) {
response.sendError(HttpServletResponse.SC_NOT_MODIFIED);
return;
}
setContentHeaders(response, fileName, resource.getContentLength());
if (head) {
return;
}
writeContent(response, resource);
}
/**
* Returns the static resource associated with the given HTTP servlet request. This returns <code>null</code> when
* the resource does actually not exist. The servlet will then return a HTTP 404 error.
* @param request The involved HTTP servlet request.
* @return The static resource associated with the given HTTP servlet request.
* @throws IllegalArgumentException When the request is mangled in such way that it's not recognizable as a valid
* static resource request. The servlet will then return a HTTP 400 error.
*/
protected abstract StaticResource getStaticResource(HttpServletRequest request) throws IllegalArgumentException;
private boolean setCacheHeaders(HttpServletRequest request, HttpServletResponse response, String fileName, long lastModified) {
String eTag = String.format(ETAG_HEADER, fileName, lastModified);
response.setHeader("ETag", eTag);
response.setDateHeader("Last-Modified", lastModified);
response.setDateHeader("Expires", System.currentTimeMillis() + DEFAULT_EXPIRE_TIME_IN_MILLIS);
return notModified(request, eTag, lastModified);
}
private boolean notModified(HttpServletRequest request, String eTag, long lastModified) {
String ifNoneMatch = request.getHeader("If-None-Match");
if (ifNoneMatch != null) {
String[] matches = ifNoneMatch.split("\\s*,\\s*");
Arrays.sort(matches);
return (Arrays.binarySearch(matches, eTag) > -1 || Arrays.binarySearch(matches, "*") > -1);
}
else {
long ifModifiedSince = request.getDateHeader("If-Modified-Since");
return (ifModifiedSince + ONE_SECOND_IN_MILLIS > lastModified); // That second is because the header is in seconds, not millis.
}
}
private void setContentHeaders(HttpServletResponse response, String fileName, long contentLength) {
response.setHeader("Content-Type", getServletContext().getMimeType(fileName));
response.setHeader("Content-Disposition", String.format(CONTENT_DISPOSITION_HEADER, fileName));
if (contentLength != -1) {
response.setHeader("Content-Length", String.valueOf(contentLength));
}
}
private void writeContent(HttpServletResponse response, StaticResource resource) throws IOException {
try (
ReadableByteChannel inputChannel = Channels.newChannel(resource.getInputStream());
WritableByteChannel outputChannel = Channels.newChannel(response.getOutputStream());
) {
ByteBuffer buffer = ByteBuffer.allocateDirect(DEFAULT_STREAM_BUFFER_SIZE);
long size = 0;
while (inputChannel.read(buffer) != -1) {
buffer.flip();
size += outputChannel.write(buffer);
buffer.clear();
}
if (resource.getContentLength() == -1 && !response.isCommitted()) {
response.setHeader("Content-Length", String.valueOf(size));
}
}
}
}
Gunakan bersama-sama dengan antarmuka di bawah ini yang mewakili sumber daya statis.
interface StaticResource {
/**
* Returns the file name of the resource. This must be unique across all static resources. If any, the file
* extension will be used to determine the content type being set. If the container doesn't recognize the
* extension, then you can always register it as <code><mime-type></code> in <code>web.xml</code>.
* @return The file name of the resource.
*/
public String getFileName();
/**
* Returns the last modified timestamp of the resource in milliseconds.
* @return The last modified timestamp of the resource in milliseconds.
*/
public long getLastModified();
/**
* Returns the content length of the resource. This returns <code>-1</code> if the content length is unknown.
* In that case, the container will automatically switch to chunked encoding if the response is already
* committed after streaming. The file download progress may be unknown.
* @return The content length of the resource.
*/
public long getContentLength();
/**
* Returns the input stream with the content of the resource. This method will be called only once by the
* servlet, and only when the resource actually needs to be streamed, so lazy loading is not necessary.
* @return The input stream with the content of the resource.
* @throws IOException When something fails at I/O level.
*/
public InputStream getInputStream() throws IOException;
}
Yang Anda butuhkan hanyalah memperluas dari servlet abstrak yang diberikan dan mengimplementasikan getStaticResource()metode sesuai javadoc.
Contoh nyata melayani dari sistem file:
Berikut ini adalah contoh nyata yang menyajikannya melalui URL seperti /files/foo.extdari sistem file disk lokal:
@WebServlet("/files/*")
public class FileSystemResourceServlet extends StaticResourceServlet {
private File folder;
@Override
public void init() throws ServletException {
folder = new File("/path/to/the/folder");
}
@Override
protected StaticResource getStaticResource(HttpServletRequest request) throws IllegalArgumentException {
String pathInfo = request.getPathInfo();
if (pathInfo == null || pathInfo.isEmpty() || "/".equals(pathInfo)) {
throw new IllegalArgumentException();
}
String name = URLDecoder.decode(pathInfo.substring(1), StandardCharsets.UTF_8.name());
final File file = new File(folder, Paths.get(name).getFileName().toString());
return !file.exists() ? null : new StaticResource() {
@Override
public long getLastModified() {
return file.lastModified();
}
@Override
public InputStream getInputStream() throws IOException {
return new FileInputStream(file);
}
@Override
public String getFileName() {
return file.getName();
}
@Override
public long getContentLength() {
return file.length();
}
};
}
}
Contoh nyata melayani dari basis data:
Berikut ini adalah contoh nyata yang menyajikannya melalui URL seperti /files/foo.extdari database melalui panggilan layanan EJB yang mengembalikan entitas Anda yang memiliki byte[] contentproperti:
@WebServlet("/files/*")
public class YourEntityResourceServlet extends StaticResourceServlet {
@EJB
private YourEntityService yourEntityService;
@Override
protected StaticResource getStaticResource(HttpServletRequest request) throws IllegalArgumentException {
String pathInfo = request.getPathInfo();
if (pathInfo == null || pathInfo.isEmpty() || "/".equals(pathInfo)) {
throw new IllegalArgumentException();
}
String name = URLDecoder.decode(pathInfo.substring(1), StandardCharsets.UTF_8.name());
final YourEntity yourEntity = yourEntityService.getByName(name);
return (yourEntity == null) ? null : new StaticResource() {
@Override
public long getLastModified() {
return yourEntity.getLastModified();
}
@Override
public InputStream getInputStream() throws IOException {
return new ByteArrayInputStream(yourEntityService.getContentById(yourEntity.getId()));
}
@Override
public String getFileName() {
return yourEntity.getName();
}
@Override
public long getContentLength() {
return yourEntity.getContentLength();
}
};
}
}