I'm running an embedded Jetty 8 server that loads a few *.war files at startup:
for (File aWebAppDirectory : aWebAppDirectories) {
if (aWebAppDirectory.exists() && aWebAppDirectory.isDirectory()) {
for (File warFile : aWebAppDirectory.listFiles(new WarFileFilter())) { String basename = warFile.getName().replaceFirst("\\.war$", "");
fHandlers.addHandler(new WebAppContext(warFile.getAbsolutePath(), "/" + basename));
}
}
}
These war-files have some dependencies on a few classes that may or may not exist in the classpath.
Right now if one of my servlets is missing a dependency, my entire embedded Jetty service fails. (Because of NoClassDefFoundExceptions)
I need a method that allows me to catch exceptions for failing servlets and simply doesn't activate them. I'm looking for the same thing that TomCat does when a servlet fails to load: It still loads the rest.
I haven't found any solutions after some time searching on Google.
Anyone know how I can tackle this problem using embedded Jetty 8?
If anyone is curious how I fixed this, I simply made sure that all my servlets have a wrapper servlet that basically has no dependencies. The wrapper tries to initialize a delegate with dependencies and explicitly checks for NoClassDefFountException. If this happens, the delegate is set to null, and all calls to the wrapper interface will result in an exception.
So on a high level:
public class ServletWrapper extends HttpServlet{
private ServletDelegate fDelegate;
//If this is false, the delegate does not work, and we should not forward anything to it.
private boolean fAvailable = false;
public ServletWrapper(){
try{
fDelegate = new ServletDelegate();
fAvailable = true;
} catch (NoClassDefFoundError e) {
fAvailable = false;
}
}
#Override
protected void doPost( HttpServletRequest request, HttpServletResponse response )
throws ServletException, IOException {
if ( !fAvailable || fDelegate==null ) {
response.sendError( HttpServletResponse.SC_SERVICE_UNAVAILABLE, LSP_MISSING_ERROR_MESSAGE );
return;
}
fDelegate.doPost(request,response);
}
}
It's simple enough, and it works.
I recently discovered the magic of using MDCs when logging. It works perfectly.
I have the following method:
public static final String MDC_CLIENT="client";
public static final String MDC_SESSION="session";
public static final String MDC_DEVICE="device";
// Called for every request.
public static void request(final HttpServletRequest request) {
// The MDC is a thread-local storage accessable from the log formatter.
MDC.put(MDC_CLIENT, String.format("%s:%s", request.getRemoteHost(), request.getRemotePort()));
HttpSession session = request.getSession();
MDC.put(MDC_SESSION, session.getId());
MDC.put(MDC_DEVICE, (String)session.getAttribute("device"));
// Also record the context.
setContext(session.getServletContext());
}
This is called as the first action in every jsp. This allows me to keep track of the details of the session in the log nicely.
However - how do I know when to remove these map entries? What event should I watch for that will allow me to tidy up the map?
I am hosting under Tomcat. If it re-uses threads then I won't leak memory because these are essentially thread-local so each put will overwrite the old put from the last time the thread was used. If it doesn't - or I am hosted under something else that doesn't - I am essentially growing the map potentially forever - or at least until the host is restarted.
I think the essence of my question is - is there an event I can detect that indicates that a particular session or thread is finished with and about to be released.
Rather than putting the call in every JSP I would register a ServletRequestListener, which gets notified both when the request starts and when it finishes:
public class MDCListener implements ServletRequestListener {
public void requestInitialized(ServletRequestEvent e) {
YourUtilityClass.request((HttpServletRequest)e.getServletRequest());
}
public void requestDestroyed(ServletRequestEvent e) {
YourUtilityClass.tearDown((HttpServletRequest)e.getServletRequest());
}
}
Alternatively you could use a filter which lets you wrap around the usual request processing flow:
void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
setupMDC();
chain.doFilter(request, response);
tearDownMDC();
}
Either way you simply register the relevant classes in web.xml and the container should take care of the rest.
Iam trying to use websockets in my already working servlet. My Problem is that i used the "writer" class to post HTML onto the broswer but I cant find a similar class for WebSockets.
My servlet looks like this:
#WebServlet("/TestServlet")
public class TestServlet extends HttpServlet {
private List<ISort> sortierListe = new ArrayList<ISort>();
private File file1;
private PrintWriter writer2;
private boolean sortFinished;
boolean bSubmitForFilenamePressedCopy;
BufferedReader in;
// private String sEingabe;
private static final long serialVersionUID = 1L;
/**
* #see HttpServlet#HttpServlet()
*/
public TestServlet() {
super();
this.initSortierverfahren();
}
private void initSortierverfahren() {
sortierListe.add(new BubbleSort());
sortierListe.add(new QuickSort());
}
/**
* #see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse
* response)
*/
protected void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException, IOException {
[...]
PrintWriter writer = response.getWriter();
writer2 = writer;
writer.println("<html>");
writer.println("<head><title>Text Sortieren!</title>");
writer.println("</head>");
writer.println("<body marginwidth='40' leftmargin='40' bgcolor='#E5E5E5'>");
writer.println("<table bgcolor='#FFFFFF' height='100%' width='57%' border='0' cellpadding=10>");
writer.println("<tr height='10%'>");
writer.println("
[...]
The code is too long to post everything, but the Servlet basicly creates a form where I can enter a path to a .txt file. The txt file will then be sorted by either bubblesort or quicksort.
My Question is: How can I use this code in a WebSocket without rewriting everything in javascript? Just some basic help for the start would help me alot I think. Thanks in advance.
First, If you want to work with websockets from tomcat, you should extend from corresponding base class WebSocketServlet.
Second, I don't think that it's worth using websocket in your case. Websockets are good for applications which require real-time interactions. Yours obviously doesn't require it.
If you still want to do this, just create some simple javascript which will write your html to the body. Something along lines with:
websocket = new WebSocket(wsUri);
websocket.onmessage = function(evt) {
document.body.innerHtml += evt.data
};
But as I said, I see no use in such a code.
Before you make move from normal servlet to websocket there are few things keep in mind.
Use latest apache tomcat version. Plder version won't support websockets. (I used version 7.0.42 in my case)
You can't simply replace your Servlet with WebSocket. Purpose of both is totally different. Google it out for more details.
This sample code for WebSocket provides server side as well as client side sample code. You should refer it to get started with.
I need to upload a file in GWT in the background, ie. not from a visual widget.
For this I've found the RequestBuilder class, but little documentation on how to use it for upload purposes.
The file content I need to upload is 100% plaintext.
My code so far looks like this:
final String filename = UUID.randomUUID().toString() + ".txt";
RequestBuilder rb = new RequestBuilder(RequestBuilder.POST, "http://localhost/upload");
rb.setRequestData(selected.getBody()); // getBody() is plain-text
rb.setHeader("Content-Type", "application/x-www-form-urlencodeddata");
rb.setCallback(new RequestCallback() {
#Override
public void onResponseReceived(Request request, Response response) {
w.setUrl("http://localhost/magic.html?hide=status&open=" + filename);
w.show();
w.maximize();
}
#Override
public void onError(Request request, Throwable exception) {
exception.printStackTrace();
}
});
// Checked Exceptions sucks *sigh*
try {
rb.send();
}
catch (RequestException e) {
e.printStackTrace();
}
I hope someone can give me some pointers towards solving this issue, thanks!
I think it's not possible to upload files to the server without user interaction using JavaScript only. I think it's blocked by the browser, because it would mean anybody could upload any file from your system when you visit a site, which would be a major security problem. I don't know why you would want to do this, but I guess you need to look at another approach to what you are trying to do.
It seems that you can upload files with gears, so in the worst case you could implement something like this with javascript: link text
I am writing a simple application that lets a user upload images. After the upload, the user can tag them or remove them.
I figured out how to upload the files and save them once the files are uploaded. I am keeping tracking of a global path where images are kept. In the database I keep the meta data about the images like file name, tags, etc.
I am using Java/JSP (specifically Stripes framework but my problem is generic).
My question is where do I keep these image files once they are uploaded?
Right now I have two web applications deployed on a Tomcat server. One main web application and other one is the where I upload the images.
But this does not work as I can not see the uploaded images in the main application until I redeploy/restart Tomcat.
It seems like Tomcat does not pick newly uploaded images automatically.
Does anyone have any solutions?
This is a simple project, so I do not want to store them in a database or use Apache for images. That is all just too complicated for this small project.
Thanks.
Definitely don't store the images in the database, but you will want to store the image path in the database. This will allow you to store the image just about anywhere.
Since you are using two tomcat applications, your best bet may be to store the images outside of either app and stream the image back to the user instead of letting tomcat manage the files. Otherwise, I would ask why you are trying to do this with two web apps.
However, storing uploaded images inside the web-app directory is not a wise thing to do, and you know it.
By the way, you might want to look this stackoverflow thread, lately discussed where to store the images. It might not solve your issue, surely will give you more confidence on what you are doing.
I've solved this in different ways.
First, the non-portable way, is that Glassfish (and I do believe Tomcat as well) allows you to map an external directory in to the webapps hierarchy. This works really well and does exactly what you want. It lets you store your images in an external directory away from your webapp, yet still serve them up.
However, this technique is not portable.
The way to I've done it portably is by creating a filter.
You place the filter someplace obvious, say "/images".
What the filter does is this:
it checks for the image (or anything, it works with any static resource) in a special directory within the webapp. For our example we'll use the url "/webapp/images".
if the file DOES NOT exist, we copy the file from your external location in to the appropriate spot within the webapp. So, let's say the reqyest url is "/images/banner.gif". And that your files are stored on disk at "/home/app/images". So, our source file is "/home/app/images/banner.gif". We then copy it to where we want it in the webapp tree. We use "ServletContext.getRealPath" for this. So, the destination will be "ServletContext.get RealPath("/webapp/images/banner.gif"). Just copy the source to the destination.
if the file already existed, or now exists, simply forward to the actual image at /webapp/images/banner.gif.
Effectively you end up having a file cache within your webapps deployment tree. The down side is that it's a cache, so it needs to be maintained (i.e. you should check if the original is newer than your cache, make sure you delete if the source is deleted, etc.). Also, it duplicates your resources, so your images will consume, eventually, twice as much disk space. Finally, there's the initial copy cost at start up.
However, it DOES work, and it prevents you from having to serve up static resources using your own code. (Which is the 3rd solution, map a filter/servlet to intercept the URLs and simply stream it your self.)
I would look at the construct within Tomcat (assuming it exists) to do the mapping for you. I know it exists in Glassfish. (Google alternatedocroot for Glassfish to see how it works.)
I was using two web applications to avoid over writing the uploaded images in case I redeploy a new main application war file.
But as you mention there is no other option but to stream them through a Servlet or something I guess I can keep them outside tomcat directory.
I wanted to avoid writing this Streaming Servlet. Just too small project to deal with all the mess (like proper content type, 404, etc.) while writing the streaming servlet.
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Image streaming Servlet.
*/
public class ImageDisplayServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
/**
* #see HttpServlet#HttpServlet()
*/
public ImageDisplayServlet() {
super();
}
/**
* #see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
*/
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
String relativePath = trimToEmpty(request.getPathInfo());
// Make sure no one try to screw with us.
// This is important as user can literally access any file if we are not careful
if(isXSSAttack(relativePath) == false) {
String pathToFile = this.getServletContext().getRealPath(request.getPathInfo());
File file = new File(pathToFile);
System.out.println("Looking for file " + file.getAbsolutePath());
// show a 404 page
if(!file.exists() || !file.isFile()) {
httpError(404, response);
} else {
try {
streamImageFile(file, response);
} catch(Exception e) {
// Tell the user there was some internal server error.\
// 500 - Internal server error.
httpError(500, response);
e.printStackTrace();
}
}
} else {
// what to do if i think it is a XSS attack ?!?
}
}
private void streamImageFile(File file, HttpServletResponse response) {
// find the right MIME type and set it as content type
response.setContentType(getContentType(file));
BufferedInputStream bis = null;
BufferedOutputStream bos = null;
try {
response.setContentLength((int) file.length());
// Use Buffered Stream for reading/writing.
bis = new BufferedInputStream(new FileInputStream(file));
bos = new BufferedOutputStream(response.getOutputStream());
byte[] buff = new byte[(int) file.length()];
int bytesRead;
// Simple read/write loop.
while (-1 != (bytesRead = bis.read(buff, 0, buff.length))) {
bos.write(buff, 0, bytesRead);
}
} catch (Exception e) {
throw new RuntimeException(e);
} finally {
if (bis != null) {
try {
bis.close();
} catch (IOException e) {
e.printStackTrace();
// To late to do anything about it now, we may have already sent some data to user.
}
}
if (bos != null) {
try {
bos.close();
} catch (IOException e) {
e.printStackTrace();
// To late to do anything about it now, we may have already sent some data to user.
}
}
}
}
private String getContentType(File file) {
if(file.getName().length() > 0) {
String[] parts = file.getName().split("\\.");
if(parts.length > 0) {
// only last part interests me
String extention = parts[parts.length - 1];
if(extention.equalsIgnoreCase("jpg")) {
return "image/jpg";
} else if(extention.equalsIgnoreCase("gif")) {
return "image/gif";
} else if(extention.equalsIgnoreCase("png")) {
return "image/png";
}
}
}
throw new RuntimeException("Can not find content type for the file " + file.getAbsolutePath());
}
private String trimToEmpty(String pathInfo) {
if(pathInfo == null) {
return "";
} else {
return pathInfo.trim();
}
}
private void httpError(int statusCode, HttpServletResponse response) {
try {
response.setStatus(statusCode);
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.append("<html><body><h1>Error Code: " + statusCode + "</h1><body></html>");
writer.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
private boolean isXSSAttack(String path) {
boolean xss = false;
// Split on the bases of know file separator
String[] parts = path.split("/|\\\\");
// Now verify that no part contains anything harmful
for(String part : parts) {
// No double dots ..
// No colons :
// No semicolons ;
if(part.trim().contains("..") || part.trim().contains(":") || part.trim().contains(";")) {
// Fire in the hole!
xss = true;
break;
}
}
return xss;
}
/**
* #see HttpServlet#doPost(Ht/promotions/some.jpgtpServletRequest request, HttpServletResponse response)
*/
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}
}
Ok Here is a Servlet that I quickly wrote that can stream images:
Here is the List of limitations and know issues:
May have XSS vulnerability use with care
Not production ready use as reference
Images need to in the web application directory. Can be easily change but I too lazy (it is not worth it the project is too small)
Only stream jpg,gif or png files.
Usage:
Let say you deploy this web application called images as separate application.
http://www.example.com/images/promotions/promo.jpg
means there should be a directory in "promotions" with image "promo.jpg" with in this images web application.
PS: Do not ask why I am doing this Servlet Container only solution that sucks big time.
<servlet>
<description></description>
<display-name>ImageDisplayServlet</display-name>
<servlet-name>ImageDisplayServlet</servlet-name>
<servlet-class>com.example.images.ImageDisplayServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>ImageDisplayServlet</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
Oh ya configure your Servlet like above for best results :P