I'm in process of making a Server to display a HTML page as a college assessment. All the files are stored locally. Using Firefox to connect to server (chrome seems to block images).
The code below works fine if i type a HTTP Response in the HTML file itself that's being transferred (I'm typing 'HTTP/1.1 200 OK' at start of HTML file)
{
byte[] pageToBytes = Files.readAllBytes(webContent.toPath());
os.write(pageToBytes);
os.flush();
os.close();
}
But if i try and send HTTP response first ,then HTML after, it refuses to load the images in my specified in my HTML code.
Here is Code i'm trying to figure out problem with:
{
byte[] pageToBytes = Files.readAllBytes(webContent.toPath());
String HttpOK = "HTTP/1.1 200 OK\n\r";
os.write(HttpOK.getBytes());
os.write(pageToBytes);
os.flush();
os.close();
}
Any insights would be much appreciated :)
You should read about HTTP requests, when the browser makes a request open a channel of communication between the server and the client, which is the stream you are writing to, this channel closes once the client has received a response.
In your code you are responding once, but the second time the stream is already closed that's why the response body is never reaching the client. Also the server automatically sends a 200 code when there is no error or the code says otherwise.
Since you are trying to make an http server it is good to look at here
it explains how to handle an http request & response.
Related
I am using Java servlets using Apache tomcat.
I've configured a threadpool and am dealing with each request.
My page is taking in many GET requests at the same time, I'm wondering if I can respond to the server after each get request before any of the logic happens?
So server gives me a request -> I respond with either 'good send another' or 'bad send another' before I start my queueing.
Any help would be much appreciated!
EDIT
Sorry that was terribly written :(
What I'm asking for is a way to send a Header to the client (in this case it's a server which sends me lots of requests). The response would just be 200 or error based on the information I get sent.
What my program is doing:
My servlet gets sent lots of GET requests from one client. (over 100,000) Which I am using tomcat to queue and put into a threadpool. It is then assigned to a worker thread which processes it and puts it into a database.
I've been told to do is send a request back to that server saying 'ok received it'. I think I can use a header response but I don't have the URL of that client (and the client can change for different campaigns). So was wondering what the best way would be to send that response.
After doing some more research I think what I'm looking for is ServletOutputStream.
response.setContentType("text/html");
ServletOutputStream output = response.getOutputStream();
output.flush();
output.close();
Using servlet output stream where do I set the <head><body> tag? and insert the header response afterwards.
The simple answer is "sure".
If these are get requests from a web page for a web page, include a refresh timer and send back some token that can be used to identify the difference between a first-time-request and an I-requested-earlier-are-you-done request. In this case the refresh timer can be set via a meta refresh tag.
If the get requests are part of a REST API then you can define "got it and I'm working" into the protocol. For instance, return a 202 to indicate "got it but not done" and return 200 to indicate "done". As with the html page, consider sending some token back with the 202 that identifies the pending request.
I have a client who is posting some data to our server with http POST method. Our server is resin 3.0 with java. When I send response whether data is saved or not the the content length of the response is not set. client is using curl library(php wrapper over it) and they are receiving content length as 0. When I try to submit a form through a browser to our server on the same url it works and response is shown.
I tried using Apache HttpClient to submit data through postmethod and I received content length as -1 but i did get the full response. I'm not able to understand where is the problem. Also I did some google and found that resin do some chunked encoding while sending the response. But i guess it does this also for GET method. But for GET method my client is getting the content length and is able to get the response as well. Need help with this.
"Content-Length" is a header in the response, which warns the client on how big the response will be. It is not the actual length of the stream.
You can set it's value with response.setContentLength(...); in your Servlet.
I'm an experienced Java programmer but a newbie web developer. I'm trying to put together a simple web service using the HttpServer class that ships with JDK 1.6. From the examples I've viewed, some typical code from an HttpHandler's handle method would look something like this:
Headers responseHeaders = exchange.getResponseHeaders();
responseHeaders.set("Content-Type", "text/plain");
exchange.sendResponseHeaders(200, 0);
OutputStream responseBody = exchange.getResponseBody();
responseBody.write(createMyResponseAsBytes());
responseBody.close();
My question: What happens if I send a response header to indicate success (i.e. response code 200) and perhaps begin to stream back data and then encounter an exception, which would necessitate sending an "internal server error" response code along with some error content? In other words, what action should I take given that I've already sent a partial "success" response back to the client at the point where I encounter the exception?
200 is not sent until you either flush the stream or close it.
But once it is sent, there is nothing you can do about it.
Usually it may happen only when you have a really large amount of data and you use chunking.
I wrote a simple server using java socket programming and intended to make that offered 2 files for download and display some html response when the download finished. What I did is use PrintWriter.print or DataOutPutStream.writeBytes to send the string including html tags and response string to the browser, then use OutputStream.write to send the file requested. The URL I typed in the browser was like 127.0.0.1/test1.zip, relevant code fragments as following:
pout.print("<html>");
pout.print("<head>");
pout.print("<meta http-equiv=\"Content-Type\" content=\"text/html; charset=ISO-8859-1/\">");
pout.print("<title>Response</title>");
pout.print("</head>");
pout.print("<body>");
pout.print(createResponseHeader(200, fileTypeCode));
pout.print("</body>");
pout.print("</html>");
pout.print(createResponseHeader(200, fileTypeCode));
pout.flush();
byte[] buffer = new byte[client.getSendBufferSize()];
int bytesRead = 0;
System.out.println("Sending...");
while((bytesRead = requestedFile.read(buffer))>-1)
{
out.write(buffer,0,bytesRead);
}
The pout is a PrintWriter while out is OutputStream.
The problem is when I try to use 127.0.0.1/test2.zip to download the file, it doesn't let me download, instead, print out the response string and a lot of non-sense character in the browser, e.g.
HTTP/1.0 200 OK
Connection: close
Server: COMP5116 Assignment Server v0
Content-Type: application/x-zip-compressed
PK‹â:Lmá^ЛàÍ test2.wmvì[y<”Ûÿ?3ÃØ—Ab¸eeË’5K"»±f_B*à Å*YÛ•¥M5h±¯u[(\·(-÷F)ß3ÏɽݺÝ×ýýñ{Íg^ÏûyžóYÏçœçyÎç¼P’>™îÝ+½Žö6A€;;ýmüH»êt©k]R#*€.G‰µÅRÏøÍLÔóZ; ´£åÑvP¹æª#õó”æÇ„‹&‡ëî9q‰Ú>LkÇÈyÖ2qãÌÆ(ãDŸã©ïÍš]Ð4iIJ0Àª3]B€ðÀ¸CôÁ`ä è1ü½¤Ã¬$ pBi
I believe it simply display the zip file as string with the response header all together. It seems once the PrintWriter is used before the code of sending the file, the whole output stream is used for sending string instead of bytes. However, if I put the part of code of sending the response AFTER the code of sending file, the download works properly but no any response message print out in the browser, just a blank page.
You've to remove your HTML code from here and send only the binary data. You can't mix them in a single servlet.
To achieve what you want to do is not easy.
I would start the download with some JavaScript code in the page, then the page will poll with Ajax for a server side servlet that will know if the download is completed for that particular session. In fact there is no download completed event in JavaScript.
To have this information the download servlet will update the session with a flag when download is completed.
When your Ajax call will return that the download is completed, you can change the text in the page or redirect to a new page.
Edit: Alternatively, if you can change your requirements, it will be much easier to show all messages that you have to show just before the download, and put target="_blank" in the download link so your page is not lost by clicking on the link.
I have Java webserver (no standard software ... self written). Everything seems to work fine, but when I try to call a page that contains pictures, those pictures are not displayed. Do I have to send images with the output stream to the client? Am I missing an extra step?
As there is too much code to post it here, here is a little outline what happens or is supposed to happen:
1. client logs in
2. client gets a session id and so on
3. the client is connected with an output stream
4. we built the response with the HTML-Code for a certain 'GET'-request
5. look what the GET-request is all about
6. send html response || file || image (not working yet)
So much for the basic outline ...
It sends css-files and stuff, but I still have a problem with images!
Does anybody have an idea? How can I send images from a server to a browser?
Thanks.
I check requests from the client and responses from the server with charles. It sends the files (like css or js) fine, but doesn't with images: though the status is "200 OK" the transfer-encoding is chunked ... I have no idea what that means!? Does anybody know?
EDIT:
Here is the file-reading code:
try{
File requestedFile = new File( file );
PrintStream out = new PrintStream( this.getHttpExchange().getResponseBody() );
// File wird geschickt:
InputStream in = new FileInputStream( requestedFile );
byte content[] = new byte[(int)requestedFile.length()];
in.read( content );
try{
// some header stuff
out.write( content );
}
catch( Exception e ){
e.printStackTrace();
}
in.close();
if(out!=null){
out.close();
System.out.println( "FILE " + uri + " SEND!" );
}
}
catch ( /*all exceptions*/ ) {
// catch it ...
}
Your browser will send separate GET image.png HTTP 1.1 requests to your server, you should handle these file-gets too. There is no good way to embed and image browser-independent in HTML, only the <img src="data:base64codedimage"> protocol handler is available in some browsers.
As you create your HTML response, you can include the contents of the external js/css files directly between <script></script> and <style></style> tags.
Edit: I advise to use Firebug for further diagnostics.
Are you certain that you send out the correct MIME type for the files?
If you need a tiny OpenSource webserver to be inspired by, then have a look at http://www.acme.com/java/software/Acme.Serve.Serve.html which serves us well for ad-hoc server needs.
Do I have to send those external files
or images with the output stream to
the client?
The client will make separate requests for those files, which your server will have to serve. However, those requests can arrive over the same persisten connection (a.k.a. keepalive). The two most likely reasons for your problem:
The client tries to send multiple requests over a persistent connection (which is the default with HTTP 1.1) and your server is not handling this correctly. The easiest way to avoid this is to send a Connection: close header with the response.
The client tries to open a separate connection and your server isn't handling it correctly.
Edit:
There's a problem with this line:
in.read( content );
This method is not guaranteed to fill the array; it will read an arbitrary number of bytes and return that number. You have to use it in a loop to make sure everything is read. Since you have to do a loop anyway, it's a good idea to use a smaller array as a buffer to avoid keeping the whole file in memory and running into an OutOfMemoryError with large files.
Proabably step #4 is where you are going wrong:
// 4. we built the response with the HTML-Code for a certain 'GET'-request
Some of the requests will be a 'GET /css/styles.css' or 'GET /js/main.js' or 'GET /images/header.jpg'. Make sure you stream those files in those circumstances - try loading those URLs directly.
Images (and css/js files) are requested by the browser as completely separate GET requests to the page, so there's definitely no need to "send those ... with the output stream". So if you're getting pages served up ok, but images aren't being loaded, my first guess would be that you're not setting your response headers appropriately (for example, setting the Content-Type of the response to text/html), so the browser isn't interpreting it as a proper page & therefore not loading the images.
Some other things to try if that doesn't work:
Check if you can access an image directly
Use something like firebug or fiddler to check whether the browser is actually requesting the image/css/js files & that all your request/response headers look ok
Use an existing web server!