Identifying the Content-Type of a file for HttpURLConnection
in [Java Help]
|
Prev: Button Animation
Next: servlet + login + cookies+ https
From: Public Network Services on 31 Jul 2010 14:42 Hi... I am playing with HttpURLConnection to upload files to a remote server and cannot seem to figure out a consistent way of identifying the Content-Type of a file to be uploaded. I assumed that "application/ octet-stream" would be a generic type to supply, but apparently this is not the case. More specifically, I can read a file into a byte array (fileBytes) and open an HttpConnection to a destination URL (url), but setting the Content-Type property does not work. The code I use is: HttpURLConnection connection = url.openConnection(); connection.setRequestProperty("Content-Length", String.valueOf(fileBytes.length)); connection.setRequestProperty("Content-Type", "application/octet- stream"); If, immediately after the above, I do a connection.getContentType() I get a null value (or an Exception saying that the connection is already connected)! Eventually, my file gets uploaded through the connection.getOutputStream(), by simply doing DataOutputStream output = new DataOutputStream(connection.getOutputStream()); output.write(fileContents); but its Content-Type not being properly set causes the server to not recognize it (e.g., if it is an MP3 file, it does not get the speakerphone icon that MP3 files get in the serverÅ web interface, when uploaded via that interface, through a browser). Obviously, this is a solved problem given the multitude of properly working Java-based web clients, so I 'd really aprpeciate someone pointing me to the correct solution. In other words, my questions are: (a) How can I (automatically) identify the Content-Type of a file in Java? (b) How can I properly set that Content-Type in an HttpURLConnection? Many thanks!
From: Arne Vajhøj on 31 Jul 2010 15:26 On 31-07-2010 14:42, Public Network Services wrote: > I am playing with HttpURLConnection to upload files to a remote server > and cannot seem to figure out a consistent way of identifying the > Content-Type of a file to be uploaded. I assumed that "application/ > octet-stream" would be a generic type to supply, but apparently this > is not the case. > > More specifically, I can read a file into a byte array (fileBytes) and > open an HttpConnection to a destination URL (url), but setting the > Content-Type property does not work. The code I use is: > > HttpURLConnection connection = url.openConnection(); > connection.setRequestProperty("Content-Length", > String.valueOf(fileBytes.length)); > connection.setRequestProperty("Content-Type", "application/octet- > stream"); > > If, immediately after the above, I do a > > connection.getContentType() > > I get a null value (or an Exception saying that the connection is > already connected)! > > Eventually, my file gets uploaded through the > connection.getOutputStream(), by simply doing > > DataOutputStream output = new > DataOutputStream(connection.getOutputStream()); > output.write(fileContents); > > but its Content-Type not being properly set causes the server to not > recognize it (e.g., if it is an MP3 file, it does not get the > speakerphone icon that MP3 files get in the serverś web interface, > when uploaded via that interface, through a browser). > > Obviously, this is a solved problem given the multitude of properly > working Java-based web clients, so I 'd really aprpeciate > someone pointing me to the correct solution. > > In other words, my questions are: > > (a) How can I (automatically) identify the Content-Type of a file in > Java? > (b) How can I properly set that Content-Type in an HttpURLConnection? application/octet-stream is fine. You need to specify method as POST. You should not use DataOutputStream just OutputStream is fine. And most important you need to know whether the receiver expects a raw POST or a form submit with a field of type FILE. Those are not send identical! Arne
From: PNS on 1 Aug 2010 21:48 On Jul 31, 10:26 pm, Arne Vajhøj <a...(a)vajhoej.dk> wrote: > On 31-07-2010 14:42, Public Network Services wrote: > > > > > I am playing with HttpURLConnection to upload files to a remote server > > and cannot seem to figure out a consistent way of identifying the > > Content-Type of a file to be uploaded. I assumed that "application/ > > octet-stream" would be a generic type to supply, but apparently this > > is not the case. > > > More specifically, I can read a file into a byte array (fileBytes) and > > open an HttpConnection to a destination URL (url), but setting the > > Content-Type property does not work. The code I use is: > > >     HttpURLConnection connection = url.openConnection(); > >     connection.setRequestProperty("Content-Length", > > String.valueOf(fileBytes.length)); > >     connection.setRequestProperty("Content-Type", "application/octet- > > stream"); > > > If, immediately after the above, I do a > > >     connection.getContentType() > > > I get a null value (or an Exception saying that the connection is > > already connected)! > > > Eventually, my file gets uploaded through the > > connection.getOutputStream(), by simply doing > > >     DataOutputStream output = new > > DataOutputStream(connection.getOutputStream()); > >     output.write(fileContents); > > > but its Content-Type not being properly set causes the server to not > > recognize it (e.g., if it is an MP3 file, it does not get the > > speakerphone icon that MP3 files get in the serverŠweb interface, > > when uploaded via that interface, through a browser). > > > Obviously, this is a solved problem given the multitude of properly > > working Java-based web clients, so I 'd really aprpeciate > > someone pointing me to the correct solution. > > > In other words, my questions are: > > > (a) How can I (automatically) identify the Content-Type of a file in > > Java? > > (b) How can I properly set that Content-Type in an HttpURLConnection? > > application/octet-stream is fine. > > You need to specify method as POST. > > You should not use DataOutputStream just OutputStream is fine. > > And most important you need to know whether the receiver expects > a raw POST or a form submit with a field of type FILE. > > Those are not send identical! > > Arne Hi... I do specify setRequestMethod("POST"). You are right about OutputStream, using DataOutputStream only for writing as I did makes no difference, as the latterŠwrite() method is inherited from the former. Knowing that OutputStream is an abstract class had rather instictively turned me to another, more "concrete" stream class. Also, I use application/octet and uploading works, but, as I said in my original post, the file type is wrong. This does not happen if I manually set the specific content type for a file (e.g., audio/mpeg for MP3), so it all boils down to identifying the file type (at least for the particular server application I send to). One would expect that calling the standard Java connection.getFileNameMap().getContentTypeFor(filename)) would return the proper type, but it returns null, at least for teh Linux OS I am running. I didn't check about the raw vs. form distinction but apparently the server is fine with raw, since it works. That still leaves me looking for a "standard Java" way to identify the content type of a file. :-)
From: Arne Vajhøj on 1 Aug 2010 22:06 On 01-08-2010 21:48, PNS wrote: > On Jul 31, 10:26 pm, Arne Vajhøj<a...(a)vajhoej.dk> wrote: >> On 31-07-2010 14:42, Public Network Services wrote: >> >> >> >>> I am playing with HttpURLConnection to upload files to a remote server >>> and cannot seem to figure out a consistent way of identifying the >>> Content-Type of a file to be uploaded. I assumed that "application/ >>> octet-stream" would be a generic type to supply, but apparently this >>> is not the case. >> >>> More specifically, I can read a file into a byte array (fileBytes) and >>> open an HttpConnection to a destination URL (url), but setting the >>> Content-Type property does not work. The code I use is: >> >>> HttpURLConnection connection = url.openConnection(); >>> connection.setRequestProperty("Content-Length", >>> String.valueOf(fileBytes.length)); >>> connection.setRequestProperty("Content-Type", "application/octet- >>> stream"); >> >>> If, immediately after the above, I do a >> >>> connection.getContentType() >> >>> I get a null value (or an Exception saying that the connection is >>> already connected)! >> >>> Eventually, my file gets uploaded through the >>> connection.getOutputStream(), by simply doing >> >>> DataOutputStream output = new >>> DataOutputStream(connection.getOutputStream()); >>> output.write(fileContents); >> >>> but its Content-Type not being properly set causes the server to not >>> recognize it (e.g., if it is an MP3 file, it does not get the >>> speakerphone icon that MP3 files get in the serverś web interface, >>> when uploaded via that interface, through a browser). >> >>> Obviously, this is a solved problem given the multitude of properly >>> working Java-based web clients, so I 'd really aprpeciate >>> someone pointing me to the correct solution. >> >>> In other words, my questions are: >> >>> (a) How can I (automatically) identify the Content-Type of a file in >>> Java? >>> (b) How can I properly set that Content-Type in an HttpURLConnection? >> >> application/octet-stream is fine. >> >> You need to specify method as POST. >> >> You should not use DataOutputStream just OutputStream is fine. >> >> And most important you need to know whether the receiver expects >> a raw POST or a form submit with a field of type FILE. >> >> Those are not send identical! > I do specify setRequestMethod("POST"). > > You are right about OutputStream, using DataOutputStream only for > writing as I did makes no difference, as the latterś write() method is > inherited from the former. Knowing that OutputStream is an abstract > class had rather instictively turned me to another, more "concrete" > stream class. > > Also, I use application/octet and uploading works, but, as I said in > my original post, the file type is wrong. This does not happen if I > manually set the specific content type for a file (e.g., audio/mpeg > for MP3), so it all boils down to identifying the file type (at least > for the particular server application I send to). > > One would expect that calling the standard Java > connection.getFileNameMap().getContentTypeFor(filename)) would return > the proper type, but it returns null, at least for teh Linux OS I am > running. > > I didn't check about the raw vs. form distinction but apparently the > server is fine with raw, since it works. > > That still leaves me looking for a "standard Java" way to identify the > content type of a file. :-) Now I don't understand what the problem is. You upload file abc.xyz to the server as application/octet-stream. The receiving script get the file and stores the file with the correct name. What do you need? Arne
From: Dimitris on 3 Aug 2010 15:38
On Aug 2, 5:06 am, Arne Vajhøj <a...(a)vajhoej.dk> wrote: > On 01-08-2010 21:48, PNS wrote: > > > > > > > On Jul 31, 10:26 pm, Arne Vajhøj<a...(a)vajhoej.dk>  wrote: > >> On 31-07-2010 14:42, Public Network Services wrote: > > >>> I am playing with HttpURLConnection to upload files to a remote server > >>> and cannot seem to figure out a consistent way of identifying the > >>> Content-Type of a file to be uploaded. I assumed that "application/ > >>> octet-stream" would be a generic type to supply, but apparently this > >>> is not the case. > > >>> More specifically, I can read a file into a byte array (fileBytes) and > >>> open an HttpConnection to a destination URL (url), but setting the > >>> Content-Type property does not work. The code I use is: > > >>>     HttpURLConnection connection = url.openConnection(); > >>>     connection.setRequestProperty("Content-Length", > >>> String.valueOf(fileBytes.length)); > >>>     connection.setRequestProperty("Content-Type", "application/octet- > >>> stream"); > > >>> If, immediately after the above, I do a > > >>>     connection.getContentType() > > >>> I get a null value (or an Exception saying that the connection is > >>> already connected)! > > >>> Eventually, my file gets uploaded through the > >>> connection.getOutputStream(), by simply doing > > >>>     DataOutputStream output = new > >>> DataOutputStream(connection.getOutputStream()); > >>>     output.write(fileContents); > > >>> but its Content-Type not being properly set causes the server to not > >>> recognize it (e.g., if it is an MP3 file, it does not get the > >>> speakerphone icon that MP3 files get in the serverŠweb interface, > >>> when uploaded via that interface, through a browser). > > >>> Obviously, this is a solved problem given the multitude of properly > >>> working Java-based web clients, so I 'd really aprpeciate > >>> someone pointing me to the correct solution. > > >>> In other words, my questions are: > > >>> (a) How can I (automatically) identify the Content-Type of a file in > >>> Java? > >>> (b) How can I properly set that Content-Type in an HttpURLConnection? > > >> application/octet-stream is fine. > > >> You need to specify method as POST. > > >> You should not use DataOutputStream just OutputStream is fine. > > >> And most important you need to know whether the receiver expects > >> a raw POST or a form submit with a field of type FILE. > > >> Those are not send identical! > > I do specify setRequestMethod("POST"). > > > You are right about OutputStream, using DataOutputStream only for > > writing as I did makes no difference, as the latterŠwrite() method is > > inherited from the former. Knowing that OutputStream is an abstract > > class had rather instictively turned me to another, more "concrete" > > stream class. > > > Also, I use application/octet and uploading works, but, as I said in > > my original post, the file type is wrong. This does not happen if I > > manually set the specific content type for a file (e.g., audio/mpeg > > for MP3), so it all boils down to identifying the file type (at least > > for the particular server application I send to). > > > One would expect that calling the standard Java > > connection.getFileNameMap().getContentTypeFor(filename)) would return > > the proper type, but it returns null, at least for teh Linux OS I am > > running. > > > I didn't check about the raw vs. form distinction but apparently the > > server is fine with raw, since it works. > > > That still leaves me looking for a "standard Java" way to identify the > > content type of a file. :-) > > Now I don't understand what the problem is. > > You upload file abc.xyz to the server as application/octet-stream. > > The receiving script get the file and stores the file with > the correct name. > > What do you need? > > Arne Hi... As I already explained, I need a solution to a two-fold problem, a theoretical and a practical one. (1) Theoretical. Given a file (name and/or its contents), which is the "standard" Java way for defining the Content-Type to use in HTTP? This is such a trivial case, that there should be a quick and easy way of doing it. For example, as I already said, given a URLConnection variable, apparently one should be able to get the Content-Type by just calling connection.getFileNameMap().getContentTypeFor(filename)). In my case (Java 6 over CentOS 5.5), I get a null value, which is really weird, given that the filename extension is .mp3! If we were to just set "application/octet-stream" everywhere, then what is the need for all the other MIME types? Clearly, there is a need, so "application/octet-stream" is not the one-size-fits-all solution. (2) Practical. The server application I send, has a web-based client. If I upload an mp3 file using that client, I can see the file listed with a nice speakerphone icon next to it, a clear sign that the server understands what it got. If I send the same file from my application, using an "audio/mpeg" Content-Type which I manually set, the same nice speakerphone appears in the web client. However, if I don't have an automated way to determine the proper Content-Type and thus use "application/octet-stream" instead, the file is copied to the server and I can download and play it just fine, but instead of the speakerphone I get a question mark icon in the web client. Obviously, the server is not fully happy with "application/octet-stream". Looking around I 've found numerous proprietary ways of solving the above (theoretical) issue, but I would rather use a pure Java one. That's all! :-) |