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Java Forum / General / September 2005Transfer received image
Hi, I am trying to write a code for a server which will do the functionality of web proxy. Client------Proxy--------Server The proxy will function as entry point to a cluster of servers, in simple terms like an application level gateway. I am able to fetch html text content from server and send to the client but unable to do the same for images. Can anyone give some input on how to do this? I am a beginner in Java. thanks and rgds, Prashant > Hi, > I am trying to write a code for a server which will do the [quoted text clipped - 6 lines] > to do this? > I am a beginner in Java. What happens when you do what you did for HTML and apply it to images? Runtime exceptions? Compilation errors? Unexpected behaviour? Your problem description is too vague. - Oliver Hi, I use BufferedReader to read the HTTP message sent to the proxy from the server. So I use the readLine() method and then write every line to the outputstream of the socket connecting the client. When I try it request images , the browser displays the message that the image cannot be displayed as it contains errors. I understand that its because it has not been sent to the browser in the right format . But how can i do that? thanks and regards, Prashant > Hi, > I use BufferedReader to read the HTTP message sent to the proxy from [quoted text clipped - 4 lines] > I understand that its because it has not been sent to the browser in > the right format . But how can i do that? I'm assuming you use writeLine(), println() or something equivalent (you should have specified what you're using to write). These methods do line ending conversion. That is, if your proxy receives "\r" because, it might write out "\n\r", thus changing the content of the data. Instead, you should read the data into an array of bytes so that no line-ending conversion occurs. See the read(char[], int, int) method in BufferedReader, and its equivalent in whatever you're using to write. - Oliver Hi, thanks for the info , I am using println( ) I will try the way you suggested, but how do i set the size of the character array? Also, I have been reading that data such as images must be read using byte streams and not character streams. And if i have to use bytestream how big should be the byte array that has to be created? thanks and rgds, Prashant > Hi, > thanks for the info , I am using println( ) > I will try the way you suggested, but how do i set the size of the > character array? char[] myCharacterArray = new char[THE_DESIRED_SIZE]; > Also, I have been reading that data such as images must be read using > byte streams and not character streams. And if i have to use bytestream > how big should be the byte array that has to be created? I don't know of any good rule for this. I think 256 and 1024 are popular sizes. - Oliver Hi, >char[] myCharacterArray = new char[THE_DESIRED_SIZE]; I know this , but i am wondering about what should be the value of THE_DESIRED_SIZE ? Anyway thanks, I found a posting of a problem which I think I am encountering as well titled 'Using Reader and Stream classes on same Input' http://groups.google.com/group/comp.lang.java.programmer/browse_thread/thread/ab a23d1bdf28b48d/9ad85c870e71d08c?q=BufferedInputStream&rnum=88#9ad85c870e71d08c rgds, Prashant >I use BufferedReader to read the HTTP message sent to the proxy from >the server. So I use the readLine() method and then write every line to [quoted text clipped - 3 lines] >I understand that its because it has not been sent to the browser in >the right format . But how can i do that? Images are binary. They are not lines of text. See http://mindprod.com/applets/fileio.html for how to read binary as opposed to character data. Think of an image as an octet-stream, 8-bit bytes read raw with no translation of any kind. BufferedReaders convert 8-bit streams to 16-bit characters. They are designed for human-readable data. See http://mindprod.com/jgloss/urlconnection.html  SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Again taking new Java programming contracts. >I am able to fetch html text content from server and send to the client >but unable to do the same for images. Can anyone give some input on how >to do this? This is a bit advanced to entrust to a newbie. You need some understanding of HTTP protocol. I suggest starting at http://mindprod.com/jgloss/cgi.html and getting a copy of Core Web Programming. Also get packet sniffer. See http://mindprod.com/jgloss/packetsniffer.html and watch a browser talking to a server to get web pages, images etc. You have to stand in the middle and look like a browser to the cluster servers and like server to the browser. There are other ways of tackling this, e.g. rotating DNS over an IP farm that distributes the load over your servers where clients talk directly to servers. See http://mindprod.com/jgloss/dns.html You can farm the incoming requests to servers and have them talk directly back to the end users, rather than you acting as proxy man-in-the-middle and potential bottleneck. Unless you are doing something quite fancy, chances are you can find and off the shelf solution. These things are pretty simple in principle, but rapidly get complicated when you start trying to make them handle heavy traffic. SignatureCanadian Mind Products, Roedy Green. http://mindprod.com Again taking new Java programming contracts. Hi, Thanks for the reply. I am already using ethereal and sniffing the packets and trying to understand whats happening , yes its complicated for a newbie, but i didnt expect it initially when i saw that the html pages were working fine. And I am not using rotating DNS , and yes I am trying to do something fancy :-). Yes I agree with you that during heavy traffic , such things might result in poor performance. thanks and rgds, Prashant Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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