Develop Reference

Handling file downloads via REST API

I want to set up the REST API to support file downloads via Java (The java part is not needed at the moment -- I am saying it in here so you can make your answer more specific for my problem).
How would I do that?
For example, I have this file in a folder (./java.jar), how can I stream it in such a way for it to be downloadable by a Java client?
I forgot to say that this, is for some paid-content.
My app should be able to do this
Client: Post to server with username,pass.
Rest: Respond accordingly to what user has bought (so if it has bought that file, download it)
Client: Download file and put it in x folder.
I thought of encoding a file in base64 and then posting the encoded result into the usual .json (maybe with a nice name -- useful for the java application, and with the code inside -- though I would not know how I should rebuild the file at this point). <- Is this plausible? Or is there an easier way?
Also, please do not downvote if unnecessary, although there is no code in the question, that doesn't mean I haven't researched it, it just means that I found nothing suitable for my situation.
Thanks.

What you need is a regular file streaming, using a valid URL.
Below code is an excerpt from here
import java.net.*;
import java.io.*;
public class URLReader {
public static void main(String[] args) throws Exception {
URL oracle = new URL("http://www.oracle.com/");
BufferedReader in = new BufferedReader(
new InputStreamReader(oracle.openStream()));
String inputLine;
while ((inputLine = in.readLine()) != null)
System.out.println(inputLine);
in.close();
}
}

For your needs, based on your updated comments on the above answer, you could call your REST endpoint after user logs in(with Auth and other headers/body you wish to receive) and proceed to the download.
Convert your jar/downloadable content to bytes. More on this
Java Convert File to Byte Array and visa versa
Later, in case if you dont want regular streaming as aforementioned in previous answers, you can put the byte content in the body as Base64 String. You can encode to Base64 from your byte array using something like below.
Base64.encodeToString(byte[], Base64.NO_WRAP + Base64.URL_SAFE);
Reference from here: How to send byte[] and strings to a restful webservice and retrieve this information in the web method implementation
Again, there are many ways to do this, this is one of the ways you can probably do using REST.

How to post a big string/json using AJAX on Play Framework 1.4.x

I have a JSON that looks more or less like this:
{"id":"id","date":"date","csvdata":"csvdata".....}
where csvdata property is a big amount of data in JSON format too.
I was trying to POST this JSON using AJAX in Play! Framework 1.4.x so I sended just like that, but when I receive the data in the server side, the csvdata looks like [object Object] and stores it in my db.
My first thought to solve this was to send the csvdata json in string format to store it like a longtext, but when I try to do this, my request fails with the following error:
413 (Request Entity Too Large)
And Play's console show me this message:
Number of request parameters 3623 is higher than maximum of 1000, aborting. Can be configured using 'http.maxParams'
I also tried to add http.maxParams=5000 in application.conf but the only result is that Play's console says nothing and in my database this field is stored as null.
Can anyone help me, or maybe suggest another solution to my problem?
Thanks you so much in advance.

Is it possible that you sent "csvdata" as an array, not a string? Each element in the array would be a separate parameter. I have sent 100KB strings using AJAX and not run into the http.maxParams limit. You can check the contents of the request body using your browser's developer tools.
If your csvdata originates as a file on the client's machine, then the easiest way to send it is as a File. Your controller action would look like:
public static void upload(String id, Date date, File csv) {
...
}
When Play! binds a parameter to the File type, it writes the contents of the parameter to a temporary file which you can read in. (This avoids running out of memory if a large file is uploaded.) The File parameter type was designed for a normal form submit, but I have used it in AJAX when the browser supported some HTML5 features (File API and Form Data).

Java as HTTP server - Is possible get a image via POST method?

I would like to know if is possible get the image via POST method with a HTTP server implemented in Java (With a simple input file form). I already implemented the Java server but I can only get text files via POST method it's because that the my application only copies the file content to another empty file creating the same file with the same characteristics. This does not work with image file or other files, this can only work with text file.
Anyone know how to implement it with images?
Some coordinates would be of great help!
Thanks in advance!

As far as i know you should create something like it:
Server-side: If you use a servlet that receive data in post you have to get the outputStream from the response. Once you have it it is done because you write the data image on the stream.
For example let's suppose your image is a file stored in the server you could do:
response.setContentLength((int) fileSize);
byte b[] = new byte[1024];
while ( fOutStream.read(b) != -1)
response.getOutputStream().write(b);
fOutStream.close() ;
Where the fOutStream is the source stream (your image).

Displaying image from byte array in browser

I have a simple TCP serversocket that will GET a byte array. This GET comes from when entering a website on this server that contains an img src link to a gif image, the requests looks like this:
GET /myHome.htm HTTP/1.1
GET /house.gif HTTP/1.1
Now the byte array is done like this:
byte[] fileByte = Files.readAllBytes(filePath);
To print the website which contains this image I do this:
out.writeBytes(new String(fileByte));
out:
DataOutputStream out= new DataOutputStream(socketClient.getOutputStream());
Now to make the image display I think I have to use something else then
out.writeBytes()
but I do not know for sure. Anybody knows how to make the image display? Right now the image just dont show at all.

First, make sure your GIF file is not corrupted. (Happened to me before, too).
If that is the case, try this code for sending the GIF file:
byte[] fileByte = Files.readAllBytes(filePath);
writer.writeBytes("HTTP/1.1 200 OK\r\n");
writer.writeBytes("Content-Type: image/gif\r\n");
writer.writeBytes("Content-Length: "+fileByte.length+"\r\n");
writer.writeBytes("\r\n");
writer.write(fileByte, 0, fileByte.length);
And then try to navigate to "house.gif" directly instead of "myHome.htm". Let me know in the comments what this does.
Previous answer attempts:
I think I may have misunderstood your question. Let me try with a different answer:
You are not sure how to figure out on the server when to return the HTML file myHome.htm and when to return house.gif?
I think for this you need to simply parse out the requested URL. Just check whether it contains "house.gif" or not. Then, depending on this, you either return the HTML file as you described above, or you send the .gif file, making sure that you use
writer.write(fileByte, 0, fileByte.length);
to send the binary data and that you set a reply header of
Content-Type: image/gif
In both cases (for the HTML file and the GIF file), though, you should prepend the data you are sending with correct HTTP response headers. Don't take the page-title the wrong way, but this site might help: http://net.tutsplus.com/tutorials/other/http-headers-for-dummies/
And just to make sure: Your server will be receiving TWO independent requests. The first one will ask for the HTML file, the second one will ask for the GIF file. So you send either one or the other. So, there's no "special way" to send the GIF instead of the HTML file. You use the same clientSocket. But it's a different connection.
Previous answer(s):
I think you might be missing the mime-type of your returned data. Try adding the following HTTP header to your reply:
Content-Type: image/gif
Actually... Are you sending a correct HTTP reply at all (including headers, specifically Content-Length)? If not, shoot me a comment and I'll post the code that you need for this.
If, for some reason, you cannot set the content-type header to let the browser know that you are sending it an image, you might be able to load the binary data on the client with an XMLHttpRequest into a JavaScript function rather than specifying it as the source Url of an img tag. Then you can use JavaScript to encode the binary data into a dataURI (http://en.wikipedia.org/wiki/Data_URI_scheme) with the correct mime type and set that as the source of the image.
Actually, I just noticed something in your code:
new String(fileByte)
might interpret the fileBytes as unicode characters rather than binary. Then, when you write this to the writer, it might screw it up as probably not all data in the image are valid unicode. Try replacing the line with this:
writer.write(fileByte, 0, fileByte.length);
Maybe this is all you need to do to fix it???

Selenium 2: Detect content type of link destinations

I am using the Selenium 2 Java API to interact with web pages. My question is: How can i detect the content type of link destinations?
Basically, this is the background: Before clicking a link, i want to be sure that the response is an HTML file. If not, i need to handle it in another way. So, let's say there is a download link for a PDF file. The application should directly read the contents of that URL instead of opening it in the browser.
The goal is to have an application which automatically knows wheather the current location is an HTML, PDF, XML or whatever to use appropriate parsers to extract useful information out of the documents.
Update
Added bounty: Will reward it to the best solution which allows me to get the content type of a given URL.

As Jochen suggests, the way to get the Content-type without also downloading the content is HTTP HEAD, and the selenium webdrivers does not seem to offer functionality like that. You'll have to find another library to help you with fetching the content type of an url.
A Java library that can do this is Apache HttpComponents, especially HttpClient.
(The following code is untested)
HttpClient httpclient = new DefaultHttpClient();
HttpHead httphead = new HttpHead("http://foo/bar");
HttpResponse response = httpclient.execute(httphead);
BasicHeader contenttypeheader = response.getFirstHeader("Content-Type");
System.out.println(contenttypeheader);
The project publishes JavaDoc for HttpClient, the documentation for the HttpClient interface contains a nice example.

You can figure out the content type will processing the data coming in.
Not sure why you need to figure this out first.
If so, use the HEAD method and look at the Content-Type header.

You can retrieve all the URLs from the DOM, and then parse the last few characters of each URL (using a java regex) to determine the link type.
You can parse characters proceeding the last dot. For example, in the url http://yoursite.com/whatever/test.pdf, extract the pdf, and enforce your test logic accordingly.
Am I oversimplifying your problem?