Develop Reference

java - HttpServlet file download

I tried to create a file, write to it and then turn the file into an input stream and transfer its bytes to the output stream of the HTTP response. But I get the message "/tmp/mozilla_xxxx/33JJ1OHw.md.part could not be saved, because the source file could not be read." when testing it.
Here's the code that does this part.
f = new File("f.md");
f.createNewFile();
fw = new FileWriter(f);
fw.append("#" + query + "\n" + queryResult);
fw.close();
resp.setContentType("text/markdown");
OutputStream out = resp.getOutputStream();
FileInputStream in = new FileInputStream(f);
byte[] buffer = new byte[4096];
int length;
while ((length = in.read(buffer)) > 0){
out.write(buffer, 0, length);
}
in.close();
out.flush();

As you can see in the documentation, File class is not meant to read the actual file content, it is just...
An abstract representation of file and directory pathnames.
But, there are many ways of getting file's content, just use one of the following classes: FileReader, BufferedReader, Scanner and Files.
Here you'll see different examples to do that, just use the one you find better. Different ways of Reading a text file in Java

How InputStream really works while reading file from socket in java?

I have a simple program which gets BufferedInputStream from URL and I have seen that while reading from the underlying stream, read(bytes) calls goes to FileInputStream from BufferedInputStream (so for this I convinced my self saying as at the other end of socket , it is actually a file may be that's why it goes to FileInputStreams (Please let me know if my assumptions are correct about this )).
When read happens in FileInputStreams read() method the "path" variable is set to the location of my class file from where the read call is being invoked , well this is very confusing to me as I was expecting the file's actual URL location here which I am downloading ..
Please help me understand these things and how actually read() happens from a remote file ??
URL url = new URL("some url for downloading a file");
BufferedInputStream bis = new BufferedInputStream(url.openStream());
FileOutputStream fis = new FileOutputStream(file);
int size = 65536;
byte[] buffer = new byte[size];
int count;
while ((count = bis.read(buffer, 0, size)) != -1) {
fis.write(buffer, 0, count);
}
fis.close();
bis.close();

Stream file from URL to File without storing it in the memory

I want to download a file from a URL and store it into the file system. However I have memory limitation and I don't want to store it in the memory before. I am not a java expert and I am a bit lost with all the class InputStream, BufferedReader, FileOutputStream, etc. Could you help me please ?
For now I have:
URLConnection ucon = url.openConnection();
ucon.connect();
InputStream is = ucon.getInputStream();
// Create a reader for the input stream.
BufferedReader br = new BufferedReader(isr);
// ?
FileOutputStream fos = context.openFileOutput(FILENAME, Context.MODE_PRIVATE);
// Here the content can be too big for the memory...
fos.write(content.getBytes());
fos.close();
Please, could you give me some clue ? I was thinking also to read it chunk by chunk, but I am not sure what would be the easiest with java...

you can use apache commons
org.apache.commons.io.FileUtils.copyURLToFile(URL, File)
I guess it may not work on android
I use this code
InputStream input = connection.getInputStream();
byte[] buffer = new byte[4096];
int cnt = - 1;
OutputStream output = new FileOutputStream(file);
while ( (cnt = input.read(buffer)) != -1)
{
output.write(buffer, 0, cnt);
}
output.close();

Writing from Datahandler to file

I created a web service using CXF/MTOM for transfering large files (over 700Mo), i managed to transfer the file to the server , now my question is to optimze writing data in disk, i will give examples :
DataHandler handler = fichier.getFichier();
InputStream is = handler.getInputStream();
OutputStream os = new FileOutputStream(new File("myFile"));
byte[] buffer = new byte[BUFFER];
int bytesRead = 0;
while ((bytesRead = is.read(buffer)) != -1) {
os.write(buffer,0,bytesRead);
}
Using bytes can lead me to an OutOfMemory, so i'd rather use this one :
DataHandler handler = fichier.getFichier();
handler.writeTo(os);
this take 2 minutes for uploading 700Mo.
what are other efficient ways ?
thanks

I suggest you to use the class IOUtils of Apache Commons IO
https://commons.apache.org/proper/commons-io/javadocs/api-release/index.html?org/apache/commons/io/input/package-summary.html
QN: org.apache.commons.io.IOUtils
DataHandler handler = docClient.getContent(sid, docId);
InputStream is = handler.getInputStream();
OutputStream os = new FileOutputStream(new File("C:/tmp/myFile.raw"));
// This will copy the file from the two streams
IOUtils.copy(is, os);
// This will close two streams catching exception
IOUtils.closeQuietly(os);
IOUtils.closeQuietly(is);

Java servlet and IO: Create a file without saving to disk and sending it to the user

I`m hoping can help me out with a file creation/response question.
I know how to create and save a file. I know how to send that file back to the user via a ServletOutputStream.
But what I need is to create a file, without saving it on the disk, and then send that file via the ServletOutputStream.
The code above explains the parts that I have. Any help appreciated. Thanks in Advance.
// This Creates a file
//
String text = "These days run away like horses over the hill";
File file = new File("MyFile.txt");
Writer writer = new BufferedWriter(new FileWriter(file));
writer.write(text);
writer.close();
// Missing link goes here
//
// This sends file to browser
//
InputStream inputStream = null;
inputStream = new FileInputStream("C:\\MyFile.txt");
byte[] buffer = new byte[8192];
ByteArrayOutputStream baos = new ByteArrayOutputStream();
int bytesRead;
while ( (bytesRead = inputStream.read(buffer)) != -1)
baos.write(buffer, 0, bytesRead);
response.setContentType("text/html");
response.addHeader("Content-Disposition", "attachment; filename=Invoice.txt");
byte[] outBuf = baos.toByteArray();
stream = response.getOutputStream();
stream.write(outBuf);

You don't need to save off a file, just use a ByteArray stream, try something like this:
inputStream = new ByteArrayInputStream(text.getBytes());
Or, even simpler, just do:
stream.write(text.getBytes());
As cHao suggests, use text.getBytes("UTF-8") or something similar to specify a charset other than the system default. The list of available charsets is available in the API docs for Charset.