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How to convert an InputStream object to a File object?

I'm trying to get a "File" instance in a servlet called from a html form, in which I can select a PDF file on my computer.
I'm successful in getting the file as an "InputStream" but then I just cannot further convert it to a "File" object.
After a lot of different attempts, I still can't figure out what I should be doing to make it work. Any idea ?
Error :
java.io.FileNotFoundException: test.pdf (Read-only file system)
at java.io.FileOutputStream.open0(Native Method)
at java.io.FileOutputStream.open(FileOutputStream.java:270)
at java.io.FileOutputStream.<init>(FileOutputStream.java:213)
at org.apache.commons.io.FileUtils.openOutputStream(FileUtils.java:360)
at org.apache.commons.io.FileUtils.openOutputStream(FileUtils.java:319)
at org.apache.commons.io.FileUtils.copyToFile(FileUtils.java:1552)
at org.apache.commons.io.FileUtils.copyInputStreamToFile(FileUtils.java:1528)
Code :
Part filePart = request.getPart("file");
InputStream fileContent = filePart.getInputStream();
if (fileContent != null)
{
File file = new File(filename.trim() + ".pdf");
FileUtils.copyInputStreamToFile(fileContent, file);
//use the "file" instance
//...
}

As the exception is telling you, the problem is not with "creating the file". The problem is the disk/partition is write-protected
You should create the file on a file system that is writable. Try to specify an absolute path, such as
File file = new File("/tmp/" + filename.trim() + ".pdf");
//or
file = new File("/home/userhome/" + filename.trim() + ".pdf");
The file should just be created on a writable file system.

How to upload file to Dropbox?

I want to upload a file to drop-box using a web-application. But the problem is that Java is asking the complete file path. What do I have to do? This is my code:
File inputFile = new File("D://New Text Document.txt");
System.out.println("inputFile.getAbsoluteFile(): " + inputFile);
FileInputStream inputStream = new FileInputStream("D://New Text Document.txt");
try {
DbxEntry.File uploadedFile = client.uploadFile("/magnum-opus.txt",
DbxWriteMode.add(), inputFile.length(), inputStream);
System.out.println("Uploaded: " + uploadedFile.toString());
} finally {
inputStream.close();
}
In the first line it is asking for the file path; how is this possible?

you can use relative path
File inputFile = new File("working-draft.txt");
FileInputStream inputStream = new FileInputStream(inputFile);
try {
DbxEntry.File uploadedFile = client.uploadFile("/magnum-opus.txt",
DbxWriteMode.add(), inputFile.length(), inputStream);
System.out.println("Uploaded: " + uploadedFile.toString());
} finally {
inputStream.close();
}
more details here

The Dropbox Java Core SDK tutorial has the following code as a sample for uploading a file:
File inputFile = new File("working-draft.txt");
FileInputStream inputStream = new FileInputStream(inputFile);
try {
DbxEntry.File uploadedFile = client.uploadFile("/magnum-opus.txt",
DbxWriteMode.add(), inputFile.length(), inputStream);
System.out.println("Uploaded: " + uploadedFile.toString());
} finally {
inputStream.close();
}
In the sample above, in the first line, "working-draft.txt" is the local path to a local file. This needs to point to an existing local file. Your code has "D://New Text Document.txt" so you should first make sure there is actually a file there.
In the fourth line, "/magnum-opus.txt", the first parameter passed to uploadFile, is the desired remote path, that is, where in the Dropbox folder you want to upload the file to. The API requires remote paths be referenced relatively like this. The uploadFile method is documented here.

Before creating the file , deleting the file of previous day

I am creating a dat file in C: drive folder named abc as shown below , Now my file is generated everyday
now suppose if my file is generated today, then tommrow it will be also generated as usual
but when tommrow it is generated I have to make sure that earlier day file is deleted as the space in that folder is limited and this check is every time need to be done previos day file to be get deleted from that folder , please advise how to achieve this..
File file = new File(FilePath + getFileName()); //filepath is being passes through //ioc //and filename through a method
if (!file.exists()) {
file.createNewFile();
}
FileOutputStream fileOutput = new FileOutputStream(
file);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(
fileOutput));

why not use file.delete() ?
File file = new File(FilePath + getFileName()); //filepath is being passes through //ioc //and filename through a method
if (file.exists()) {
file.delete(); //you might want to check if delete was successfull
}
file.createNewFile();
FileOutputStream fileOutput = new FileOutputStream(file);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(fileOutput));

If your file name same in time to time no need to delete that. By running your code tomorrow, will over write file created today.
Consider following case
BufferedWriter bw=new BufferedWriter(new FileWriter("D:\\Test\test.txt"));
bw.write("abbbb");
bw.close(); // now this will create a test.txt in side Test folder
now run this by change writing String
BufferedWriter bw=new BufferedWriter(new FileWriter("D:\\test.txt"));
bw.write("hihi");
bw.close(); // now you can see file only containing hihi

You can change your code this way:
if (file.exists()) {
file.delete();
}
file.createNewFile();
And if it does not work, it's a matter of permission.

If you are using Java 7 then there is standard way to get file creation time, So that you can check if file is created in previous day and should be delete.
Path path = Paths.get("/filepath/");
BasicFileAttributes fileAttributes = Files.readAttributes(path, BasicFileAttributes.class);
System.out.println("creationTime:"+ fileAttributes.creationTime());

Filehandling file path

Basically i have two questions. i am using the below code to read and write z text file.
File myFile = new File("/sdcard/mysdfile.txt");
myFile.createNewFile();
FileOutputStream fOut = new FileOutputStream(myFile);
OutputStreamWriter myOutWriter =
new OutputStreamWriter(fOut);
myOutWriter.append("my text here");
myOutWriter.close();
this create a new file every time i want this to OPEN_OR_CREATE(if file already exist don't create a new one)
Ad my second question is that how to change the path "/sdcard/mysdfile.txt" i want this file to stored in my sdcard -> subFolder1 -> SubFolder2
Thnaks

Do not use hardcoded /sdcard or /mnt/sdcard or your app will fail as devices vary on location or mountpoint of that storage. To get the right location use
Environment.getExternalStorageDirectory();
See docs here.
To append content to existing file use new FileOutputStream(myFile, true); instead of just new FileOutputStream(myFile); - see docs on that constructor here.
As for
how to change the path "/sdcard/mysdfile.txt"
Aside from getting rid of /sdcard as said above, just add subfolders to the paths: MyFolder1/MyFolder2/mysdfile.txt. Note these folder have to exists or the path will be invalid. You can always create it by calling myFile.mkdirs().

Replace
FileOutputStream fOut = new FileOutputStream(myFile);
with
FileOutputStream fOut = new FileOutputStream(myFile, true); //true means append mode.
Appart from that I have one suggestion for you.
Never never hardcode /sdcard in code,Rather consider writing.
File myFile = new File(Environment.getExternalStorageDirectory(),"mysdfile.txt");

Try my solution to write to end of text file
private void writeFile (String str){
try {
File f = new File(Environment.getExternalStorageDirectory().toString(),"tasklist.txt");
FileWriter fw = new FileWriter(f, true);
fw.write(str+"\n");
fw.flush();
fw.close();
} catch (Exception e) {
}
}
*File(Environment.getExternalStorageDirectory().toString()+"your/pth/here","tasklist.txt");

File dir = Environment.getExternalStorageDirectory();
File f = new File(dir+"/subFolder1/",xyz.txt); <-- HOW TO USE SUB FOLDER
if(file.exists())
{
// code to APPEND
}
else
{
// code to write new one
}

1> OPEN_OR_CREATE
You can try or can replace MODE_APPEND with true like #Vipul's suggestion
FileOutputStream fOut = openFileOutput(your_path_file, MODE_APPEND);
//it means if the file is exist the content you want write will append into it.
2> stored in my sdcard -> subFolder1 -> SubFolder2
you can use Environment.getExternalStorageDirectory().getAbsolutePath() to get full file path the SDCard. Then concat strings to get the file path you want. Ex:
String baseDir = Environment.getExternalStorageDirectory().getAbsolutePath();
String fileName = "myFile.txt";
File f = new File(baseDir + File.separator + subfolder1 + File.separator + subfoler2, fileName);

In Java 7 we can do it this way:
Path path = Paths.get("/sdcard/mysdfile.txt");
BufferedWriter wrt = Files.newBufferedWriter(path, StandardCharsets.UTF_8, StandardOpenOption.APPEND);

Create pdf through java.io

I tried creating a pdf file out of another one(in my local drive) using java.io. The thing is a file with a .pdf extension got created but im unable to open the file, it says the file is already in use and most importantly the size of the file is too large and it keeps on increasing (origin file size : 5,777kB and the newly created one file size as of now is 38,567kB). Im not that much of skilled java programmer but still i would appreciate if anyone can give me an explanation ..
String path = "D:\\priya_Docs\\Android pdfs\\Professional_Android_Application_Development.pdf";
File file = new File(path);
System.out.println("Located a file " + file.isFile());
String filesArray = file.getPath();
File getFile = file.getAbsoluteFile();
FileInputStream fis = new FileInputStream(getFile);
FileOutputStream fos = new FileOutputStream(
"D:\\priya_Docs\\Androiddoc.pdf");
for (int b = fis.read(); b != -1;) {
fos.write(b);
}

Simple use,
FileUtils.copyFile()

you meet the two problems
first,you have to close the resource: fis and fos,or it will say the file already in use
second,you have to use the byte[] to receive the data because pdf file is organized in byte arrays
String path = "D:\\priya_Docs\\Android pdfs\\Professional_Android_Application_Development.pdf";
File file = new File(path);
System.out.println("Located a file " + file.isFile());
String filesArray = file.getPath();
File getFile = file.getAbsoluteFile();
FileInputStream fis = new FileInputStream(getFile);
FileOutputStream fos = new FileOutputStream(
"D:\\priya_Docs\\Androiddoc.pdf");
byte[] buff=new byte[1024];
int len;
while((len=fis.read(buff))>=0) {
fos.write(buff,0,len);
}
fis.close();
fos.close();