Develop Reference

Create and delete a zip file

I wrote a JUnit 5 test and I need to create a zip file, put some text files on it and remove the zip file.
I don't have any problem for creating the zip file and the text files inside it, but whenever I call file.delete() it returns false.
I even tried to create an empty zip file and it also fails to delete it. Is there a way to solve this ?
static File file;
#BeforeAll
static void setUp() throws IOException {
ZipOutputStream out = new ZipOutputStream(new FileOutputStream(file=File.createTempFile("tempDir",".zip")));
ZipEntry e = new ZipEntry("emptyFile.txt");
out.putNextEntry(e);
out.closeEntry();
e = new ZipEntry("oneLineFile.txt");
out.putNextEntry(e);
StringBuilder sb;
byte[] data;
sb = new StringBuilder();
sb.append("route_id,agency_id,route_short_name,route_long_name,route_type");
data = sb.toString().getBytes();
out.write(data, 0, data.length);
out.closeEntry();
out.close();
}
#AfterAll
static void set(){
file.delete(); // return false
}

If you don't create too many temporary files use File.deleteOnExit():
Requests that the file or directory denoted by this abstract pathname be deleted when the virtual machine terminates. Files (or directories) are deleted in the reverse order that they are registered. Invoking this method to delete a file or directory that is already registered for deletion has no effect. Deletion will be attempted only for normal termination of the virtual machine, as defined by the Java Language Specification.
File system operations can be unsafe e.g. Windows likes to lock the files used by the JVM process.
Moreover your test code can terminate with exception without properly closing ZipOutputStream potentially locking the file and preventing deletion. You should use finally:
ZipOutputStream out = null;
try {
out = ...
} finally {
if (out != null)
out.close();
}

FileOutputStream(FileDescriptor) that overwrites instead of appending data?

Im writing to a file through a FileOutputStream that is opened via its constructor taking a FileDescriptor.
My desired behavior: When I write to the file I want that to be the only content of it. E.g. writing "Hello" should result in the file containing just "Hello".
Actual behavior: Each time I write something, it is simply appeneded. E.g. in the above example I will get "HelloHello".
How can I open a FileOutputStream like Im doing, and have it not be in append mode?
Note: I am forced to use a FileDescriptor.

According to the ContentProvider.java file documentation, you can use "rwt" mode to read and write in file in truncating it.
ParcelFileDescriptor pfd = context.getContentResolver.openFileDescriptor(uri, "rwt");
FileOutputStream fos = new FileOutputStream(pfd.getFileDescriptor());
#param mode Access mode for the file. May be "r" for read-only access,
"rw" for read and write access, or "rwt" for read and write access
that truncates any existing file.
Hope this help despite that the question was posted a long time ago.

If you use FileOutoutStream then the ctor provides an option for you to specify whether you want to open the file to append or not. Set it to false and it will work.
OutputStream out = null;
try {
out = new FileOutputStream("OutFile", false);
} catch (FileNotFoundException e) {
e.printStackTrace();
}

FileOutputStream(File file, boolean append)
Make the argument append to false, so it overrides the existing data everytime when you call.
https://docs.oracle.com/javase/7/docs/api/java/io/FileOutputStream.html#FileOutputStream(java.io.File,%20boolean)

FileOutputStream outputStream;
try {
outputStream = openFileOutput("your_file", Context.MODE_PRIVATE);
//Context.MODE_PRIVATE -> override / MODE_APPEND -> append
outputStream.write("your content");
outputStream.close();
} catch (Exception e) {
e.printStackTrace();
}

Unable to delete text file using delete()

I am trying to transfer the data from old textfile to new textfile. Although the code below is able to transfer successfully, it does not delete the old textfile. May I know why is this so?
private void dataTransfer(String oldFilePath, String newFilePath) {
byte[] buffer = new byte[10000];
try {
FileInputStream fileInput = new FileInputStream(oldFilePath);
BufferedInputStream bufferedInput = new BufferedInputStream(fileInput);
FileOutputStream fileOutput = new FileOutputStream(newFilePath);
BufferedOutputStream bufferedOutput = new BufferedOutputStream(fileOutput);
while(true) {
int length = fileInput.read(buffer);
if(length == -1) {
break;
} else {
bufferedOutput.write(buffer);
bufferedOutput.flush();
}
}
fileInput.close();
bufferedInput.close();
fileOutput.close();
bufferedOutput.close();
File oldFile = new File(oldFilePath);
oldFile.delete();
} catch (IOException e) {
e.printStackTrace();
System.out.println(ERROR_TRANSFER_DATA);
}
}

Update the JRE and JDK, make sure you have the rights on the file. Try with a file created by you.
Also, add a catch block for SecurityException

For deleting a file it should work fine but for deleting a directory you have to make sure that Directory is Empty.

You can use the following code block. It works, though don't know. Even without setWritable, it works,
oldFile.setWritable(true);
if(!oldFile.delete()){
System.out.println("de;eted");
}

According to Oracle's docs, the delete method does not guarantee that it will delete the file.
http://docs.oracle.com/javase/7/docs/api/java/io/File.html#delete()
Deleting a file will fail if:
file does not exist
there is a lock on that file it might be opened by another process
file does not exist on the disk
you don't have enough permissions to delete that file (in this case a SecurityException is thrown)

I agree with #panagdu that you might not have sufficient rights to delete the file.
Just as a fluke try closing bufferedStream before fileInputStream
like
bufferedInput.close();
fileInput.close();
bufferedOutput.close();
fileOutput.close();
But I don't think this will help.
Test your code for files with sufficient permission. For example Java does not allow the delete() for system files.

How to make a copy of a file containing images and text using java

I have some word documents and excel sheets which has some images along with the file text content. I want to create a copy of that file and keep it at a specific location. I tried the following method which is creating file at specified location but the file is corrupted and cannot be read.
InputStream document = Thread.currentThread().getContextClassLoader().getResourceAsStream("upgradeworkbench/Resources/Upgrade_TD_Template.docx");
try {
OutputStream outStream = null;
Stage stage = new Stage();
stage.setTitle("Save");
byte[] buffer= new byte[document.available()];
document.read(buffer);
FileChooser fileChooser = new FileChooser();
fileChooser.setInitialFileName(initialFileName);
if (flag) {
fileChooser.getExtensionFilters().addAll(new FileChooser.ExtensionFilter("Microsoft Excel Worksheet", "*.xls"));
} else {
fileChooser.getExtensionFilters().addAll(new FileChooser.ExtensionFilter("Microsoft Word Document", "*.docx"));
}
fileChooser.setTitle("Save File");
File file = fileChooser.showSaveDialog(stage);
if (file != null) {
outStream = new FileOutputStream(file);
outStream.write(buffer);
// IOUtils.copy(document, outStream);
}
} catch (IOException ex) {
System.out.println(ex.getMessage());
}
Can anyone suggest me any different ways to get the proper file.
PS: I am reading the file using InputStream because it is inside the project jar.
PPS: I also tried Files.copy() but it didnt work.

I suggest you never trust on InputStream.available to know the real size of the input, because it just returns the number of bytes ready to be immediately read from the buffer. It might return a small number, but doesn't mean the file is small, but that the buffer is temporarily half-full.
The right algorithm to read an InputStream fully and write it over an OutputStream is this:
int n;
byte[] buffer=new byte[4096];
do
{
n=input.read(buffer);
if (n>0)
{
output.write(buffer, 0, n);
}
}
while (n>=0);

You can use the Files.copy() methods.
Copies all bytes from an input stream to a file. On return, the input stream will be at end of stream.

Use:
Files.copy(document, file.toPath(), StandardCopyOption.REPLACE_EXISTING);
As the class says, the second argument is a Path, not a File.
Generally, since this is 2015, use Path and drop File; if an API still uses File, make it so that it uses it at the last possible moment and use Path all the way.

java.io.FileNotFoundException: /tmp/ (Too many open files)

I have a rest service in Java EE and for some weird backward compatibility reasons I have to return an .mdb file from a URL request after adding some rows inside it.
At first I simply opened an mdb file, cleared all rows in it, wrote my rows and returned it to the caller, however I realized the .mdb kept growing this way because Access doesn't purge the rows on deletion but only erases it and the library I am using (Jackcess) doesn't support purging completely the rows.
So I switched to creating a copy of an empty .mdb file with java.io.File.createTempFile() and returning it however a dangling pointer to the file in the /tmp/ folder is left and after several days I get a
java.io.FileNotFoundException: /tmp/tmpdb.mdb04949499 (Too many open files)
The only solutions I found so far are:
Set MAX_FILE_HANDLES_FOR_READ_ENDS_MAP to a very high number (which only postpones the problem)
deleting the temp file, which however is not viable because I return it from a function and once returned I lose control of the pointer.
below what I currently have:
GET
#Path("/get/database/{filename}")
#Produces("application/jet")
public StreamingOutput getDatabase(#PathParam("filename") String fileName)
{
//access files increase indefinitely in size because deleted rows are simply marked "deleted" and not removed
//so we create a temporary file equal to the template .mdb file and use it instead
java.io.File myDBFile = null;
try
{
java.io.File templateDBFile = new java.io.File(url + "resources/clean_tmpdb.mdb");
myDBFile = java.io.File.createTempFile("tmpdb", ".mdb");
myDBFile.deleteOnExit(); //useless hint
FileChannel src = new FileInputStream(templateDBFile).getChannel();
FileChannel dest = new FileOutputStream(myDBFile).getChannel();
dest.transferFrom(src, 0, src.size());
}
catch (IOException ex)
{
Logger.getLogger(FileResource.class.getName()).log(Level.SEVERE, null, ex);
}
finally
{
if (src != null)
{
try
{
src.close();
}
catch (IOException ex)
{
Logger.getLogger(FileResource.class.getName()).log(Level.SEVERE, null, ex);
}
}
if (dest != null)
{
try
{
dest.close();
}
catch (IOException ex)
{
Logger.getLogger(FileResource.class.getName()).log(Level.SEVERE, null, ex);
}
}
/* work on the file inserting rows */
return new FileStreamingOutput(myDBFile);
}
EDIT: found a similar question, with a vague accepted answer: How to delete file after REST response, the accepted answer is "just write directly to the output stream contained in the Response."

You aren't closing either src or dest. So as to ensure they are closed, close them in finally blocks, or use the try-with-resources syntax.
return new FileStreamingOutput(myDBFile);
/* here I should call myDBFile.close(); and myDBFile.delete(); */
Here you can't call myDBFile.close(), as there is no such method. You can't call myDBFile.delete() either, as otherwise the caller will receive a File that doesn't exist. If the File needs to be deleted, the caller will have to do it. Your stated requirement doesn't make sense.