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Java: Why does my program receive java.io.FileNotFoundException error for creating an input file when it successfully creates an output file?

I created two files in this program: "OutputFile.txt" and "InputFile.txt". When I run my code, it displays an error called "java.io.FileNotFoundException" but it created "OutputFile.txt" in my system but not "InputFile.txt"
Why is that?
public static void main(String[] args) throws IOException{
// 2 File objects are created: outFile and inFile, this will create text files in my system
File outFile = new File("OutputFile.txt");
File inFile = new File("InputFile.txt");
// These FileWriter Objects are created to allow the File Object to be writable to readable
FileWriter out = new FileWriter(outFile);
FileReader in = new FileReader(inFile);
// these closes files after use in program
out.close();
in.close();
}

2 File objects are created: outFile and inFile, this will create text files in my system
The first part of this is correct; the second is not. Creation of a File object is not creation of a file; new File(...) just makes an object that stores a path, basically, and does not touch the disk in any way. Per docs, a File object is
An abstract representation of file and directory pathnames.
FileWriter and FileReader do touch the disk. FileWriter writes to a file, and will create one if it does not exist; FileReader does not write, it reads — and if the file does not exist, it complains.

Read excel file byte array

byte[] test = getByteArry(excelfikepath)
I have one method where it returns the bytearray of the excel .xlsx file. To read this file i need to write these byte array using FileOutputStream on one server and from there i am calling another method which will read and process that excel from the server.
There is some limitation because of which i cant read excel file directly i have to put it onto another server and process.
Just wanted to know is there any way by which i can make use of this byte array and read excel file IN MEMORY instead of writing it on server.

This will help to get byte array out of an excel file.
public static byte[] getFileByteArr(String fileName) throws InvalidFormatException, IOException {
try (OPCPackage opcPackage = OPCPackage.open(new File(fileName))) {
try (XSSFWorkbook workbook = (XSSFWorkbook) WorkbookFactory.create(opcPackage)) {
try (ByteArrayOutputStream bos = new ByteArrayOutputStream()) {
workbook.write(bos);
return bos.toByteArray();
}
}
}
}

Java - how to replace file contents? [duplicate]

This question already has answers here:
Is this the best way to rewrite the content of a file in Java?
(8 answers)
Closed 6 years ago.
I have a file that contains only a very small amount of information that needs to be updated periodically. In other words, I want to truncate the file before writing to it. The easiest solution I found was to delete and create it again as shown here:
File myFile = new File("path/to/myFile.txt");
myFile.delete();
myFile.createNewFile();
// write new contents
This 'works' fine, but is there a better way?

There is no need to delete the file and recreate one. If you are writing to the file, for instance using PrintWriter, it will overwrite your current file content.
Example:
public static void main(String[] args) throws IOException
{
PrintWriter prw= new PrintWriter (“MyFile.txt”);
prw.println("These text will replace all your file content");
prw.close();
}
It will only append to the end of the file if you use the overloaded version of the PrintWriter constructor:
PrintWriter prw= new PrintWriter (new FileOutputStream(new File("MyFile.txt"), true));
//true: set append mode to true

In the below example, the "false" causes the file to be overwritten, true would cause the opposite.
File file=new File("C:\Path\to\file.txt");
DataOutputStream outstream= new DataOutputStream(new FileOutputStream(file,false));
String body = "new content";
outstream.write(body.getBytes());
outstream.close();

file input out append

I am trying to write some coordinates to a file and later read it in as a string. So I need to have them written to file attached...without space or a new line, but my code writes only the first coordinate, that is pos_Let, but does not write pos_Num at all, not even with a space or on a new line.
So how can I get the code to write to file pos_LetposNum like that? Obviously I mean their references ;) ..thanks in advance
protected void writeCoordtoFile () throws IOException
{
File file = new File("FermiPresentCoord.txt");
boolean yes = file.createNewFile() ;
//boolean yes = exists();
if (yes == true)
{
// create a FileWriter Object
FileWriter writer = new FileWriter(file, true);
// Writes the content to the file
writer.write("");
writer.flush();
writer.write(pos_Let);
writer.flush();
writer.write(pos_Num);
writer.close();
}
else
{
// creates the file
file.createNewFile();
// creates a FileWriter Object
FileWriter out = new FileWriter(file);
// Writes the content to the file
out.write(pos_Let);
out.flush();
out.write(pos_Num);
out.flush();
out.close();
}
}

Quoting the method createNewFile():
Atomically creates a new, empty file named by this abstract pathname if and only if a file with this name does not yet exist. The check for the existence of the file and the creation of the file if it does not exist are a single operation that is atomic with respect to all other filesystem activities that might affect the file.
Note: this method should not be used for file-locking, as the resulting protocol cannot be made to work reliably. The FileLock facility should be used instead.
Returns:
true if the named file does not exist and was successfully created; false if the named file already exists
in your case, you first create the file, and createNewFile() returns true, so you go to the if block, appending the line to the current file. Then, createNewFile() returns false, since, the file exists! So, you go to the else block, and create the file again from scratch...
So, basically, just inverse the if with else, and don't call createNewFile() twice... With the least possible changes (so that you do not get confused) here is my simple suggestion:
protected void writeCoordtoFile () throws IOException
{
File file = new File("FermiPresentCoord.txt");
boolean fileDoesNotExist = file.createNewFile() ;
//boolean fileDoesNotExist = file does **not** exist!
if (fileDoesNotExist)
{
// create a FileWriter Object
FileWriter writer = new FileWriter(file);
// Writes the content to the file
writer.write(pos_Let);
writer.write(pos_Num);
writer.close();
}
else
{
// creates a FileWriter Object
FileWriter out = new FileWriter(file,true);
// Writes the content to the file
out.write(""); //not sure why you need that...
out.write(pos_Let);
out.write(pos_Num);
out.close();
}
}

I can not find out why you are checking the existence of the output file. Because, when you are using FileWriter if the file specified in the path does not exist, it would create it and open a character output stream to it. Also if it exists in that path, only opens the output stream and it is ready to write into.
Try the following code and see whats happening when you run it more than one times:
float posLat = 156.23589965f;
float posLon = 12.987564f;
File file = new File("c:/FermiPresentCoord.txt");
FileWriter writer = new FileWriter(file, true);
writer.append(posLat+",");
writer.append(posLon+",");
writer.flush();
writer.close();
There is no need to invoke the file.createNewFile() and/or checking the for the existence of the file when you want to write into it.
The second argument for the FileWriter constructor is append flag. So every time you create an output stream to a file with FileWriter(file, true) constructor it automatically appends to the data of the file.
Good Luck.

Saving to an object file in Java: getParentFile()

public void save() throws IOException {
File f = new File(path);
if (!f.getParentFile().exists()) {
f.getParentFile().mkdirs();
}
FileOutputStream fout = new FileOutputStream(f, false);//overwrite, append set to false
ObjectOutputStream out = new ObjectOutputStream(fout);
out.writeObject(this.vehicles);
out.close();
}
I Have the following code that saves an object of type vehicule into a file. However, I don't understand quite well how it works since it was a sample provided for me, and since I am new in the java field.
I am wondering what is the interpretation of these lines if (!f.getParentFile().exists()) {
f.getParentFile().mkdirs();
} I am wondering what getParentFile().exists() does and why are we searching for the parent file while we are interested in the file itself. same question for the next line: why are we interested in the parent directory when we are going to create the file?
I would like to know also the difference between FileOutputStream and ObjectOutputStream and why both are used one next to another in the following lines FileOutputStream fout = new FileOutputStream(f, false);//overwrite, append set to false
ObjectOutputStream out = new ObjectOutputStream(fout);
Thank you in advance

Files are pointers to file or directory locations on a File System. If you intend to write to a file, though, the parent directory in which it will reside must exist. Otherwise, you'll get an IOException. The mkdirs call will create the necessary parent directory (or directories) to avoid that IOException.
I don't think the exists check is really necessary, though, since the mkdirs method returns false if it actually didn't create anything.
Also, you should close your OutputStream within a finally block or use the Java 7 try-with-resources:
try (ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream(f, false))) {
out.writeObject(vehicles);
}