Develop Reference

How to extract part of file name of a CSV file in Java

I have a CSV file and I want to extract part of the file name using Java code.
For example if the name of the file is --> StudentInfo_Mike_Brown_Log.csv
I want to be able to just extract what is between the first two _'s in the file name. Therefore in this case I would be extracting Mike
So far I am doing the following:
String fileName = "C:\\User\\StudentInfo_Mike_Brown_Log.csv";
File file = new File(fileName);
String extractedInfo= fileName.substring(fileName.indexOf("_"), fileName.indexOf("."));
System.out.println(extractedInfo);
This code currently gives me _Mike_Brown_brown_Log but I want to only print out Mike.

You can use split with a Regex to split the String into substrings.
Here is an example:
final String fileName = "C:\\User\\StudentInfo_Mike_Brown_Log.csv";
final String[] split = fileName.split("_");
System.out.println(split[1]);

Try this:
int indexOfFirstUnderscore = fileName.indexOf("_");
int indexOfSecondUnderscore = fileName.indexOf("_", indexOfFirstUnderscore+2 );
String extractedInfo= fileName.substring(indexOfFirstUnderscore+1 , indexOfSecondUnderscore );
System.out.println(extractedInfo);

You could use the getName() method from the File object to return just the name of the file (with extension but without trailing path) and than do a split("_") like #Chasmo mentioned.
E.g.
File input = new File(file);
String fileName = input.getName();
String[] partsOfName = fileName.split("_");
System.out.println(Arrays.toString(partsOfName));

You can use lastIndexOf(), in addition to indexOf():
String fileName = "C:\\User\\StudentInfo_Mike_Brown_Log.csv";
File file = new File(fileName);
filename = file.getName();
String extractedInfo= fileName.substring(
fileName.indexOf("_"),
fileName.lastIndexOf("_"));
System.out.println(extractedInfo);
It is important to firstly call file.getName() so this method does not get confused with underscore '_' characters in the file path.
Hope this helps.

Use indexOf and substring method of String class:
String fileName = "C:\\User\\StudentInfo_Mike_Brown_Log.csv";
int indexOfUnderScore = fileName.indexOf("_");
int indexOfSecondUnderScore = fileName.indexOf("_",
indexOfUnderScore + 1);
if (indexOfUnderScore < 0 || indexOfSecondUnderScore < 0) {
throw new IllegalArgumentException(
"string is not of the form string1_string2_ " + fileName);
}
System.out.println(fileName.substring(indexOfUnderScore + 1,
indexOfSecondUnderScore));

Solved from the previous answer:
String fileName = "C:\\User\\StudentInfo_Mike_Brown_Log.csv";
File file = new File(fileName);
fileName = file.getName();
System.out.println(fileName.split("\\.")[0]);

Case study: Is this an effective way to split a file?

So om working my way trough a task in my java-course at school. For better understanding of what the code is supposed to do ill quote it:
"(Split files) Suppose you want to back up a huge file(e.g., a 10-GB AVI file) to a CD-R. You can achieve it by splitting the file into smaller pieces and backing up these pieces separately. Write a utility program that splits a large file into smaller ones using the following command: java ClassName SourceFile numberOfPieces
The command creates the files SourceFile.1, SourceFile2...etc
Now to be clear. This post is in no way an attempt to get a "solution" for the problem. I have solved it (with what i know). And i merely want to get more enlightned on some matters that crossed my mind when writing the code.
Is it neccesary to create a new output for every single file im
copying to? Doesn`t this demand unneccesary system power?
The first file that gets copied(SourceFile is in this case a .png
file) is possible to view. And show a fraction of the original
picture. (If i split into two. i can view half the picture.) But
the latter ones i cant view.. Why is that?
Is it possible to reassemble the splitted files in any way? if my
pictures was split into two files, can i put them back together and
view the whole picture?
The code, if you want to look at it.
All feedback is welcome,
Have a good day! :)
package oblig2;
import java.io.*;
import java.util.*;
public class Test {
/**
* Main method
*
* #param args[0] for source file
* #param args[1] for number of pieces
* #throws IOException
*/
public static void main(String[] args) throws IOException {
// The program needs to be executed with two parameters in order to
// work. This sentence check for it.
if (args.length != 2) {
System.out.println("Usage: java Copy sourceFile numberOfPieces");
System.exit(1);
}
// Check whether or not the sourcefile exists
File sourceFile = new File(args[0]);
if (!sourceFile.exists()) {
System.out.println("Source file " + args[0] + " does not exist");
System.exit(2);
}
// Need an Array to store all the new files that is supposed to contain
// parts of the original file
ArrayList<File> fileArray = new ArrayList<File>();
// All the new files need their own output(or do they?)
ArrayList<BufferedOutputStream> outputArray = new ArrayList<BufferedOutputStream>();
// Using randomAccessFile on the sourcefile to easier read parts of it
RandomAccessFile inOutSourceFile = new RandomAccessFile(sourceFile,
"rw");
// This loop changes the name for the new files, so they match the
// sourcefile with an appended digit
for (int i = 0; i < Integer.parseInt(args[1]); i++) {
String nameAppender = String.valueOf(i);
String nameBuilder;
int suffix = args[0].indexOf(".");
nameBuilder = args[0].substring(0, suffix);
fileArray.add((new File(nameBuilder + nameAppender + ".dat")));
}
// Here i create the output needed for all the new files
for (int i = 0; i < Integer.parseInt(args[1]); i++) {
outputArray.add(new BufferedOutputStream(new FileOutputStream(
new File(fileArray.get(i).getAbsolutePath()))));
}
// Now i determine in how many parts the sourcefile needs to be split,
// and the size of each.
float size = inOutSourceFile.length();
double parts = Integer.parseInt(args[1]);
double partSize = size / parts;
int r, numberOfBytesCopied = 0;
// This loop actually does the job of copying the parts into the new
// files
for (int i = 1; i <= parts; i++) {
while (inOutSourceFile.getFilePointer() < partSize * i) {
r = inOutSourceFile.readByte();
outputArray.get(i - 1).write((byte) r);
numberOfBytesCopied++;
}
}
// Here i close the input and outputs
inOutSourceFile.close();
for (int i = 0; i < parts; i++) {
outputArray.get(i).close();
}
// Display the operations
System.out.println(args[0] + " Has been split into " + args[1]
+ " pieces. " + "\n" + "Each file containig " + partSize
+ " Bytes each.");
}
}

Of course it is necessary to open all output files. But you don't have to open them at all times. You can open the first file, write to it, close it, open the second file, write to it, close it, etc.
File format, .png for example, have a structure that have to follow. It may have special header, and may have special footer. That's why when this file split into two or more, the first will lose its footer, the middle will lose its header and footer, and the last will lose it's header. This make them unusable as individual file.
Of course it is possible. By combining back all the parts, the original file fill be restructured.

Change files names in parent and child directories

I am a beginner in Java trying to work with Files and Directories. I wanted to create a program where I could change file names automatically while searching through all the child directories for file names that are not valid. I am actually trying to load a huge amount of files on to a server but the server settings do not allow file names containing special characters. To start with I was able to write the code where if I pass the path to a directory it renames all the files with invalid names in that directory:
public class reNaming {
public static String baseLoc = "C:/Users/Developer/Desktop/.../Data Cleanup";
public static void main(String[] args) {
//LinkedList<File> fileList = new LinkedList<File>();
File obj = new File(baseLoc);
int count = 0;
for (File file: obj.listFiles())
{
String origName = file.getName();
if (origName.contains("&") || origName.contains("#") || origName.contains("#"))
{
System.out.println("Original name: "+origName);
origName = origName.replaceAll("&", "_and_");
origName = origName.replaceAll("#", "_at_");
String newName = origName.replaceAll("#", "_");
System.out.println("New Name: "+newName);
String newLoc = baseLoc+"/"+newName;
File newFile = new File(newLoc);
System.out.println(file.renameTo(newFile));
count++;
}
}
}
}
Now I want to do the same but only this time I want all the files to be reNamed even in the child directories. Can somebody please guide me how I can achieve that?

Recursion is your friend
/**Removes 'invalid' characters (&,#,#) from pathnames in the given folder, and subfolders, and returns the number of files renamed*/
public int renameDirectory(File base){
//LinkedList<File> fileList = new LinkedList<File>();
int count=0;//count the renamed files in this directory + its sub. You wanted to do this?
//Process each file in this folder.
for (File file: base.listFiles()){
String origName = file.getName();
File resultFile=file;
if (origName.contains("&") || origName.contains("#") || origName.contains("#")){
//I would replace the if statement with origName.matches(".*[&##].*") or similar, shorter but more error prone.
System.out.println("Original name: "+origName);
origName = origName.replaceAll("&", "_and_");
origName = origName.replaceAll("#", "_at_");
String newName = origName.replaceAll("#", "_");
System.out.println("New Name: "+newName);
String newLoc = baseLoc+File.separator+newName;//having "/" hardcoded is not cross-platform.
File newFile = new File(newLoc);
System.out.println(file.renameTo(newFile));
count++;
resultFile=newFile;//not sure if you could do file=newFile, tired
}
//if this 'file' in the base folder is a directory, process the directory
if(resultFile.isDirectory()){//or similar function
count+=renameDirectory(resultFile);
}
}
return count;
}

Move the code you have to a utility method (e.g. public void renameAll(File f){}). Have a condition that checks if the file is a directory and recursively call your method with it's contents. After that do what you are currently doing.
public void renameAll(File[] files){
for(File f: files){
if(f.isDirectory){
renameAll(f.listFiles());
}
rename(f);
}
}
public void rename(File f){ }

Search for a matching string through more then one files in Java

I am attmpting to search through more then one text files in java for a matching random string ( given from the user ). I got myself a loop which loops throug filenames in the current directory in the project but i can't figure out how to open the files and check if i have a match somewhere int them. Here is the code that i have written to loop through the filenames.
String path = "."; //current directory
java.io.File folder = new java.io.File( path );
java.io.File[] fileList = folder.listFiles();
for( int i = 0; i < fileList.length; i++ ) {
// I should add code for searching int the files probably here
}
My research got me to some code for searching matches but in only one file and it looks like this:
final Scanner scanner = new Scanner(FileName);
while (scanner.hasNextLine()) {
final String lineFromFile = scanner.nextLine();
if(lineFromFile.contains("Address")) {
// a match!
System.out.println("I found " + CurrClient.getClientName()
+ " in file " +FileName+"txt");
break;
}
}
But it works only with one file or it seems to me like this.
Can you please give me a push? :)

Replace FileName with fileList[i] and your should be on your way.
By the way, you must remember to close the scanner in the end of each iteration of the loop, by calling scanner.close(). See more the examples in the documentation

Text input and output java

I am trying to read 2 files after i read the files i want to get their contents and manipulate the contents of the two files then update a new file which is the output. The files are in the same folder as the program but the program always throws a FileNotFoundException.
Below is my code:-
import java.io.*;
import java.util.Scanner;
public class UpdateMaster {
public static void main(String[] args)
{
String master = "Customer.dat";
String trans = "Transactns.dat";
String newMaster = "Temp.txt";
Scanner inputStreamMaster = null;
Scanner inputStreamTrans = null;
PrintWriter inputStreamNewMaster = null;
try
{
inputStreamMaster = new Scanner(new File(master));
inputStreamTrans = new Scanner(new File(trans));
inputStreamNewMaster = new PrintWriter(newMaster);
}
catch(FileNotFoundException e)
{
System.out.println("Error: you opend a file that does not exist.");
System.exit(0);
}
catch(IOException e)
{
System.out.println("Error.");
System.exit(0);
}
do
{
String transLine = inputStreamTrans.nextLine();
String masterLine = inputStreamMaster.nextLine();
String[] transLineArr = transLine.split(",");
String[] masterLineArr = masterLine.split(",");
int trAccNo = Integer.parseInt(transLineArr[0]);
int sales = Integer.parseInt(transLineArr[1]);
int masterAccNo = Integer.parseInt(masterLineArr[0]);
int balance = Integer.parseInt(masterLineArr[1]);
while(masterAccNo== trAccNo){
inputStreamNewMaster.println(trAccNo+ " , "+masterAccNo);
masterLine = inputStreamMaster.nextLine();
masterLineArr = masterLine.split(",");
masterAccNo = Integer.parseInt(masterLineArr[0]);
balance = Integer.parseInt(masterLineArr[1]);
}
balance = balance + sales;
inputStreamNewMaster.println(masterAccNo+ " , "+balance);
}while(inputStreamTrans.hasNextLine());
inputStreamMaster.close();
inputStreamTrans.close();
inputStreamNewMaster.close();
//System.out.println(" the line were written to "+ newMaster);
}
}

Like #Ankit Rustagi said in the comments, you need the full path of the files if you want to keep the current implementation.
However, there is a solution where you only need the file names: use BufferedReader / BufferedWriter. See here an example on how to use these classes (in the example it uses the full path but it works without it too).

Use absolute path
String master = "C:/Data/Customer.dat";
String trans = "C:/Data/Transactns.dat";
String newMaster = "C:/Data/Temp.txt";

The code works for me, i guess you misspelled some filename(s) or your files are in the wrong folder. I created your files on the same level as the src or the project. Also this is the folder where the files are exspected.

There's nothing wrong with using relative paths like tihis. What's happening is that your program is looking for the files in the directory where you execute the program, which doesn't have to be the folder of the program. You can confirm this by logging the absolute path of the files before you try to read them. For example:
File masterFile = new File(master);
System.out.printf("Using master file '%s'%n", masterFile.getAbsolutePath());
inputStreamMaster = new Scanner(masterFile);
In general you should not hardcode file paths but allow the user to specify them in someway, for example using command line arguments, a configuration file with a well known path, or an interactive user interface.
There is a way to locate the program's class file but it's a little tricky because Java allows classes to be loaded from compressed archives that may be located in remote systems. It's better to solve this problem in some other manner.

Try this:
String current = new java.io.File( "." ).getCanonicalPath();
System.out.println("I look for files in:"+current);
To see what directory your program expects to find its input files. If it shows the correct directory, check spelling of filenames. Otherwise, you have a clue as to what's gone wrong.