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Read one line of a csv file in Java

I have a csv file that currently has 20 lines of data.
The data contains employee info and is in the following format:
first name, last name, Employee ID
So one line would like this: Emma, Nolan, 2
I know how to write to the file in java and have all 20 lines print to the console, but what I'm not sure how to do is how to get Java to print one specific line to the console.
I also want to take the last employee id number in the last entry and have java add 1 to it one I add new employees. I thinking this needs to be done with a counter just not sure how.

You can do something like this:
BufferedReader reader = new BufferedReader(new FileReader(<<your file>>));
List<String> lines = new ArrayList<>();
String line = null;
while ((line = reader.readLine()) != null) {
lines.add(line);
}
System.out.println(lines.get(0));
With BufferedReader you are able to read lines directly. This example reads the file line by line and stores the lines in an array list. You can access the lines after that by using lines.get(lineNumber).

You can read text from a file one line at a time and then do whatever you want to with that line, print it, compare it, etc...
// Construct a BufferedReader object from the input file
BufferedReader r = new BufferedReader(new FileReader("employeeData.txt"));
int i = 1;
try {
// "Prime" the while loop
String line = r.readLine();
while (line != null) {
// Print a single line of input file to console
System.out.print("Line "+i+": "+line);
// Prepare for next loop iteration
line = r.readLine();
i++;
}
} finally {
// Free up file descriptor resources
r.close();
}
// Remember the next available employee number in a one-up scheme
int nextEmployeeId = i;

BufferedReader reader =new BufferedReader(new FileReader("yourfile.csv"));
String line = "";
while((line=reader.readLine())!=null){
String [] employee =line.trim().split(",");
// if you want to check either it contains some name
//index 0 is first name, index 1 is last name, index 2 is ID
}

Alternatively, If you want more control over read CSV files then u can think about CsvBeanReader that will give you more access over files contents..

Here is an algorithm which I use for reading csv files. The most effective way is to read all the data in the csv file into a 2D array first. It just makes it a lot more flexible to manipulate the data.
That way you can specify which line of the file to print to the console by specifying it in the index of the array and using a for. I.e: System.out.println(employee_Data[1][y]); for record 1. y is the index variable for fields. You would need to use a For Loop of course, to print every element for each line.
By the way, if you want to use the employee data in a larger program, in which it may for example store the data in a database or write to another file, I'd recommend encapsulating this entire code block into a function named Read_CSV_File(), which will return a 2D String array.
My Code
// The return type of this function is a String.
// The CSVFile_path can be for example "employeeData.csv".
public static String[][] Read_CSV_File(String CSVFile_path){
String employee_Data[][];
int x;
int y;
int noofFields;
try{
String line;
BufferedReader in = new BufferedReader(new FileReader(CSVFile_path));
// reading files in specified directory
// This assigns the data to the 2D array
// The program keeps looping through until the line read in by the console contains no data in it i.e. the end of the file.
while ( (( line = in.readLine()) != null ){
String[] current_Record = line.split(",");
if(x == 0) {
// Counts the number of fields in the csv file.
noofFields = current_Record.length();
}
for (String str : values) {
employee_Data[x][y] = str;
System.out.print(", "+employee_Data[x][y]);
// The field index variable, y is incremented in every loop.
y = y + 1;
}
// The record index variable, x is incremented in every loop.
x = x + 1;
}
// This frees up the BufferedReader file descriptor resources
in.close();
/* If an error occurs, it is caught by the catch statement and an error message
* is generated and displayed to the user.
*/
}catch( IOException ioException ) {
System.out.println("Exception: "+ioException);
}
// This prints to console the specific line of your choice
System.out.println(("Employee 1:);
for(y = 0; y < noofFields ; y++){
// Prints out all fields of record 1
System.out.print(employee_Data[1][y]+", ");
}
return employee_Data;
}

For reading large file,
log.debug("****************Start Reading CSV File*******");
copyFile(inputCSVFile);
StringBuilder stringBuilder = new StringBuilder();
String line= "";
BufferedReader brOldFile = null;
try {
String inputfile = inputCSVFile;
log.info("inputfile:" + inputfile);
brOldFile = new BufferedReader(new FileReader(inputfile));
while ((line = brOldFile.readLine()) != null) {
//line = replaceSpecialChar(line);
/*do your stuff here*/
stringBuilder.append(line);
stringBuilder.append("\n");
}
log.debug("****************End reading CSV File**************");
} catch (Exception e) {
log.error(" exception in readStaffInfoCSVFile ", e);
}finally {
if(null != brOldFile) {
try {
brOldFile.close();
} catch (IOException e) {
}
}
}
return stringBuilder.toString();

java RandomAccessFile parameter

I am trying to follow the below example found it here Java: Find if the last line of a file is empty to determine if a file finish by CRLF(empty line) however when I pass a String to the method RandomAccessFile says file Not Found. the problem is I cant feed it the file path, but I have the contents of the file as a String, so I tried to create a file using File f = new File(myString); and then pass the method the created file but it didnt work and it gave me the same error (File not Found) (it consideres the first line of the file as the path)!
how can I create a file accepted by RandomAccessFile, from my String that contains the contents of the file I want to check if it finishs by CRLF.
Hope I was clear.
public static boolean lastLineisCRLF(String filename) {
RandomAccessFile raf = null;
try {
raf = new RandomAccessFile(filename, "r");
long pos = raf.length() - 2;
if (pos < 0) return false; // too short
raf.seek(pos);
return raf.read() == '\r' && raf.read() == '\n';
} catch (IOException e) {
return false;
} finally {
if (raf != null) try {
raf.close();
} catch (IOException ignored) {
}
}
}

If you have the file contents already in memory as a string, you don't need to write it to a file again to determine if the last line is empty. Just split the contents by an end-of-line character and then trim whitespace off the last line and see if anything is left:
String fileContent = "line1\nline2\nline3\nline4\n";
// -1 limit tells split to keep empty fields
String[] fileLines = fileContent.split("\n", -1);
String lastLine = fileLines[fileLines.length - 1];
boolean lastLineIsEmpty = false;
if(lastLine.trim().isEmpty())
{
lastLineIsEmpty = true;
}
//prints true, line4 followed by carriage return but
//no line 5
System.out.println("lastLineEmpty: " + lastLineIsEmpty);

Scanner to reset pointer at previous line

My problem could be solved if Scanner class had previous() method on it. I am asking this question to know if there are any methods to achieve this functionality.
Input:
a file with contents like
a,1
a,2
a,3
b,1
c,1
c,2
c,3
c,4
d,1
d,2
d,3
e,1
f,1
I need to create a list of all lines that has same alphabet.
try {
Scanner scanner = new Scanner(new File(fileName));
List<String> procList = null;
String line =null;
while (scanner.hasNextLine()){
line = scanner.nextLine();
System.out.println(line);
String[] sParts = line.split(",");
procList = new ArrayList<String>();
procList.add(line);
boolean isSamealpha = true;
while(isSamealpha){
String s1 = scanner.nextLine();
if (s1.contains(sParts[0])){
procList.add(s1);
}else{
isSamealpha = false;
System.out.println(procList);
}
}
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
I get output like
a,1
[a,1, a,2, a,3]
c,1
[c,1, c,2, c,3, c,4]
d,2
[d,2, d,3]
f,1
[f,1]
As you can see it missed list for b and e. If I has scanner.previous() method, I would have put it in else of second while loop. Because there is no previous method, I am stuck.
Please let me know if there are any methods I can use. I can't use FileUtils.readLines() because its a 3GB file and I don't want to use my java memory to store all the file.

I would suggest reconsidering your algorithm instead. You are missing tokens because your algorithm involves reading ahead to determine when the sequence has broken, yet you aren't collecting that next line of input into the same structures that you are placing "duplicate" entries.
You can solve this without needing to read backwards. If you know that the input is always sorted, just read line by line and keep a reference to the last line (to compare with the current one).

Below is some sample code that should help. (I only typed this; I did no checking.)
Scanner scanner = new Scanner(new File(fileName));
List<String> procList = null;
String line = null;
String previousAlpha = null;
while (scanner.hasNextLine()){
line = scanner.nextLine();
if (previousAlpha == null) {
// very first line in the file
procList = new ArrayList<String>();
procList.add(line);
System.out.println(line);
previousAlpha = line.split(",")[0];
}
else if (line.contains(previousAlpha)) {
// same letter as before
procList.add(line);
}
else {
// new letter, but not the very first
// line
System.out.println(procList);
procList = new ArrayList<String>();
procList.add(line);
System.out.println(line);
previousAlpha = line.split(",")[0];
}
}

Get the offset of previous line in a file

I'm extracting data from a file line by line into a database and i can't figure out a proper way to flag lines that I've already read into my database.
I have the following code that I use to iterate through the file lines and I attempt to verify
that the line has my flag or else I try to append the flag to the file line
List<String> fileLines = new ArrayList<String>();
File logFile = new File("C:\\MyStuff\\SyslogCatchAllCopy.txt");
try {
RandomAccessFile raf = new RandomAccessFile(logFile, "rw");
String line = "";
String doneReadingFlag = "##";
Scanner fileScanner = new Scanner(logFile);
while ((line = raf.readLine()) != null && !line.contains(doneReading)) {
Scanner s = new Scanner(line);
String temp = "";
if (!s.hasNext(doneReadingFlag)) {
fileLines.add(line);
raf.write(doneReadingFlag.getBytes(), (int) raf.getFilePointer(),
doneReadingFlag.getBytes().length);
} else {
System.err.println("Allready Red");
}
}
} catch (FileNotFoundException e) {
System.out.println("File not found" + e);
} catch (IOException e) {
System.out.println("Exception while reading the file ");
}
// return fileLines;
// MoreProccessing(fileLines);
This code appends the flag to the next line and it overwrites the characters in that position
Any Help ?

When you write to a file, it doesn't insert do you should expect it to replace the characters.
You need to reserve space in the file for information you want to change or you can add information to another file.
Or instead of marking each file, you can store somewhere the lines number (or better the character position) you have read up to.
If you are not restarting your process you can have process read the file as it is appended (meaning you might not need to store where you are up to anywhere)

#Peter Lawrey I did as you said and it worked for me like that:
as follows:
ArrayList<String> fileLines=new ArrayList<String>();
File logFile=new File("C:\\MyStuff\\MyFile.txt");
RandomAccessFile raf = new RandomAccessFile(logFile, "rw");
String line="";
String doneReadingFlag="#";
long oldOffset=raf.getFilePointer();
long newOffset=oldOffset;
while ((line=raf.readLine())!=null)
{
newOffset=raf.getFilePointer();
if(!line.contains(doneReadingFlag))
{
fileLines.add(line);
raf.seek((long)oldOffset);
raf.writeChars(doneReadingFlag);
raf.seek(newOffset);
System.out.println("Line added and flaged");
}
else
{
System.err.println("Already Red");
}
oldOffset=newOffset;
}

InputStreamReader and reading random lines from .txt file

I have a method for my app to read a random line from a text file and return it. Im using the randTxt() to read and return a random line from the txt file.
but it only shows the same line (1st line) everytime.
public String randTxt(){
// Read in the file into a list of strings
InputStreamReader inputStream = new InputStreamReader(getResources().openRawResource(R.raw.randomstuff));
//ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
String theLine="";
int i;
try {
i = inputStream.read();
while (i != -1) {
i = inputStream.read();
}
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
LineNumberReader rdr = new LineNumberReader(inputStream);
int numLines = 30;
Random r = new Random();
rdr.setLineNumber(r.nextInt(numLines));
try {
theLine = rdr.readLine();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return theLine;
}
How can I fix it? and Can someone explain what's wrong in my code?

Here's the framework for doing what you need using BufferedReader. In this case, you don't need to store the values in a temp array.
InputStreamReader inputStream = new InputStreamReader
(getResources().openRawResource(R.raw.randomstuff));
BufferedReader br = new BufferedReader(inputStream);
int numLines = 30;
Random r = new Random();
int desiredLine = r.nextInt(numLines);
String theLine="";
int lineCtr = 0;
while ((theLine = br.readLine()) != null) {
if (lineCtr == desiredLine) {
break;
}
lineCtr++;
}
...
Log.d(TAG, "Magic line is: " +theLine);

You have gotten an answer of how to fix your code, but no explanation of why our original code did not work.
LineNumberReader.setLineNumber(int) does not go to the actual line, it just changes what number you call the current line.
So, say you read two lines, getLineNumber() will now return 2 (it started at 0 and increased by 1 each time a newline was encountered). if you now setLineNumber(10), getLineNumber() will return 10. Reading yet another line (your third) will cause getLineNumber() to return 11.
This is described in the Java Doc.

inputStream.read does not return a line number. it returns the byte that was read. this isn't how you would read line by line. to read line by line, you should use buffered reader's readLine method. its probably easier at that point to read it all into a local array and use that array to randomly get an entry, rather than using a line number reader.

I think Random() function returns a value between 0 and 1. hence, you may have to multiply it with 100 to get an integer value. May even consider a MOD "your upper limit" operation to guarentee that the index you finally get is between 0 and your upper limit
Use the index you calculated thus, in your setLineNumber() method.
Edit:
As john said, we can get whole number using Random() object.

public String getRandomLine(String fileLoc) throws IOException
{
BufferedReader reader = new BufferedReader(new FileReader(fileLoc));
ArrayList<String> lines = new ArrayList<String>();
String line =null;
while( (line = reader.readLine())!= null )
lines.add(line);
// Choose a random one from the list
return lines.get(new Random().nextInt(lines.size()));
}
public String getRandomLineOpt(String fileLoc)throws IOException
{
File f=new File(fileLoc);
RandomAccessFile rcf=new RandomAccessFile(f, "r");
long rand = (long)(new Random().nextDouble()*f.length());
rcf.seek(rand);
rcf.readLine();
return rcf.readLine();
}