Develop Reference

Is there a way to get the updated part of a file (for example a game log) that continuesly updates? [duplicate]

What's the quickest and most efficient way of reading the last line of text from a [very, very large] file in Java?

Below are two functions, one that returns the last non-blank line of a file without loading or stepping through the entire file, and the other that returns the last N lines of the file without stepping through the entire file:
What tail does is zoom straight to the last character of the file, then steps backward, character by character, recording what it sees until it finds a line break. Once it finds a line break, it breaks out of the loop. Reverses what was recorded and throws it into a string and returns. 0xA is the new line and 0xD is the carriage return.
If your line endings are \r\n or crlf or some other "double newline style newline", then you will have to specify n*2 lines to get the last n lines because it counts 2 lines for every line.
public String tail( File file ) {
RandomAccessFile fileHandler = null;
try {
fileHandler = new RandomAccessFile( file, "r" );
long fileLength = fileHandler.length() - 1;
StringBuilder sb = new StringBuilder();
for(long filePointer = fileLength; filePointer != -1; filePointer--){
fileHandler.seek( filePointer );
int readByte = fileHandler.readByte();
if( readByte == 0xA ) {
if( filePointer == fileLength ) {
continue;
}
break;
} else if( readByte == 0xD ) {
if( filePointer == fileLength - 1 ) {
continue;
}
break;
}
sb.append( ( char ) readByte );
}
String lastLine = sb.reverse().toString();
return lastLine;
} catch( java.io.FileNotFoundException e ) {
e.printStackTrace();
return null;
} catch( java.io.IOException e ) {
e.printStackTrace();
return null;
} finally {
if (fileHandler != null )
try {
fileHandler.close();
} catch (IOException e) {
/* ignore */
}
}
}
But you probably don't want the last line, you want the last N lines, so use this instead:
public String tail2( File file, int lines) {
java.io.RandomAccessFile fileHandler = null;
try {
fileHandler =
new java.io.RandomAccessFile( file, "r" );
long fileLength = fileHandler.length() - 1;
StringBuilder sb = new StringBuilder();
int line = 0;
for(long filePointer = fileLength; filePointer != -1; filePointer--){
fileHandler.seek( filePointer );
int readByte = fileHandler.readByte();
if( readByte == 0xA ) {
if (filePointer < fileLength) {
line = line + 1;
}
} else if( readByte == 0xD ) {
if (filePointer < fileLength-1) {
line = line + 1;
}
}
if (line >= lines) {
break;
}
sb.append( ( char ) readByte );
}
String lastLine = sb.reverse().toString();
return lastLine;
} catch( java.io.FileNotFoundException e ) {
e.printStackTrace();
return null;
} catch( java.io.IOException e ) {
e.printStackTrace();
return null;
}
finally {
if (fileHandler != null )
try {
fileHandler.close();
} catch (IOException e) {
}
}
}
Invoke the above methods like this:
File file = new File("D:\\stuff\\huge.log");
System.out.println(tail(file));
System.out.println(tail2(file, 10));
Warning
In the wild west of unicode this code can cause the output of this function to come out wrong. For example "Mary?s" instead of "Mary's". Characters with hats, accents, Chinese characters etc may cause the output to be wrong because accents are added as modifiers after the character. Reversing compound characters changes the nature of the identity of the character on reversal. You will have to do full battery of tests on all languages you plan to use this with.
For more information about this unicode reversal problem read this:
https://codeblog.jonskeet.uk/2009/11/02/omg-ponies-aka-humanity-epic-fail/

Apache Commons has an implementation using RandomAccessFile.
It's called ReversedLinesFileReader.

Have a look at my answer to a similar question for C#. The code would be quite similar, although the encoding support is somewhat different in Java.
Basically it's not a terribly easy thing to do in general. As MSalter points out, UTF-8 does make it easy to spot \r or \n as the UTF-8 representation of those characters is just the same as ASCII, and those bytes won't occur in multi-byte character.
So basically, take a buffer of (say) 2K, and progressively read backwards (skip to 2K before you were before, read the next 2K) checking for a line termination. Then skip to exactly the right place in the stream, create an InputStreamReader on the top, and a BufferedReader on top of that. Then just call BufferedReader.readLine().

Using FileReader or FileInputStream won't work - you'll have to use either FileChannel or RandomAccessFile to loop through the file backwards from the end. Encodings will be a problem though, as Jon said.

You can easily change the below code to print the last line.
MemoryMappedFile for printing last 5 lines:
private static void printByMemoryMappedFile(File file) throws FileNotFoundException, IOException{
FileInputStream fileInputStream=new FileInputStream(file);
FileChannel channel=fileInputStream.getChannel();
ByteBuffer buffer=channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
buffer.position((int)channel.size());
int count=0;
StringBuilder builder=new StringBuilder();
for(long i=channel.size()-1;i>=0;i--){
char c=(char)buffer.get((int)i);
builder.append(c);
if(c=='\n'){
if(count==5)break;
count++;
builder.reverse();
System.out.println(builder.toString());
builder=null;
builder=new StringBuilder();
}
}
channel.close();
}
RandomAccessFile to print last 5 lines:
private static void printByRandomAcessFile(File file) throws FileNotFoundException, IOException{
RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
int lines = 0;
StringBuilder builder = new StringBuilder();
long length = file.length();
length--;
randomAccessFile.seek(length);
for(long seek = length; seek >= 0; --seek){
randomAccessFile.seek(seek);
char c = (char)randomAccessFile.read();
builder.append(c);
if(c == '\n'){
builder = builder.reverse();
System.out.println(builder.toString());
lines++;
builder = null;
builder = new StringBuilder();
if (lines == 5){
break;
}
}
}
}

as far as I know The fastest way to read the last line of a text file is using FileUtils Apache class which is in "org.apache.commons.io". I have a two-million-line file and by using this class, it took me less than one second to find the last line. Here is the my code:
LineIterator lineIterator = FileUtils.lineIterator(newFile(filePath),"UTF-8");
String lastLine="";
while (lineIterator.hasNext()){
lastLine= lineIterator.nextLine();
}

try(BufferedReader reader = new BufferedReader(new FileReader(reqFile))) {
String line = null;
System.out.println("======================================");
line = reader.readLine(); //Read Line ONE
line = reader.readLine(); //Read Line TWO
System.out.println("first line : " + line);
//Length of one line if lines are of even length
int len = line.length();
//skip to the end - 3 lines
reader.skip((reqFile.length() - (len*3)));
//Searched to the last line for the date I was looking for.
while((line = reader.readLine()) != null){
System.out.println("FROM LINE : " + line);
String date = line.substring(0,line.indexOf(","));
System.out.println("DATE : " + date); //BAM!!!!!!!!!!!!!!
}
System.out.println(reqFile.getName() + " Read(" + reqFile.length()/(1000) + "KB)");
System.out.println("======================================");
} catch (IOException x) {
x.printStackTrace();
}

In C#, you should be able to set the stream's position:
From: http://bytes.com/groups/net-c/269090-streamreader-read-last-line-text-file
using(FileStream fs = File.OpenRead("c:\\file.dat"))
{
using(StreamReader sr = new StreamReader(fs))
{
sr.BaseStream.Position = fs.Length - 4;
if(sr.ReadToEnd() == "DONE")
// match
}
}

To avoid the Unicode problems related to reverting the string (or the StringBuilder), as discussed in Eric Leschinski excellent answer, one can read to a byte list, from the end of the file, revert it to a byte array and then create the String from the byte array.
Below are the changes to Eric Leschinski answer's code, to do it with a byte array. The code changes are below the commented lines of code:
static public String tail2(File file, int lines) {
java.io.RandomAccessFile fileHandler = null;
try {
fileHandler = new java.io.RandomAccessFile( file, "r" );
long fileLength = fileHandler.length() - 1;
//StringBuilder sb = new StringBuilder();
List<Byte> sb = new ArrayList<>();
int line = 0;
for(long filePointer = fileLength; filePointer != -1; filePointer--){
fileHandler.seek( filePointer );
int readByte = fileHandler.readByte();
if( readByte == 0xA ) {
if (filePointer < fileLength) {
line = line + 1;
}
} else if( readByte == 0xD ) {
if (filePointer < fileLength-1) {
line = line + 1;
}
}
if (line >= lines) {
break;
}
//sb.add( (char) readByte );
sb.add( (byte) readByte );
}
//String lastLine = sb.reverse().toString();
//Revert byte array and create String
byte[] bytes = new byte[sb.size()];
for (int i=0; i<sb.size(); i++) bytes[sb.size()-1-i] = sb.get(i);
String lastLine = new String(bytes);
return lastLine;
} catch( java.io.FileNotFoundException e ) {
e.printStackTrace();
return null;
} catch( java.io.IOException e ) {
e.printStackTrace();
return null;
}
finally {
if (fileHandler != null )
try {
fileHandler.close();
} catch (IOException e) {
}
}
}

Code is 2 lines only
// Please specify correct Charset
ReversedLinesFileReader rlf = new ReversedLinesFileReader(file, StandardCharsets.UTF_8);
// read last 2 lines
System.out.println(rlf.toString(2));
Gradle:
implementation group: 'commons-io', name: 'commons-io', version: '2.11.0'
Maven:
<dependency>
<groupId>commons-io</groupId><artifactId>commons-io</artifactId><version>2.11.0</version>
</dependency>

how to read csv file without specific number of column in java and without change the code after every additional column

I tried to write code to read csv file, and I stored the data in an array of object
but after every change in the number of columns, I should read another column and change the code.
because I want to use the same class for different csv files with different number of columns without need to change the code for every file.
public class Read_CSV {
public static Object[][]readCSVdata(String csvFilePath){
//String csvFilePath = null;
ArrayList<Object[]>dataList = new ArrayList <Object[]>();
String line = "";
String cvsSplitBy = ",";
try (BufferedReader br = new BufferedReader(new FileReader(csvFilePath))) {
int iteration = 0;
while ((line = br.readLine()) != null) {
if(iteration == 0) {
iteration++;
continue;
}
String[] arri = line.split(cvsSplitBy);
Object[]arri1= {arri[0] , arri[1],arri[2] };
//here after every additional column I should add another cell
dataList.add(arri1);
}
br.close();
return dataList.toArray(new Object[dataList.size()][]);
} catch (IOException e) {
e.printStackTrace();
return null;
}
}
}

You could use the array of strings after splitting each line:
while ((line = br.readLine()) != null) {
if(iteration == 0) {
iteration++;
continue;
}
String[] arri = line.split(cvsSplitBy);
dataList.add(arri);
}
Then dataList will contain arrays of strings.
Or you have some other requirements?

Having trouble with parsing csv files in Java

I'm trying to parse a folder of csv files (balance sheets), and have everythings gone smoothly up until I tried to separate the row names from the values.
It looks like the last cell on the previous row is combining with the first cell (the row name in column A) in the next row.
File path = new File("/Users/Zack/Desktop/JavaDB/BALANCESHEETS");
for(File file: path.listFiles()) {
if (file.isFile()) {
String fileName = file.getName();
String ticker = fileName.split("\\_")[0];
if (ticker.equals("ASB") || ticker.equals("FRC")) {
if (ticker.equals("ASB")) {
ticker = ticker + "PRD";
}
if (ticker.equals("FRC")) {
ticker = ticker + "PRD";
}
}
Reader reader = new BufferedReader(new FileReader(file));
StringBuilder builder = new StringBuilder();
int c;
while ((c = reader.read()) != -1) {
builder.append((char) c);
}
String string = builder.toString();
ArrayList<String> stringResult = new ArrayList<String>();
if (string != null) {
String[] splitData = string.split("\\s*,\\s*");
for (int i = 0; i <splitData.length; i++) {
if (!(splitData[i] == null) || !(splitData[i].length() ==0)) {
stringResult.add(splitData[i].trim());
}
}
}
for (int i = 0; i < stringResult.size(); i++) {
int cL = stringResult.get(i).length();
for (int x = 0; x < cL; x++) {
if (Character.isLetter(stringResult.get(i).charAt(x))) {
System.out.println("index: " + i);
System.out.println(stringResult.get(i));
break;
}
}
}
Here are some photos of what's happening
https://postimg.org/image/a9qc1qggz/
https://postimg.org/image/mvna7p7s3/
Any idea on how to fix this?
I also noticed there is a space in front of the row names in the spreadsheets, which I suspect may be part of the problem.

The problem is coming from where you are reading in the file, here:
Reader reader = new BufferedReader(new FileReader(file));
StringBuilder builder = new StringBuilder();
int c;
while ((c = reader.read()) != -1) {
builder.append((char) c);
}
String string = builder.toString();
This reads all the characters into a single string, including the new line character(s). When you then split the string, you are not splitting on the new line character(s) and so you end up with what you are seeing.
As mentioned but others I strongly urge you to use one of the many csv parsers that already exist.
The simple (but ugly) fix would be to also split on newlines. A better fix would be to use the readLine() method of the BufferedReader.
Also != is your friend.

As Erwin stated in the comments, your Pattern that you are splitting on just looks for commas with whitespace around them. It looks like you know what format your data will be in since you know that the data will be separated by either whitespace comma whitespace or a newline. Seems to me you just need to change your input to "\\s*,\\s*|$", which is the regex that says that. Like has been mentioned you need to know beforehand that the data doesn't include whitespace comma whitespace in any of the fields or this breaks.

I would like to add (insert) column numbers (from 1 to 1000) at first column in the .CSV file

For Example
My input.csv contains data like this..
Row_No ,User , Actions
John , SQL transaction
Suman , Transaction failed
Ram , Button pressed to retrieve details
And this i what I am looking for.. Advance thanks to each one of you those who have tried this
output.csv
Row_No ,User , Actions
1 ,John , SQL transaction
2 ,Suman , Transaction failed
3 ,Ram , Button pressed to retrieve details
please help me
This is what I have tried
public class MapWriter
{
public static void main(String[] args) throws IOException {
CsvMapReader mapReader = null;
ICsvMapWriter mapWriter = null;
try
{
CsvPreference prefs = CsvPreference.STANDARD_PREFERENCE;
mapReader = new CsvMapReader(new FileReader("D:\\input.csv"), prefs);
mapWriter = new CsvMapWriter(new FileWriter("D:\\output.csv"), prefs);
// header used to read the original file
final String[] readHeader = mapReader.getHeader(true);
// header used to write the new file
// (same as 'readHeader', but with additional column)
final String[] writeHeader = new String[readHeader.length + 1];
System.arraycopy(readHeader, 0, writeHeader, 0, readHeader.length);
final String timeHeader = " ";
writeHeader[writeHeader.length-1]= timeHeader;
mapWriter.writeHeader(writeHeader);
int count=1;
Map<String, String> row;
while( (row = mapReader.read(readHeader)) != null ) {
// add your column with desired value
row.put(timeHeader, String.valueOf(count));
mapWriter.write(row, writeHeader);
count++;
}
}
finally {
if( mapReader != null )
{
mapReader.close();
}
if( mapWriter != null )
{
mapWriter.close();
}
}
}
}

As far as I can tell, you're trying to use a verifying CSV parser on invalid data (e.g. Row_No is blank everywhere but the header in your input file). I'm not certain if that's allowed with your parser, but I don't believe you need to parse the file yet. As an example, I would do it with StringTokenizer and a Scanner like so -
public static void main(String[] args) {
String inputFile = "c:/input.csv";
String outputFile = "c:/output.csv";
int lineNumber = 0; // <-- keep a line count.
Scanner scanner = null;
PrintWriter pw = null;
try {
pw = new PrintWriter(outputFile); // <-- output
File source = new File(inputFile);
scanner = new Scanner(source); // <-- input
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
line = (line != null) ? line.trim() : "";
if (line.length() < 1) {
continue;
}
// line 0 is the header.
if (lineNumber != 0) {
pw.print(lineNumber);
pw.print(", ");
}
int tokenCount = 0;
StringTokenizer st = new StringTokenizer(line, ",");
while (st.hasMoreTokens()) {
String token = st.nextToken();
if (tokenCount != 0) {
pw.print(", ");
}
pw.print(token.trim());
tokenCount++;
}
pw.println();
lineNumber++;
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} finally {
if (scanner != null) {
scanner.close();
}
if (pw != null) {
pw.close();
}
}
}
After running the above, I generated the output.csv (based on your input.csv) -
Row_No, User, Actions
1, John, SQL transaction
2, Suman, Transaction failed
3, Ram, Button pressed to retrieve details

Quickly read the last line of a text file?

What's the quickest and most efficient way of reading the last line of text from a [very, very large] file in Java?

Below are two functions, one that returns the last non-blank line of a file without loading or stepping through the entire file, and the other that returns the last N lines of the file without stepping through the entire file:
What tail does is zoom straight to the last character of the file, then steps backward, character by character, recording what it sees until it finds a line break. Once it finds a line break, it breaks out of the loop. Reverses what was recorded and throws it into a string and returns. 0xA is the new line and 0xD is the carriage return.
If your line endings are \r\n or crlf or some other "double newline style newline", then you will have to specify n*2 lines to get the last n lines because it counts 2 lines for every line.
public String tail( File file ) {
RandomAccessFile fileHandler = null;
try {
fileHandler = new RandomAccessFile( file, "r" );
long fileLength = fileHandler.length() - 1;
StringBuilder sb = new StringBuilder();
for(long filePointer = fileLength; filePointer != -1; filePointer--){
fileHandler.seek( filePointer );
int readByte = fileHandler.readByte();
if( readByte == 0xA ) {
if( filePointer == fileLength ) {
continue;
}
break;
} else if( readByte == 0xD ) {
if( filePointer == fileLength - 1 ) {
continue;
}
break;
}
sb.append( ( char ) readByte );
}
String lastLine = sb.reverse().toString();
return lastLine;
} catch( java.io.FileNotFoundException e ) {
e.printStackTrace();
return null;
} catch( java.io.IOException e ) {
e.printStackTrace();
return null;
} finally {
if (fileHandler != null )
try {
fileHandler.close();
} catch (IOException e) {
/* ignore */
}
}
}
But you probably don't want the last line, you want the last N lines, so use this instead:
public String tail2( File file, int lines) {
java.io.RandomAccessFile fileHandler = null;
try {
fileHandler =
new java.io.RandomAccessFile( file, "r" );
long fileLength = fileHandler.length() - 1;
StringBuilder sb = new StringBuilder();
int line = 0;
for(long filePointer = fileLength; filePointer != -1; filePointer--){
fileHandler.seek( filePointer );
int readByte = fileHandler.readByte();
if( readByte == 0xA ) {
if (filePointer < fileLength) {
line = line + 1;
}
} else if( readByte == 0xD ) {
if (filePointer < fileLength-1) {
line = line + 1;
}
}
if (line >= lines) {
break;
}
sb.append( ( char ) readByte );
}
String lastLine = sb.reverse().toString();
return lastLine;
} catch( java.io.FileNotFoundException e ) {
e.printStackTrace();
return null;
} catch( java.io.IOException e ) {
e.printStackTrace();
return null;
}
finally {
if (fileHandler != null )
try {
fileHandler.close();
} catch (IOException e) {
}
}
}
Invoke the above methods like this:
File file = new File("D:\\stuff\\huge.log");
System.out.println(tail(file));
System.out.println(tail2(file, 10));
Warning
In the wild west of unicode this code can cause the output of this function to come out wrong. For example "Mary?s" instead of "Mary's". Characters with hats, accents, Chinese characters etc may cause the output to be wrong because accents are added as modifiers after the character. Reversing compound characters changes the nature of the identity of the character on reversal. You will have to do full battery of tests on all languages you plan to use this with.
For more information about this unicode reversal problem read this:
https://codeblog.jonskeet.uk/2009/11/02/omg-ponies-aka-humanity-epic-fail/

Apache Commons has an implementation using RandomAccessFile.
It's called ReversedLinesFileReader.

Have a look at my answer to a similar question for C#. The code would be quite similar, although the encoding support is somewhat different in Java.
Basically it's not a terribly easy thing to do in general. As MSalter points out, UTF-8 does make it easy to spot \r or \n as the UTF-8 representation of those characters is just the same as ASCII, and those bytes won't occur in multi-byte character.
So basically, take a buffer of (say) 2K, and progressively read backwards (skip to 2K before you were before, read the next 2K) checking for a line termination. Then skip to exactly the right place in the stream, create an InputStreamReader on the top, and a BufferedReader on top of that. Then just call BufferedReader.readLine().

Using FileReader or FileInputStream won't work - you'll have to use either FileChannel or RandomAccessFile to loop through the file backwards from the end. Encodings will be a problem though, as Jon said.

You can easily change the below code to print the last line.
MemoryMappedFile for printing last 5 lines:
private static void printByMemoryMappedFile(File file) throws FileNotFoundException, IOException{
FileInputStream fileInputStream=new FileInputStream(file);
FileChannel channel=fileInputStream.getChannel();
ByteBuffer buffer=channel.map(FileChannel.MapMode.READ_ONLY, 0, channel.size());
buffer.position((int)channel.size());
int count=0;
StringBuilder builder=new StringBuilder();
for(long i=channel.size()-1;i>=0;i--){
char c=(char)buffer.get((int)i);
builder.append(c);
if(c=='\n'){
if(count==5)break;
count++;
builder.reverse();
System.out.println(builder.toString());
builder=null;
builder=new StringBuilder();
}
}
channel.close();
}
RandomAccessFile to print last 5 lines:
private static void printByRandomAcessFile(File file) throws FileNotFoundException, IOException{
RandomAccessFile randomAccessFile = new RandomAccessFile(file, "r");
int lines = 0;
StringBuilder builder = new StringBuilder();
long length = file.length();
length--;
randomAccessFile.seek(length);
for(long seek = length; seek >= 0; --seek){
randomAccessFile.seek(seek);
char c = (char)randomAccessFile.read();
builder.append(c);
if(c == '\n'){
builder = builder.reverse();
System.out.println(builder.toString());
lines++;
builder = null;
builder = new StringBuilder();
if (lines == 5){
break;
}
}
}
}

as far as I know The fastest way to read the last line of a text file is using FileUtils Apache class which is in "org.apache.commons.io". I have a two-million-line file and by using this class, it took me less than one second to find the last line. Here is the my code:
LineIterator lineIterator = FileUtils.lineIterator(newFile(filePath),"UTF-8");
String lastLine="";
while (lineIterator.hasNext()){
lastLine= lineIterator.nextLine();
}

try(BufferedReader reader = new BufferedReader(new FileReader(reqFile))) {
String line = null;
System.out.println("======================================");
line = reader.readLine(); //Read Line ONE
line = reader.readLine(); //Read Line TWO
System.out.println("first line : " + line);
//Length of one line if lines are of even length
int len = line.length();
//skip to the end - 3 lines
reader.skip((reqFile.length() - (len*3)));
//Searched to the last line for the date I was looking for.
while((line = reader.readLine()) != null){
System.out.println("FROM LINE : " + line);
String date = line.substring(0,line.indexOf(","));
System.out.println("DATE : " + date); //BAM!!!!!!!!!!!!!!
}
System.out.println(reqFile.getName() + " Read(" + reqFile.length()/(1000) + "KB)");
System.out.println("======================================");
} catch (IOException x) {
x.printStackTrace();
}

In C#, you should be able to set the stream's position:
From: http://bytes.com/groups/net-c/269090-streamreader-read-last-line-text-file
using(FileStream fs = File.OpenRead("c:\\file.dat"))
{
using(StreamReader sr = new StreamReader(fs))
{
sr.BaseStream.Position = fs.Length - 4;
if(sr.ReadToEnd() == "DONE")
// match
}
}

To avoid the Unicode problems related to reverting the string (or the StringBuilder), as discussed in Eric Leschinski excellent answer, one can read to a byte list, from the end of the file, revert it to a byte array and then create the String from the byte array.
Below are the changes to Eric Leschinski answer's code, to do it with a byte array. The code changes are below the commented lines of code:
static public String tail2(File file, int lines) {
java.io.RandomAccessFile fileHandler = null;
try {
fileHandler = new java.io.RandomAccessFile( file, "r" );
long fileLength = fileHandler.length() - 1;
//StringBuilder sb = new StringBuilder();
List<Byte> sb = new ArrayList<>();
int line = 0;
for(long filePointer = fileLength; filePointer != -1; filePointer--){
fileHandler.seek( filePointer );
int readByte = fileHandler.readByte();
if( readByte == 0xA ) {
if (filePointer < fileLength) {
line = line + 1;
}
} else if( readByte == 0xD ) {
if (filePointer < fileLength-1) {
line = line + 1;
}
}
if (line >= lines) {
break;
}
//sb.add( (char) readByte );
sb.add( (byte) readByte );
}
//String lastLine = sb.reverse().toString();
//Revert byte array and create String
byte[] bytes = new byte[sb.size()];
for (int i=0; i<sb.size(); i++) bytes[sb.size()-1-i] = sb.get(i);
String lastLine = new String(bytes);
return lastLine;
} catch( java.io.FileNotFoundException e ) {
e.printStackTrace();
return null;
} catch( java.io.IOException e ) {
e.printStackTrace();
return null;
}
finally {
if (fileHandler != null )
try {
fileHandler.close();
} catch (IOException e) {
}
}
}

Code is 2 lines only
// Please specify correct Charset
ReversedLinesFileReader rlf = new ReversedLinesFileReader(file, StandardCharsets.UTF_8);
// read last 2 lines
System.out.println(rlf.toString(2));
Gradle:
implementation group: 'commons-io', name: 'commons-io', version: '2.11.0'
Maven:
<dependency>
<groupId>commons-io</groupId><artifactId>commons-io</artifactId><version>2.11.0</version>
</dependency>