How can I remove or trim a line in a text file in Java?
This is my program but it does not work.
I want to remove a line in text file, a line contain the word of user input
try {
File inputFile = new File("temp.txt");
File tempFile = new File("temp1.txt");
BufferedReader reader = new BufferedReader(new FileReader(inputFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
String lineToRemove = name;
String currentLine;
while((currentLine = reader.readLine()) != null)
{
//trim newline when comparing with lineToRemove
String trimmedLine = currentLine.trim();
if(!trimmedLine.startsWith(lineToRemove))
{
// if current line not start with lineToRemove then write to file
writer.write(currentLine);
}
}
writer.close();
reader.close();
}
catch(IOException ex)
{
System.out.println("Error reading to file '" + fileName + "'");
}
You are not separating the lines with a line break character, so the resulting file will have one single long line. One possible way to fix that is just writing the line separator after each line.
Another possible problem is that you are only checking if the current line starts with the given string. If you want to check if the line contains the string you should use the contains method.
A third problem is that you are not writing the trimmed line, but the line as it is. You really don't say what you expect from the program, but if you are supposed to output trimmed lines it should look like this:
if(!trimmedLine.contains(lineToRemove)) {
writer.write(trimmedLine);
writer.newLine();
}
startsWith() is the culprit. You are checking if the line starts with "lineToRemove". As #Joni suggested use contains.
Related
I trying to remove a specific line from a file. But I have a problem in deleting a particular line from the text file. Let's said, my text file I want to remove Blueberry in the file following:
Old List Text file:
Chocolate
Strawberry
Blueberry
Mango
New List Text file:
Chocolate
Strawberry
Mango
I tried to run my Java program, when I input for delete and it didn't remove the line from the text file.
Output:
Please delete:
d
Blueberry
Remove:Blueberry
When I open my text file, it keep on looping with the word "Blueberry" only.
Text file:
Blueberry
Blueberry
Blueberry
Blueberry
Blueberry
Blueberry
Blueberry
Blueberry
My question is how to delete the specific line from the text file?
Here is my Java code:
String input="Please delete: ";
System.out.println(input);
try
{
BufferedReader reader = new BufferedReader
(new InputStreamReader (System.in));
line = reader.readLine();
String inFile="list.txt";
String line = "";
while(!line.equals("x"))
{
switch(line)
{
case "d":
line = reader.readLine();
System.out.println("Remove: " + line);
String lineToRemove="";
FileWriter removeLine=new FileWriter(inFile);
BufferedWriter change=new BufferedWriter(removeLine);
PrintWriter replace=new PrintWriter(change);
while (line != null) {
if (!line.trim().equals(lineToRemove))
{
replace.println(line);
replace.flush();
}
}
replace.close();
change.close();
break;
}
System.out.println(input);
line = reader.readLine();
}
}
catch(Exception e){
System.out.println("Error!");
}
Let's take a quick look at your code...
line = reader.readLine();
//...
while (line != null) {
if (!line.trim().equals(lineToRemove))
{
replace.println(line);
replace.flush();
}
}
Basically, you read the first line of the file and then repeatedly compare it with the lineToRemove, forever. This loop is never going to exit
This is a proof of concept, you will need to modify it to your needs.
Basically, what you need to ensure you're doing, is you're reading each line of the input file until there are no more lines
// All the important information
String inputFileName = "...";
String outputFileName = "...";
String lineToRemove = "...";
// The traps any possible read/write exceptions which might occur
try {
File inputFile = new File(inputFileName);
File outputFile = new File(outputFileName);
// Open the reader/writer, this ensure that's encapsulated
// in a try-with-resource block, automatically closing
// the resources regardless of how the block exists
try (BufferedReader reader = new BufferedReader(new FileReader(inputFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(outputFile))) {
// Read each line from the reader and compare it with
// with the line to remove and write if required
String line = null;
while ((line = reader.readLine()) != null) {
if (!line.equals(lineToRemove)) {
writer.write(line);
writer.newLine();
}
}
}
// This is some magic, because of the compounding try blocks
// this section will only be called if the above try block
// exited without throwing an exception, so we're now safe
// to update the input file
// If you want two files at the end of his process, don't do
// this, this assumes you want to update and replace the
// original file
// Delete the original file, you might consider renaming it
// to some backup file
if (inputFile.delete()) {
// Rename the output file to the input file
if (!outputFile.renameTo(inputFile)) {
throw new IOException("Could not rename " + outputFileName + " to " + inputFileName);
}
} else {
throw new IOException("Could not delete original input file " + inputFileName);
}
} catch (IOException ex) {
// Handle any exceptions
ex.printStackTrace();
}
Have a look at Basic I/O and The try-with-resources Statement for some more details
Reading input from console, reading file and writing to a file needs to be distinguished and done separately. you can not read and write file at the same time. you are not even reading your file. you are just comparing your console input indefinitely in your while loop.In fact, you are not even setting your lineTobeRemoved to the input line. Here is one way of doing it.
Algorithm:
Read the console input (your line to delete) then start reading the file and looking for line to delete by comparing it with your input line. if the lines do not match match then store the read line in a variable otherwise throw this line since you want to delete it.
Once finished reading, start writing the stored lines on the file. Now you will have updated file with one line removed.
public static void main(String args[]) {
String input = "Please delete: ";
System.out.println(input);
try {
BufferedReader reader = new BufferedReader(new InputStreamReader(
System.in));
String line = reader.readLine();
reader.close();
String inFile = "list.txt";
System.out.println("Remove: " + line);
String lineToRemove = line;
StringBuffer newContent = new StringBuffer();
BufferedReader br = new BufferedReader(new FileReader(inFile));
while ((line = br.readLine()) != null) {
if (!line.trim().equals(lineToRemove)) {
newContent.append(line);
newContent.append("\n"); // new line
}
}
br.close();
FileWriter removeLine = new FileWriter(inFile);
BufferedWriter change = new BufferedWriter(removeLine);
PrintWriter replace = new PrintWriter(change);
replace.write(newContent.toString());
replace.close();
}
catch (Exception e) {
e.printStackTrace();
}
}
Can anyone tell me why my code never reads the 2nd line of my file? if my 2nd line in the file (for example .txt file) start at a new line and indent that line, it will not read it.But if it is in a new line and it isn't indented , it will read. also it reads 3rd line fine. Is it something with the while loop ?
Scanner keyboard = new Scanner (System.in);
System.out.println("Input the file name");
String fileName = keyboard.nextLine();
File input = new File (fileName);
BufferedReader reader = new BufferedReader(new FileReader(input));
String content = reader.readLine();
content.replaceAll("\\s+","");
while (reader.readLine() != null) {
content = content + reader.readLine();
}
System.out.println(content);
See my comments in the code below.
String content = reader.readLine(); //here you read a line
content.replaceAll("\\s+","");
while (reader.readLine() != null) //here you read a line (once per loop iteration)
{
content = content + reader.readLine(); //here you read a line (once per loop iteration)
}
As you can see, you are reading the second line in the beginning of your while loop, and you are checking if it is equal to null before moving on. However, you do nothing with that value, and it is lost. A better solution would look like this:
String content = ""
String input = reader.readLine();
while (input != null)
{
content = content + input;
input = reader.readLine();
}
This avoids the problem of reading and then throwing away every other line by storing the line in a variable and checking the variable for null instead.
Each time you call readLine() it reads the next line. The statement
while (reader.readLine() != null)
reads a line but does not do anything with it. What you want is
String line;
StringBuilder buf;
while ( (line = reader.readLine()) != null)
{
buf.append(line);
}
content = buf.toString();
Using a StringBuilder is much better as it avoids reallocating and copying the entire string each time you append.
the code below is from a reference i saw online, so there might be some similarities i'm trying to implement the code to remove an entire line based on the 1st field in this instance it is (aaaa or bbbb) the file which has a delimiter "|", but it is not working. Hope someone can advise me on this. Do i need to split the line first? or my method is wrong?
data in player.dat (e.g)
bbbb|aaaaa|cccc
aaaa|bbbbbb|cccc
Code is below
public class testcode {
public static void main(String[] args)throws IOException
{
File inputFile = new File("players.dat");
File tempFile = new File ("temp.dat");
BufferedReader read = new BufferedReader(new FileReader(inputFile));
BufferedWriter write = new BufferedWriter(new FileWriter(tempFile));
Scanner UserInput = new Scanner(System.in);
System.out.println("Please Enter Username:");
String UserIn = UserInput.nextLine();
String lineToRemove = UserIn;
String currentLine;
while((currentLine = read.readLine()) != null) {
// trim newline when comparing with lineToRemove
String trimmedLine = currentLine.trim();
if(trimmedLine.equals(lineToRemove)) continue;
write.write(currentLine + System.getProperty("line.separator"));
}
write.close();
read.close();
boolean success = tempFile.renameTo(inputFile);
}
}
Your code compares the entire line it reads from the file to the user name the user enters, but you say in your question that you actually only want to compare to the first part up to the first pipe (|). Your code doesn't do that.
What you need to do is read the line from the file, get the part of the string up to the first pipe symbol (split the string) and skip the line based on comparing the first part of the split string to the lineToRemove variable.
To make it easier, you could also add the pipe symbol to the user input and then do this:
string lineToRemove = UserIn + "|";
...
if (trimmedLine.startsWith(lineToRemove)) continue;
This spares you from splitting the string.
I'm currently not sure whether UserInput.nextLine(); returns the newline character or not. To be safe here, you could change the above to:
string lineToRemove = UserIn.trim() + "|";
I'm having a hard time deleting a row of lines in a text file, I've use this code but i end up deleting all the lines instead, need some help.
try //vacation leave/
{
File inputFile = new File("Adlawan" + code1);
File tempFile = new File("AdalwanTempFile");
BufferedReader reader = new BufferedReader(new FileReader(inputFile));
BufferedWriter writer = new BufferedWriter(new FileWriter(tempFile));
String lineToRemove = "AdlawanJan2012";
String currentLine;
while((currentLine = reader.readLine()) != null)
{
//trim newline when comparing with lineToRemove
String trimmedLine = currentLine.trim();
if(trimmedLine.equals(lineToRemove))
{
writer.write(currentLine);
}
}
writer.close();
reader.close();
if(!inputFile.delete())
{
JOptionPane.showMessageDialog(null, "Could not rename file");
return;
}
if(!tempFile.renameTo(inputFile))
JOptionPane.showMessageDialog(null, "Could not rename file");
}
catch(Exception e)
{
JOptionPane.showMessageDialog(null, " ");
}
The data on the file looks like this:
AdlawanJan2012 Vacation-Leave-Credits -0.6875
AdlawanFeb2012 Vacation-Leave-Credits -0.6875
AdlawanMar2012 Vacation-Leave-Credits -0.6875
Desired result after trimming the lines:
AdlawanFeb2012 Vacation-Leave-Credits -0.6875
AdlawanMar2012 Vacation-Leave-Credits -0.6875
Thank you...
I think you're trying to delete line in a file if the line starts with the "lineToRemove" variable, in that case you might want to use "startsWith" method instead of "equal" method.
while((currentLine = reader.readLine()) != null)
{
//trim newline when comparing with lineToRemove
String trimmedLine = currentLine.trim();
if(!trimmedLine.startsWith(lineToRemove))
{
// if current line not start with lineToRemove then write to file
writer.write(currentLine);
}
}
trim() method only removes leading and trailing white spaces and not characters after white space.
String lineToRemove = "AdlawanJan2012";
....
String trimmedLine = currentLine.trim();
if(trimmedLine.substring(0, 14).equals(lineToRemove)) {
//Your deletion logic
}
It'a a good idea to read the file content line by line and copy them to another file(temporal file) preferably a Random Access file and omit the line you want to remove. just copy the rest to the temporal file and omit the line(s) you want to delete. then rename the file to original name. No samples Please. I need you to do this on your own that way you'll learn all by your self. good luck
Currently I am trying something very simple. I am looking through an XML document for a certain phrase upon which I try to replace it. The problem I am having is that when I read the lines I store each line into a StringBuffer. When I write the it to a document everything is written on a single line.
Here my code:
File xmlFile = new File("abc.xml")
BufferedReader br = new BufferedReader(new FileReade(xmlFile));
String line = null;
while((line = br.readLine())!= null)
{
if(line.indexOf("abc") != -1)
{
line = line.replaceAll("abc","xyz");
}
sb.append(line);
}
br.close();
BufferedWriter bw = new BufferedWriter(new FileWriter(xmlFile));
bw.write(sb.toString());
bw.close();
I am assuming I need a new line character when I prefer sb.append but unfortunately I don't know which character to use as "\n" does not work.
Thanks in advance!
P.S. I figured there must be a way to use Xalan to format the XML file after I write to it or something. Not sure how to do that though.
The readline reads everything between the newline characters so when you write back out, obviously the newline characters are missing. These characters depend on the OS: windows uses two characters to do a newline, unix uses one for example. To be OS agnostic, retrieve the system property "line.separator":
String newline = System.getProperty("line.separator");
and append it to your stringbuffer:
sb.append(line).append(newline);
Modified as suggested by Brel, your text-substituting approach should work, and it will work well enough for simple applications.
If things start to get a little hairier, and you end up wanting to select elements based on their position in the XML structure, and if you need to be sure to change element text but not tag text (think <abc>abc</abc>), then you'll want to call in in the cavalry and process the XML with an XML parser.
Essentially you read in a Document using a DocuemntBuilder, you hop around the document's nodes doing whatever you need to, and then ask the Document to write itself back to file. Or do you ask the parser? Anyway, most XML parsers have a handful of options that let you format the XML output: You can specify indentation (or not) and maybe newlines for every opening tag, that kinda thing, to make your XML look pretty.
Sb would be the StringBuffer object, which has not been instantiated in this example. This can added before the while loop:
StringBuffer sb = new StringBuffer();
Scanner scan = new Scanner(System.in);
String filePath = scan.next();
String oldString = "old_string";
String newString = "new_string";
String oldContent = "";
BufferedReader br = null;
FileWriter writer = null;
File xmlFile = new File(filePath);
try {
br = new BufferedReader(new FileReader(xmlFile));
String line = br.readLine();
while (line != null) {
oldContent = oldContent + line + System.lineSeparator();
line = br.readLine();
}
String newContent = oldContent.replaceAll(oldString, newString);
writer = new FileWriter(xmlFile);
writer.write(newContent);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
scan.close();
br.close();
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}