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How do I replace a line of text found within a text file?
I have a string such as:
Do the dishes0
And I want to update it with:
Do the dishes1
(and vise versa)
How do I accomplish this?
ActionListener al = new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
JCheckBox checkbox = (JCheckBox) e.getSource();
if (checkbox.isSelected()) {
System.out.println("Selected");
String s = checkbox.getText();
replaceSelected(s, "1");
} else {
System.out.println("Deselected");
String s = checkbox.getText();
replaceSelected(s, "0");
}
}
};
public static void replaceSelected(String replaceWith, String type) {
}
By the way, I want to replace ONLY the line that was read. NOT the entire file.
At the bottom, I have a general solution to replace lines in a file. But first, here is the answer to the specific question at hand. Helper function:
public static void replaceSelected(String replaceWith, String type) {
try {
// input the file content to the StringBuffer "input"
BufferedReader file = new BufferedReader(new FileReader("notes.txt"));
StringBuffer inputBuffer = new StringBuffer();
String line;
while ((line = file.readLine()) != null) {
inputBuffer.append(line);
inputBuffer.append('\n');
}
file.close();
String inputStr = inputBuffer.toString();
System.out.println(inputStr); // display the original file for debugging
// logic to replace lines in the string (could use regex here to be generic)
if (type.equals("0")) {
inputStr = inputStr.replace(replaceWith + "1", replaceWith + "0");
} else if (type.equals("1")) {
inputStr = inputStr.replace(replaceWith + "0", replaceWith + "1");
}
// display the new file for debugging
System.out.println("----------------------------------\n" + inputStr);
// write the new string with the replaced line OVER the same file
FileOutputStream fileOut = new FileOutputStream("notes.txt");
fileOut.write(inputStr.getBytes());
fileOut.close();
} catch (Exception e) {
System.out.println("Problem reading file.");
}
}
Then call it:
public static void main(String[] args) {
replaceSelected("Do the dishes", "1");
}
Original Text File Content:
Do the dishes0
Feed the dog0
Cleaned my room1
Output:
Do the dishes0
Feed the dog0
Cleaned my room1
----------------------------------
Do the dishes1
Feed the dog0
Cleaned my room1
New text file content:
Do the dishes1
Feed the dog0
Cleaned my room1
And as a note, if the text file was:
Do the dishes1
Feed the dog0
Cleaned my room1
and you used the method replaceSelected("Do the dishes", "1");,
it would just not change the file.
Since this question is pretty specific, I'll add a more general solution here for future readers (based on the title).
// read file one line at a time
// replace line as you read the file and store updated lines in StringBuffer
// overwrite the file with the new lines
public static void replaceLines() {
try {
// input the (modified) file content to the StringBuffer "input"
BufferedReader file = new BufferedReader(new FileReader("notes.txt"));
StringBuffer inputBuffer = new StringBuffer();
String line;
while ((line = file.readLine()) != null) {
line = ... // replace the line here
inputBuffer.append(line);
inputBuffer.append('\n');
}
file.close();
// write the new string with the replaced line OVER the same file
FileOutputStream fileOut = new FileOutputStream("notes.txt");
fileOut.write(inputBuffer.toString().getBytes());
fileOut.close();
} catch (Exception e) {
System.out.println("Problem reading file.");
}
}
Since Java 7 this is very easy and intuitive to do.
List<String> fileContent = new ArrayList<>(Files.readAllLines(FILE_PATH, StandardCharsets.UTF_8));
for (int i = 0; i < fileContent.size(); i++) {
if (fileContent.get(i).equals("old line")) {
fileContent.set(i, "new line");
break;
}
}
Files.write(FILE_PATH, fileContent, StandardCharsets.UTF_8);
Basically you read the whole file to a List, edit the list and finally write the list back to file.
FILE_PATH represents the Path of the file.
If replacement is of different length:
Read file until you find the string you want to replace.
Read into memory the part after text you want to replace, all of it.
Truncate the file at start of the part you want to replace.
Write replacement.
Write rest of the file from step 2.
If replacement is of same length:
Read file until you find the string you want to replace.
Set file position to start of the part you want to replace.
Write replacement, overwriting part of file.
This is the best you can get, with constraints of your question. However, at least the example in question is replacing string of same length, So the second way should work.
Also be aware: Java strings are Unicode text, while text files are bytes with some encoding. If encoding is UTF8, and your text is not Latin1 (or plain 7-bit ASCII), you have to check length of encoded byte array, not length of Java string.
I was going to answer this question. Then I saw it get marked as a duplicate of this question, after I'd written the code, so I am going to post my solution here.
Keeping in mind that you have to re-write the text file. First I read the entire file, and store it in a string. Then I store each line as a index of a string array, ex line one = array index 0. I then edit the index corresponding to the line that you wish to edit. Once this is done I concatenate all the strings in the array into a single string. Then I write the new string into the file, which writes over the old content. Don't worry about losing your old content as it has been written again with the edit. below is the code I used.
public class App {
public static void main(String[] args) {
String file = "file.txt";
String newLineContent = "Hello my name is bob";
int lineToBeEdited = 3;
ChangeLineInFile changeFile = new ChangeLineInFile();
changeFile.changeALineInATextFile(file, newLineContent, lineToBeEdited);
}
}
And the class.
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
public class ChangeLineInFile {
public void changeALineInATextFile(String fileName, String newLine, int lineNumber) {
String content = new String();
String editedContent = new String();
content = readFile(fileName);
editedContent = editLineInContent(content, newLine, lineNumber);
writeToFile(fileName, editedContent);
}
private static int numberOfLinesInFile(String content) {
int numberOfLines = 0;
int index = 0;
int lastIndex = 0;
lastIndex = content.length() - 1;
while (true) {
if (content.charAt(index) == '\n') {
numberOfLines++;
}
if (index == lastIndex) {
numberOfLines = numberOfLines + 1;
break;
}
index++;
}
return numberOfLines;
}
private static String[] turnFileIntoArrayOfStrings(String content, int lines) {
String[] array = new String[lines];
int index = 0;
int tempInt = 0;
int startIndext = 0;
int lastIndex = content.length() - 1;
while (true) {
if (content.charAt(index) == '\n') {
tempInt++;
String temp2 = new String();
for (int i = 0; i < index - startIndext; i++) {
temp2 += content.charAt(startIndext + i);
}
startIndext = index;
array[tempInt - 1] = temp2;
}
if (index == lastIndex) {
tempInt++;
String temp2 = new String();
for (int i = 0; i < index - startIndext + 1; i++) {
temp2 += content.charAt(startIndext + i);
}
array[tempInt - 1] = temp2;
break;
}
index++;
}
return array;
}
private static String editLineInContent(String content, String newLine, int line) {
int lineNumber = 0;
lineNumber = numberOfLinesInFile(content);
String[] lines = new String[lineNumber];
lines = turnFileIntoArrayOfStrings(content, lineNumber);
if (line != 1) {
lines[line - 1] = "\n" + newLine;
} else {
lines[line - 1] = newLine;
}
content = new String();
for (int i = 0; i < lineNumber; i++) {
content += lines[i];
}
return content;
}
private static void writeToFile(String file, String content) {
try (Writer writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file), "utf-8"))) {
writer.write(content);
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private static String readFile(String filename) {
String content = null;
File file = new File(filename);
FileReader reader = null;
try {
reader = new FileReader(file);
char[] chars = new char[(int) file.length()];
reader.read(chars);
content = new String(chars);
reader.close();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
return content;
}
}
Sharing the experience with Java Util Stream
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public static void replaceLine(String filePath, String originalLineText, String newLineText) {
Path path = Paths.get(filePath);
// Get all the lines
try (Stream<String> stream = Files.lines(path, StandardCharsets.UTF_8)) {
// Do the line replace
List<String> list = stream.map(line -> line.equals(originalLineText) ? newLineText : line)
.collect(Collectors.toList());
// Write the content back
Files.write(path, list, StandardCharsets.UTF_8);
} catch (IOException e) {
LOG.error("IOException for : " + path, e);
e.printStackTrace();
}
}
Usage
replaceLine("test.txt", "Do the dishes0", "Do the dishes1");
//Read the file data
BufferedReader file = new BufferedReader(new FileReader(filepath));
StringBuffer inputBuffer = new StringBuffer();
String line;
while ((line = file.readLine()) != null) {
inputBuffer.append(line);
inputBuffer.append('\n');
}
file.close();
String inputStr = inputBuffer.toString();
// logic to replace lines in the string (could use regex here to be generic)
inputStr = inputStr.replace(str, " ");
//'str' is the string need to update in this case it is updating with nothing
// write the new string with the replaced line OVER the same file
FileOutputStream fileOut = new FileOutputStream(filer);
fileOut.write(inputStr.getBytes());
fileOut.close();
Well you would need to get a file with JFileChooser and then read through the lines of the file using a scanner and the hasNext() function
http://docs.oracle.com/javase/7/docs/api/javax/swing/JFileChooser.html
once you do that you can save the line into a variable and manipulate the contents.
just how to replace strings :) as i do
first arg will be filename second target string third one the string to be replaced instead of targe
public class ReplaceString{
public static void main(String[] args)throws Exception {
if(args.length<3)System.exit(0);
String targetStr = args[1];
String altStr = args[2];
java.io.File file = new java.io.File(args[0]);
java.util.Scanner scanner = new java.util.Scanner(file);
StringBuilder buffer = new StringBuilder();
while(scanner.hasNext()){
buffer.append(scanner.nextLine().replaceAll(targetStr, altStr));
if(scanner.hasNext())buffer.append("\n");
}
scanner.close();
java.io.PrintWriter printer = new java.io.PrintWriter(file);
printer.print(buffer);
printer.close();
}
}
I'm trying to read a text file to get a version number but for some reason no matter what I put in the text file it always returns 0 (zero).
The text file is called version.txt and it contains no spaces or letters, just 1 character that is a number. I need it to return that number. Any ideas on why this doesn't work?
static int i;
public static void main(String[] args) {
String strFilePath = "/version.txt";
try
{
FileInputStream fin = new FileInputStream(strFilePath);
DataInputStream din = new DataInputStream(fin);
i = din.readInt();
System.out.println("int : " + i);
din.close();
}
catch(FileNotFoundException fe)
{
System.out.println("FileNotFoundException : " + fe);
}
catch(IOException ioe)
{
System.out.println("IOException : " + ioe);
}
}
private final int VERSION = i;
Here is the default solution that i use whenever i require to read a text file.
public static ArrayList<String> readData(String fileName) throws Exception
{
ArrayList<String> data = new ArrayList<String>();
BufferedReader in = new BufferedReader(new FileReader(fileName));
String temp = in.readLine();
while (temp != null)
{
data.add(temp);
temp = in.readLine();
}
in.close();
return data;
}
Pass the file name to readData method. You can then use for loop to read the only line in the arraylist, and can use the same loop to read multiple lines from different file...I mean do whatever you like with the arraylist.
Please don't use a DataInputStream
Per the linked Javadoc, it lets an application read primitive Java data types from an underlying input stream in a machine-independent way. An application uses a data output stream to write data that can later be read by a data input stream.
You want to read a File (not data from a data output stream).
Please do use try-with-resources
And since you seem to want an ascii integer, I'd suggest you use a Scanner.
public static void main(String[] args) {
String strFilePath = "/version.txt";
File f = new File(strFilePath);
try (Scanner scanner = new Scanner(f)) {
int i = scanner.nextInt();
System.out.println(i);
} catch (Exception e) {
e.printStackTrace();
}
}
Use an initializing block
An initializing block will be copied into the class constructor, in your example remove public static void main(String[] args), something like
private int VERSION = -1; // <-- no more zero!
{
String strFilePath = "/version.txt";
File f = new File(strFilePath);
try (Scanner scanner = new Scanner(f)) {
VERSION = scanner.nextInt(); // <-- hope it's a value
System.out.println("Version = " + VERSION);
} catch (Exception e) {
e.printStackTrace();
}
}
Extract it to a method
private final int VERSION = getVersion("/version.txt");
private static final int getVersion(String strFilePath) {
File f = new File(strFilePath);
try (Scanner scanner = new Scanner(f)) {
VERSION = scanner.nextInt(); // <-- hope it's a value
System.out.println("Version = " + VERSION);
return VERSION;
} catch (Exception e) {
e.printStackTrace();
}
return -1;
}
or even
private final int VERSION = getVersion("/version.txt");
private static final int getVersion(String strFilePath) {
File f = new File(strFilePath);
try (Scanner scanner = new Scanner(f)) {
if (scanner.hasNextInt()) {
return scanner.nextInt();
}
} catch (Exception e) {
e.printStackTrace();
}
return -1;
}
I am have a project that need to modify some text in the text file.
Like BB,BO,BR,BZ,CL,VE-BR
I need make it become BB,BO,BZ,CL,VE.
and HU, LT, LV, UA, PT-PT/AR become HU, LT, LV, UA,/AR.
I have tried to type some code, however the code fail to loop and also,in this case.
IN/CI, GH, KE, NA, NG, SH, ZW /EE, HU, LT, LV, UA,/AR, BB
"AR, BB,BO,BR,BZ,CL, CO, CR, CW, DM, DO,VE-AR-BR-MX"
I want to delete the AR in second row, but it just delete the AR in first row.
I got no idea and seeking for helps.
Please
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileWriter;
import java.util.Scanner;
public class tomy {
static StringBuffer stringBufferOfData = new StringBuffer();
static StringBuffer stringBufferOfData1 = stringBufferOfData;
static String filename = null;
static String input = null;
static String s = "-";
static Scanner sc = new Scanner(s);
public static void main(String[] args) {
boolean fileRead = readFile();
if (fileRead) {
replacement();
writeToFile();
}
System.exit(0);
}
private static boolean readFile() {
System.out.println("Please enter your files name and path i.e C:\\test.txt: ");
filename = "C:\\test.txt";
Scanner fileToRead = null;
try {
fileToRead = new Scanner(new File(filename));
for (String line; fileToRead.hasNextLine()
&& (line = fileToRead.nextLine()) != null;) {
System.out.println(line);
stringBufferOfData.append(line).append("\r\n");
}
fileToRead.close();
return true;
} catch (FileNotFoundException ex) {
System.out.println("The file " + filename + " could not be found! "+ ex.getMessage());
return false;
} finally {
fileToRead.close();
return true;
}
}
private static void writeToFile() {
try {
BufferedWriter bufwriter = new BufferedWriter(new FileWriter(
filename));
bufwriter.write(stringBufferOfData.toString());
bufwriter.close();
} catch (Exception e) {// if an exception occurs
System.out.println("Error occured while attempting to write to file: "+ e.getMessage());
}
}
private static void replacement() {
System.out.println("Please enter the contents of a line you would like to edit: ");
String lineToEdit = sc.nextLine();
int startIndex = stringBufferOfData.indexOf(lineToEdit);
int endIndex = startIndex + lineToEdit.length() + 2;
String getdata = stringBufferOfData.substring(startIndex + 1, endIndex);
String data = " ";
Scanner sc1 = new Scanner(getdata);
Scanner sc2 = new Scanner(data);
String lineToEdit1 = sc1.nextLine();
String replacementText1 = sc2.nextLine();
int startIndex1 = stringBufferOfData.indexOf(lineToEdit1);
int endIndex1 = startIndex1 + lineToEdit1.length() + 3;
boolean test = lineToEdit.contains(getdata);
boolean testh = lineToEdit.contains("-");
System.out.println(startIndex);
if (testh = true) {
stringBufferOfData.replace(startIndex, endIndex, replacementText1);
stringBufferOfData.replace(startIndex1, endIndex1 - 2,
replacementText1);
System.out.println("Here is the new edited text:\n"
+ stringBufferOfData);
} else {
System.out.println("nth" + stringBufferOfData);
System.out.println(getdata);
}
}
}
I wrote a quick method for you that I think does what you want, i.e. remove all occurrences of a token in a line, where that token is embedded in the line and is identified by a leading dash.
The method reads the file and writes it straight out to a file after editing for the token. This would allow you to process a huge file without worrying about about memory constraints.
You can simply rename the output file after a successful edit. I'll leave it up to you to work that out.
If you feel you really must use string buffers to do in memory management, then grab the logic for the line editing from my method and modify it to work with string buffers.
static void onePassReadEditWrite(final String inputFilePath, final String outputPath)
{
// the input file
Scanner inputScanner = null;
// output file
FileWriter outputWriter = null;
try
{
// open the input file
inputScanner = new Scanner(new File(inputFilePath));
// open output file
File outputFile = new File(outputPath);
outputFile.createNewFile();
outputWriter = new FileWriter(outputFile);
try
{
for (
String lineToEdit = inputScanner.nextLine();
/*
* NOTE: when this loop attempts to read beyond EOF it will throw the
* java.util.NoSuchElementException exception which is caught in the
* containing try/catch block.
*
* As such there is NO predicate required for this loop.
*/;
lineToEdit = inputScanner.nextLine()
)
// scan all lines from input file
{
System.out.println("START LINE [" + lineToEdit + "]");
// get position of dash in line
int dashInLinePosition = lineToEdit.indexOf('-');
while (dashInLinePosition != -1)
// this line has needs editing
{
// split line on dash
String halfLeft = lineToEdit.substring(0, dashInLinePosition);
String halfRight = lineToEdit.substring(dashInLinePosition + 1);
// get token after dash that is to be removed from whole line
String tokenToRemove = halfRight.substring(0, 2);
// reconstruct line from the 2 halves without the dash
StringBuilder sb = new StringBuilder(halfLeft);
sb.append(halfRight.substring(0));
lineToEdit = sb.toString();
// get position of first token in line
int tokenInLinePosition = lineToEdit.indexOf(tokenToRemove);
while (tokenInLinePosition != -1)
// do for all tokens in line
{
// split line around token to be removed
String partLeft = lineToEdit.substring(0, tokenInLinePosition);
String partRight = lineToEdit.substring(tokenInLinePosition + tokenToRemove.length());
if ((!partRight.isEmpty()) && (partRight.charAt(0) == ','))
// remove prefix comma from right part
{
partRight = partRight.substring(1);
}
// reconstruct line from the left and right parts
sb.setLength(0);
sb = new StringBuilder(partLeft);
sb.append(partRight);
lineToEdit = sb.toString();
// find next token to be removed from line
tokenInLinePosition = lineToEdit.indexOf(tokenToRemove);
}
// handle additional dashes in line
dashInLinePosition = lineToEdit.indexOf('-');
}
System.out.println("FINAL LINE [" + lineToEdit + "]");
// write line to output file
outputWriter.write(lineToEdit);
outputWriter.write("\r\n");
}
}
catch (java.util.NoSuchElementException e)
// end of scan
{
}
finally
// housekeeping
{
outputWriter.close();
inputScanner.close();
}
}
catch(FileNotFoundException e)
{
e.printStackTrace();
}
catch(IOException e)
{
inputScanner.close();
e.printStackTrace();
}
}
How do I replace a line of text found within a text file?
I have a string such as:
Do the dishes0
And I want to update it with:
Do the dishes1
(and vise versa)
How do I accomplish this?
ActionListener al = new ActionListener() {
#Override
public void actionPerformed(ActionEvent e) {
JCheckBox checkbox = (JCheckBox) e.getSource();
if (checkbox.isSelected()) {
System.out.println("Selected");
String s = checkbox.getText();
replaceSelected(s, "1");
} else {
System.out.println("Deselected");
String s = checkbox.getText();
replaceSelected(s, "0");
}
}
};
public static void replaceSelected(String replaceWith, String type) {
}
By the way, I want to replace ONLY the line that was read. NOT the entire file.
At the bottom, I have a general solution to replace lines in a file. But first, here is the answer to the specific question at hand. Helper function:
public static void replaceSelected(String replaceWith, String type) {
try {
// input the file content to the StringBuffer "input"
BufferedReader file = new BufferedReader(new FileReader("notes.txt"));
StringBuffer inputBuffer = new StringBuffer();
String line;
while ((line = file.readLine()) != null) {
inputBuffer.append(line);
inputBuffer.append('\n');
}
file.close();
String inputStr = inputBuffer.toString();
System.out.println(inputStr); // display the original file for debugging
// logic to replace lines in the string (could use regex here to be generic)
if (type.equals("0")) {
inputStr = inputStr.replace(replaceWith + "1", replaceWith + "0");
} else if (type.equals("1")) {
inputStr = inputStr.replace(replaceWith + "0", replaceWith + "1");
}
// display the new file for debugging
System.out.println("----------------------------------\n" + inputStr);
// write the new string with the replaced line OVER the same file
FileOutputStream fileOut = new FileOutputStream("notes.txt");
fileOut.write(inputStr.getBytes());
fileOut.close();
} catch (Exception e) {
System.out.println("Problem reading file.");
}
}
Then call it:
public static void main(String[] args) {
replaceSelected("Do the dishes", "1");
}
Original Text File Content:
Do the dishes0
Feed the dog0
Cleaned my room1
Output:
Do the dishes0
Feed the dog0
Cleaned my room1
----------------------------------
Do the dishes1
Feed the dog0
Cleaned my room1
New text file content:
Do the dishes1
Feed the dog0
Cleaned my room1
And as a note, if the text file was:
Do the dishes1
Feed the dog0
Cleaned my room1
and you used the method replaceSelected("Do the dishes", "1");,
it would just not change the file.
Since this question is pretty specific, I'll add a more general solution here for future readers (based on the title).
// read file one line at a time
// replace line as you read the file and store updated lines in StringBuffer
// overwrite the file with the new lines
public static void replaceLines() {
try {
// input the (modified) file content to the StringBuffer "input"
BufferedReader file = new BufferedReader(new FileReader("notes.txt"));
StringBuffer inputBuffer = new StringBuffer();
String line;
while ((line = file.readLine()) != null) {
line = ... // replace the line here
inputBuffer.append(line);
inputBuffer.append('\n');
}
file.close();
// write the new string with the replaced line OVER the same file
FileOutputStream fileOut = new FileOutputStream("notes.txt");
fileOut.write(inputBuffer.toString().getBytes());
fileOut.close();
} catch (Exception e) {
System.out.println("Problem reading file.");
}
}
Since Java 7 this is very easy and intuitive to do.
List<String> fileContent = new ArrayList<>(Files.readAllLines(FILE_PATH, StandardCharsets.UTF_8));
for (int i = 0; i < fileContent.size(); i++) {
if (fileContent.get(i).equals("old line")) {
fileContent.set(i, "new line");
break;
}
}
Files.write(FILE_PATH, fileContent, StandardCharsets.UTF_8);
Basically you read the whole file to a List, edit the list and finally write the list back to file.
FILE_PATH represents the Path of the file.
If replacement is of different length:
Read file until you find the string you want to replace.
Read into memory the part after text you want to replace, all of it.
Truncate the file at start of the part you want to replace.
Write replacement.
Write rest of the file from step 2.
If replacement is of same length:
Read file until you find the string you want to replace.
Set file position to start of the part you want to replace.
Write replacement, overwriting part of file.
This is the best you can get, with constraints of your question. However, at least the example in question is replacing string of same length, So the second way should work.
Also be aware: Java strings are Unicode text, while text files are bytes with some encoding. If encoding is UTF8, and your text is not Latin1 (or plain 7-bit ASCII), you have to check length of encoded byte array, not length of Java string.
I was going to answer this question. Then I saw it get marked as a duplicate of this question, after I'd written the code, so I am going to post my solution here.
Keeping in mind that you have to re-write the text file. First I read the entire file, and store it in a string. Then I store each line as a index of a string array, ex line one = array index 0. I then edit the index corresponding to the line that you wish to edit. Once this is done I concatenate all the strings in the array into a single string. Then I write the new string into the file, which writes over the old content. Don't worry about losing your old content as it has been written again with the edit. below is the code I used.
public class App {
public static void main(String[] args) {
String file = "file.txt";
String newLineContent = "Hello my name is bob";
int lineToBeEdited = 3;
ChangeLineInFile changeFile = new ChangeLineInFile();
changeFile.changeALineInATextFile(file, newLineContent, lineToBeEdited);
}
}
And the class.
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.FileReader;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
public class ChangeLineInFile {
public void changeALineInATextFile(String fileName, String newLine, int lineNumber) {
String content = new String();
String editedContent = new String();
content = readFile(fileName);
editedContent = editLineInContent(content, newLine, lineNumber);
writeToFile(fileName, editedContent);
}
private static int numberOfLinesInFile(String content) {
int numberOfLines = 0;
int index = 0;
int lastIndex = 0;
lastIndex = content.length() - 1;
while (true) {
if (content.charAt(index) == '\n') {
numberOfLines++;
}
if (index == lastIndex) {
numberOfLines = numberOfLines + 1;
break;
}
index++;
}
return numberOfLines;
}
private static String[] turnFileIntoArrayOfStrings(String content, int lines) {
String[] array = new String[lines];
int index = 0;
int tempInt = 0;
int startIndext = 0;
int lastIndex = content.length() - 1;
while (true) {
if (content.charAt(index) == '\n') {
tempInt++;
String temp2 = new String();
for (int i = 0; i < index - startIndext; i++) {
temp2 += content.charAt(startIndext + i);
}
startIndext = index;
array[tempInt - 1] = temp2;
}
if (index == lastIndex) {
tempInt++;
String temp2 = new String();
for (int i = 0; i < index - startIndext + 1; i++) {
temp2 += content.charAt(startIndext + i);
}
array[tempInt - 1] = temp2;
break;
}
index++;
}
return array;
}
private static String editLineInContent(String content, String newLine, int line) {
int lineNumber = 0;
lineNumber = numberOfLinesInFile(content);
String[] lines = new String[lineNumber];
lines = turnFileIntoArrayOfStrings(content, lineNumber);
if (line != 1) {
lines[line - 1] = "\n" + newLine;
} else {
lines[line - 1] = newLine;
}
content = new String();
for (int i = 0; i < lineNumber; i++) {
content += lines[i];
}
return content;
}
private static void writeToFile(String file, String content) {
try (Writer writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream(file), "utf-8"))) {
writer.write(content);
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private static String readFile(String filename) {
String content = null;
File file = new File(filename);
FileReader reader = null;
try {
reader = new FileReader(file);
char[] chars = new char[(int) file.length()];
reader.read(chars);
content = new String(chars);
reader.close();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (reader != null) {
try {
reader.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
return content;
}
}
Sharing the experience with Java Util Stream
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Collectors;
import java.util.stream.Stream;
public static void replaceLine(String filePath, String originalLineText, String newLineText) {
Path path = Paths.get(filePath);
// Get all the lines
try (Stream<String> stream = Files.lines(path, StandardCharsets.UTF_8)) {
// Do the line replace
List<String> list = stream.map(line -> line.equals(originalLineText) ? newLineText : line)
.collect(Collectors.toList());
// Write the content back
Files.write(path, list, StandardCharsets.UTF_8);
} catch (IOException e) {
LOG.error("IOException for : " + path, e);
e.printStackTrace();
}
}
Usage
replaceLine("test.txt", "Do the dishes0", "Do the dishes1");
//Read the file data
BufferedReader file = new BufferedReader(new FileReader(filepath));
StringBuffer inputBuffer = new StringBuffer();
String line;
while ((line = file.readLine()) != null) {
inputBuffer.append(line);
inputBuffer.append('\n');
}
file.close();
String inputStr = inputBuffer.toString();
// logic to replace lines in the string (could use regex here to be generic)
inputStr = inputStr.replace(str, " ");
//'str' is the string need to update in this case it is updating with nothing
// write the new string with the replaced line OVER the same file
FileOutputStream fileOut = new FileOutputStream(filer);
fileOut.write(inputStr.getBytes());
fileOut.close();
Well you would need to get a file with JFileChooser and then read through the lines of the file using a scanner and the hasNext() function
http://docs.oracle.com/javase/7/docs/api/javax/swing/JFileChooser.html
once you do that you can save the line into a variable and manipulate the contents.
just how to replace strings :) as i do
first arg will be filename second target string third one the string to be replaced instead of targe
public class ReplaceString{
public static void main(String[] args)throws Exception {
if(args.length<3)System.exit(0);
String targetStr = args[1];
String altStr = args[2];
java.io.File file = new java.io.File(args[0]);
java.util.Scanner scanner = new java.util.Scanner(file);
StringBuilder buffer = new StringBuilder();
while(scanner.hasNext()){
buffer.append(scanner.nextLine().replaceAll(targetStr, altStr));
if(scanner.hasNext())buffer.append("\n");
}
scanner.close();
java.io.PrintWriter printer = new java.io.PrintWriter(file);
printer.print(buffer);
printer.close();
}
}
I have a list of log files, and I need to find which one has a latest edition of a specific line, and all or none could have this line.
The lines in the files look like this:
2013/01/06 16:01:00:283 INFO ag.doLog: xxxx xxxx xxxx xxxx
And I need a line lets say
xx/xx/xx xx:xx:xx:xxx INFO ag.doLog: the line i need
I know how to get an array of files, and if I scan backwards I could find the latest latest line in each file (if it exists).
Biggest problem is that the file could be big (2k lines?) and I want to find the line in a relative fast way (a few seconds), so I am open for suggestion.
Personal ideas:
If a file has the line at X time, then any file that has not found the line before X time should not be scan anymore. This will require to search all files at the same time, which i dont know how.
Atm the code breaks, and I suppose if lack of memory.
Code:
if(files.length>0) { //in case no log files exist
System.out.println("files.length: " + files.length);
for(int i = 0; i < files.length; i++) { ///for each log file look for string
System.out.println("Reading file: " + i + " " + files[i].getName());
RandomAccessFile raf = new RandomAccessFile(files[i].getAbsoluteFile(), "r"); //open log file
long lastSegment = raf.length(); //Finds how long is the files
lastSegment = raf.length()-5; //Sets a point to start looking
String leido = "";
byte array[] = new byte[1024];
/*
* Going back until we find line or file is empty.
*/
while(!leido.contains(lineToSearch)||lastSegment>0) {
System.out.println("leido: " + leido);
raf.seek(lastSegment); //move the to that point
raf.read(array); //Reads 1024 bytes and saves in array
leido = new String(array); //Saves what is read as a string
lastSegment = lastSegment-15; //move the point a little further back
}
if(lastSegment<0) {
raf.seek(leido.indexOf(lineToSearch) - 23); //to make sure we get the date (23 characters long) NOTE: it wont be negative.
raf.read(array); //Reads 1024 bytes and saves in array
leido = new String(array); //make the array into a string
Date date = new SimpleDateFormat("MMMM d, yyyy", Locale.ENGLISH).parse(leido.substring(0, leido.indexOf(" INFO "))); //get only the date part
System.out.println(date);
//if date is bigger than the other save file name
}
}
}
I find the code difficult to verify. One could split the task in a backwards reader, which reads lines from file end to start. And use that for parsing dates line wise.
Mind, I am not going for nice code, but something like this:
public class BackwardsReader implements Closeable {
private static final int BUFFER_SIZE = 4096;
private String charset;
private RandomAccessFile raf;
private long position;
private int readIndex;
private byte[] buffer = new byte[BUFFER_SIZE];
/**
* #param file a text file.
* #param charset with bytes '\r' and '\n' (no wide chars).
*/
public BackwardsReader(File file, String charset) throws IOException {
this.charset = charset;
raf = new RandomAccessFile(file, "r");
position = raf.length();
}
public String readLine() throws IOException {
if (position + readIndex == 0) {
raf.close();
raf = null;
return null;
}
String line = "";
for (;;) { // Loop adding blocks without newline '\n'.
// Search line start:
boolean lineStartFound = false;
int lineStartIndex = readIndex;
while (lineStartIndex > 0) {
if (buffer[lineStartIndex - 1] == (byte)'\n') {
lineStartFound = true;
break;
}
--lineStartIndex;
}
String line2;
try {
line2 = new String(buffer, lineStartIndex, readIndex - lineStartIndex,
charset).replaceFirst("\r?\n?", "");
readIndex = lineStartIndex;
} catch (UnsupportedEncodingException ex) {
Logger.getLogger(BackwardsReader.class.getName())
.log(Level.SEVERE, null, ex);
return null;
}
line = line2 + line;
if (lineStartFound) {
--readIndex;
break;
}
// Read a prior block:
int toRead = BUFFER_SIZE;
if (position - toRead < 0) {
toRead = (int) position;
}
if (toRead == 0) {
break;
}
position -= toRead;
raf.seek(position);
raf.readFully(buffer, 0, toRead);
readIndex = toRead;
if (buffer[readIndex - 1] == (byte)'\r') {
--readIndex;
}
}
return line;
}
#Override
public void close() throws IOException {
if (raf != null) {
raf.close();
}
}
}
And a usage example:
public static void main(String[] args) {
try {
File file = new File(args[0]);
BackwardsReader reader = new BackwardsReader(file, "UTF-8");
int lineCount = 0;
for (;;) {
String line = reader.readLine();
if (line == null) {
break;
}
++lineCount;
System.out.println(line);
}
reader.close();
System.out.println("Lines: " + lineCount);
} catch (IOException ex) {
Logger.getLogger(App.class.getName()).log(Level.SEVERE, null, ex);
}
}