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();
}
}
public class FileSplitter2 {
public static void main(String[] args) throws IOException {
String filepath = "D:\\temp\\test.txt";
BufferedReader reader = new BufferedReader(new FileReader(filepath));
String strLine;
boolean isFirst = true;
String strGroupByColumnName = "city";
int positionOgHeader = 0;
FileWriter objFileWriter;
Map<String, FileWriter> groupByMap = new HashMap<String, FileWriter>();
while ((strLine = reader.readLine()) != null) {
String[] splitted = strLine.split(",");
if (isFirst) {
isFirst = false;
for (int i = 0; i < splitted.length; i++) {
if (splitted[i].equalsIgnoreCase(strGroupByColumnName)) {
positionOgHeader = i;
break;
}
}
}
String strKey = splitted[positionOgHeader];
if (!groupByMap.containsKey(strKey)) {
groupByMap.put(strKey, new FileWriter("D:/TestExample/" + strKey + ".txt"));
}
FileWriter fileWriter = groupByMap.get(strKey);
fileWriter.write(strLine);
}
for (Map.Entry<String,FileWriter> entry : groupByMap.entrySet()) {
entry.getKey();
}
}
}
This is my code. I am not getting a proper result. The file contains 10 columns, and the 5th column is 'city'. There are 10 different cities in a file. I need to split each city a separate file.
You are not calling close on all the FileWriter and hence the data may not get flushed to the file.
See FileWriter is not writing in to a file
At the end of the processing,
groupByMap.values().forEach(fileWriter -> {
try {
fileWriter.close();
} catch (IOException e) {
e.printStackTrace(); //Add appropriate error handling
}
});
There is a bug in your code. You need to move the statements after the if (isFirst) block into the else block. Else, it will create a city.txt file too.
class Start
{
File plikIN;
Scanner in;
PrintWriter out;
Start(String input, String output)
{
plikIN = new File(input);
try{
in = new Scanner(plikIN);
out = new PrintWriter(output);
} catch (FileNotFoundException e) {System.out.println("Nie odnaleziono podanego pliku\n"+e);}
}
private void saveing() throws IOException
{
String word;
int wordLength;
String wordTable[];
char c;
while((word = in.next()) != null)
{
wordLength = word.length();
wordTable = new String[wordLength];
for(int k=0; k<wordTable.length; ++k)
{
c = word.charAt(k);
out.println(c);
}
}
out.close();
}
public static void main(String[] args) throws IOException
{
String nazwaPlikuWejsciowego = args[0];
String nazwaPlikuWyjsciowego = args[1];
Start doit = new Start(nazwaPlikuWejsciowego, nazwaPlikuWyjsciowego);
doit.saveing();
}
}
My problem is saving to file. After the saveing method above, the file does not contain any single character. When I move the out.close() to while for instance, the file contains one word. When out.close() is in for, the program saves one character only. Why?
add out.flush() before out.close().
You need to flush the bytes to disk before you close it..
This ((word = in.next()) != null) will throw an exception.
in.next() doesn't return null when there are no more elements. Take a look at the API
I have a file that contain 100 line
each line contain one tag
I need to obtain the tag value given its rank which is the "id" of TagVertex Class
public abstract class Vertex <T>{
String vertexId ;// example Tag1
T vertexValue ;
public abstract T computeVertexValue();
}
public class TagVertex extends Vertex<String> {
#Override
public String computeVertexValue() {
// How to get the String from my file?
return null;
}
T try this but it doesnt work
public static void main(String args[]) {
File source //
int i=90;
int j=0;
String s = null;
try {
Scanner scanner = new Scanner(source);
while (scanner.hasNextLine()) {
if (j==i) s= scanner.nextLine();
else j++;
}
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(s);
}}
Although there is a way to skip characters with BufferedReader, I don't think there's is a built-in way to skip whole lines.
BufferedReader bf = new BufferedReader(new FileReader("MyFile.txt"));
for(int i = 1; i < myVertex.vertexId; i++){
bf.readLine();
}
String n = bf.readLine();
if(n != null){
System.out.println(n);
}
I think there may be a better idea though.
This is command u can use to read from file:
BufferedReader bf = new BufferedReader(new FileReader("filename"));
This will read the file to the buffer.
Now, for reading each line u should use a while loop and read each line into string.
Like:
String str;
while((str = bf.readLine()) != null){
//handle each line untill the end of file which will be null and quit the loop
}
I am trying to read a text file in java using FileReader and BufferedReader classes. Following an online tutorial I made two classes, one called ReadFile and one FileData.
Then I tried to extract a small part of the text file (i.e. between lines "ENTITIES" and "ENDSEC"). Finally l would like to tell the program to find a specific line between the above-mentioned and store it as an Xvalue, which I could use later.
I am really struggling to figure out how to do the last part...any help would be very much apprciated!
//FileData Class
package textfiles;
import java.io.IOException;
public class FileData {
public static void main (String[] args) throws IOException {
String file_name = "C:/Point.txt";
try {
ReadFile file = new ReadFile (file_name);
String[] aryLines = file.OpenFile();
int i;
for ( i=0; i < aryLines.length; i++ ) {
System.out.println( aryLines[ i ] ) ;
}
}
catch (IOException e) {
System.out.println(e.getMessage() );
}
}
}
// ReadFile Class
package textfiles;
import java.io.IOException;
import java.io.FileReader;
import java.io.BufferedReader;
import java.lang.String;
public class ReadFile {
private String path;
public ReadFile (String file_path) {
path = file_path;
}
public String[] OpenFile() throws IOException {
FileReader fr = new FileReader (path);
BufferedReader textReader = new BufferedReader (fr);
int numberOfLines = readLines();
String[] textData = new String[numberOfLines];
String nextline = "";
int i;
// String Xvalue;
for (i=0; i < numberOfLines; i++) {
String oneline = textReader.readLine();
int j = 0;
if (oneline.equals("ENTITIES")) {
nextline = oneline;
System.out.println(oneline);
while (!nextline.equals("ENDSEC")) {
nextline = textReader.readLine();
textData[j] = nextline;
// xvalue = ..........
j = j + 1;
i = i+1;
}
}
//textData[i] = textReader.readLine();
}
textReader.close( );
return textData;
}
int readLines() throws IOException {
FileReader file_to_read = new FileReader (path);
BufferedReader bf = new BufferedReader (file_to_read);
String aLine;
int numberOfLines = 0;
while (( aLine = bf.readLine()) != null ) {
numberOfLines ++;
}
bf.close ();
return numberOfLines;
}
}
I don't know what line you are specifically looking for but here are a few methods you might want to use to do such operation:
private static String START_LINE = "ENTITIES";
private static String END_LINE = "ENDSEC";
public static List<String> getSpecificLines(Srting filename) throws IOException{
List<String> specificLines = new LinkedList<String>();
Scanner sc = null;
try {
boolean foundStartLine = false;
boolean foundEndLine = false;
sc = new Scanner(new BufferedReader(new FileReader(filename)));
while (!foundEndLine && sc.hasNext()) {
String line = sc.nextLine();
foundStartLine = foundStartLine || line.equals(START_LINE);
foundEndLine = foundEndLine || line.equals(END_LINE);
if(foundStartLine && !foundEndLine){
specificLines.add(line);
}
}
} finally {
if (sc != null) {
sc.close();
}
}
return specificLines;
}
public static String getSpecificLine(List<String> specificLines){
for(String line : specificLines){
if(isSpecific(line)){
return line;
}
}
return null;
}
public static boolean isSpecific(String line){
// What makes the String special??
}
When I get it right you want to store every line between ENTITIES and ENDSEC?
If yes you could simply define a StringBuffer and append everything which is in between these to keywords.
// This could you would put outside the while loop
StringBuffer xValues = new StringBuffer();
// This would be in the while loop and you append all the lines in the buffer
xValues.append(nextline);
If you want to store more specific data in between these to keywords then you probably need to work with Regular Expressions and get out the data you need and put it into a designed DataStructure (A class you've defined by our own).
And btw. I think you could read the file much easier with the following code:
BufferedReader reader = new BufferedReader(new
InputStreamReader(this.getClass().getResourceAsStream(filename)));
try {
while ((line = reader.readLine()) != null) {
if(line.equals("ENTITIES") {
...
}
} (IOException e) {
System.out.println("IO Exception. Couldn't Read the file!");
}
Then you don't have to read first how many lines the file has. You just start reading till the end :).
EDIT:
I still don't know if I understand that right. So if ENTITIES POINT 10 1333.888 20 333.5555 ENDSEC is one line then you could work with the split(" ") Method.
Let me explain with an example:
String line = "";
String[] parts = line.split(" ");
float xValue = parts[2]; // would store 10
float yValue = parts[3]; // would store 1333.888
float zValue = parts[4]; // would store 20
float ... = parts[5]; // would store 333.5555
EDIT2:
Or is every point (x, y, ..) on another line?!
So the file content is like that:
ENTITIES POINT
10
1333.888 // <-- you want this one as xValue
20
333.5555 // <-- and this one as yvalue?
ENDSEC
BufferedReader reader = new BufferedReader(new
InputStreamReader(this.getClass().getResourceAsStream(filename)));
try {
while ((line = reader.readLine()) != null) {
if(line.equals("ENTITIES") {
// read next line
line = reader.readLine();
if(line.equals("10") {
// read next line to get the value
line = reader.readLine(); // read next line to get the value
float xValue = Float.parseFloat(line);
}
line = reader.readLine();
if(line.equals("20") {
// read next line to get the value
line = reader.readLine();
float yValue = Float.parseFloaT(line);
}
}
} (IOException e) {
System.out.println("IO Exception. Couldn't Read the file!");
}
If you have several ENTITIES in the file you need to create a class which stores the xValue, yValue or you could use the Point class. Then you would create an ArrayList of these Points and just append them..