Develop Reference

BufferedReader do not read the entire text file

I read about someone having troubles with BufferedReader: the reader simply do not read the first lines. I have instead the opposite problem. For example, in a text file with 300 lines, it arrives at 200, read it half of it and then the following string is given null, so it stops.
private void readerMethod(File fileList) throws IOException {
BigInteger steps = BigInteger.ZERO;
BufferedReader br = new BufferedReader(new FileReader(fileList));
String st;
//reading file line by line
try{
while (true){
st = br.readLine();
if(st == null){
System.out.println("Null string at line " + steps);
break;
}
System.out.println(steps + " - " + st);
steps = steps.add(BigInteger.ONE);
}
}catch(Exception e){
e.printStackTrace();
}
finally{
try{
br.close();
}catch(Exception e){}
}
}
The output of the previous slice of code is as expected until it reaches line 199 (starting from 0). Consider a file with 300 lines.
...
198 - 3B02D5D572B66A82F9D21EE809320DB3E250C6C9
199 - 6E2C69795CB712C27C4097119CE2C5765
Null string at line 200
Notice that, all lines have the same length, so in this output line 199 is not even complete. I checked the file text, and it's correct: it contains all 300 lines and they are all of the same length. Also, in the text there are only capitals letters and numbers, as you can see.
My question is: how can i fix this? I need that the BufferedReader read all the text, not just a part of it.
As someone asked i add here the remaining part of the code. Please notice that all capital names are constant of various type (int, string etc).
This is the method that is called by the main thread:
public void init(){
BufferedWriter bw = null;
List<String> allLines = createRandomStringLines(LINES);
try{
String fileName = "SHA1_encode_text.txt";
File logFile = new File(fileName);
System.out.println(logFile.getCanonicalPath());
bw = new BufferedWriter(new FileWriter(logFile));
for(int i = 0; i < allLines.size(); i++){
//write file
String o = sha1FromString(allLines.get(i));
//sha1FromString is a method that change the aspect of the string,
//replacing char by char. Is not important at the moment.
bw.write(o + "\n");
}
}catch(Exception e){
e.printStackTrace();
}finally{
try{
bw.close();
}catch(Exception e){}
}
}
The method that create the list of random string is the following. "SYMBOLS" is just a String contains all avaiable chars.
private List<String> createRandomStringLines(int i) {
List<String> list = new ArrayList<String>();
while(i!=0){
StringBuilder builder = new StringBuilder();
int count = 64;
while (count-- != 0) {
int character = (int)(Math.random()*SYMBOLS.length());
builder.append(SYMBOLS.charAt(character));
}
String generatedString = builder.toString();
list.add(generatedString);
i--;
}
return list;
}
Note that, the file written is totally correct.

Okay, thanks to the user ygor, i manage to resolve it. The problem was that the BufferReader stars his job when the BufferWriter isn't closed yet. It was sufficient to move the command line that require the reader to work, after the bufferWriter.close() command.

Read file, replace string and create a new one with all content

I am trying to replace ? with - in my text document but just the ArrayList<String> is being written in the new file without all lines of the old one. How can I fix that?
File file = new File("D:\\hl_sv\\L09MF.txt");
ArrayList<String> lns = new ArrayList<String>();
Scanner scanner;
try {
scanner = new Scanner(file);
int lineNum = 0;
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
lineNum++;
if (line.contains("?")) {
line = line.replace("?", "-");
lns.add(line);
// System.out.println("I found it on line " + lineNum);
}
}
lines.clear();
lines = lns;
System.out.println("Test: " + lines);
FileWriter writer;
try {
writer = new FileWriter("D:\\hl_sv\\L09MF2.txt");
for (String str : lines) {
writer.write(str);
}
writer.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

I don't understand why you're storing the lines in a List to begin with. I would perform the transform and print while I read. You don't need to test for the presence of the ? (replace won't alter anything if it isn't present). And, I would also use a try-with-resources. Something like
File file = new File("D:\\hl_sv\\L09MF.txt");
try (PrintWriter writer = new PrintWriter("D:\\hl_sv\\L09MF2.txt");
Scanner scanner = new Scanner(file)) {
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
writer.println(line.replace('?', '-'));
}
} catch (Exception e) {
e.printStackTrace();
}

Examine this code:
if (line.contains("?")) {
line = line.replace("?", "-");
lns.add(line);
}
You are only adding the current line (with the replacement) if it had a ? in it, ignoring other lines. Restructure it to always add the existing line.
if (line.contains("?")) {
line = line.replace("?", "-");
}
lns.add(line);
Additionally, the part
if (line.contains("?"))
scans line to look for a ?, and then the code
line.replace("?", "-");
does the same thing, but this time also replacing any ? with -. You may as well scan line just once:
lns.add(line.replace("?", "-"));
Note that creating an ArrayList just to hold the new lines wastes a fair amount of memory if the file is large. A better pattern would be to write each line, modified if necessary, right after you read in the corresponding line.

Within your while loop you have an if statement checking the line which adds the altered line to the array. You also need to add the unaltered lines to the array.

This should fix your issue:
int lineNum = 0;
while (scanner.hasNextLine()) {
String line = scanner.nextLine();
lineNum++;
if (line.contains("?")) {
line = line.replace("?", "-");
lns.add(line);
// System.out.println("I found it on line " + lineNum);
}
else{
lns.add(line);
}
Previously, you were only adding the line to your ArrayList if it contained a "?" character. You need to add the line to the ArrayList whether or not it contains "?"

I would use a different approach if I'm trying to work on the functionality you want to implement, please check this approach and tell me if this helps you :)
public void saveReplacedFile() {
//1. Given a file in your system
File file = new File("D:\\hl_sv\\L09MF.txt");
try {
//2. I will read it, not necessarily with Scanner, but use a BufferedReader instead
BufferedReader bufferedReader = new BufferedReader(new FileReader(file));
//3. Define a variable that will hold the value of each line
String line = null;
//and also the information of your file
StringBuilder contentHolder = new StringBuilder();
//why not get your line separator based on your O.S?
String lineSeparator = System.getProperty("line.separator");
//4. Check your file line by line
while ((line = bufferedReader.readLine()) != null) {
contentHolder.append(line);
contentHolder.append(lineSeparator);
}
//5. By this point, your contentHolder will contain all the data of your text
//But it is still a StringBuilder type object, why not convert it to a String?
String contentAsString = contentHolder.toString();
//6. Now we can replace your "?" with "-"
String replacedString = contentAsString.replace("?", "-");
//7. Now, let's save it in a new file using BufferedWriter :)
File fileToBeSaved = new File("D:\\hl_sv\\L09MF2.txt");
BufferedWriter bufferedWriter = new BufferedWriter(new FileWriter(fileToBeSaved));
bufferedWriter.write(replacedString);
//Done :)
} catch (FileNotFoundException e) {
// Exception thrown if the file does not exist in your system
e.printStackTrace();
} catch (IOException e) {
// Exception thrown due to an issue with IO
e.printStackTrace();
}
}
Hope this is helpful. Happy coding :)

If you can use Java 8 then your code can be simplified to
try (PrintStream ps = new PrintStream("D:\\hl_sv\\L09MF2.txt");
Stream<String> stream = Files.lines(Paths.get("D:\\hl_sv\\L09MF.txt"))) {
stream.map(line -> line.replace('?', '-')).forEach(ps::println);
} catch (IOException e) {
e.printStackTrace();
}

Find String in text file, delete line and ones below

I have a bit of code to find a string in a text file, print the line the string is on and then print the 5 lines below it. However, I need to modify it so that instead of printing, it deletes/removes the line after the string is found. How would I go about doing this?
File file = new File("./output.txt");
Scanner in = null;
try {
in = new Scanner(file);
while (in.hasNext()) {
String line = in.nextLine();
if (line.contains("(1)")) {
for (int a = 0; in.hasNextLine() && a < 6; a++) {
System.out.println(line);
line = in.nextLine();
}
}
}
} catch (Exception e) {
}

Find a small snippet you can start with.
Assuming your question.txt has the following input.
line 1
line 2
line 3 (1)
line 4
line 5
line 6
line 7
line 8
line 9
line 10
This snippet will print all lines and skip the line line 3 (1) as well the five lines after.
List<String> lines = Files.readAllLines(Paths.get("question.txt"), Charset.defaultCharset());
for (int i = 0; i < lines.size(); i++) {
if (lines.get(i).contains("(1)")) {
i = i + 6;
}
System.out.println(lines.get(i));
}
output
line 1
line 2
line 9
line 10
To store the lines into the file is left for you.

My Suggestion is you first declare and initialise a StringBuilder say output before your above code like:
StringBuilder output = new StringBuilder();
Now after the close of the if statement before the closing of the while loop append the line to the output and add a "\n" at the end like this:
output.append(line+"\n");
Now finally after your code that you have posted create a FileWriter say writer and then use the writer to write the output as shown below:
try(FileWriter writer = new FileWriter(file, false)){
writer.write(output);
}catch IOException(e){
e.printStackTrace();
}
Also don't forget to remove or comment out the following line if you do not want them printed in the output.
System.out.println(line);

SubOtimal has a good, concise answer that will work for most cases. The following is more complex but avoids loading the whole file into memory. That probably isn't an issue for you but just in case...
public void deleteAfter(File file, String searchString, int lineCountToDelete) {
// Create a temporary file to write to
File temp = new File(file.getAbsolutePath() + ".tmp");
try (BufferedReader reader = new BufferedReader(new FileReader(file));
PrintWriter writer = new PrintWriter(new FileWriter(temp)) ) {
// Read up to the line we are searching for
// and write each to the temp file
String line;
while((line = reader.readLine()) != null && !line.equals(searchString)){
writer.println(line);
}
// Skip over the number of lines we want to "delete"
// as well as watching out for hitting the end of the file
for(int i=0;i < lineCountToDelete && line != null; i++){
line = reader.readLine();
}
// Write the remaining lines to the temp file.
while((line = reader.readLine()) != null){
writer.println(line);
}
} catch (IOException e) {
throw new IllegalStateException("Unable to delete the lines",e);
}
// Delete the original file
if(!file.delete()){
throw new IllegalStateException("Unable to delete file: " + file.getAbsolutePath());
}
// Rename the temp file to the original name
if(!temp.renameTo(file)){
throw new IllegalStateException("Unable to rename " +
temp.getAbsolutePath() + " to " + file.getAbsolutePath());
}
}
I tested this with multiple conditions, including a line that doesn't exist, a line at the end and a line with fewer lines left than the number to skip. All worked and gave the appropriate results.

Line when reading a file is empty but the line is not null

I have a problem in java and i dont understand why, since i think i am doing text-book stuff.
An overview in what of want to do is:
I want to create a file that contains in each line two strings: documentPath, documentID (in this format: "documentPath;documentID;")
I want to be able to add lines at the end of the file and load the file to a Java Data Structure, lets say a HashSet.
Each time i want to add a new line, i load all the file in a HashSet, check if the line i want to add is not already there and eventually add it at the end. (small number of data - don't care about efficiency)
The code
Add file:
public void addFile(String documentPath) {
this.loadCollection(); //METHOD IS NOT CONTINUING: ERROR HERE
if (!documentsInfo.contains(documentPath)) {
try {
PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(this.collectionFile, true)));
DocumentInfo documentInfo = new DocumentInfo(documentPath, ++this.IDcounter);
out.close();
} catch (IOException e) {
e.printStackTrace();
}
}
Load file:
public void loadCollection() {
if (loaded) {return;}
BufferedReader br;
try {
br = new BufferedReader(new FileReader(collectionFile));
String line;
while ( (line = br.readLine())!= null ) { //PROBLEM HERE
System.out.println("the line readed from file-" + line + "-");
System.out.println("is the line null: "+ (line==null));
System.out.println("line length: " + line.length());
DocumentInfo documentInfo = new DocumentInfo(line);
documentsInfo.add(documentInfo);
}
br.close();
open = true;
} catch (IOException e) {
e.printStackTrace();
}
}
create the line to add:
public DocumentInfo(String fileLine) {
String delimiter = Repository.DOCUMENT_FILE_SEPARATOR;
StringTokenizer tok = new StringTokenizer(fileLine, delimiter);
System.out.println("Tokenizer starts with string: " + fileLine);
this.documentPath = tok.nextToken(); //EXCEPTION here
this.documentId = Integer.parseInt(tok.nextToken());
}
public String toString() {
String sep = Repository.DOCUMENT_FILE_SEPARATOR;
return this.getDocumentPath()+sep+this.getDocumentId()+sep+"\n";
}
I am getting the exception at the Tokenizer method (java.util.NoSuchElementException) when i try to get the nextToken, but the problem comes from the loadCollection() method. The first time i read the contents of the file nothing is there, the line is empty (lenght: 0) but the line is not null, so the while-condition fails to stop the while iteration.
Here is what i get from the debbuging prints:
the line readed from file--
is the line null: false
line length: 0
Tokenizer starts with string:
Can anyone help me with this?

You get a null only when you have exhausted the stream. But the first line of the stream (your file) is just an empty line - and you load it, the result of the empty line, is an empty string (""). It can be easily solved by skipping lines with string.length() == 0, by adding the following in your while loop:
if (line.length() == 0) continue;
You might want to consider using trim() before checking the length as well, to avoid nasty spaces making the string.length() > 0

Android Development - Using Inputstream/BufferStream, how do I throw all the lines of a text file into an array?

This is another question. So it seems that I have already set up the code with InputStream and Bufferstream to retrieve a String from a text file using this code:
// Read Text File entitled wordsEn.txt
public String readFromFile() {
String words = "";
try {
InputStream inputstream = openFileInput("wordsEn.txt");
if (inputstream != null) {
InputStreamReader inputStreamReader = new InputStreamReader(inputstream);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader);
String receiveString = "";
StringBuilder stringBuilder = new StringBuilder();
while ( (receiveString = bufferedReader.readLine()) != null ) {
stringBuilder.append(receiveString);
}
inputstream.close();
words = stringBuilder.toString();
}
}
catch (FileNotFoundException e) {
Log.e("login activity", "File not found: " + e.toString());
} catch (IOException e) {
Log.e("login activity", "Can not read file: " + e.toString());
}
return words;
}
So what I want to do is store each string on each line of the text file into an array. I then want to be able to use this array to select a random string everytime I press a button.
Let me know.
Thanks
Colin

Just put below line into your class varialble
ArrayList<String> wordLineArray = new ArrayList<String>();
Than use add method array list to add each line of word into it.
wordLineArray.add(receiveString);
Use this line before appending it to previous buffer.
Now use this arraylist as per your requirment.
If it is helpful to you than don't forget to accept this answer.

Try using BreakIterator.getLineInstance(). Set the text to your "words" string, then iterate through each line, adding each line to a String[] array.