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.

How can I read from the next line of a text file, and pause, allowing me to read from the line after that later?

I wrote a program that generates random numbers into two text files and random letters into a third according the two constant files. Now I need to read from each text file, line by line, and put them together. The program is that the suggestion found here doesn't really help my situation. When I try that approach it just reads all lines until it's done without allowing me the option to pause it, go to a different file, etc.
Ideally I would like to find some way to read just the next line, and then later go to the line after that. Like maybe some kind of variable to hold my place in reading or something.
public static void mergeProductCodesToFile(String prefixFile,
String inlineFile,
String suffixFile,
String productFile) throws IOException
{
try (BufferedReader br = new BufferedReader(new FileReader(prefixFile)))
{
String line;
while ((line = br.readLine()) != null)
{
try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(productFile, true))))
{
out.print(line); //This will print the next digit to the right
}
catch (FileNotFoundException e)
{
System.err.println("File error: " + e.getMessage());
}
}
}
}
EDIT: The digits being created according to the following. Basically, constants tell it how many digits to create in each line and how many lines to create. Now I need to combine these together without deleting anything from either text file.
public static void writeRandomCodesToFile(String codeFile,
char fromChar, char toChar,
int numberOfCharactersPerCode,
int numberOfCodesToGenerate) throws IOException
{
for (int i = 1; i <= PRODUCT_COUNT; i++)
{
int I = 0;
if (codeFile == "inline.txt")
{
for (I = 1; I <= CHARACTERS_PER_CODE; I++)
{
int digit = (int)(Math.random() * 10);
try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(codeFile, true))))
{
out.print(digit); //This will print the next digit to the right
}
catch (FileNotFoundException e)
{
System.err.println("File error: " + e.getMessage());
System.exit(1);
}
}
}
if ((codeFile == "prefix.txt") || (codeFile == "suffix.txt"))
{
for (I = 1; I <= CHARACTERS_PER_CODE; I++)
{
Random r = new Random();
char digit = (char)(r.nextInt(26) + 'a');
digit = Character.toUpperCase(digit);
try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(codeFile, true))))
{
out.print(digit);
}
catch (FileNotFoundException e)
{
System.err.println("File error: " + e.getMessage());
System.exit(1);
}
}
}
//This will take the text file to the next line
if (I >= CHARACTERS_PER_CODE)
{
{
Random r = new Random();
char digit = (char)(r.nextInt(26) + 'a');
try (PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter(codeFile, true))))
{
out.println(""); //This will return a new line for the next loop
}
catch (FileNotFoundException e)
{
System.err.println("File error: " + e.getMessage());
System.exit(1);
}
}
}
}
System.out.println(codeFile + " was successfully created.");
}// end writeRandomCodesToFile()

Being respectfull with your code, it will be something like this:
public static void mergeProductCodesToFile(String prefixFile, String inlineFile, String suffixFile, String productFile) throws IOException {
try (BufferedReader prefixReader = new BufferedReader(new FileReader(prefixFile));
BufferedReader inlineReader = new BufferedReader(new FileReader(inlineFile));
BufferedReader suffixReader = new BufferedReader(new FileReader(suffixFile))) {
StringBuilder line = new StringBuilder();
String prefix, inline, suffix;
while ((prefix = prefixReader.readLine()) != null) {
//assuming that nothing fails and the files are equals in # of lines.
inline = inlineReader.readLine();
suffix = suffixReader.readLine();
line.append(prefix).append(inline).append(suffix).append("\r\n");
// write it
...
}
} finally {/*close writers*/}
}
Some exceptions may be thrown.
I hope you don't implement it in one single method.
You can make use of iterators too, or a very simple reader class (method).
I wouldn't use List to load the data at least I guarantee that the files will be low sized and that I can spare the memory usage.

My approach as we discussed by storing the data and interleaving it. Like Sergio said in his answer, make sure memory isn't a problem in terms of the size of the file and how much memory the data structures will use.
//the main method we're working on
public static void mergeProductCodesToFile(String prefixFile,
String inlineFile,
String suffixFile,
String productFile) throws IOException
{
try {
List<String> prefix = read(prefixFile);
List<String> inline = read(inlineFile);
List<String> suffix = read(productFile);
String fileText = interleave(prefix, inline, suffix);
//write the single string to file however you want
} catch (...) {...}//do your error handling...
}
//helper methods and some static variables
private static Scanner reader;//I just prefer scanner. Use whatever you want.
private static StringBuilder sb;
private static List<String> read(String filename) throws IOException
{
List<String> list = new ArrayList<String>;
try (reader = new Scanner(new File(filename)))
{
while(reader.hasNext())
{ list.add(reader.nextLine()); }
} catch (...) {...}//catch errors...
}
//I'm going to build the whole file in one string, but you could also have this method return one line at a time (something like an iterator) and output it to the file to avoid creating the massive string
private static String interleave(List<String> one, List<String> two, List<String> three)
{
sb = new StringBuilder();
for (int i = 0; i < one.size(); i++)//notice no checking on size equality of words or the lists. you might want this
{
sb.append(one.get(i)).append(two.get(i)).append(three.get(i)).append("\n");
}
return sb.toString()
}
Obviously there is still some to be desired in terms of memory and performance; additionally there are ways to make this slightly more extensible to other situations, but it's a good starting point. With c#, I could more easily make use of the iterator to make interleave give you one line at a time, potentially saving memory. Just a different idea!

Reading textfile line by line and put in object array

I have to make an EPG app using java, but I am kind of new in programming and it's due tomorrow and it's still not working properly.
I have a question about a small part: I have to read the programs from a text file. Each line contains multiple things, the channel, the title of the program, a subtitle, a category, etcetera.
I have to make sure that I can read the separate parts of each line, but it's not really working, it's only printing the parts from the first line.
I am trying, but I can't find why it's not printing all the parts from all the lines in stead of printing only the parts from the first line. Here's the code:
BufferedReader reader = new BufferedReader(newFileReader(filepath));
while (true) {
String line = reader.readLine();
if (line == null) {
break;
}
}
String[] parts = line.split("\\|", -1);
for(int i = 0; i < parts.length; i++) {
System.out.println(parts[i]);
}
reader.close();
Does anybody know how to get all the lines in stead of only the first?
Thank you!

readLine() only reads one line, so you need to loop it, as you said.
BUT with reading to the String inside of the while loop you always overwrite that String.
You would need to declare the String above the while loop that you can access it from outside, too.
BTW, it seems that your braces for the if don't match.
Anyway, I'd fill the information into an ArrayList, look below:
List<String> list = new ArrayList<>();
String content;
// readLine() and close() may throw errors, so they require you to catch it…
try {
while ((content = reader.readLine()) != null) {
list.add(content);
}
reader.close();
} catch (IOException e) {
// This just prints the error log to the console if something goes wrong
e.printStackTrace();
}
// Now proceed with your list, e.g. retrieve first item and split
String[] parts = list.get(0).split("\\|", -1);
// You can simplify the for loop like this,
// you call this for each:
for (String s : parts) {
System.out.println(s);
}

Use apache commons lib
File file = new File("test.txt");
List<String> lines = FileUtils.readLines(file);

As ArrayList is Dynamic,try,
private static List<String> readFile(String filepath) {
String line = null;
List<String> list = new ArrayList<String>();
try {
BufferedReader reader = new BufferedReader(new FileReader(filepath));
while((line = reader.readLine()) != null){
list.add(line);
}
} catch (Exception e) {
e.printStackTrace();
}
return list;
}

i want to change the text in a file, my code is searching the word but not replacing the word

I am trying to replace a string from a js file which have content like this
........
minimumSupportedVersion: '1.1.0',
........
now 'm trying to replace the 1.1.0 with 1.1.1. My code is searching the text but not replacing. Can anyone help me with this. Thanks in advance.
public class replacestring {
public static void main(String[] args)throws Exception
{
try{
FileReader fr = new FileReader("G:/backup/default0/default.js");
BufferedReader br = new BufferedReader(fr);
String line;
while((line=br.readLine()) != null) {
if(line.contains("1.1.0"))
{
System.out.println("searched");
line.replace("1.1.0","1.1.1");
System.out.println("String replaced");
}
}
}
catch(Exception e){
e.printStackTrace();
}
}
}

First, make sure you are assigning the result of the replace to something, otherwise it's lost, remember, String is immutable, it can't be changed...
line = line.replace("1.1.0","1.1.1");
Second, you will need to write the changes back to some file. I'd recommend that you create a temporary file, to which you can write each `line and when finished, delete the original file and rename the temporary file back into its place
Something like...
File original = new File("G:/backup/default0/default.js");
File tmp = new File("G:/backup/default0/tmpdefault.js");
boolean replace = false;
try (FileReader fr = new FileReader(original);
BufferedReader br = new BufferedReader(fr);
FileWriter fw = new FileWriter(tmp);
BufferedWriter bw = new BufferedWriter(fw)) {
String line = null;
while ((line = br.readLine()) != null) {
if (line.contains("1.1.0")) {
System.out.println("searched");
line = line.replace("1.1.0", "1.1.1");
bw.write(line);
bw.newLine();
System.out.println("String replaced");
}
}
replace = true;
} catch (Exception e) {
e.printStackTrace();
}
// Doing this here because I want the files to be closed!
if (replace) {
if (original.delete()) {
if (tmp.renameTo(original)) {
System.out.println("File was updated successfully");
} else {
System.err.println("Failed to rename " + tmp + " to " + original);
}
} else {
System.err.println("Failed to delete " + original);
}
}
for example.
You may also like to take a look at The try-with-resources Statement and make sure you are managing your resources properly

If you're working with Java 7 or above, use the new File I/O API (aka NIO) as
// Get the file path
Path jsFile = Paths.get("C:\\Users\\UserName\\Desktop\\file.js");
// Read all the contents
byte[] content = Files.readAllBytes(jsFile);
// Create a buffer
StringBuilder buffer = new StringBuilder(
new String(content, StandardCharsets.UTF_8)
);
// Search for version code
int pos = buffer.indexOf("1.1.0");
if (pos != -1) {
// Replace if found
buffer.replace(pos, pos + 5, "1.1.1");
// Overwrite with new contents
Files.write(jsFile,
buffer.toString().getBytes(StandardCharsets.UTF_8),
StandardOpenOption.TRUNCATE_EXISTING);
}
I'm assuming your script file size doesn't cross into MBs; use buffered I/O classes otherwise.

Unusual output from using split()

I'm reading from a file that has the following format:
name : symptoms : causes : treatments : rate : prognosis
There are a total of 21 entries but when I try to read from the file and use .split(":");, the output changes each time but is always along the lines of: [Ljava.lang.String;#614951ff. I'm guessing it's the pointer or memory address but I want the String value. I'm not getting any exceptions though so I'm not sure where I've gone wrong. The purpose of the method is to read the file and split into an array using the delimiter for the given file row selected.
public String[] readCancer(int row) {
cancers = new String[22];
FileInputStream fis;
InputStreamReader isr;
BufferedReader br = null;
String eachCancer;
String[] splitCancer = null;
int j = 0;
try {
fis = new FileInputStream(myData);
isr = new InputStreamReader(fis);
br = new BufferedReader(isr);
input = new Scanner(br);
while(input.hasNext() && j < 23) {
cancers[j++] = input.nextLine();
}
eachCancer = cancers[row].toString();
splitCancer = eachCancer.split(":");
} catch (IOException iox) {
JOptionPane.showMessageDialog(null, "Problem with file input");
} finally {
try {
if(br != null) {
br.close();
}
} catch (IOException iox) {
JOptionPane.showMessageDialog(null, "Problem closing the file");
}
}
return splitCancer;
}

To print the contents of array :
1) System.out.println(Arrays.deepToString(splitCancer));
2) System.out.println(Arrays.toString(splitCancer));
3) System.out.println(Arrays.asList(splitCancer));

If you want to display the string array, you should use:
System.out.println(Arrays.toString(splitCancer));
Because when you print splitCancer you'll get the address of the array and not the content of it.
Of course you can print the content in other ways:
for(String str : splitCancer) {
System.out.println(str);
}

Currently I have the following:
public String[] readCancer() {
cancers = new String[22];
split = new String[22];
FileInputStream fis;
InputStreamReader isr;
BufferedReader br = null;
String eachCancer;
int j = 0;
try {
fis = new FileInputStream(myData);
isr = new InputStreamReader(fis);
br = new BufferedReader(isr);
input = new Scanner(br);
while(input.hasNext() && j < 23) {
cancers[j] = input.nextLine().toString();
//cancers[j] = input.nextLine();
split[j] = cancers[j].split(":");
//split[j] = "blah"; this line works
j++;
}
System.out.println(Arrays.toString(split));
} catch (IOException iox) {
JOptionPane.showMessageDialog(null, "Problem with file input");
} finally {
try {
if(br != null) {
br.close();
}
} catch (IOException iox) {
JOptionPane.showMessageDialog(null, "Problem closing the file");
}
}
return split;
//return split[j]; does not work
}
In my while loop, I keep getting compile errors saying it requires a String but found Stirng[] for split. When I try something simpler, such as split[j] = "blah";, there are no compile errors. I can return cancers perfectly but I need to split by the : delimiter and that seems to be something I cant get my head around. When I try return split[j], then I get another compile error saying it requires a String[] but found String. I've been at this for more than an hour, read through examples in my textbook and tutorials online for using split but it still isn't working. This is the only part of my program that I'm not sure how to do.

I tried pasting the entire file but it came a horrid block of text, so here are 2 lines from it. Each line has the same format but differing lengths:
The general format of the file is name : symptoms : causes : treatment : rate : prognosis
The rate is a String since it is unknown for some diseases and when it is known, the rate is not always out of 250,000. Sometimes it is out of 1,000,000 or 100,000, etc... .
acute promyelocytic leukemia : easy bruising, rapid internal bleeding, fatigue, anemia, frequent fever, infection, blood clots : PML and RARA genes : Medications, chemotherapy : 1 in 250,000 : Good
familial cylindromatosis : numerous skin tumours, ulcers, infection, impaired eyesight, hearing, smell, balance : CYLD gene : Surgery, chemotherapy : Unknown : Unknown
My most recent code attempt is at Unusual output from using split()
The 2 arrays of cancers and split are private String[] as field variables declared outside any of the methods. The variable myData is a private File also declared as a field variable outside any of the methods. I have checked and already verified the file path is correct.
The main method that calls the method:
public static void main(String[] args) {
CancerGUI _gui = new CancerGUI();
String[] resultCancer;
resultCancer = _gui.readCancer();
//System.out.println(resultCancer);
System.out.println(Arrays.toString(resultCancer));
}
I am only calling it in the main method to test whether it correctly returns the String[]. Once it does, then I will call it in a different method that adds the data to a GUI (this part I am reasonably confident I know how to do and have examples from my instructor and textbook to follow).