Using Scanner, i'm not sure how to read a file with multiple lines and store it all into a String. I use a loop like :
while(file.hasNext())
{
string += file.nextLine();
}
I find that the file.hasNext method eats up all of the data in the file and so file.nextInt() doesn't have any values to find and so it returns and error. What can I do to "reset" the Scanner? I tried creating a new Scanner object but that didn't change anything. I have to run this string through a method and I have run into this problem many times. What should I do?
Maybe you should try StringBuilder.
StringBuilder builder = new StringBuilder();
try (BufferedReader br = new BufferedReader(new FileReader(file))) {
String line;
while ((line = br.readLine()) != null) {
builder.append(line);
// process the line.
}
}
later
String text = builder.toString();
To read the entire contents of a Scanner source into a String, set the Scanner's delimiter to the end of the file:
String contents = file.useDelimiter("\\Z").next();
Related
I am trying to read parts of a text file with the format
John Smith
72
160
The first line being the name (string), and the second and third lines being height and weight (both ints). However, I cannot find a way to store each of these into their own variables, instead I can only figure out how to store the whole thing into one variable and print it. This is the code that I have as of now
try
{
File file = new File("person.txt");
FileReader fileReader = new FileReader(file);
BufferedReader bufferedReader = new BufferedReader(fileReader);
StringBuffer stringBuffer = new StringBuffer();
String line;
while ((line = bufferedReader.readLine()) != null)
{
stringBuffer.append(line);
stringBuffer.append("\n");
}
fileReader.close();
System.out.println(stringBuffer);
}
In this part
stringBuffer.append(line);
stringBuffer.append("\n");
I was thinking of trying to add a part in the middle of both those lines that stored a variable, but it did not seem possible. I also thought of using a for loop and using that to my advantage somehow, but could not figure out a way to do it with that either.
Is there any possible way to do this that I do not know about? Thank you
Reading and parsing a text file in Java has been getting easier in every new version. You can try the following way:
List<String> lines = Files.lines(Paths.get("person.txt")).collect(Collectors.toList());
String name = lines.get(0);
Integer height = Integer.parseInt(lines.get(1));
Integer weight = Integer.parseInt(lines.get(2));
File file = new File("person.txt");
FileReader fileReader = new FileReader(file);
BufferedReader bufferedReader = new BufferedReader(fileReader);
String firstline = bufferedReader.readLine();
String secondline = bufferedReader.readLine();
String thirdline = bufferedReader.readLine();
fileReader.close();
i am writing a java program to read a file and print output to another string variable.which is working perfectly as intended using is code.
{
String key = "";
FileReader file = new FileReader("C:/Users/raju/Desktop/input.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while (line != null) {
key += line;
line = reader.readLine();
}
System.out.println(key); //this prints contents of .txt file
}
this prints whole text in the file.But i want to only print the lines till word END is encountered in file.
example: if input.txt file contains following text : this test file END extra in
it should print only :
this test file
Just do a simple indexOf to see where it is and if it exists in the line. If the instance is found one option would be using substring to cut off everything up until the index of the keyword. For a bit more control though try using java regular expressions.
String key = "";
FileReader file = new FileReader("C:/Users/raju/Desktop/input.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while ((line = reader.readLine()) != null && line.indexOf("Keyword to look for") == -1)
key += line;
System.out.println(key);
I am not sure why it needs to be any more complicated than this:
BufferedReader re = new BufferedReader(new InputStreamReader(System.in));
while (true) {
String str = re.readLine();
if (str.equals("exit")) break;
// whatever other code.
}
You can do it in many ways. one of them is using indexOf method to specify the start index of "END" in input and then using subString method.
for more information, read documentation of String calss. HERE
This will work for your issue.
public static void main(String[] args) throws IOException {
String key = "";
FileReader file = new FileReader("/home/halil/khalil.txt");
BufferedReader reader = new BufferedReader(file);
String line = reader.readLine();
while (line != null) {
key += line;
line = reader.readLine();
} String output = "";
if(key.contains("END")) {
output = key.split("END")[0];
System.out.println(output);
}
}
You have to change your logic to check if the line contains "END".
If END not found in a line, add the line to key stringin your program
If yes, split that line into word array, read the line till you encounter the word "END" and append it to your key string. Consider using Stringbuilder for key.
while (line != null) {
line = reader.readLine();
if(!line.contains("END")){
key += line;
}else{
//Note that you can use split logic like below, or use java substring
String[] words = line.split("");
for(String s : words){
if(s.equals("END")){
return key;
}
key += s;
}
}
}
I know how to read in lines with Scanner, but how do I use a BufferedReader? I want to be able to read lines into an array. I am able to use the hasNext() function with a Scanner but not a BufferedReader, that is the only thing I don't know how to do. How do I check when the end of the file text has been reached?
BufferedReader reader = new BufferedReader(new FileReader("weblog.txt"));
String[] fileRead = new String[2990];
int count = 0;
while (fileRead[count] != null) {
fileRead[count] = reader.readLine();
count++;
}
readLine() returns null after reaching EOF.
Just
do {
fileRead[count] = reader.readLine();
count++;
} while (fileRead[count-1]) != null);
Of course this piece of code is not the recommended way of reading the file, but shows how it might be done if you want to do it exactly the way you attempted to ( some predefined size array, counter etc. )
The documentation states that readLine() returns null if the end of the stream is reached.
The usual idiom is to update the variable that holds the current line in the while condition and check if it's not null:
String currentLine;
while((currentLine = reader.readLine()) != null) {
//do something with line
}
As an aside, you might not know in advance the number of lines you will read, so I suggest you use a list instead of an array.
If you plan to read all the file's content, you can use Files.readAllLines instead:
//or whatever the file is encoded with
List<String> list = Files.readAllLines(Paths.get("weblog.txt"), StandardCharsets.UTF_8);
using readLine(), try-with-resources and Vector
try (BufferedReader bufferedReader = new BufferedReader(new FileReader("C:\\weblog.txt")))
{
String line;
Vector<String> fileRead = new Vector<String>();
while ((line = bufferedReader.readLine()) != null) {
fileRead.add(line);
}
} catch (IOException exception) {
exception.printStackTrace();
}
I have a text file like this:
Item 1
Item 2
Item 3
I need to be able to read each "Item X" into a string and ideally store all the strings as a vector / ArrayList.
I tried:
InputStream is = new FileInputStream("file.txt");
is.read(); //looped for every line of text
but that seems to only handle integers.
Thanks
You have several answers here, the easiest would be to us a Scanner (in java.util).
It has several convenience methods like nextLine() and next() and nextInt(), so you could simply do the following:
Scanner scanner = new Scanner(new File("file.txt"));
List<String> text = new ArrayList<String>();
while (scanner.hasNextLine()) {
text.add(scanner.nextLine());
}
Alternatively you could use a BufferedReader (in java.io):
BufferedReader reader = new BufferedReader(new FileReader("file.txt"));
List<String> text = new ArrayList<String>();
for (String line; (line = reader.readLine()) != null; ) {
text.add(line);
}
However Scanners are generally easier to work with.
You should use FileUtils to do this. It has a method named readLines
public static List<String> readLines(File file, Charset encoding) throws IOException
Reads the contents of a file line by line to a List of Strings. The file is always closed.
See #BackSlash's comment above to see how you're using InputStream.read() wrong.
#BackSlash also mentioned you can use java.nio.file.Files#readAllLines but only if you're using Java 1.7 or later.
You could use Java 7's Files#readAllLines. A short one-liner and no 3rd party library imports necessary :)
List<String> lines =
Files.readAllLines(Paths.get("file.txt"), StandardCharsets.UTF_8);
BufferedReader br = new BufferedReader(new FileReader("file.txt"));
try {
StringBuilder sb = new StringBuilder();
String line = br.readLine();
String [] tmp ;
while (line != null) {
sb.append(line);
tmp = line.Split(" ");
line = br.readLine();
}
String everything = sb.toString();
} finally {
br.close();
}
Scanner scan = new Scanner(new FileInputStream("file.txt"));
scan.nextLine();
I'm trying to read a csv file from my java code. using the following piece of code:
public void readFile() throws IOException {
BufferedReader br = new BufferedReader(new FileReader(fileName));
lines = new ArrayList<String>();
String newLine;
while ((newLine = br.readLine()) != null) {
newLine = br.readLine();
System.out.println(newLine);
lines.add(newLine);
}
br.close();
}
The output I get from the above piece of code is every alternative line [2nd, 4th, 6th lines] is read and returned by the readLine() method. I'm not sure why this behavior exists. Please correct me if I am missing something while reading the csv file.
The first time you're reading the line without processing it in the while loop, then you're reading it again but this time you're processing it. readLine() method reads a line and displaces the reader-pointer to the next line in the file. Hence, every time you use this method, the pointer will be incremented by one pointing to the next line.
This:
while ((newLine = br.readLine()) != null) {
newLine = br.readLine();
System.out.println(newLine);
lines.add(newLine);
}
Should be changed to this:
while ((newLine = br.readLine()) != null) {
System.out.println(newLine);
lines.add(newLine);
}
Hence reading a line and processing it, without reading another line and then processing.
You need to remove the first line in a loop body
newLine = br.readLine();
In java 8, we can easily achieve it
InputStream is = new ByteArrayInputStream(byteArr);
BufferedReader br = new BufferedReader(new InputStreamReader(is));
List<List<String>> dataList = br.lines()
.map(k -> Arrays.asList(k.split(",")))
.collect(Collectors.toCollection(LinkedList::new));
outer list will have rows and inner list will have corresponding column values