Reading and displaying data from a .txt file - java

How do you read and display data from .txt files?

BufferedReader in = new BufferedReader(new FileReader("<Filename>"));
Then, you can use in.readLine(); to read a single line at a time. To read until the end, write a while loop as such:
String line;
while((line = in.readLine()) != null)
{
System.out.println(line);
}
in.close();

If your file is strictly text, I prefer to use the java.util.Scanner class.
You can create a Scanner out of a file by:
Scanner fileIn = new Scanner(new File(thePathToYourFile));
Then, you can read text from the file using the methods:
fileIn.nextLine(); // Reads one line from the file
fileIn.next(); // Reads one word from the file
And, you can check if there is any more text left with:
fileIn.hasNext(); // Returns true if there is another word in the file
fileIn.hasNextLine(); // Returns true if there is another line to read from the file
Once you have read the text, and saved it into a String, you can print the string to the command line with:
System.out.print(aString);
System.out.println(aString);
The posted link contains the full specification for the Scanner class. It will be helpful to assist you with what ever else you may want to do.

In general:
Create a FileInputStream for the file.
Create an InputStreamReader wrapping the input stream, specifying the correct encoding
Optionally create a BufferedReader around the InputStreamReader, which makes it simpler to read a line at a time.
Read until there's no more data (e.g. readLine returns null)
Display data as you go or buffer it up for later.
If you need more help than that, please be more specific in your question.

I love this piece of code, use it to load a file into one String:
File file = new File("/my/location");
String contents = new Scanner(file).useDelimiter("\\Z").next();

Below is the code that you may try to read a file and display in java using scanner class. Code will read the file name from user and print the data(Notepad VIM files).
import java.io.*;
import java.util.Scanner;
import java.io.*;
public class TestRead
{
public static void main(String[] input)
{
String fname;
Scanner scan = new Scanner(System.in);
/* enter filename with extension to open and read its content */
System.out.print("Enter File Name to Open (with extension like file.txt) : ");
fname = scan.nextLine();
/* this will reference only one line at a time */
String line = null;
try
{
/* FileReader reads text files in the default encoding */
FileReader fileReader = new FileReader(fname);
/* always wrap the FileReader in BufferedReader */
BufferedReader bufferedReader = new BufferedReader(fileReader);
while((line = bufferedReader.readLine()) != null)
{
System.out.println(line);
}
/* always close the file after use */
bufferedReader.close();
}
catch(IOException ex)
{
System.out.println("Error reading file named '" + fname + "'");
}
}
}

If you want to take some shortcuts you can use Apache Commons IO:
import org.apache.commons.io.FileUtils;
String data = FileUtils.readFileToString(new File("..."), "UTF-8");
System.out.println(data);
:-)

public class PassdataintoFile {
public static void main(String[] args) throws IOException {
try {
PrintWriter pw = new PrintWriter("C:/new/hello.txt", "UTF-8");
PrintWriter pw1 = new PrintWriter("C:/new/hello.txt");
pw1.println("Hi chinni");
pw1.print("your succesfully entered text into file");
pw1.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
BufferedReader br = new BufferedReader(new FileReader("C:/new/hello.txt"));
String line;
while((line = br.readLine())!= null)
{
System.out.println(line);
}
br.close();
}
}

In Java 8, you can read a whole file, simply with:
public String read(String file) throws IOException {
return new String(Files.readAllBytes(Paths.get(file)));
}
or if its a Resource:
public String read(String file) throws IOException {
URL url = Resources.getResource(file);
return Resources.toString(url, Charsets.UTF_8);
}

You most likely will want to use the FileInputStream class:
int character;
StringBuffer buffer = new StringBuffer("");
FileInputStream inputStream = new FileInputStream(new File("/home/jessy/file.txt"));
while( (character = inputStream.read()) != -1)
buffer.append((char) character);
inputStream.close();
System.out.println(buffer);
You will also want to catch some of the exceptions thrown by the read() method and FileInputStream constructor, but those are implementation details specific to your project.

Related

How can i remove a particular text from a file in java?

I have tried to implement a simple program to delete a particular text from a file, some how it is not able to delete it. I am reading entire file content into a temp file , delete the user input string from it and update the content to the original file.
Any help would be highly appreciated.
public class TextEraser{
public static void main(String[] args) throws IOException {
System.out.print("Enter a string to remove : ");
Scanner scanner = new Scanner(System. in);
String inputString = scanner. nextLine();
// Locate the file
File file = new File("/Users/lobsang/documents/input.txt");
//create temporary file
File temp = File.createTempFile("file", ".txt", file.getParentFile());
String charset = "UTF-8";
try {
// Create a buffered reader
// to read each line from a file.
BufferedReader in = new BufferedReader(new FileReader(file));
PrintWriter writer = new PrintWriter(new OutputStreamWriter(new FileOutputStream(temp), charset));
String s = in.readLine();
// Read each line from the file and echo it to the screen.
while (s !=null) {
s=s.replace(inputString,"");
s = in.readLine();
}
writer.println(s);
// Close the buffered reader
in.close();
writer.close();
file.delete();
temp.renameTo(file);
} catch (FileNotFoundException e1) {
// If this file does not exist
System.err.println("File not found: " + file);
}
}
After replace with input string, write string immediate in file.
while (s != null) {
s = s.replace(inputString, "");
writer.write(s);
// writer.newLine();
s = in.readLine();
}
For new line , use BufferedWriter in place of PrintWriter, it contains method newLine()
writer.newLine();
Remove this
writer.println(s);

How to read data from more than 1 text files using regular Expression in java?

Given more than one files in a directory
I have to read only the text files from a directory and print all the information inside it.
My Implementation:
File filepath=new File("c:/test");
Pattern p=Pattern.compile("[a-zA-Z0-9_]+.txt");
String s1[]=filepath.list();
for (int i=0;i<s1.length;i++){
Matcher m=p.matcher(s1[i]);
if(m.find()&&m.equals(s1));
System.out.println(s1[i]);
File file1=new File(s1[i]);
readFromFile(file1);
}
static void readFromFile(File filename) throws IOException{
String line = null;
FileReader fileReader = new FileReader(filename); //1
BufferedReader bufferedReader = new BufferedReader(fileReader);
while((line = bufferedReader.readLine()) != null) {
System.out.println(line);
}
bufferedReader.close();
fileReader.close();
}
While running the above program i am getting NullPointer at position 1 as indicated in the code.
Though I know the approaches using fileList method in file class I can read all the files in a directory and I also know that i can use endsWith method in String classto read only text file.
But I wanted to know how using above implementation I can read all the data inside the text files.
Can anyone guide me on this how to correctly handle the above approach.
You probably have a problem while reading the file.
To understand what problem exactly do you have - "file not found" or maybe "insufficient read permissions" - always catch and print the exception when opening files for reading or writing (and also for reading directories):
public static void main (String[] args) {
readFromFile(new File("nonexistant.txt"));
}
public static void readFromFile(File file) {
try (FileReader fileReader = new FileReader(file);
BufferedReader bufferedReader = new BufferedReader(fileReader)) {
for (String line = bufferedReader.readLine();
line != null;
line = bufferedReader.readLine()) {
System.out.println(line);
}
} catch (Exception ex) {
System.err.print(ex);
}
}
Here it prints the reason:
java.io.FileNotFoundException: nonexistant.txt (No such file or directory)
Once you have fixed this issue, move to the file parsing.

Java IO: Using scanner and printWriter to copy the contents of a text file and put them in another text file

Alright so I have a very small program I'm working on designed to take the contents of a text file, test.txt, and put them in another empty file testCopied.txt . The trick is that I want to use Scanner and printWriter as I am trying to understand these a bit better.
Here is what my code looks like:
import java.io.*;
import java.util.*;
public class CopyA
{
public static void main(String [] args)
{
String Input_filename = args[0];
String Output_filename = args[1];
char r = args[2].charAt(0);
try
{
Scanner sc = new Scanner(new File(Input_filename));
FileWriter fw = new FileWriter(Output_filename);
PrintWriter printer = new PrintWriter(fw);
while(sc.hasNextLine())
{
String s = sc.nextLine();
printer.write(s);
}
sc.close();
}
catch(IOException ioe)
{
System.out.println(ioe);
}
}
}
This compiles, but when I look at testCopied.txt it is still blank, and hasn't had test.txt's content transferred to it. What am I doing wrong? Java IO is pretty confusing to me, so I'm trying to get a better grasp on it. Any help is really appreciated!
You have missed out flush() and close() for the PrintWriter object which you need to add
and then use the line separator using System.getProperty("line.separator") while writing each line into second file.
You can refer the below code:
PrintWriter printer = null;
Scanner sc = null;
try
{
String lineSeparator = System.getProperty("line.separator");
sc = new Scanner(new File(Input_filename));
FileWriter fw = new FileWriter(Output_filename);
printer = new PrintWriter(fw);
while(sc.hasNextLine())
{
String s = sc.nextLine()+lineSeparator; //Add line separator
printer.write(s);
}
}
catch(IOException ioe)
{
System.out.println(ioe);
} finally {
if(sc != null) {
sc.close();
}
if(printer != null) {
printer.flush();
printer.close();
}
}
Also, ensure that you are always closing resources in the finally block (which you have missed out for Scanner object in your code).

Converting a .java file to a .txt document

I am trying to figure out how to load a .java doc and out put it into a text document...
What needs to be done:
Write a program that opens a Java source file, adds line numbers, and
saves the result in a new file. Line numbers are numbers which
indicate the different lines of a source file, they are useful when
trying to draw someone's attention to a particular line (e.g.,
"there's a bug on line 4"). Your program should prompt the user to
enter a filename, open it, and then save each line to an output fix
with the line numbers prepended to the beginning of each line.
Afterward, display the name of the output file. The name of the output
file should based on the input file with the '.' replaced by a '_',
and ".txt" added to the end. (Hint: if you are using a PrintWriter
object called pw to save the text file, then the line
"pw.printf("%03d", x);" will display an integer x padded to three
digits with leading zeros.)
The text.java needs to output into the text document with numbered lines such as:
001 public class dogHouse {
002 public static void main (String[] args) {
003 and so on...
004
import java.io.*;
public class dogHouse {
public static void main(String [] args) throws IOException {
// The name of the file to open.
String fileName = "test.java";
// This will reference one line at a time
String line = null;
try {
// FileReader reads text files in the default encoding.
FileReader fileReader =
new FileReader(fileName);
// Always wrap FileReader in BufferedReader.
BufferedReader bufferedReader =
new BufferedReader(fileReader);
while((line = bufferedReader.readLine()) != null) {
System.out.println(line);
}
// Always close files.
bufferedReader.close();
}
// The name of the file to open.
finally {
// Assume default encoding.
FileWriter fileWriter =
new FileWriter(fileName);
// Always wrap FileWriter in BufferedWriter.
BufferedWriter bufferedWriter =
new BufferedWriter(fileWriter);
// Note that write() does not automatically
// append a newline character.
bufferedWriter.write("Hello there,");
// Always close files.
bufferedWriter.close();
}
}
}
You need to print and count the line(s) as you read them. You also need to differentiate between your output file and your input file. And, I would prefer to use try-with-resources Statements. Something like,
String fileName = "test.java";
String outputFileName = String.format("%s.txt", fileName.replace('.', '_'));
try (BufferedReader br = new BufferedReader(new FileReader(fileName));
PrintWriter pw = new PrintWriter(new FileWriter(outputFileName))) {
int count = 1;
String line;
while ((line = br.readLine()) != null) {
pw.printf("%03d %s%n", count, line);
count++;
}
} catch (Exception e) {
e.printStackTrace();
}

Import Textfile and read line by line in Java

I was wondering how one would go about importing a text file. I want to import a file and then read it line by line.
thanks!
I've no idea what you mean by "importing" a file, but here's the simplest way to open and read a text file line by line, using just standard Java classes. (This should work for all versions of Java SE back to JDK1.1. Using Scanner is another option for JDK1.5 and later.)
BufferedReader br = new BufferedReader(
new InputStreamReader(new FileInputStream(fileName)));
try {
String line;
while ((line = br.readLine()) != null) {
// process line
}
} finally {
br.close();
}
This should cover just about everything you need.
http://download.oracle.com/javase/tutorial/essential/io/index.html
And for a specific example: http://www.java-tips.org/java-se-tips/java.io/how-to-read-file-in-java.html
This might also help: Read text file in Java
I didnt get what you meant by 'import'. I assume you want to read contents of a file. Here is an example method that does it
/** Read the contents of the given file. */
void read() throws IOException {
System.out.println("Reading from file.");
StringBuilder text = new StringBuilder();
String NL = System.getProperty("line.separator");
Scanner scanner = new Scanner(new File(fFileName), fEncoding);
try {
while (scanner.hasNextLine()){
text.append(scanner.nextLine() + NL);
}
}
finally{
scanner.close();
}
System.out.println("Text read in: " + text);
}
For details you can see here
Apache Commons IO offers a great utility called LineIterator that can be used explicitly for this purpose. The class FileUtils has a method for creating one for a file: FileUtils.lineIterator(File).
Here's an example of its use:
File file = new File("thing.txt");
LineIterator lineIterator = null;
try
{
lineIterator = FileUtils.lineIterator(file);
while(lineIterator.hasNext())
{
String line = lineIterator.next();
// Process line
}
}
catch (IOException e)
{
// Handle exception
}
finally
{
LineIterator.closeQuietly(lineIterator);
}

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