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get Data from text file in java [duplicate]

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.

Unable to a read a large file using BufferedReader in Java

I am trying to read a file using BufferedReader, but when I tried to print, It is returning some weird characters.
Code of reading file is:
private static String readJsonFile(String fileName) throws IOException{
BufferedReader br = null;
try {
StringBuilder sb = new StringBuilder();
br = new BufferedReader(new FileReader(fileName));
String line = br.readLine();
while(line != null ){
sb.append(line);
System.out.println(line);
line=br.readLine();
}
return sb.toString();
} finally{
br.close();
}
}
This function is being called as :
String jsonString = null;
try {
jsonString = readJsonFile(fileName);
} catch (IOException e) {
e.printStackTrace();
}
But when I tried to print this in console using System.out.println(jsonString);, It is returning some fancy pictures.
Note: It is Working file when file size is small.
Is there any limit on size of file it can read ?

You're using the platform default encoding to read the file, which is probably encoded in UTF8. Check the actual encoding of the file, and specify the encoding:
BufferedReader r = new BufferedReader(new InputStreamReader(new FileInputStream("...", StandardCharsets.UTF_8));
Note that since you simply want to read everything from the file, you could simply use
String json = new String(Files.readAllBytes(...), StandardCharsets.UTF_8);

Find and replace in Java using regular expression without changing file format

I've a code which replaces 10:A to 12:A in a text file called sample.txt. Also, the code I've now is changing the file format, which shouldn't. Can someone please let me know how to do the same using regular expression in Java which doesn't change the file format? File has original format as below 10:A 14:Saxws But after executing the code it outputs as 10:A 14:Saxws.
import java.io.*;
import java.util.*;
public class FileReplace
{
List<String> lines = new ArrayList<String>();
String line = null;
public void doIt()
{
try
{
File f1 = new File("sample.txt");
FileReader fr = new FileReader(f1);
BufferedReader br = new BufferedReader(fr);
while ((line = br.readLine()) != null)
{
if (line.contains("10:A"))
line = line.replaceAll("10:A", "12:A") + System.lineSeparator();
lines.add(line);
}
fr.close();
br.close();
FileWriter fw = new FileWriter(f1);
BufferedWriter out = new BufferedWriter(fw);
for(String s : lines)
out.write(s);
out.flush();
out.close();
}
catch (Exception ex)
{
ex.printStackTrace();
}
}
public static void main(String[] args)
{
FileReplace fr = new FileReplace();
fr.doIt();
}
}

It looks like your OS or editor is not able to print correctly line separators generated by System.lineSeparator(). In that case consider
reading content of entire file to string (including original line separators), - then replacing part which you are interested in
and writing replaced string back to your file
You can do it using this code:
Path file = Paths.get("sample.txt");
//read all bytes from file (they will include bytes representing used line separtors)
byte[] bytesFromFile = Files.readAllBytes(file);
//convert themm to string
String textFromFile = new String(bytesFromFile, StandardCharsets.UTF_8);//use proper charset
//replace what you need (line separators will stay the same)
textFromFile = textFromFile.replaceAll("10:A", "12:A");
//write back data to file
Files.write(file, textFromFile.getBytes(StandardCharsets.UTF_8), StandardOpenOption.CREATE);

Parsing in Java with C style?

I am new to java text parsing and I'm wondering what is the best way to parse a file when the format of each line is known.
I have a file that has the following format for each line:
Int;String,double;String,double;String,double;String,double;String,double
Note how the String,double act as a pair separated by a comma and each pair is separated by a semicolon.
A few examples:
1;art,0.1;computer,0.5;programming,0.6;java,0.7;unix,0.3
2;291,0.8;database,0.6;computer,0.2;java,0.9;undegraduate,0.7
3;coffee,0.5;colombia,0.2;java,0.1;export,0.4;import,0.5
I'm using the following code to read each line:
public static void main(String args[]) {
try {
// Open the file that is the first
// command line parameter
FileInputStream fstream = new FileInputStream("textfile.txt");
// Get the object of DataInputStream
DataInputStream in = new DataInputStream(fstream);
BufferedReader br = new BufferedReader(new InputStreamReader(in));
String strLine;
// Read File Line By Line
while ((strLine = br.readLine()) != null) {
// Print the content on the console
System.out.println(strLine);
}
// Close the input stream
in.close();
} catch (Exception e) {// Catch exception if any
System.err.println("Error: " + e.getMessage());
}
}
Thanks in advance :)

You could use the Scanner class, for starters:
A simple text scanner which can parse primitive types and strings using regular expressions.

If you are truly trying to do "C" style parsing, where is the buffer which contains the characters being accumulated for the "next" field? Where is the check that sees if the field separator was read, and where is the code that flushes the current field into the correct data structure once the end of line / field separator is read?
A character by character read loop in Java looks like
int readChar = 0;
while ((readChar = in.read()) != -1) {
// do something with the new readChar.
}

You can provide a pattern and use the Scanner
String input = "fish1-1 fish2-2";
java.util.Scanner s = new java.util.Scanner(input);
s.findInLine("(\\d+)");
java.util.regex.MatchResult result = s.match();
for (int i=1; i<=result.groupCount(); i++)
System.out.println(result.group(i));
s.close();

Read XML, Replace Text and Write to same XML file via Java

Currently I am trying something very simple. I am looking through an XML document for a certain phrase upon which I try to replace it. The problem I am having is that when I read the lines I store each line into a StringBuffer. When I write the it to a document everything is written on a single line.
Here my code:
File xmlFile = new File("abc.xml")
BufferedReader br = new BufferedReader(new FileReade(xmlFile));
String line = null;
while((line = br.readLine())!= null)
{
if(line.indexOf("abc") != -1)
{
line = line.replaceAll("abc","xyz");
}
sb.append(line);
}
br.close();
BufferedWriter bw = new BufferedWriter(new FileWriter(xmlFile));
bw.write(sb.toString());
bw.close();
I am assuming I need a new line character when I prefer sb.append but unfortunately I don't know which character to use as "\n" does not work.
Thanks in advance!
P.S. I figured there must be a way to use Xalan to format the XML file after I write to it or something. Not sure how to do that though.

The readline reads everything between the newline characters so when you write back out, obviously the newline characters are missing. These characters depend on the OS: windows uses two characters to do a newline, unix uses one for example. To be OS agnostic, retrieve the system property "line.separator":
String newline = System.getProperty("line.separator");
and append it to your stringbuffer:
sb.append(line).append(newline);

Modified as suggested by Brel, your text-substituting approach should work, and it will work well enough for simple applications.
If things start to get a little hairier, and you end up wanting to select elements based on their position in the XML structure, and if you need to be sure to change element text but not tag text (think <abc>abc</abc>), then you'll want to call in in the cavalry and process the XML with an XML parser.
Essentially you read in a Document using a DocuemntBuilder, you hop around the document's nodes doing whatever you need to, and then ask the Document to write itself back to file. Or do you ask the parser? Anyway, most XML parsers have a handful of options that let you format the XML output: You can specify indentation (or not) and maybe newlines for every opening tag, that kinda thing, to make your XML look pretty.

Sb would be the StringBuffer object, which has not been instantiated in this example. This can added before the while loop:
StringBuffer sb = new StringBuffer();

Scanner scan = new Scanner(System.in);
String filePath = scan.next();
String oldString = "old_string";
String newString = "new_string";
String oldContent = "";
BufferedReader br = null;
FileWriter writer = null;
File xmlFile = new File(filePath);
try {
br = new BufferedReader(new FileReader(xmlFile));
String line = br.readLine();
while (line != null) {
oldContent = oldContent + line + System.lineSeparator();
line = br.readLine();
}
String newContent = oldContent.replaceAll(oldString, newString);
writer = new FileWriter(xmlFile);
writer.write(newContent);
} catch (IOException e) {
e.printStackTrace();
} finally {
try {
scan.close();
br.close();
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
}