Develop Reference

Writing to File From Input Log

So I'm having a few troubles here. I need to be able to write my output to a file, and have it contain only the keywords specified in the code. This code is writing nothing to the file, and it only opens another box for user input. How do I get it to close the input box after the user inputs the file name, get it to write the output to the file, and get the output to display in the compiler? Thanks!
import java.util.*;
import java.io.*;
public class Classname {
static Scanner sc = new Scanner(System.in);
public static void main(String args[]) throws IOException,
FileNotFoundException {
String filename;
// Connecting to a file with a buffer
PrintWriter outFile = new PrintWriter(
new BufferedWriter(
new FileWriter("chatOutput.log")));
// Get the file
System.out.print("Please enter full name of the file: ");
filename = sc.next();
// Assign the name of the text file to a file object
File log = new File( filename);
String textLine = null; // Null
String outLine = ""; // Null
while(sc.hasNext())
{
String line=sc.nextLine();
if(line.contains("LANTALK"))
System.out.println(line);
}
try
{
// assigns the file to a filereader object..this will throw an error if
the file does not exist or cannot be found
BufferedReader infile = new BufferedReader(new FileReader(log));
try
{
// read data from a file..this will throw and error if something goes
wrong reading (empty or past end of file)
while((textLine = infile.readLine()) != null)
{
//System.out.printf("%s\n",textLine);
outLine = textLine.toUpperCase();
outFile.printf("%s\n",outLine);
}// end of while
} // end of try
finally // finally blocks get executed even if an exception is thrown
{
infile.close();
outFile.close();
}
}// end of try
catch (FileNotFoundException nf) // this goes with the first try because it
will throw a FileNotFound exception
{
System.out.println("The file \""+log+"\" was not found");
}
catch (IOException ioex) // this goes with the second try because it will
throw an IOexception
{
System.out.println("Error reading the file");
}
} /// end of main
} // end of class

What you need is to end the while(sc.hasNext()) while loop because the Scanner sc will always have a next because you are literally saying asking yourself if you got the line from the user then wait for next line with sc.nextLine(); then you are putting it into a string so next time you ask yourself do i have the line the answer is yes,anyways it's a little complicated to get over this issue you need to change the while loop to have a special word that will brake it,so you have to change it from:
while(sc.hasNext()){
String line=sc.nextLine();
if(line.contains("LANTALK"))
System.out.println(line);
}
To,for example:
while(true){
String line=sc.nextLine();
if(line.contains("LANTALK"))
System.out.println(line);
if(line.contains("END"))
break;
}
Also you need to check if the file entered by the user exists and actually add the text from the console to the file,so it would look something like this:
if(!log.exists())log.createNewFile();
// Connecting to a file with a buffer
PrintWriter logFile = new PrintWriter(
new BufferedWriter(
new FileWriter(log.getAbsolutePath())));
while(true){
String line=sc.nextLine();
if(line.contains("LANTALK"))
System.out.println(line);
if(line.contains("END"))
break;
logFile.println(line);
}
logFile.close();
Now all we have to do is print the output to the console when writing it to the logFile,so the while((textLine = infile.readLine()) != null),will now look a little something like this:
while((textLine = infile.readLine()) != null)
{
//System.out.printf("%s\n",textLine);
outLine = textLine.toUpperCase();
outFile.println(outLine);
System.out.println(outLine);
}// end of while
} // end of try
So in the end the hole thing should look a little something like this:
import java.util.*;
import java.io.*;
public class Classname{
static Scanner sc = new Scanner(System.in);
public static void main(String args[]) throws IOException,
FileNotFoundException {
String filename;
// Connecting to a file with a buffer
PrintWriter outFile = new PrintWriter(
new BufferedWriter(
new FileWriter("chatOutput.log")));
// Get the file
System.out.print("Please enter full name of the file: ");
filename = sc.next();
// Assign the name of the text file to a file object
File log = new File(filename);
String textLine = null; // Null
String outLine = ""; // Null
if(!log.exists())log.createNewFile();
// Connecting to a file with a buffer
PrintWriter logFile = new PrintWriter(
new BufferedWriter(
new FileWriter(log.getAbsolutePath())));
while(true){
String line=sc.nextLine();
if(line.contains("LANTALK"))
System.out.println(line);
if(line.contains("END"))
break;
logFile.println(line);
}
logFile.close();
try{
// assigns the file to a filereader object..this will throw an error if the file does not exist or cannot be found
BufferedReader infile = new BufferedReader(new FileReader(log));
try
{
// read data from a file..this will throw and error if something goes wrong reading (empty or past end of file)
while((textLine = infile.readLine()) != null)
{
//System.out.printf("%s\n",textLine);
outLine = textLine.toUpperCase();
outFile.println(outLine);
System.out.println(outLine);
}// end of while
} // end of try
finally // finally blocks get executed even if an exception is thrown
{
infile.close();
outFile.close();
}
}// end of try
catch (FileNotFoundException nf) // this goes with the first try because it will throw a FileNotFound exception
{
System.out.println("The file \""+log+"\" was not found");
}
catch (IOException ioex) // this goes with the second try because it will throw an IOexception
{
System.out.println("Error reading the file");
}
} /// end of main
} // end of class
If this is not what you are looking for i'm sorry,but i tried to make it do want you described you wanted,i mean it does write the output to the file, and get the output to display in the compiler,here's what the compiler console looks like:
Please enter full name of the file: test.txt
hi
hi
hi
END
HI
HI
HI
I'm sorry if this is not what you wanted but i tried my best,hope it helps.

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.

Multiprocess via processbuilder Communication, freeze at readline() for BufferedReader()

I am trying to allow communication between one program (the program launcher, if you will) and the programs it launches via processbuilder. I have the output working fine, but the input seems to stop when it reaches the readline() method in helloworld (the created process).
Below is helloworld.java:
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
public class helloworld {
public static void main (String[] args) {
System.out.println ("println(\"Hello World!\")");
System.out.println ("getInput()");
Scanner in = new Scanner(System.in);
BufferedReader br = new BufferedReader(
new InputStreamReader(System.in));
String input = "";
try {
// wait until we have data to complete a readLine()
while (!br.ready()) {
Thread.sleep(200);
}
System.out.println("println(\"Attempting to resolve input\")");
input = br.readLine();
^This is where program hangs^
if(input != null){
System.out.println("println(\"This should appear\")");
}
System.out.println("println(\"input recieved " + input + "\")");
} catch (InterruptedException | IOException e) {
System.out.println("ConsoleInputReadTask() cancelled");
}
System.out.println("println(\"You said: " + input + "\")");
//System.out.println("println(\"You said: " + in. + "!\")");
in.close();
System.exit(0);
}
}
This is where the output (println) from the other process is recieved:
public void run() {
try {
//cfile = files[indexval].getAbsolutePath();
String[] commands =
{
"java", //Calling a java program
"-cp" , //Denoting class path
cfile.substring(0,cfile.lastIndexOf(File.separator) ), //File path
program}; //Class name
ProcessBuilder probuilder = new ProcessBuilder( commands );
//start the process
Process process = probuilder.start();
//Read out dir output
//probuilder.inheritIO(); //Can inherit all IO calls
InputStream is = process.getInputStream();
OutputStream os = process.getOutputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(os));
BufferedReader br = new BufferedReader(isr);
String line;
/*System.out.printf("Output of running %s is:\n",
Arrays.toString(commands));*/
while ((line = br.readLine()) != null) {
myController.runCommand(line, "Please enter something!", bw);
//System.out.println(line);
}
br.close();
os.close();
} catch (IOException e){
e.printStackTrace();
}
System.out.println("programclosed");
}
And here is the function that it calls:
public synchronized void runCommand(String line, Object... arguments) throws IOException {
String[] tokens;
if(line.contains("(")){
tokens = line.split("\\(",2);
switch(tokens[0]){
case "println": //Println - format println(String strng)
tokens[1] = tokens[1].substring(1, tokens[1].length() - 2);
System.out.println(tokens[1]);
break;
case "getInput": //Get input - format getInput(String command, String message, BufferedWriter br)
Scanner reader = new Scanner(System.in);
System.out.println(arguments.length);
System.out.println(((String)arguments[0]));
BufferedWriter in = ((BufferedWriter)arguments[1]);
in.write(reader.nextLine());
System.out.println("sending input");
in.flush();
reader.close();
break;
default:
System.out.println("Invalid command recieved!");
}
} else
System.out.println("Invalid command recieved!");
}
The output I recieve is:
Hello World!
2
Please enter something!
This is a test input
sending input
Attempting to resolve input
As you can see, I successfully exit the while(!br.ready()) loop, and I stop at br.readLine();
I am aware inheritIO() exist, but for this case I am using the BufferedOuput to send commands which are then parsed and sent to the switch statement, which in turn calls the corresponding function. This is because multiple processes could be launched from the process manager, think of the fun when multiple System.in calls arrive, with nothing to determine which process it is for! In addition, this allows for me to call any type of function, even those not related to println or input.

I believe the issue here is a result of the following:
BufferedReader.ready() returns true if there are any characters available to be read. It does not guarantee that there are any carriage returns among them. (docs)
BufferedReader.readLine() looks for a carriage return to complete a line. If one is not found, it blocks.
BufferedWriter.write() does not automatically write a terminating carriage return.
To test whether this is actually the problem, replace this line in runCommand():
in.write(reader.nextLine());
with:
in.write(reader.nextLine() + "\n");

how to remove particular lines when reading text file in java

i want to delete that line where it finds "RxTracker"
this is my text file
INFO http-bio-80-exec-1 root - Received data;863071018134228;12.964624;77.523682;NE;23.22376;3.82;0;2013-01-06^08:41:00;
INFO http-bio-80-exec-1 root - RxTracker; IMEINO is 863071018134228
INFO http-bio-80-exec-2 root - RxTracker Invoked. Reading Parameters
INFO http-bio-80-exec-2 root - Received data;863071018134228;12.964624;77.523682;NE;37.66936;3.82;0;2013-01-06^08:42:52;
INFO http-bio-80-exec-2 root - RxTracker; IMEINO is 863071018134228
INFO http-bio-80-exec-5 root - RxTracker Invoked. Reading Parameters
INFO http-bio-80-exec-5 root - Received data;863071018134228;12.964624;77.523682;NE;20.92728;3.82;0;2013-01-06^08:44:51;
INFO http-bio-80-exec-5 root - RxTracker; IMEINO is 863071018134228
INFO http-bio-80-exec-3 root - RxTracker Invoked. Reading Parameters
this is my java code
public void Insert1()
{
try{
File f=new File("E:/c.txt");
FileReader fr=new FileReader(f);
BufferedReader br=new BufferedReader(fr);
int lineNum = 0;
String line = null;
while ( (line = br.readLine() ) != null ) {
lineNum++;
if(br.readLine().equalsIgnoreCase("RxTracker"))
{
System.out.println("ji");
}
else
{
System.out.println("ji");
}
//if ( lineNum %2 == 0 ) continue;
//else deal with it
System.out.println(br.readLine());
}
}
catch(FileNotFoundException e){
e.printStackTrace();
}
catch(IOException e1){
e1.printStackTrace();
}

Try something like this. The code reads each line of a file and writes it to another file.Every time it checks if that line contains RxTracker If that line doesn't contain the RxTracker then it will write that line to the new file and if it contains that string then it will skip that line,
for eg
String lineToRemove = "RxTracker ;
if(!trimmedLine.contains(lineToRemove)) { // check if t he line does not contains it then write it to another file
writer.write(trimmedLine);
writer.newLine();
}

Reading and displaying data from a .txt file

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.