Right, I've been trying to find a solution to this for a good while, but it's just not working for some reason.
In short, what I want to do is save every input String the user inputs into a file. Every time the activity is created again, I want to re-input these strings into a new instance of an object.
This code is what I use to create the file and read info from it, used in the onCreate() method of activity
try {
String brain = "brain";
File file = new File(this.getFilesDir(), brain);
if (!file.exists()) {
file.createNewFile();
}
BufferedReader in = new BufferedReader(new FileReader(file));
String s; // This feeds the object MegaAndroid with the strings, sequentially
while ((s = in.readLine()) != null) {
MegaAndroid.add(s);
}
in.close();
} catch (IOException e) {
e.printStackTrace();
}
After that, every time the user inputs some text, the strings are saved onto the file:
try {
String brain = "brain";
File file = new File(this.getFilesDir(), brain);
if (!file.exists()) {
file.createNewFile();
}
BufferedWriter out = new BufferedWriter(new FileWriter(file));
out.write(message); // message is a string that holds the user input
out.close();
} catch (IOException e) {
e.printStackTrace();
}
For some reason, however, every time the application is killed, the data is lost.
What am I doing wrong?
EDIT: Also, if I were to access this file from another class, how can I?
As we discussed in the commend section the chief problem with the code is that your execution of FileWriter occurred prior to your FileReader operation while truncating the file. For you to maintain the file contents you want to set the write operation to an append:
BufferedWriter out = new BufferedWriter(new FileWriter(file,true));
out.write(message);
out.newLine();
out.close();
However, if every entry on the EditText is received then shipped into the file you'll just be writing data byte after byte beside it. It is easy to get contents similar to
This is line #1This is line #2
Instead of the desired
This is line #1
This is line #2
which would be corrected by having the BufferedWriter pass a newline after each write to the file.
This is what I do for file reading.
try{
File sdCard = Environment.getExternalStorageDirectory();
File dir = new File (sdCard.getAbsolutePath() + "/whereyouwantfile");
dir.mkdirs();
Log.d(TAG,"path: "+dir.getAbsolutePath());
File file = new File(dir, "VERSION_FILENAME");
FileInputStream f = new FileInputStream(file);
//FileInputStream fis = context.openFileInput(VERSION_FILENAME);
BufferedReader reader = new BufferedReader(new InputStreamReader(f));
String line = reader.readLine();
Log.d(TAG,"first line versions: "+line);
while(line != null){
Log.d(TAG,"line: "+line);
//Process line how you need
line = reader.readLine();
}
reader.close();
f.close();
}
catch(Exception e){
Log.e(TAG,"Error retrieving cached data.");
}
And the following for writing
try{
File sdCard = Environment.getExternalStorageDirectory();
File dir = new File (sdCard.getAbsolutePath() + "/whereyouwantfile");
dir.mkdirs();
File file = new File(dir, "CONTENT_FILENAME");
FileOutputStream f = new FileOutputStream(file);
//FileOutputStream fos = context.openFileOutput(CONTENT_FILENAME, Context.MODE_PRIVATE);
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(f));
Set<String> keys = Content.keySet();
for(String key : keys){
String data = Content.get(key);
Log.d(TAG,"Writing: "+key+","+data);
writer.write(data);
writer.newLine();
}
writer.close();
f.close();
}
catch(Exception e){
e.printStackTrace();
Log.e(TAG,"Error writing cached data.");
}
You can use the private mode if you don't want the rest of the world to be able to see your files, but it is often useful to see them when debugging.
Related
This is code i Have written instead of editing a particular line new name gets appened at the last...
please help me out....
PrintWriter writer = new PrintWriter(new BufferedWriter(
new FileWriter("d:\\book.txt", true)));
BufferedReader br = null;
FileReader reader = null;
try {
reader = new FileReader("d:\\book.txt");
br = new BufferedReader(reader);
String line;
System.out.println((";;;;;;;;;;;;;;;;" + request
.getParameter("hname")));
System.out.println(request.getParameter("book"));
while ((line = br.readLine()) != null) {
if (request.getParameter("hname").equals(line)) {
line = line.replace(request.getParameter("hname"),
request.getParameter("book"));
writer.println(line);
writer.close();
}
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}finally{
reader.close();
}
Unless you aren't changing the (byte) length of the line, you need to rewrite the whole file, adding the changed line where appropriate. This is actually just a simple change from your current code. First, initialize your FileWriter without the append (since you don't want to just append to the end of the file, which is what you're doing now).
PrintWriter writer = new PrintWriter(new BufferedWriter(new FileWriter("d:\\book.txt")));
Then, either read the whole file into memory (if the file is small enough) or else write a temp file as you go and then copy it over when you're done. The second way is more robust, and requires less code changing; just modify your while loop to write every line, modified or not.
// Open a temporary file to write to.
PrintWriter writer = new PrintWriter(new BufferedWriter(new FileWriter("d:\\book.temp")));
// ... then inside your loop ...
while ((line = br.readLine()) != null) {
if (request.getParameter("hname").equals(line)) {
line = line.replace(request.getParameter("hname"),
request.getParameter("book"));
}
// Always write the line, whether you changed it or not.
writer.println(line);
}
// ... and finally ...
File realName = new File("d:\\book.txt");
realName.delete(); // remove the old file
new File("d:\\book.temp").renameTo(realName); // Rename temp file
Don't forget to close all your file handles when you're done!
I would like to create a temporary txt file for my program. In the code below, "student1.txt" is a txt file that has already created but for "temporarystudent.txt" is is not. I have tried to run with Line 6 (while in Line 7 & 8 in comment) as well as Line 7 & 8 (while Line 6 in comment) but neither of them are able to create "temporarystudent.txt". When I run the program, it didn't show any error neither in VS Code Terminal nor in the Program Output. It just won't create the "temporarystudent.txt". May I know what's wrong here?
try
{
//Locate the file.
File file = new File("student1.txt");
//Create a temporary file
//File temp = File.createTempFile("temporarystudent", ".txt", file.getParentFile());
File temp = new File("temporarystudent.txt");
temp.createNewFile();
//Determine the charset.
String charset = "UTF-8";
//Open the file for reading.
BufferedReader reader = new BufferedReader(new InputStreamReader(new FileInputStream(file), charset));
//Open the temp file for writing.
PrintWriter writer = new PrintWriter(new OutputStreamWriter(new FileOutputStream(temp), charset));
//Read the file line by line.
for (String line; (line = reader.readLine()) != null;) {
line = line.replace("null\n", "");
writer.println(line);
}
//Close the reader and writer (preferably in the finally block).
reader.close();
writer.close();
//Delete the file.
file.delete();
//Rename the temp file.
temp.renameTo(file);
}
catch (IOException e)
{
System.out.println("An error occurred.");
e.printStackTrace();
}
First of all, I would like you to say that I am quite new here and I'm also a beginner in Android Studio and Java.
My problem/question is:
I have an App in Android Studio which should write a string to a text file at a specific point and also should read the same file on App startup.
Writing to the file is working but not reading. When I create a text file manually, and insert it manually to the folder it reads the string.
I already added permissions and try to find my error with LogCat but I have no clue at the moment what could be wrong.
Variables:
File root = android.os.Environment.getExternalStorageDirectory();
File dir = new File(root.getAbsolutePath() + "/myApp");
My reading function:
String myData = "";
try {
FileReader fileIn = new FileReader(dir + "/data.txt");
Scanner input = new Scanner(fileIn);
while (input.hasNextLine()) {
String line = input.nextLine();
myData = myData + line;
}
input.close();
} catch (Exception ex) {
ex.printStackTrace();
}
My writing function:
try {
File file = new File(dir, "data.txt");
FileOutputStream f = new FileOutputStream(file);
PrintWriter pw = new PrintWriter(f);
pw.println("answer42");
pw.flush();
pw.close();
f.close();
} catch (Exception ex) {
ex.printStackTrace();
}
I'm doing a program that needs to take a text file (test.txt) and make a copy of it and print it out. So far I am only able to print out the original file. I have searched for a way of doing this but there doesn't seem to be any help that I can understand, I am very new to java. I am at least looking for guidance, not just the full answer.
my code so far...
import java.io.*;
public class Copy{
public static void main(String [] args){
try{
FileInputStream fis = new FileInputStream("test.txt");
InputStreamReader isr = new InputStreamReader(fis);
BufferedReader br = new BufferedReader(isr);
File a = new File("test.txt");
FileReader fr = new FileReader(a);
File b = new File("Copied.txt");
FileWriter fw = new FileWriter(b);
while(true){
String line = br.readLine();
if(line != null){
System.out.println(line);
} else{
br.close();
break;
}
}
} catch(FileNotFoundException e){
System.out.println("Error: " + e.getMessage());
} catch(IOException e){
System.out.println("Error: " + e.getMessage());
}
}
}
Again any bit of help will be greatly appreciated since I am trying to learn this. Thank you
Normally, I'd recommend using Files.copy just for it's simplicty, but since you need to "print" the content at the same time, we can make use of your code.
First, however, as a general rule of thumb, if you open it, you should close it. This makes sure that you're not leaving resources open which might affect other parts of your code.
See The try-with-resources Statement for more details.
Next, once you've read a line of text from the source file, you actually need to write it to the destination file, for example...
try (BufferedReader br = new BufferedReader(new FileReader("test.txt"))) {
try (BufferedWriter bw = new BufferedWriter(new FileWriter("Copied.txt"))) {
String text = null;
while ((text = br.readLine()) != null) {
System.out.println(text);
bw.write(text);
bw.newLine();
}
}
} catch (FileNotFoundException e) {
System.out.println("Error: " + e.getMessage());
} catch (IOException e) {
System.out.println("Error: " + e.getMessage());
}
You can use Files.copy() if you are using Java 1.7 or higher
File src = "your File";
File dest = "your copy target"
Files.copy(src.toPath(),dest.toPath());
Link to Javadoc
Change your FileWriter into a PrintStream:
PrintStream fw = new PrintStream(b);
Then you should be able to write to that file using:
fw.println(line);
This is code i Have written instead of editing a particular line new name gets appened at the last...
please help me out....
PrintWriter writer = new PrintWriter(new BufferedWriter(
new FileWriter("d:\\book.txt", true)));
BufferedReader br = null;
FileReader reader = null;
try {
reader = new FileReader("d:\\book.txt");
br = new BufferedReader(reader);
String line;
System.out.println((";;;;;;;;;;;;;;;;" + request
.getParameter("hname")));
System.out.println(request.getParameter("book"));
while ((line = br.readLine()) != null) {
if (request.getParameter("hname").equals(line)) {
line = line.replace(request.getParameter("hname"),
request.getParameter("book"));
writer.println(line);
writer.close();
}
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}finally{
reader.close();
}
Unless you aren't changing the (byte) length of the line, you need to rewrite the whole file, adding the changed line where appropriate. This is actually just a simple change from your current code. First, initialize your FileWriter without the append (since you don't want to just append to the end of the file, which is what you're doing now).
PrintWriter writer = new PrintWriter(new BufferedWriter(new FileWriter("d:\\book.txt")));
Then, either read the whole file into memory (if the file is small enough) or else write a temp file as you go and then copy it over when you're done. The second way is more robust, and requires less code changing; just modify your while loop to write every line, modified or not.
// Open a temporary file to write to.
PrintWriter writer = new PrintWriter(new BufferedWriter(new FileWriter("d:\\book.temp")));
// ... then inside your loop ...
while ((line = br.readLine()) != null) {
if (request.getParameter("hname").equals(line)) {
line = line.replace(request.getParameter("hname"),
request.getParameter("book"));
}
// Always write the line, whether you changed it or not.
writer.println(line);
}
// ... and finally ...
File realName = new File("d:\\book.txt");
realName.delete(); // remove the old file
new File("d:\\book.temp").renameTo(realName); // Rename temp file
Don't forget to close all your file handles when you're done!