The following code does not produce a file (I can't see the file anywhere).
What is missing?
try {
//create a temporary file
String timeLog = new SimpleDateFormat("yyyyMMdd_HHmmss").format(
Calendar.getInstance().getTime());
File logFile=new File(timeLog);
BufferedWriter writer = new BufferedWriter(new FileWriter(logFile));
writer.write (string);
//Close writer
writer.close();
} catch(Exception e) {
e.printStackTrace();
}
I think your expectations and reality don't match (but when do they ever ;))
Basically, where you think the file is written and where the file is actually written are not equal (hmmm, perhaps I should write an if statement ;))
public class TestWriteFile {
public static void main(String[] args) {
BufferedWriter writer = null;
try {
//create a temporary file
String timeLog = new SimpleDateFormat("yyyyMMdd_HHmmss").format(Calendar.getInstance().getTime());
File logFile = new File(timeLog);
// This will output the full path where the file will be written to...
System.out.println(logFile.getCanonicalPath());
writer = new BufferedWriter(new FileWriter(logFile));
writer.write("Hello world!");
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
// Close the writer regardless of what happens...
writer.close();
} catch (Exception e) {
}
}
}
}
Also note that your example will overwrite any existing files. If you want to append the text to the file you should do the following instead:
writer = new BufferedWriter(new FileWriter(logFile, true));
I would like to add a bit more to MadProgrammer's Answer.
In case of multiple line writing, when executing the command
writer.write(string);
one may notice that the newline characters are omitted or skipped in the written file even though they appear during debugging or if the same text is printed onto the terminal with,
System.out.println("\n");
Thus, the whole text comes as one big chunk of text which is undesirable in most cases.
The newline character can be dependent on the platform, so it is better to get this character from the java system properties using
String newline = System.getProperty("line.separator");
and then using the newline variable instead of "\n". This will get the output in the way you want it.
In java 7 can now do
try(BufferedWriter w = ....)
{
w.write(...);
}
catch(IOException)
{
}
and w.close will be done automatically
It's not creating a file because you never actually created the file. You made an object for it. Creating an instance doesn't create the file.
File newFile = new File("directory", "fileName.txt");
You can do this to make a file:
newFile.createNewFile();
You can do this to make a folder:
newFile.mkdir();
Using java 8 LocalDateTime and java 7 try-with statement:
public class WriteFile {
public static void main(String[] args) {
String timeLog = DateTimeFormatter.ofPattern("yyyyMMdd_HHmmss").format(LocalDateTime.now());
File logFile = new File(timeLog);
try (BufferedWriter bw = new BufferedWriter(new FileWriter(logFile)))
{
System.out.println("File was written to: " + logFile.getCanonicalPath());
bw.write("Hello world!");
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
You can try a Java Library. FileUtils, It has many functions that write to Files.
It does work with me. Make sure that you append ".txt" next to timeLog. I used it in a simple program opened with Netbeans and it writes the program in the main folder (where builder and src folders are).
The easiest way for me is just like:
try {
FileWriter writer = new FileWriter("C:/Your/Absolute/Path/YourFile.txt");
writer.write("Wow, this is so easy!");
writer.close();
} catch (IOException e) {
e.printStackTrace();
}
Useful tips & tricks:
Give it a certain path:
new FileWriter("C:/Your/Absolute/Path/YourFile.txt");
New line
writer.write("\r\n");
Append lines into existing txt
new FileWriter("log.txt");
Hope it works!
Related
I have been encountering a problem for a while now, and have tested every possibility I can think of. Unfortunately, these possibilities did not work.
Basically, I am trying to write to a .txt file using BufferedWriter in Java. I need this setup so that I can have a line in between each piece of data. Imagine this is the text file produced from Java, it should look like this:
line1
line2
Here is my code:
public static void main(String[] args) {
Path path = Paths.get("test.txt");
if (!Files.exists(path)) {
try {
Files.createFile(path);
} catch (IOException e) {
System.out.println("Error in creating test.txt! Read the stacktrace
below.");
e.printStackTrace();
}
}
Charset charset = Charset.forName("UTF-8");
try (BufferedWriter writer = Files.newBufferedWriter(path, charset)) {
String string = "line1";
writer.write(string, 0, string.length());
writer.newLine();
writer.newLine();
writer.flush();
} catch (IOException e) {
System.out.println("Unable to write to file! Read the StackTrace below.");
e.printStackTrace();
}
try (BufferedWriter writer = Files.newBufferedWriter(path, charset)) {
String string = "line2";
writer.write(string, 0, string.length());
writer.flush();
} catch (IOException e) {
System.out.println("Unable to write to file! Read the StackTrace below.");
e.printStackTrace();
}
}
The output of this produces a text file as so:
line2
Now, I know I could just combine my two try/catches, and it would work. But this is just a test representation; in my real code, I need to do this separately so I can write in .txt files whenever specific events are triggered.
Basically, the newLine() methods are not saving unless I write text directly after them.
Any help is appreciated, as always!
The second BufferedWriter, or rather the second implicit FileWriter, overwrites the file created by the first one.
Combine the statements as you suggest, or use append mode (inefficient in this case).
How to write real time data to file in Java?
I'm trying to get real time twitter feed to text file. Here is a code that I have written:
public void onStatus(Status status)
{
User user = status.getUser();
BufferedWriter bufferedWriter = null;
try
{
bufferedWriter = new BufferedWriter(new FileWriter("c:\\twitterDumponFile.txt"));
String username = status.getUser().getScreenName();
bufferedWriter.write(username);
String profileLocation = user.getLocation();
bufferedWriter.write(profileLocation);
String content = status.getText();
bufferedWriter.write(content);
bufferedWriter.newLine();
}
catch (FileNotFoundException ex)
{
ex.printStackTrace();
}
catch (IOException ex)
{
ex.printStackTrace();
}
finally
{
//Closing the BufferedWriter
try
{
if (bufferedWriter != null)
{
bufferedWriter.flush();
bufferedWriter.close();
}
}
catch (IOException ex)
{
ex.printStackTrace();
}
}
}
When I open the file twitterDumponFile.txt it contains a single line of data. Everytime I open it it has a different data but a single line, it is not appending the new data on to the file.
Please help me where I'm getting wrong.
You need to open the FileWriter in append mode.
replace
bufferedWriter = new BufferedWriter(new FileWriter("c:\\twitterDumponFile.txt"));
by
bufferedWriter = new BufferedWriter(new FileWriter("c:\\twitterDumponFile.txt", true));
FileWriter("c:\\twitterDumponFile.txt")
This won't append the data to the file, it will write from the beginning of the file, use this instead :
FileWriter("c:\\twitterDumponFile.txt", true)
This will write to the end of the file rather than the beginning.
See the documentation of FileWriter.
You are overwriting the data already on the file instead of appending it.
Use API link to know how to append instead of overwriting...
It's always good way to use the api to know how and abouts of the methods and classes.
so I'm designing a text editor. For the Open/Save methods, I'm trying to use a TextArea (it doesn't have to be one, it's just my current method). Now, I have two problems right now:
1) When I load a file, it currently doesn't remove the contents currently in the text editor. For example, if I typed in "Owl", then loaded a file that contained "Rat", it would end up as "OwlRat". To solve this, I plan to use the replaceRange method (again however, it isn't absolute, any suggestions would be great!). However, I must replace all the contents of the text editor, not just selected text, and I can't figure out how to do that. Any tips?
2) Currently, when I load a file, nothing will happen unless I saved that file the same time I ran the application. So, for example, running the program, saving a file, closing the program, running the program again, and then loading the file will give nothing. I know this is because the String x doesn't carry over, but I can't think of anyway to fix it. Somebody suggested Vectors, but I don't see how they would help...
Here is the code for the Open/Save methods:
Open:
public void Open(String name){
File textFile = new File(name + ".txt.");
BufferedReader reader = null;
try
{
textArea.append(x);
reader = new BufferedReader( new FileReader( textFile));
reader.read();
}
catch ( IOException e)
{
}
finally
{
try
{
if (reader != null)
reader.close();
}
catch (IOException e)
{
}
}
}
Save:
public void Save(String name){
File textFile = new File(name + ".txt");
BufferedWriter writer = null;
try
{
writer = new BufferedWriter( new FileWriter(textFile));
writer.write(name);
x = textArea.getText();
}
catch ( IOException e)
{
}
finally
{
try
{
if ( writer != null)
writer.close( );
}
catch ( IOException e)
{
}
}
}
I had this same problem my guy friend, after much thought and research I even found a solution.
You can use the ArrayList to put all the contents of the TextArea and send as parameter by calling the save, as the writer just wrote string lines, then we use the "for" line by line to write our ArrayList in the end we will be content TextArea in txt file.
if something does not make sense, I'm sorry is google translator and I who do not speak English.
Watch the Windows Notepad, it does not always jump lines, and shows all in one line, use Wordpad ok.
private void SaveActionPerformed(java.awt.event.ActionEvent evt) {
String NameFile = Name.getText();
ArrayList< String > Text = new ArrayList< String >();
Text.add(TextArea.getText());
SaveFile(NameFile, Text);
}
public void SaveFile(String name, ArrayList< String> message) {
path = "C:\\Users\\Paulo Brito\\Desktop\\" + name + ".txt";
File file1 = new File(path);
try {
if (!file1.exists()) {
file1.createNewFile();
}
File[] files = file1.listFiles();
FileWriter fw = new FileWriter(file1, true);
BufferedWriter bw = new BufferedWriter(fw);
for (int i = 0; i < message.size(); i++) {
bw.write(message.get(i));
bw.newLine();
}
bw.close();
fw.close();
FileReader fr = new FileReader(file1);
BufferedReader br = new BufferedReader(fr);
fw = new FileWriter(file1, true);
bw = new BufferedWriter(fw);
while (br.ready()) {
String line = br.readLine();
System.out.println(line);
bw.write(line);
bw.newLine();
}
br.close();
fr.close();
} catch (IOException ex) {
ex.printStackTrace();
JOptionPane.showMessageDialog(null, "Error in" + ex);
}
There's a lot going on here...
What is 'x' (hint: it's not anything from the file!), and why are you appending it to the text area?
BufferedReader.read() returns one character, which is probably not what you're expecting. Try looping across readline().
Follow Dave Newton's advice to handle your exceptions and provide better names for your variables.
The text file will persist across multiple invocation of your program, so the lack of data has nothing to do with that.
Good luck.
Use textArea.setText(TEXT); rather than append; append means to add on to, so when you append text to a TextArea, you add that text to it. setText on the other hand will set the text, replacing the old text with the new one (which is what you want).
As far as why it's failing to read, you are not reading correctly. First of all, .read() just reads a single character (not what you want). Second, you don't appear to do anything with the returned results. Go somewhere (like here) to find out how to read the file properly, then take the returned string and do textArea.setText(readString);.
And like the others said, use e.printStackTrace(); in all of your catch blocks to make the error actually show up in your console.
I'm having memory problem as working with very large dataset and getting memory leaks with char[] and Strings, don't know why! So I am thinking of writing some processed data in a file and not store in memory. So, I want to write texts from an arrayList in a file using a loop. First the program will check if the specific file already exist in the current working directory and if not then create a file with the specific name and start writing texts from the arrayList line by line using a loop; and if the file is already exist then open the file and append the 1st array value after the last line(in a new line) of the file and start writing other array values in a loop line by line.
Can any body suggest me how can I do this in Java? I'm not that good in Java so please provide some sample code if possible.
Thanks!
I'm not sure what parts of the process you are unsure of, so I'll start at the beginning.
The Serializable interface lets you write an object to a file. Any object that implemsents Serializable can be passed to an ObjectOutputStream and written to a file.
ObjectOutputStream accepts a FileOutputStream as argument, which can append to a file.
ObjectOutputstream outputStream = new ObjectOutputStream(new FileOutputStream("filename", true));
outputStream.writeObject(anObject);
There is some exception handling to take care of, but these are the basics. Note that anObject should implement Serializable.
Reading the file is very similar, except it uses the Input version of the classes I mentioned.
Try this
ArrayList<String> StringarrayList = new ArrayList<String>();
FileWriter writer = new FileWriter("output.txt", true);
for(String str: StringarrayList ) {
writer.write(str + "\n");
}
writer.close();
// in main
List<String> SarrayList = new ArrayList<String>();
.....
fill it with content
enter content to SarrayList here.....
write to file
appendToFile (SarrayList);
.....
public void appendToFile (List<String> SarrayList) {
BufferedWriter bw = null;
boolean myappend = true;
try {
bw = new BufferedWriter(new FileWriter("myContent.txt", myappend));
for(String line: SarrayList ) {
bw.write(line);
bw.newLine();
}
bw.flush();
} catch (IOException ioe) {
ioe.printStackTrace();
} finally {
if (bw != null) try {
bw.close();
} catch (IOException ioe2) {
// ignore it or write notice
}
}
}
I have a result being entered into a file. This result is being done on a loop. So, every time a new result comes, it has to be appended into a file, but it is being overwritten. What should I use in order to append my results into a single file?
Try
BufferedWriter out = null;
try {
out = new BufferedWriter(new FileWriter("filename", true));
out.write("aString");
}
catch (IOException e) {
// handle exception
}
finally{
if(out != null){
try{
out.close();
}
catch(IOException e){
// handle exception
}
}
}
According to the API,
Constructs a FileWriter object given a
File object. If the second argument is
true, then bytes will be written to
the end of the file rather than the
beginning.
here is the basic snippet
FileWriter fstream = new FileWriter("out.txt",true);
BufferedWriter out = new BufferedWriter(fstream);
out.write("Hello Java 1");
out.write("Hello Java 2");
See Also
FileWritter - Javadoc
You should either keep the file open (sometimes it better, but usually not...) or open the output stream in append mode:
OutputStream os = new FileOutputStream(file, true);