This question already has answers here:
How to append text to an existing file in Java?
(31 answers)
Java: How to read a text file
(9 answers)
Closed 5 years ago.
I have a txt file that I want to load into Java, and I've been trying to use
PrintWriter writer = new PrintWriter(new File("location/name.txt"));
But instead of loading the existing file, it writes over the old one and creates a new blank one. How can I load the existing file into Java?
You must use a Reader instead of Writer.
There are various ways to read a text file in Java e.g. you can use FileReader, BufferedReader or Scanner to read a text file. Each class has its own purpose e.g. BufferedReader is used to buffer data for reading fast, and Scanner provides parsing ability.
Example using BufferedReader :
public class ReadFile {
public static void main(String[] args)throws Exception
{
File file = new File("C:\\location\\test.txt");
BufferedReader br = new BufferedReader(new FileReader(file));
String st;
while ((st = br.readLine()) != null)
System.out.println(st);
}
}
I think this is what you want:
try(PrintWriter pw = new PrintWriter(new BufferedWriter(new FileWriter("location/yourFileName.txt", true)))) {
pw.println("what you want to write to the file");
pw.close();
} catch (IOException e) {
//Exception handling goes here.
}
The FileWriter constructor's second argument is what sets the append condition. Also, as stated in the comments(and pretty obvious) that you need a reader to load or input data.
You can try
File f = new File(filePathString);
Related
This question already has answers here:
How to append text to an existing file in Java?
(31 answers)
Closed 2 years ago.
Im trying to add multiple strings to a file.
FileWriter myWriter = new FileWriter("cache.txt");
BufferedWriter bw=new BufferedWriter(myWriter);
bw.write(marker);
bw.newLine();
bw.close();
But whenever I write a new String it keeps overriding.
So I only have one string in my file.
How would I make it add a new line to the file.
Here is an example
What should happen.
file(cache.txt):
fd174d5b4bbc85295a649f9d70a4adf4
9b854017b04d62732ac00f2ee8007968
...
What happens for me
file(cache.txt):
9b854017b04d62732ac00f2ee8007968(last entry)
Because that's what BufferedWriter's .write is supposed to do.
If the file doesn't exists, create and write to it.
If the file exists, truncate (remove all content) and write to it
To append, use this:
try {
PrintWriter out = new PrintWriter(new BufferedWriter(new FileWriter("myfile.txt", true)));
out.println("text");
out.close();
} catch (IOException e) {
//exception handling
}
Use the "append" flag to the FileWriter constructor:
FileWriter myWriter = new FileWriter("cache.txt", true);
Otherwise the file will be reset to the beginning each time it is opened.
This question already has answers here:
How do I create a file and write to it?
(35 answers)
Closed 4 years ago.
It seems fine but the the content is not write into file with write() method. I ask the user input with JoptionPane and add that data to ArrayList . The data is added , but when I try to output that data into file, it's not write to file.
public class fileArray {
public static void main(String[] args) throws IOException {
ArrayList al = new ArrayList();
File f =new File("notworking.txt");
String names = " ";
while(!names.isEmpty())
{
names=JOptionPane.showInputDialog("EnterName");
if(!names.isEmpty()){
al.add(names);}
}
FileWriter fw = new FileWriter(f.getAbsoluteFile());
BufferedWriter bw = new BufferedWriter(fw);
int sz= al.size();
for(int i =0;i<sz;i++){
bw.write((String) al.get(i));
System.out.println(al.get(i));
}
}
}
You need to close the writer after you are done with writing.
bw.close();
Either you have to flush or close the buffer afte you write to the file. Better you close the buffer in finally block, make it habit to close the buffer in finally block.
sample code:
PrintWriter writer = new PrintWriter("the-file-name.txt", "UTF-8");
writer.println("The first line");
writer.println("The second line");
writer.close(); // CLOSE
This question already has answers here:
Reading a plain text file in Java
(31 answers)
Closed 5 years ago.
I have text file which i have read once user upload, how can i read using java code, can any one give some suggestion which would very helpful to me
sample file looks like below
SNR Name
1 AAR
2 BAT
3 VWE
A common pattern is to use
try (BufferedReader br = new BufferedReader(new FileReader(file)) ) {
String line;
while ((line = br.readLine()) != null) {
// process the line to insert in database.
}}
The easiest way is use Scanner() object
Scanner sc = new Scanner(new File("myFile.txt"));
use
boolean hasNext = sc.hasNext();
to know if there are more items in the file
and
String item = sc.next();
to get items secuentially.
I attach the documentation (it provides very good code examples)
https://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html
You can use BufferedReader to read file line by line.
So, even if your file is too big, then also it will read line by line only. It won't load entire file. Declaration will be similar to this.
BufferedReader br = new BufferedReader(new FileReader(FILENAME));
And
you can use command
while ((sCurrentLine = br.readLine()) != null) { .....// process
}
to read file till end.
Obviously, you have to use seperator in file to split the records in each line. And store accordingly in java objects.
After that you can store in DB through DAO.
This question already has answers here:
How to append text to an existing file in Java?
(31 answers)
Closed 6 years ago.
How can I write a new row of data to a .CSV file that already has data in it. So far my code just clears the file and doesn't actually write anything?
BufferedReader br = null;
BufferedWriter bw = null;
String fileString = "patients.csv";
String fileLine = "";
File file = new File(fileString);
br = new BufferedReader(new FileReader(file));
FileWriter fw = new FileWriter(fileString);
bw = new BufferedWriter(fw);
while((fileLine = br.readLine()) != null){
bw.write(fileLine);
}
br.close();
bw.close();
specify true in the constructor java FileWriter to know that the true and append be added to the end of the file if you place it does not overwrite information
FileWriter fw = new FileWriter(fileString,true);
If you want to append to a file using FileWriter then use this Constructor
As per Javadocs
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.
But, back to your code, you will only need to write new data to the FileWriter and not rewrite existing data.
This question already has answers here:
PrintWriter append method not appending
(5 answers)
Closed 9 years ago.
So I got this piece of code in my Java program;
String filename = "direct.txt";
String s = fil.getAbsolutePath();
Process p = Runtime.getRuntime().exec(s);
try
{
PrintWriter outputStream = new PrintWriter(filename);
outputStream.println(s);
outputStream.close();
}
catch (FileNotFoundException e1) {e1.printStackTrace();};
But when it writes to the file, it overwrites it when it writes something new, how can I make it so it doesn't overwrite but instead goes to the next line and prints it there?
You could make a FileWriter object and pass it as an argument when making the PrintWriter object. That way if the file already exists then it won't be overwritten, but if it does not exist then it will be created. From there you can use the PrintWriter methods as normal:
FileWriter objectName = new FileWriter("filename", true);
PrintWriter outputStream = new PrintWriter(objectName);