I have an file, where I am writing data to it. I've tried googling, but all examples I have tried have just confused me more.
I am inputting data into a file, and this is happening correctly, where the items selected are being appended to the file. Where my issue is, is that I want to check whether the string being inputted already exists in the file, and if it does, I want to skip it.
The code I am using to input the data to the file is below, but I am not sure how to change it to check for a duplicate.
for (EventsObj p : boxAdapter.getBox()) {
if (p.box){
String result = p.name + " " + p.price;
try {
// open file for writing
OutputStreamWriter out= new OutputStreamWriter(openFileOutput("UserEvents.txt",MODE_APPEND));
// write the contents to the file
out.write(result);
out.write('\n');
// close the file
out.close();
}
catch (java.io.IOException e) {
//do something if an IOException occurs.
Toast.makeText(this, "Sorry Text could't be added", Toast.LENGTH_LONG).show();
}
}
}
It is getting the checkboxes ticked, then getting the name and price related to it and appending it to file. But I want to carry out a check that this does not already exist. Any help would be appreciated and I've exhausted google and tried many things.
So, if I understood your question correctly the file contains a number of strings delimited by newline.
What you want to do is to read the file contents line by line, and store the lines in a HashSet<String>. Then, you open the file for appending and append the additional string, but only if the file did not contain the string already. As the other answer suggested, you use the contains method. However, unlike the other answer I'm not suggesting to use a list of strings; instead, I'm suggesting the use of a HashSet as it's more efficient.
While reading the file contents line by line, you can perform some basic checks: does the file already contain duplicate rows? You may want to handle those by giving the user a warning that the file format is invalid. Or you may want to proceed nevertheless.
You should firstly read from the file and create a list of strings with all your inputs.
Then before adding to the file you can check if the list of strings contains the string you want to add (just make sure that the strings share the same format such that a match will be found). If it returns false add to the file, if yes don't add to the file.
Shouldn't be such a tremendous task. You can make use of the contains method.
You might need to keep the contents of the file in a String in your program. A little inefficient, but at the moment I do not see any other way but to keep track of things in your program instead of on the file.
So before you run the program which appends text to the file, the very first thing you should probably do is parse the file for all text:
File yourFile = new File("file-path-goes-here");
Scanner input = null;
try {
input = new Scanner (new FileInputStream(yourFile) );
}
catch (FileNotFoundException e) {;;;}
String textFromFile = "";
while (input.hasNextLine())
textFromFile += input.nextLine() + "\n";
//Now before adding to the file simply run something like this
if(textFromFile.indexOf("string-to-write-to-file") != -1)
;//do not write to file
else {
;//write to file and add to textFromFile
textFromFile += "string-you-added-to-file" + "\n";
}
Hope this answers your question. Let me know if something is not clear.
Related
I have one csv with one row who have diferent users (users.csv), in the other hand I also have a csv with users (users2.csv)..
The problem is that I want to "compare?" these two documents and discard users from users2.csv to users1.csv if they exist in this file.
Please ideas or advice, how could I do it??
Load the first file into a List<String> users.
Load the second file into a List<String> users2.
use apache commons-collections CollectionUtils.removeAll(Collection<E> users, Collection<?> users2)
To load a file in a list you can find inspiration here.
Et voilà.
This only works if the size of the files is acceptable to load in memory. Otherwise it requires another approach like sorting both files using command line sort commands and walk through both files reading line by line and decide to write to output or not.
You can use BeyondCompare to compare the two csvs. It will distinctively identify the missing user along with other data mismatch if any. In case if you want to do it programatically, you can create a user bean (and override equals method to compare username or any other you want) after copying csv into list/map of beans.
Best way I see,
1) Read both the files using Java NIO Api (That's actually very fast)separately and store them into list.
Path path = Paths.get("src/main/resources/shakespeare.txt");
try {
Files.lines(path).forEach(System.out::println);//print each line
} catch (IOException ex) {
ex.printStackTrace();//handle exception here
}
2) Compare both list using java 8 predictor.
public static List < String > filterAndGetEmployees(List < String> employees,
Predicate < String > predicate) {
return list.stream().filter(predicate).collect(Collectors. < String > toList());
}
3) If you wish to write file again , You can go like,
Path path = Paths.get("src/main/resources/shakespeare.txt");
try(BufferedWriter writer = Files.newBufferedWriter(path, Charset.forName("UTF-8"))){
writer.write("To be, or not to be. That is the question.");
}catch(IOException ex){
ex.printStackTrace();
}
Hope this will help you..
What I am trying to do is write a record to new line in my text file. Every time someone clicks sign up on my program, I want to call a method that opens a file and adds a record. This is what I have now:
To open the file:
try {
l = new Formatter("chineses.txt");
System.out.println("Did create");
} catch (Exception e){
System.out.println("Did not create");
}
To add the record:
public void addRecord(){
l.format("%s", nameField.getText());
}
Every time I put in a name in the name field and click sign up in my GUI, it always replaces whatever is on the first line in the text file.
How can I make it write to the second line while retaining what is on the first line?
Have you thought about using RandomAccessFile? You can seek to the end, then write.
According to the javadoc a formater created with a single String argument will first empty the file (truncate to zero length) before writing to it. This is why your file is not appended to. The program first removes whatever is in the file and then writes the new content to it when you call l.format().
What you probably want to do is format your data to a String using Formatter(). Open your record file for appending and then write that string to the file. This link should have plenty of details on how you might do this. (I googled "java open and write a file" to find that resource)
I was wondering how to make the program show a specific text it's ran by the first time, I know in android programming, a way to do this is by making a specification in the manifest. So I hope you'd understand me and can help me.
If you need to create a flag file use this
String FLAG_PTH="path/to file/flag.txt";
String flag="";
Use this code at load event of the page
try{
byte[] bfr=new byte[50];
FileInputStream IPS=new FileInputStream(COL_PTH);
int tn=0;
int nread=0;
while((nread=IPS.read(bfr))!=-1){
String clr=new String(bfr);
flag=clr;
}
IPS.close();
}
catch(FileNotFoundException fe){
System.out.println("ERR:9"+fe);
}
catch(IOException IOe){
System.out.println("ERR:10"+IOe);
}
if(flag=="True"){
// type your code for showing some text,or whatever it is.
try{
FileWriter FW=new FileWriter(FLAG_PTH);
BufferedWriter BF_Wr=new BufferedWriter(FW);
BF_Wr.write("TRUE");
BF_Wr.close();
}
catch(IOException e){
System.out.println("ERR:06"+e);
}
}
else {
//hide text and go through normal open
}
Well, I would have a text file with the word false in it,right at the top.Then in the programme you read that line, if it reads true then make it display whatever text you wish.After that you delete the file and make a new one(inside the if statement) with the same name only with true at the top this time.Therefore that if statement can only run again if that text file is changed to true.This is going to need buffered streams so read up on that: https://docs.oracle.com/javase/tutorial/essential/io/index.html .Alsojust a piece of advice keep all of your resources inside your jar file in a source folder as best as you can(its a lot less easier for users to mess with) doing this will cause you to need to use getResourceAsStream : https://m.youtube.com/watch?v=yksgU4SxoJY .I assure you it won't take long to go throught this.
I want to write a few arguments in a .txt file and I want to sort them. To do that I want to go to the next line for every groop of arguments but I dont know how to do that.I have tried the:
x.nextLine();
statement, but that is only for scanning and not for formatting.
How can I go to the next line of a file while formatting? Is there another statement for that?
This is the code I created:
try{
w = new Formatter("data.txt");
}
catch(Exception e){
JOptionPane.showMessageDialog(null, "Fatal Error, please Reboot or reinstal program", "Error", JOptionPane.PLAIN_MESSAGE);
}
w.format("%s,%s,%s,%s%n", book,code,author,editor);
w.close();
You write
w.format("%s,%s,%s,%s%n", book,code,author,editor);
and I assume you want a newline where you write %n. But newline is \n, so change your code to
w.format("%s,%s,%s,%s\n", book,code,author,editor);
Also, you may want to revise the error catching logic in the program: right now if opening the file fails, you show an error message, which is good, but after that your program continues execution and will crash and burn on the first write operation...
EDIT: every time you execute the line w.format("%s,%s,%s,%s\n", book,code,author,editor); a line terminated by a new line will be added to the file, as long as you don't close the file or restart the program, because the Javadoc for the constructor you use says:
fileName - The name of the file to use as the destination of this formatter. If the file exists then it will be truncated to zero size; otherwise, a new file will be created. The output will be written to the file and is buffered.
So, if you need a file that grows instead of being overwritten you should use one of the other available constructors, eg one accepting an Appendable as argument. This would lead to the following code:
FileWriter fstream = new FileWriter("data.txt",true);
Formatter w = new Formatter(fstream);
// do whatever your program needs to do
w.close();
Of course surrounded by the necessary exception handling.
I work on query latencies and have a requirement where I have several files which contain data. I want to aggregate this data into a single file. I use a naive technique where I open each file and collect all the data in a global file. I do this for all the files but this is time taking. Is there a way in which you can stitch the end of one file to the beginning of another and create a big file containing all the data. I think many people might have faced this problem before. Can anyone kindly help ?
I suppose you are currently doing the opening and appending by hand; otherwise I do not know why it would take a long time to aggregate the data, especially since you describe the amount of files using multiple and several which seem to indicate it's not an enormous number.
Thus, I think you are just looking for a way to automatically to the opening and appending for you. In that case, you can use an approach similar to below. Note this creates the output file or overwrites it if it already exists, then appends the contents of all specified files. If you want to call the method multiple times and append to the same file instead of overwriting an existing file, an alternative is to use a FileWriter instead with true as a second argument to its constructor so it will append to an existing file.
void aggregateFiles(List<String> fileNames, String outputFile) {
PrintWriter writer = null;
try {
writer = new PrintWriter(outputFile);
for(String fileName : fileNames) {
Path path = Paths.get(fileName);
String fileContents = new String(Files.readAllBytes(path));
writer.println(fileContents);
}
} catch(IOException e) {
// Handle IOException
} finally {
if(writer != null) writer.close();
}
}
List<String> files = new ArrayList<>();
files.add("f1.txt");
files.add("someDir/f2.txt");
files.add("f3.txt");
aggregateFiles(files, "output.txt");