Develop Reference

How do I read a CSV File with JAVA

I have a probem, and I didnt find any solution yet. Following Problem: I have to read a CSV File which has to look like this:
First Name,Second Name,Age,
Lucas,Miller,17,
Bob,Jefferson,55,
Andrew,Washington,31,
The assignment is to read this CSV File with JAVA and display it like this:
First Name: Lucas
Second Name: Miller
Age: 17
The Attribut Names are not always the same, so it also could be:
Street,Number,Postal Code,ID,
Schoolstreet,93,20000,364236492,
("," has to be replaced with ";")
Also the file Adress is not always the same.
I already have the view etc. I only need the MODEL.
Thanks for your help. :))
I already have a FileChooser class in Controller, which returns an URI.

If your CSV file(s) always contains a Header Line which indicates the Table Column Names then it's just a matter of catching this line and splitting it so as to place those column names into a String Array (or collection, or whatever). The length of this array determines the amount of data expected to be available for each record data line. Once you have the Column Names it's gets relatively easy from there.
How you acquire your CSV file path and it's format type is obviously up to you but here is a general concept how to carry out the task at hand:
public static void readCsvToConsole(String csvFilePath, String csvDelimiter) {
String line; // To hold each valid data line.
String[] columnNames = new String[0]; // To hold Header names.
int dataLineCount = 0; // Count the file lines.
StringBuilder sb = new StringBuilder(); // Used to build the output String.
String ls = System.lineSeparator(); // Use System Line Seperator for output.
// 'Try With Resources' to auto-close the reader
try (BufferedReader br = new BufferedReader(new FileReader(csvFilePath))) {
while ((line = br.readLine()) != null) {
// Skip Blank Lines (if any).
if (line.trim().equals("")) {
continue;
}
dataLineCount++;
// Deal with the Header Line. Line 1 in most CSV files is the Header Line.
if (dataLineCount == 1) {
/* The Regular Expression used in the String#split()
method handles any delimiter/spacing situation.*/
columnNames = line.split("\\s{0,}" + csvDelimiter + "\\s{0,}");
continue; // Don't process this line anymore. Continue loop.
}
// Split the file data line into its respective columnar slot.
String[] lineParts = line.split("\\s{0,}" + csvDelimiter + "\\s{0,}");
/* Iterate through the Column Names and buld a String
using the column names and its' respective data along
with a line break after each Column/Data line. */
for (int i = 0; i < columnNames.length; i++) {
sb.append(columnNames[i]).append(": ").append(lineParts[i]).append(ls);
}
// Display the data record in Console.
System.out.println(sb.toString());
/* Clear the StringBuilder object to prepare for
a new string creation. */
sb.delete(0, sb.capacity());
}
}
// Trap these Exceptions
catch (FileNotFoundException ex) {
System.err.println(ex.getMessage());
}
catch (IOException ex) {
System.err.println(ex.getMessage());
}
}
With this method you can have 1 to thousands of columns, it doesn't matter (not that you would ever have thousands of data columns in any given record but hey....you never know... lol). And to use this method:
// Read CSV To Console Window.
readCsvToConsole("test.csv", ",");

Here is some code that I recently worked on for an interview that might help: https://github.com/KemarCodes/ms3_csv/blob/master/src/main/java/CSVProcess.java
If you always have 3 attributes, I would read the first line of the csv and set values in an object that has three fields: attribute1, attribute2, and attribute3. I would create another class to hold the three values and read all the lines after, creating a new instance each time and reading them in an array list. To print I would just print the values in the attribute class each time alongside each set of values.

Remove stop words from file - going over it multiple times causes content duplication and does not remove the words

I am trying to go over a bunch of files, read each of them, and remove all stopwords from a specified list with such words. The result is a disaster - the content of the whole file copied over and over again.
What I tried:
- Saving the file as String and trying to look with regex
- Saving the file as String and going over line by line and comparing tokens to the stopwords that are stored in a LinkedHashSet, I can also store them in a file
- tried to twist the logic below in multiple ways, getting more and more ridiculous output.
- tried looking into text / line with the .contains() method, but no luck
My general logic is as follows:
for every word in the stopwords set:
while(file has more lines):
save current line into String
while (current line has more tokens):
assign current token into String
compare token with current stopword:
if(token equals stopword):
write in the output file "" + " "
else: write in the output file the token as is
Tried what's in this question and many other SO questions, but just can't achieve what I need.
Real code below:
private static void removeStopWords(File fileIn) throws IOException {
File stopWordsTXT = new File("stopwords.txt");
System.out.println("[Removing StopWords...] FILE: " + fileIn.getName() + "\n");
// create file reader and go over it to save the stopwords into the Set data structure
BufferedReader readerSW = new BufferedReader(new FileReader(stopWordsTXT));
Set<String> stopWords = new LinkedHashSet<String>();
for (String line; (line = readerSW.readLine()) != null; readerSW.readLine()) {
// trim() eliminates leading and trailing spaces
stopWords.add(line.trim());
}
File outp = new File(fileIn.getPath().substring(0, fileIn.getPath().lastIndexOf('.')) + "_NoStopWords.txt");
FileWriter fOut = new FileWriter(outp);
Scanner readerTxt = new Scanner(new FileInputStream(fileIn), "UTF-8");
while(readerTxt.hasNextLine()) {
String line = readerTxt.nextLine();
System.out.println(line);
Scanner lineReader = new Scanner(line);
for (String curSW : stopWords) {
while(lineReader.hasNext()) {
String token = lineReader.next();
if(token.equals(curSW)) {
System.out.println("---> Removing SW: " + curSW);
fOut.write("" + " ");
} else {
fOut.write(token + " ");
}
}
}
fOut.write("\n");
}
fOut.close();
}
What happens most often is that it looks for the first word from the stopWords set and that's it. The output contains all the other words even if I manage to remove the first one. And the first will be there in the next appended output in the end.
Part of my stopword list
about
above
after
again
against
all
am
and
any
are
as
at
With tokens I mean words, i.e. getting every word from the line and comparing it to the current stopword

After awhile of debugging I believe I have found the solution. This problem is very tricky as you have to use several different scanners and file readers etc. Here is what I did:
I changed how you added to your StopWords set, as it wasn't adding them correctly. I used a buffered reader to read each line, then a scanner to read each word, then added it to the set.
Then when you compared them I got rid of one of your loops as you can easily use the .contains() method to check if the word was a stopWord.
I left you to do the part of writing to the file to take out the stop words, as I'm sure you can figure that out now that everything else is working.
-My sample stop words txt file:
Stop words
Words
-My samples input file was the exact same, so it should catch all three words.
The code:
// create file reader and go over it to save the stopwords into the Set data structure
BufferedReader readerSW = new BufferedReader(new FileReader("stopWords.txt"));
Set<String> stopWords = new LinkedHashSet<String>();
String stopWordsLine = readerSW.readLine();
while (stopWordsLine != null) {
// trim() eliminates leading and trailing spaces
Scanner words = new Scanner(stopWordsLine);
String word = words.next();
while(word != null) {
stopWords.add(word.trim()); //Add the stop words to the set
if(words.hasNext()) {
word = words.next(); //If theres another line, read it
}
else {
break; //else break the inner while loop
}
}
stopWordsLine = readerSW.readLine();
}
BufferedReader outp = new BufferedReader(new FileReader("Words.txt"));
String line = outp.readLine();
while(line != null) {
Scanner lineReader = new Scanner(line);
String line2 = lineReader.next();
while(line2 != null) {
if(stopWords.contains(line2)) {
System.out.println("removing " + line2);
}
if(lineReader.hasNext()) { //If theres another line, read it
line2 = lineReader.next();
}
else {
break; //else break the first while loop
}
}
lineReader.close();
line = outp.readLine();
}
OutPut:
removing Stop
removing words
removing Words
Let me know if I can elaborate any more on my code or why I did something!

Searching a text file in java and Listing the results

I've really searched around for ideas on how to go about this, and so far nothing's turned up.
I need to search a text file via keywords entered in a JTextField and present the search results to a user in an array of columns, like how google does it. The text file has a lot of content, about 22,000 lines of text. I want to be able to sift through lines not containing the words specified in the JTextField and only present lines containing at least one of the words in the JTextField in rows of search results, each row being a line from the text file.
Anyone has any ideas on how to go about this? Would really appreciate any kind of help. Thank you in advance

You can read the file line by line and search in every line for your keywords. If you find one, store the line in an array.
But first split you text box String by whitespaces and create the array:
String[] keyWords = yourTextBoxString.split(" ");
ArrayList<String> results = new ArrayList<String>();
Reading the file line by line:
void readFileLineByLine(File file) {
BufferedReader br = new BufferedReader(new FileReader(file));
String line;
while ((line = br.readLine()) != null) {
processOneLine(line);
}
br.close();
}
Processing the line:
void processOneLine(String line) {
for (String currentKey : keyWords) {
if (line.contains(currentKey) {
results.add(line);
break;
}
}
}
I have not testst this, but you should get a overview on how you can do this.
If you need more speed, you can also use a RegularExpression to search for the keywords so you don't need this for loop.

Read in file, as per the Oracle tutorial, http://docs.oracle.com/javase/tutorial/essential/io/file.html#textfiles Iterate through each line and search for your keyword(s) using String's contain method. If it contains the search phrase, place the line and line number in a results List. When you've finished you can display the results list to the user.

You need a method as follows:
List<String> searchFile(String path, String match){
List<String> linesToPresent = new ArrayList<String>();
File f = new File(path);
FileReader fr;
try {
fr = new FileReader(f);
BufferedReader br = new BufferedReader(fr);
String line;
do{
line = br.readLine();
Pattern p = Pattern.compile(match);
Matcher m = p.matcher(line);
if(m.find())
linesToPresent.add(line);
} while(line != null);
br.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return linesToPresent;
}
It searches a file line by line and checks with regex if a line contains a "match" String. If you have many Strings to check you can change the second parameter to String[] match and with a foreach loop check for each String match.

You can use :
FileUtils
This will read each line and return you a List<String>.
You can iterate over this List<String> and check whether the String contains the word entered by the user, if it contains, add it to another List<String>. then at the end you will be having another List<String> which contains all the lines which contains the word entered by the user. You can iterate this List<String> and display the result to the user.

Read text file and split each newline into a string array

So basically I'm reading a text file that has a bunch of lines. I need to extract certain lines from the text file and add those specific lines into string array. I've been trying to split each newLine with: "\n" , "\r". This did not work. I keep getting this error as well:
Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException: 1
at A19010.main(A19010.java:47)
Here is the code:
Path objPath = Paths.get("dirsize.txt");
if (Files.exists(objPath)){
File objFile = objPath.toFile();
try(BufferedReader in = new BufferedReader(
new FileReader(objFile))){
String line = in.readLine();
while(line != null){
String[] linesFile = line.split("\n");
String line0 = linesFile[0];
String line1 = linesFile[1];
String line2 = linesFile[2];
System.out.println(line0 + "" + line1);
line = in.readLine();
}
}
catch(IOException e){
System.out.println(e);
}
}
else
{
System.out.println(
objPath.toAbsolutePath() + " doesn't exist");
}

String[] linesFile = new String[] {line}; // this array is initialized with a single element
String line0 = linesFile[0]; // fine
String line1 = linesFile[1]; // not fine, the array has size 1, so no element at second index
String line2 = linesFile[2];
You're creating a String[] linesFile with one element, line, but then trying to access elements at index 1 and 2. This will give you an ArrayIndexOutOfBoundsException
You're not actually splitting anything here. in.readLine();, as the method says, reads a full line from the file.
Edit: You can add lines (Strings) dynamically to a list instead of an array, since you don't know the size.
List<String> lines = new LinkedList<String>(); // create a new list
String line = in.readLine(); // read a line at a time
while(line != null){ // loop till you have no more lines
lines.add(line) // add the line to your list
line = in.readLine(); // try to read another line
}

readLine() method reads a entire line from the input but removes the newLine characters from it. When you split the line on \n character, you will not find one in the String. Hence, you get the exception.
Please, refer the answer in this link for more clarity.

You are initializing your String array with 1 element, namely line. linesFile[0] is therefore line and the rest of your array is out of bounds.

Try this:
String[] linesFile = line.split("SPLIT-CHAR-HERE");
if(linesFile.length >= 3)
{
String line0 = linesFile[0];
String line1 = linesFile[1];
String line2 = linesFile[2];
// further logic here
}else
{
//handle invalid lines here
}

You are using array to store the strings. Instead use ArrayList from Java as ArrayList are dynamically growing. after your reading operation completes convert it into array.
String line = in.readLine();
ArrayList<String> str_list = new ArrayList<String>();
String[] strArr = new String[str_list.size()];
while(line != null){
str_list.add(line);
line = in.readLine();
}
// at the end of the operation convert Arraylist to array
return str_list.toArray(strArr);

The issue here is that you are creating a new String array every time your parser reads in a new line. You then populate only the very first element in that String array with the line that is being read in with:
String[] linesFile = new String[] {line};
Since you create a new String[] with one element every single time your while loop runs from the top, you lose the values it stored from the previous iteration.
The solution is to use new String[]; right before you enter the while loop. If you don't know how to use ArrayList, then I suggest a while loop like this:
int numberOfLine = 0;
while (in.readLine() != null)
{
numberOfLine++;
}
String linesFile = new String[numberOfLine];
This will let you avoid using a dynamically resized ArrayList because you know how many lines your file contains from the above while loop. Then you would keep an additional counter (or resuse numberOfLine since we have no use for it anymore) so that you can populate this array:
numberOfLine = 0;
in = new BufferedReader(new FileReader(objFile)); // reset the buffer
while ((String line = in.readLine()) != null)
{
linesFile[numberOfLine] = line;
numberOfLine++;
}
At this point linesFile should be correctly populated with the lines in your file, such that linesFile[i] can be used to access the i'th line in the file.

Read two lines of CSV at a time (Java)

Is there a way to read two lines of a csv file at a time in Java?
I can read one at a time using Scanner (it has to be done like this):
String line = input.nextLine();
String[] nline = line.split ("[,]");
......
Here is some sample data and a short explanation. I need these read two at a time so I can can go about my other processing.
the first line that starts with "Create" creates a person
the second line "action" is the action of the created person
create,Mr. Jones,blah,blah
action,1,3
create,Mrs.Smith,blah,blah
action,4,10
....
Thanks in advance.

If you're looking to parse CSV files in Java I'd avoid line split via the string.split() method. You can run into issues if your field contains commas. For Java I'd recommend opencsv to parse the data. Similar to using the scanner you can read it in line by line, or slurp the entire file if it's not too large, and just iterate over the list to items at a time.
CSVReader reader = ...
String[] firstLine; // fields from first line
String[] secondLine; // fields from second line
while ((firstLine = reader.next()) != null && (secondLine = reader.next()) != null) {
// do something with two lines
}
Or
CSVReader reader = ...
List<String[]> allLines = reader.readAll();
// TODO: validate we have an even number of lines
for (int i = 0; i < allLines.size(); i += 2) {
String[] firstLine = allLines.get(i);
String[] secondLine = allLines.get(i+1);
// do something with two lines
}

String line = input.nextLine() + input.nextLine();

Cory's answer is good but for your next part to work
String[] nline = line.split ("[,]");
......
You need to add the comma in there
String line = input.nextLine() + "," + input.nextLine();