How to Convert List<String[]> to Comma Separated String without " " in Java

Question

I'm trying to remove fist line from the CSV file after reading it. Code is working properly but it's adding "" to my data when it's rewriting. for an example:

before write to csv file: 100,COMRADE,CAMPBELL
after write to csv file: "100","COMRADE","CAMPBELL"

Here is the code.

========================================================================

public void deleteLineFromCsv() throws IOException {
        List<PatientsTabData> list = new ArrayList<>();
        BufferedReader reader = new BufferedReader(new FileReader(new File("src/main/resources/patients.csv")));
        String line = reader.readLine();
        while(line != null) {
            String[] split = line.split(",");
            list.add(new PatientsTabData().patientId(Integer.parseInt(split[0])).patName(split[1]).patLastName(split[2]));
            line = reader.readLine();
        }
        list.remove(0);
        CSVWriter writer = new CSVWriter(new FileWriter(new File("src/main/resources/patients.csv")));
        List<String[]> newlist = list.stream().map(item -> new String[]
                {String.valueOf(item.getPatientId()), item.getPatName(), item.getPatLastName()})
                .collect(Collectors.toList());
        writer.writeAll(newlist);
        writer.close();
    }

Library:

        <dependency>
            <groupId>net.sf.opencsv</groupId>
            <artifactId>opencsv</artifactId>
            <version>2.3</version>
        </dependency>

If your requirement is really just that: removing the first line from a file, then I would wouldnt use a csv reader/writer here. Just read the file line by line with a normal buffered reader, and omit writing the first line. — GhostCat
– GhostCat, Commented Mar 18, 2019 at 12:54
Please step back. I really dont understand what exactly you intend to achieve. I mean: what is the actual purpose of your code? What exactly goes in and is expected to happen? What data needs to be in the file, and "in memory" after the method ran? — GhostCat
– GhostCat, Commented Mar 18, 2019 at 12:57

Eritrean · Accepted Answer · 2019-03-18 13:03:42Z

1

You can use another constructor when creating your writer. Change

CSVWriter writer = new CSVWriter(new FileWriter(new File("src/main/resources/patients.csv")));

to

CSVWriter writer = new CSVWriter(new FileWriter(new File("src/main/resources/patients.csv")),',',CSVWriter.NO_QUOTE_CHARACTER);

answered Mar 18, 2019 at 13:03

Eritrean

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Syed Khalid Ahmed · Accepted Answer · 2019-03-18 12:20:28Z

0

this is the way to convert List to comma Seprated Single String.

List<String[]> oldList= . . . ;
String requiredString = oldList
.stream()
    .map(Arrays::asList)
    .flatMap(Collection::stream)
    .collect(Collectors.joining(","));

edited Mar 18, 2019 at 12:20

answered Mar 18, 2019 at 12:16

Syed Khalid Ahmed

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5 Comments

SanjX Over a year ago

what about this part (item -> new String[] {String.valueOf(item.getPatientId()), item.getPatName(), item.getPatLastName()}) ?

Syed Khalid Ahmed Over a year ago

@SanjX see my updated answer.. If you have List<String[]> then it converts in String comma seprated without "". perform above operation on your newList.

SanjX Over a year ago

it won't work like that. Because I'm using write.writeAll(); writeAll (java.util.List<java.lang.String[]>) in CSVWriter cannot be applied to (java.lang.String)

Syed Khalid Ahmed Over a year ago

@SanjX what is your title. Read again. I answered it according to your title.

SanjX Over a year ago

then how this person understood it correct :) stackoverflow.com/a/55222066/7758011 never mind thanks!

Umar Hussain · Accepted Answer · 2019-03-18 12:25:50Z

0

Your CSV writer is writing each element as string in the csv file. This can be by design in library as it will keep any comma in your data in the string and later will not add extra column if your data has comma as well.

"name","class","house, street, city","value"

See the documentation of your library and check if it provides the option to not treat every element as string.

But my opinion is to keep the strings in quotes to avoid data descripency during reads.

answered Mar 18, 2019 at 12:25

Umar Hussain

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