java write the list string into csv file

问题

I have some array strings like the following (note that there is space after each player which shows different lines...),

["user1","track1","player1", "user1","track2","player2", "user1","track3","player3", ...]

I would like to divide this array into two parts (almost equal) based on the number of lines (spaces here). So, for example if there is 40 spaces in this array, I need to store the lines starting from the first to the half(20th line) in a file (let's call it file A) and put the rest in file B. I could divide the arraylist, but I could not write it in the correct way in the CSV file.

Here is my code:

public static void main(String[] args) throws java.lang.Exception { 
BufferedReader userlines = new BufferedReader(new FileReader("/..../usertrackplayer.csv"));       
FileWriter output = new FileWriter(new File("/.../output.csv"));

String uLine = null;    
ArrayList<String> list = new ArrayList<String>();
List<String> arrayList = new ArrayList<String>();
String currentUserId = null;        

while ((uLine = userlines.readLine()) != null) {

    String[] userData = uLine.split(",");
    String userId = userData[0];            
    if (userId.equals(currentUserId)) {
      // Do what ever we need while buffering same userId               
    }
    else{
        list.add(uLine);
        int division = (int) Math.ceil(list.size()/2);

        List<String> sublist = list.subList(0, division); //TO DEVIDE THE DATA OF EACH USERID INTO TWO ALMOST EQUAL PARTS, IT PUT THE FIRST HALF IN SUBLIST

     //HERE I NEED TO WRITE THE OUTPUT OF SUBLIST INTO A CSV FILE, BUT HOW????
            output.write(sublits); //--> THIS DOES NOT WORK SINCE SUBLIST IS NOT A STRING
            currentUserId = userId;
            list.clear();
    }       
     list.add(uLine);
}
    userlines.close();
    output.close();
}

Could someone please help me know how could I write the data in a list string into an empty csv file?? My second question is: how could I split them wherever there is space and consider it as a line..

Thanks,

回答1:

have you considered using OpenCSV for writing your values:http://opencsv.sourceforge.net/

There is an example of how to write CSV files and it is very easy.

As to your problem, it appears you can't write the values because the Arraylist toString method will not return a comma separated string. You can use this:

public static void main(String[] args) throws IOException {

    FileWriter writer = new FileWriter("/Users/artur/tmp/csv/sto1.csv");

    List<String> test = new ArrayList<>();
    test.add("Word1");
    test.add("Word2");
    test.add("Word3");
    test.add("Word4");

    String collect = test.stream().collect(Collectors.joining(","));
    System.out.println(collect);

    writer.write(collect);
    writer.close();

}

See the collector impl - it will collect all String objects and concatinate them, using the separator you provide. The output then loolks like:

Word1,Word2,Word3,Word4

I hope that fixes your problem. Let me know if something's not clear.

Artur

Edit 2, for your question.

If your input is a String that you read, you can split it by the space first to get it in separated lines. If it is an actual array, it won't work. This is my example:

public static void main(String[] args) throws IOException {

        String input = "[\"user1\",\"track1\",\"player1\", \"user1\",\"track2\",\"player2\", \"user1\",\"track3\",\"player3\"]";
        input = input.substring(1, input.length() - 1); // get rid of brackets
        String[] split = input.split(" ");

        FileWriter writer = new FileWriter("/Users/artur/tmp/csv/sto1.csv");

        for(String s : split) {
            String[] split2 = s.split(",");
            writer.write(Arrays.asList(split2).stream().collect(Collectors.joining(",")));
            writer.write("\n"); // newline
        }

        writer.close();

    }

The resulting file looks like this:

"user1","track1","player1"
"user1","track2","player2"
"user1","track3","player3"

来源：https://stackoverflow.com/questions/35749250/java-write-the-list-string-into-csv-file

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java

arrays

csv

writer