Read and write CSV files with opencsv files

First understand what the CSV file looks for:

• Open in Excel becomes a table, you can not see the details
• It is recommended to use other simple and crude editors, such as notepad++,

The contents of the CSV file are as follows:

The CSV file is separated by commas by default.

Get a basic understanding of the topic, read and write CSV files with Opencsv

• READ: Csvreader
• Written by: Csvwriter

Here's a look at the methods Opencsv provides for us (here are just a few of the most common):

READ: Csvreader

There are three parameters involved in a constructor:

• Reader: Is the stream object that reads the file, commonly has bufferedreader,inputstreamreader and so on
• Separator: Used to define the delimiter mentioned earlier, the default is comma "csvwriter. Default_separator "for separating columns;
• QuoteChar: Used to define the quotation marks for each column, sometimes the CSV file will enclose a column in quotation marks or other symbols, such as a row may be: "1", "2", "3", if the character you want to read does not include quotation marks, you can set the parameter to: "csvwriter. No_quote_character "

A csvreader that defines a comma as a delimiter and ignores quotes when Read is:

Csvreader reader = new Csvreader (new InputStreamReader (New FileInputStream (CSVFile), "GBK"), Csvwriter.default_ SEPARATOR, Csvwriter.no_quote_character);

The second method in the table above is relatively inferior to the other three, and close () does not say much,

• ReadAll (): Read all
• Readnext (): reads a row

Note: If the first Readnext, and then Readall,readall also from the Readnext after the line began, that is, Readnext read it will not read again.

Written by: Csvwriter

Constructors and methods are relatively easy to understand, and reader can correspond to understand, there is not much to say.

Here's a simple example:

 Public classOpencsv { Public Static voidMain (string[] args)throwsException {opencsv oc=Newopencsv (); Oc.        Csvreadall (); Oc.    Csvwriter (); }     PublicString dir = system.getproperty ("User.dir") + "/testmaven";  Public voidCsvreadall ()throwsException {File csv=NewFile (dir + "/file", "Readertest.csv"); Csvreader Reader=NewCsvreader (NewInputStreamReader (NewFileInputStream (CSV), "GBK"), ', '); String [] Header= Reader.readnext ();//after reading with Readnext, it doesn't exist in the stream.         for(String s:header) {System.out.print (s+ ","); } System.out.println (""); List<String[]> list = Reader.readall ();//Now the second line is read .System.out.println (list.get (0) [0]); System.out.println (""); }     Public voidCsvwriter ()throwsexception{File csv=NewFile (dir + "/file", "Writertest.csv"); if(!csv.exists ()) csv.createnewfile (); List<String[]> list =NewArraylist<>(); String S1= "123";  for(inti = 0; I < 22; i++) {string[] SS={string.valueof (i), string.valueof (i), string.valueof (i), string.valueof (i)};        List.add (ss); } csvwriter writer=NewCsvwriter (NewOutputStreamWriter (NewFileOutputStream (CSV), "GBK"), Csvwriter.default_separator, Csvwriter.no_quote_character);        Writer.writenext (S1, S1, S1, S1); Writer.writenext ("#","#","#","#");        Writer.writeall (list);        Writer.flush ();    Writer.close (); }}

Read and write CSV files with opencsv files