Question

I have a comma delimited configuration file. The empty lines are ignored and there need to be errors on invalid lines:

foo,bar

foo2, bar3

I want to read this file into a HashMap where the key (foo) is mapped with a value (bar).

What is the best way to do this?

Answer 1

If you can use x = y instead of x, y then you can use the Properties class.

If you do need to have x, y then look at the java.util.Scanner you can set the delimiter to use as a separator (the javadoc shows examples of doing that).

import java.io.File; import java.io.FileNotFoundException; import java.util.Scanner;  class Main {     public static void main(final String[] argv)     {         final File file;          file = new File(argv[0]);          try         {             final Scanner scanner;              scanner = new Scanner(file);              while(scanner.hasNextLine())             {                 if(scanner.hasNext('.*,'))                 {                     String key;                     final String value;                      key = scanner.next('.*,').trim();                      if(!(scanner.hasNext()))                     {                         // pick a better exception to throw                         throw new Error('Missing value for key: ' + key);                     }                      key   = key.substring(0, key.length() - 1);                     value = scanner.next();                      System.out.println('key = ' + key + ' value = ' + value);                 }             }         }         catch(final FileNotFoundException ex)         {             ex.printStackTrace();         }     } } 

and the Properties version (way simpler for the parsing, as there is none)

import java.io.BufferedReader; import java.io.FileReader; import java.io.IOException; import java.io.Reader; import java.util.Properties;  class Main {     public static void main(final String[] argv)     {         Reader reader;          reader = null;          try         {             final Properties properties;              reader = new BufferedReader(                             new FileReader(argv[0]));             properties = new Properties();             properties.load(reader);             System.out.println(properties);         }         catch(final IOException ex)         {             ex.printStackTrace();         }         finally         {             if(reader != null)             {                 try                 {                     reader.close();                 }                 catch(final IOException ex)                 {                     ex.printStackTrace();                 }             }         }     } }