What is the easiest way to parse an INI file in Java?

Question

I am writing a drop-in replacement for a legacy application in Java. One of the requirements is that the ini files that the older application used have to be read as-is into the new Java Application. The format of this ini files is the common windows style, with header sections and key=value pairs, using # as the character for commenting.

I tried using the Properties class from Java, but of course that won't work if there is name clashes between different headers.

So the question is, what would be the easiest way to read in this INI file and access the keys?

Answer 1

The library I've used is ini4j. It is lightweight and parses the ini files with ease. Also it uses no esoteric dependencies to 10,000 other jar files, as one of the design goals was to use only the standard Java API

This is an example on how the library is used:

Ini ini = new Ini(new File(filename));
java.util.prefs.Preferences prefs = new IniPreferences(ini);
System.out.println("grumpy/homePage: " + prefs.node("grumpy").get("homePage", null));

Answer 2

As mentioned, ini4j can be used to achieve this. Let me show one other example.

If we have an INI file like this:

[header]
key = value

The following should display value to STDOUT:

Ini ini = new Ini(new File("/path/to/file"));
System.out.println(ini.get("header", "key"));

Check the tutorials for more examples.

Answer 3

As simple as 80 lines:

package windows.prefs;

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class IniFile {

   private Pattern  _section  = Pattern.compile( "\\s*\\[([^]]*)\\]\\s*" );
   private Pattern  _keyValue = Pattern.compile( "\\s*([^=]*)=(.*)" );
   private Map< String,
      Map< String,
         String >>  _entries  = new HashMap<>();

   public IniFile( String path ) throws IOException {
      load( path );
   }

   public void load( String path ) throws IOException {
      try( BufferedReader br = new BufferedReader( new FileReader( path ))) {
         String line;
         String section = null;
         while(( line = br.readLine()) != null ) {
            Matcher m = _section.matcher( line );
            if( m.matches()) {
               section = m.group( 1 ).trim();
            }
            else if( section != null ) {
               m = _keyValue.matcher( line );
               if( m.matches()) {
                  String key   = m.group( 1 ).trim();
                  String value = m.group( 2 ).trim();
                  Map< String, String > kv = _entries.get( section );
                  if( kv == null ) {
                     _entries.put( section, kv = new HashMap<>());   
                  }
                  kv.put( key, value );
               }
            }
         }
      }
   }

   public String getString( String section, String key, String defaultvalue ) {
      Map< String, String > kv = _entries.get( section );
      if( kv == null ) {
         return defaultvalue;
      }
      return kv.get( key );
   }

   public int getInt( String section, String key, int defaultvalue ) {
      Map< String, String > kv = _entries.get( section );
      if( kv == null ) {
         return defaultvalue;
      }
      return Integer.parseInt( kv.get( key ));
   }

   public float getFloat( String section, String key, float defaultvalue ) {
      Map< String, String > kv = _entries.get( section );
      if( kv == null ) {
         return defaultvalue;
      }
      return Float.parseFloat( kv.get( key ));
   }

   public double getDouble( String section, String key, double defaultvalue ) {
      Map< String, String > kv = _entries.get( section );
      if( kv == null ) {
         return defaultvalue;
      }
      return Double.parseDouble( kv.get( key ));
   }
}

Answer 4

Here's a simple, yet powerful example, using the apache class HierarchicalINIConfiguration:

HierarchicalINIConfiguration iniConfObj = new HierarchicalINIConfiguration(iniFile); 

// Get Section names in ini file     
Set setOfSections = iniConfObj.getSections();
Iterator sectionNames = setOfSections.iterator();

while(sectionNames.hasNext()){

 String sectionName = sectionNames.next().toString();

 SubnodeConfiguration sObj = iniObj.getSection(sectionName);
 Iterator it1 =   sObj.getKeys();

    while (it1.hasNext()) {
    // Get element
    Object key = it1.next();
    System.out.print("Key " + key.toString() +  " Value " +  
                     sObj.getString(key.toString()) + "\n");
}

Commons Configuration has a number of runtime dependencies. At a minimum, commons-lang and commons-logging are required. Depending on what you're doing with it, you may require additional libraries (see previous link for details).

Answer 5

Or with standard Java API you can use java.util.Properties:

Properties props = new Properties();
try (FileInputStream in = new FileInputStream(path)) {
    props.load(in);
}

Answer 6

In 18 lines, extending the java.util.Properties to parse into multiple sections:

public static Map<String, Properties> parseINI(Reader reader) throws IOException {
    Map<String, Properties> result = new HashMap();
    new Properties() {

        private Properties section;

        @Override
        public Object put(Object key, Object value) {
            String header = (((String) key) + " " + value).trim();
            if (header.startsWith("[") && header.endsWith("]"))
                return result.put(header.substring(1, header.length() - 1), 
                        section = new Properties());
            else
                return section.put(key, value);
        }

    }.load(reader);
    return result;
}

Answer 7

Another option is Apache Commons Config also has a class for loading from INI files. It does have some runtime dependencies, but for INI files it should only require Commons collections, lang, and logging.

I've used Commons Config on projects with their properties and XML configurations. It is very easy to use and supports some pretty powerful features.

Answer 8

You could try JINIFile. Is a translation of the TIniFile from Delphi, but for java

https://github.com/SubZane/JIniFile

Answer 9

I personally prefer Confucious.

It is nice, as it doesn't require any external dependencies, it's tiny - only 16K, and automatically loads your ini file on initialization. E.g.

Configurable config = Configuration.getInstance();  
String host = config.getStringValue("host");   
int port = config.getIntValue("port"); 
new Connection(host, port);

Answer 10

It is just as simple as this.....

//import java.io.FileInputStream;
//import java.io.FileInputStream;

Properties prop = new Properties();
//c:\\myapp\\config.ini is the location of the ini file
//ini file should look like host=localhost
prop.load(new FileInputStream("c:\\myapp\\config.ini"));
String host = prop.getProperty("host");