Java Ini Parser

There is a open source project named [ini4j] for processing Windows .ini configuration files. However, I found it an overkill for my purposes. So here is my simple implementation of a .ini parser. It mimics the standard java.util.Properties class with enhancements to get and set properties by section name.

There are only a few simple rules:

1. Leading and trailing spaces are trimmed from section names, property names and property values.
2. Section names are enclosed between [ and ].
3. Properties following a section header belong to that section
4. Properties defined before the appearance of any section headers are considered global properties and should be set and get with no section names.
5. You can use either equal sign (=) or colon (:) to assign property values
6. Comments begin with either a semicolon (;), or a sharp sign (#) and extend to the end of line. It doesn't have to be the first character.
7. A backslash (\) escapes the next character (e.g., \# is a literal #, \\ is a literal \).
8. If the last character of a line is backslash (\), the value is continued on the next line with new line character included.

Example Code

import java.util.*;
import java.io.*;

public class IniProperties {
    private Properties globalProperties;
    private Map<String,Properties> properties;

    enum ParseState {
        NORMAL,
        ESCAPE,
        ESC_CRNL,
        COMMENT
    }

    public IniProperties() {
        globalProperties = new Properties();
        properties = new HashMap<String,Properties>();
    }

    /**
     * Load ini as properties from input stream.
     */
    public void load(InputStream in) throws IOException {
        int bufSize = 4096;
        byte[] buffer = new byte[bufSize];
        int n = in.read(buffer, 0, bufSize);

        ParseState state = ParseState.NORMAL;
        boolean section_open = false;
        String current_section = null;
        String key = null, value = null;
        StringBuilder sb = new StringBuilder();
        while (n >= 0) {
            for (int i = 0; i < n; i++) {
                char c = (char) buffer[i];

                if (state == ParseState.COMMENT) { 
      // comment, skip to end of line
                    if ((c == '\r') ||(c == '\n')) {
                        state = ParseState.NORMAL;
                    }
                    else {
                        continue;
                    }
                }

                if (state == ParseState.ESCAPE) {
                    sb.append(c);
                    if (c == '\r') {
                        // if the EOL is \r\n, \ escapes both chars
                        state = ParseState.ESC_CRNL; 
                    }
                    else {
                        state = ParseState.NORMAL;
                    }
                    continue;
                }

                switch (c) {
                    case '[': // start section
                        sb = new StringBuilder();
                        section_open = true;
                        break;
                    
                    case ']': // end section
                        if (section_open) {
                            current_section = sb.toString().trim();
                            sb = new StringBuilder();
                            properties.put(current_section, new Properties());
                            section_open = false;
                        }
                        else {
                            sb.append(c);
                        }
                        break;

                    case '\\': // escape char, take the next char as is
                        state = ParseState.ESCAPE;
                        break;

                    case '#': 
                    case ';': 
                        state = ParseState.COMMENT;
                        break;

                    case '=': // assignment operator
                    case ':':
                        if (key == null) {
                            key = sb.toString().trim();
                            sb = new StringBuilder();
                        }
                        else {
                            sb.append(c);
                        }
                        break;

                    case '\r':
                    case '\n':
                        if ((state == ParseState.ESC_CRNL) && (c == '\n')) {
                            sb.append(c);
                            state = ParseState.NORMAL;
                        }
                        else {
                            if (sb.length() > 0) {
                                value = sb.toString().trim();
                                sb = new StringBuilder();
                        
                                if (key != null) {
                                    if (current_section == null) {
                                        this.setProperty(key, value);
                                    }
                                    else {
                                        this.setProperty(current_section, key, value);
                                    }
                                }
                            }
                            key = null;
                            value = null;
                        }
                        break;

                    default: 
                        sb.append(c);
                }
            }
            n = in.read(buffer, 0, bufSize);
        }
    }

    /**
     * Get global property by name.
     */
    public String getProperty(String name) {
        return globalProperties.getProperty(name);
    }

    /**
     * Set global property.
     */
    public void setProperty(String name, String value) {
        globalProperties.setProperty(name, value);
    }

    /**
     * Return iterator of global properties.
     */
    @SuppressWarnings("unchecked")
    public Iterator<String> properties() {
        return new IteratorFromEnumeration<String>(
                   (Enumeration<String>)globalProperties.propertyNames());
    }

    /**
     * Get property value for specified section and name. Returns null
     * if section or property does not exist.
     */
    public String getProperty(String section, String name) {
        Properties p = properties.get(section);
        return p == null ? null : p.getProperty(name);
    }

    /**
     * Set property value for specified section and name. Creates section
     * if not existing.
     */
    public void setProperty(String section, String name, String value) {
        Properties p = properties.get(section);
        if (p == null) {
            p = new Properties();
            properties.put(section, p);
        }
        p.setProperty(name, value);
    }

    /**
     * Return property iterator for specified section. Returns null if
     * specified section does not exist.
     */
    @SuppressWarnings("unchecked")
    public Iterator<String> properties(String section) {
        Properties p = properties.get(section);
        if (p == null) {
            return null;
        }
        return new IteratorFromEnumeration<String>(
                   (Enumeration<String>)p.propertyNames());
    }

    /**
     * Return iterator of names of section.
     */
    public Iterator<String> sections() {
        return properties.keySet().iterator();
    }

    /**
     * Dumps properties to output stream.
     */
    public void dump(PrintStream out) throws IOException {
        // Global properties
        Iterator<String> props = this.properties();
        while (props.hasNext()) {
            String name = props.next();
            out.printf("%s = %s\n", name, dumpEscape(getProperty(name)));
        }

        // sections
        Iterator<String> sections = this.sections();
        while (sections.hasNext()) {
            String section = sections.next();
            out.printf("\n[%s]\n", section);
            props = this.properties(section);
            while (props.hasNext()) {
                String name = props.next();
                out.printf("%s = %s\n", name, dumpEscape(getProperty(section, name)));
            }
        }
    }

    private static String dumpEscape(String s) {
        return s.replaceAll("\\\\", "\\\\\\\\")
                .replaceAll(";", "\\\\;")
                .replaceAll("#", "\\\\#")
                .replaceAll("(\r?\n|\r)", "\\\\$1");
    }

    // private class used to coerce Enumerator to Iterator.
    private static class IteratorFromEnumeration<E> implements Iterator {
        private Enumeration<E> e;

        public IteratorFromEnumeration(Enumeration<E> e) {
            this.e = e;
        }

        public boolean hasNext() {
            return e.hasMoreElements();
        }

        public E next() {
            return e.nextElement();
        }

        public void remove() {
            throw new UnsupportedOperationException("Can't  
                                       change underlying enumeration");
        }
    }

    public static void main(String[] args) throws IOException {
        IniProperties props = new IniProperties();
        InputStream in = new BufferedInputStream(new FileInputStream("test.ini"));
        props.load(in);
        in.close();
        
        props.dump(System.out);
    }
}

The test file
Following ini4j, here is a test file:

; Global properties
story = Snow White and the Seven Dwarfs
year = 1937
url = www.imdb.com/title/tt0029583/
; A backslash at the end of the line escapes the new line
; character, the property value continues to the next line.
; Since the ; character (after Dwarfs) starts a comment 
; (either at the beginning or middle of the line, we have 
; to escape it with a backslash.
plot = Snow White, pursued by a jealous queen, hides with the Dwarfs\; \
the queen feeds her a poison apple, but Prince Charming \
awakens her with a kiss. # this is a comment

# This is also a comment line
# The first : can also be used as assignment operator
Tagline: Walt Disney's New characters in his first full-length production!
file = C:\\local\\snowwhite.mpg

; Bashful
[bashful]
weight = 45.7
height = 98.8
age = 67
homePage = http://snowwhite.tale/~bashful

; Doc
[doc]
weight = 49.5
height = 87.7
age = 63
homePage = http://doc.dwarfs