Design Patterns : Singleton

	package com.tvidushi;
	import java.io.File;
	import java.io.FileInputStream;
	import java.io.IOException;
	import java.io.InputStream;
	import java.util.Enumeration;
	import java.util.Hashtable;
	import java.util.Properties;
	public final class PropertyFilesUtils {
	private static PropertyFilesUtils instance = new PropertyFilesUtils();
	private Hashtable propsMap = new Hashtable();
	private PropertyFilesUtils() {}
	public static PropertyFilesUtils getInstance() {
	return instance;
	}
	private Properties loadProperties(String fileName) {
	Properties properties = null;
	InputStream iStream = null;
	try {
	properties = new Properties();
	File file = new File(fileName);
	if (file.exists()) {
	iStream = new FileInputStream(fileName);
	properties.load(iStream);
	propsMap.put(fileName, properties);
	}
	// can throw npe here
	} catch (Exception e) {
	e.printStackTrace();
	} finally {
	if (iStream != null) {
	try {
	iStream.close();
	} catch (IOException e) {
	//ignore
	}
	}
	}
	return properties;
	}
	public String getProperty(String propertyFileName, String key) {
	Properties properties = getProperties(propertyFileName);
	return properties != null ? properties.getProperty(key) : null;
	}
	public String[] getAllKeys(String propertyFileName) {
	Properties properties = getProperties(propertyFileName);
	String[] keys = null;
	int size = properties == null ? 0 : properties.size();
	if (size > 0) {
	keys = new String[size];
	Enumeration enumKeys = properties.keys();
	int i = 0;
	while (enumKeys.hasMoreElements()) {
	keys[i++] = (String) enumKeys.nextElement();
	}
	}
	return keys;
	}
	public Properties getProperties(String fileName) {
	Properties properties = (Properties) propsMap.get(fileName);
	if (properties == null) {
	properties = loadProperties(fileName);
	}
	return properties;
	}
	}

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