java单例读取配置文件

源代码取自：云之讯短信接口类的api demo

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Iterator;
import java.util.Properties;

import org.apache.commons.lang.StringUtils;
import org.apache.log4j.Logger;

/**
 * 单例模式，加载配置文件
 * @author dhh
 *
 */
public class SysConfig{
	private Properties props = null;  //messageConfig.properties
	private static Logger log = Logger.getLogger(SysConfig.class);
	/**
	 * synchronized 同步块大家都比较熟悉，通过 synchronized 关键字来实现，所有加上synchronized块语句，在多线程访问的时候，
	 * 同一时刻只能有一个线程能够用synchronized 修饰的方 或者代码块。
	 * volatile修饰的变量，线程在每次使用变量的时候，都会读取变量修改后的最的值。volatile很容易被误用，用来进行原子性操作。
	 */
	private static volatile SysConfig conf;

	private SysConfig() {
		props = new Properties();
		loadConfigProps();
	}

	public static SysConfig getInstance() {
		if (conf == null) {
			synchronized (SysConfig.class) {
				if (conf == null) {
					conf = new SysConfig();
				}
			}
		}
		return conf;
	}

	public void loadConfigProps() {
		InputStream is = null;
		try {
			is = getClass().getResourceAsStream(
					"/WEB-INF/classes/messageConfig.properties");
			if (is == null) {
				is = getClass().getResourceAsStream("/messageConfig.properties");
			}
			InputStreamReader reader = new InputStreamReader(is, "UTF-8");
			props.load(reader);
			Iterator iter = props.stringPropertyNames().iterator();
			while (iter.hasNext()) {
				String key = iter.next();
				props.setProperty(key, props.getProperty(key));
			}
		} catch (IOException e) {
			e.printStackTrace();
			log.error("load config.properties error!please check the file!", e);
		} finally {
			if (is != null) {
				try {
					is.close();
					is = null;
				} catch (Exception e) {
					e.printStackTrace();
				}
			}
		}
	}

	public String getProperty(String key) {
		String tmp = props.getProperty(key);
		if (StringUtils.isNotEmpty(tmp)) {
			return tmp.trim();
		}
		return tmp;
	}

	public String getProperty(String key, String defaultValue) {
		String tmp = props.getProperty(key, defaultValue);
		if (StringUtils.isNotEmpty(tmp)) {
			return tmp.trim();
		}
		return tmp;
	}

	public int getPropertyInt(String key) {
		String tmp = props.getProperty(key);
		if (StringUtils.isNotEmpty(tmp)) {
			return Integer.parseInt(tmp.trim());
		}
		return 0;

	}

	public int getPropertyInt(String key, int defaultValue) {
		String tmp = props.getProperty(key);
		if (StringUtils.isNotEmpty(tmp)) {
			return Integer.parseInt(tmp.trim());
		}
		return defaultValue;
	}

	public long getPropertyLong(String key, long defaultValue) {
		String tmp = props.getProperty(key);
		if (StringUtils.isNotEmpty(tmp)) {
			return Integer.parseInt(tmp.trim());
		}
		return defaultValue;
	}
}

调用代码：

public String version=SysConfig.getInstance().getProperty("version");

我之前用的加载配置文件的代码：

import java.io.IOException;
import java.util.Properties;

public class PropertiesReader {
	private static Properties properties = new Properties();
	static{
		try {
			properties.load(PropertiesReader.class.getClassLoader().getResourceAsStream("setting.properties"));
		} catch (IOException e) {
			e.printStackTrace();
		}
	}

	public static String readUrl(String key){		
		return (String)properties.get(key);
	}
}

调用：

String api_key = PropertiesReader.readUrl("api_key")