java读取properties文件

package com.properties.test;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Properties;


public class PropertiesUnit
{
	private String filename;
	private Properties properties;
	private FileInputStream in;
	private FileOutputStream out;
	
	public PropertiesUnit()
	{
		properties = new Properties();
	}
	
	public PropertiesUnit(String filename)
	{
		this.filename = filename;
		properties = new Properties();
		File file = new File(filename);
		try
		{
			in = new FileInputStream(file);
			
			properties.load(in);
			in.close();
		}
		catch (FileNotFoundException e)
		{
			System.err.println("配置文件config.properties找不到！"); 
			e.printStackTrace(); 
		}
		catch (IOException e)
		{
			System.err.println("读取配置文件config.properties错误！"); 
			e.printStackTrace(); 

		}
	}
	
	public String getValue(String key)
	{
			
		if(properties.containsKey(key))
		{
			String value = properties.getProperty(key);
			return value;
		}
		else
		{
			return "";
		}
	}
	
	public String getValue(String fileName,String key)
	{
		try
		{
			String value="";
			in = new FileInputStream(fileName);
			properties.load(in);
			in.close();
			if(properties.containsKey(key))
			{
				value = properties.getProperty(key);
				return value;
			}
			else
			{
				return value;
			}
		}
		catch (FileNotFoundException e)
		{
			System.err.println("配置文件config.properties找不到！"); 
			e.printStackTrace(); 
			return "";
		}
		catch (IOException e)
		{
			System.err.println("读取配置文件config.properties错误！"); 
			e.printStackTrace();
			return "";

		}
	}
	
	public void clear()
	{
		properties.clear();	
	}
	
	public void setValue(String key,String value)
	{
		properties.setProperty(key,value);
	}
	
	
	public void saveFile(String fileName,String description)
	{
		try
		{
			out = new FileOutputStream(fileName);
			properties.store(out,description);
			out.close();
		}
		catch (FileNotFoundException e)
		{
			System.err.println("配置文件config.properties找不到！"); 
			e.printStackTrace(); 
		}
		catch (IOException e)
		{
			System.err.println("读取配置文件config.properties错误！"); 
			e.printStackTrace();
		}
	}
	
	public static void main(String[] args)
	{
		PropertiesUnit pu = new PropertiesUnit("./config.properties");
		String key = pu.getValue("key");
		System.out.println(key);
	}
}