利用Spring实现配置文件动态替换 -

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利用Spring实现配置文件动态替换

博客分类：

Java服务器编程

Spring 配置管理 Java Bean XML

在很多项目里面都有后缀名为properties的配置文件，我们一般会把这些文件放到名为conf之类的目录下面，随同jar一起发布。运行时会把conf目录加到jvm的classpath下面去。麻烦的是，程序运行时，我们改动了配置文件，如何让我们的配置文件无需重启程序起作用。我这里有个比较简陋的解决方案，有兴趣的可以看看，应该还可以做些优化。

解决方案的技术思路：

起一个定时器，定时的监控配置的文件的修改时间，如果一旦发现修改，重新装载文件。由于Spring的配置值表达式不支持OGNL类的表达式，于是使用Spring自带的method replace(方法替换)来模拟OGNL类的表达。

代码并不复杂，用到包有asm，cglib，spring2.x，commons-logging4个而已。demo结构如下：

文件简介：

FileListener：监测配置文件修改的接口

FileMonitor：一个TimeTask的子类，检查文件有无改动

ConfigManager：核心类，里面有个Properties成员装载配置文件信息

ConcreteConfig：配置的“反射”类

Main：测试类

conf/monitor.properties 配置文件

conf/monitorContext.xml Spring配置文件

具体实现代码为：

FileListener.java

import java.io.File;

/**
 * an interface to listen the notifications when the file has been changed
 * 
 */
public interface FileListener {

	/**
	 * a notification when the file changed
	 * 
	 * @param file
	 *            the file which has been changed
	 */
	public void onFileChanged(File file);
}

FileMonitor.java

import java.io.File;
import java.util.TimerTask;


/**
 * a class to monitor if the file has been changed
 * 
 */
public class FileMonitor extends TimerTask {
	private FileListener listener;
	private File file;
	private long lastModified;

	/**
	 * constructor
	 * 
	 * @param file
	 *            a file which will be monitor
	 * @param listener
	 *            a listener which will be notified when the file has been
	 *            changed
	 */
	public FileMonitor(File file, FileListener listener) {
		if (file == null || listener == null) {
			throw new NullPointerException();
		}

		this.file = file;
		this.lastModified = this.file.lastModified();
		this.listener = listener;
	}

	@Override
	public void run() {		
		long lastModified = this.file.lastModified();
		if (this.lastModified != lastModified) {
			this.lastModified = lastModified;
			this.listener.onFileChanged(this.file);
		}
	}
}

ConfigManager.java

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.lang.reflect.Method;
import java.net.URISyntaxException;
import java.net.URL;
import java.util.Properties;
import java.util.Set;
import java.util.Timer;

import org.springframework.beans.factory.support.MethodReplacer;

public class ConfigManager implements FileListener, MethodReplacer{
	private static final long FILE_MONITOR_INTERVAL = 5000;
	private static final String MONITOR_CONF_FILE_PATH = "monitor.properties";
	private FileMonitor monitor;
	private Timer timer = new Timer("Timer", true);
	
	private Properties properties = new Properties();
	
	
	private ConfigManager() throws IOException {
		properties.load(getClass().getResourceAsStream("/monitor.properties"));
		
		// monitor the configuration file change
		monitor = new FileMonitor(getFileByClassPath(MONITOR_CONF_FILE_PATH), this);
		timer.schedule(monitor, FILE_MONITOR_INTERVAL, FILE_MONITOR_INTERVAL);
		
	}
	private File getFileByClassPath(String filepath) {
		URL url = getClass().getResource(
				filepath);
		if (url == null) {
			System.err.println("failed to find the file " + filepath);
			return null;
		}

		try {
			File file = new File(url.toURI());
			return file;
		} catch (URISyntaxException e) {
			e.printStackTrace();
		}

		return null;
	}

	@Override
	public synchronized void onFileChanged(File file) {
		Properties newProperties = new Properties();
		try {
			newProperties.load(new FileInputStream(file));
		} catch (IOException e) {
			e.printStackTrace();
			return;
		}
		Set<String> keys = properties.stringPropertyNames();
		for(String key : keys) {
			String newValue = (String)newProperties.get(key);
			String oldValue = properties.getProperty(key);
			System.out.println("newValue:"+newValue+" oldValue:"+oldValue);
			if(newValue != null) {
				properties.setProperty(key, newValue);
			}
			else {
				properties.remove(key);
			}
		}
	}
	
	public synchronized  String getProperty(String key) {
		return properties.getProperty(key);
	}
	
	@Override
	public Object reimplement(Object arg0, Method arg1, Object[] arg2)
			throws Throwable {
		String methodName = arg1.getName();
		String tmp = methodName.substring("get".length());
		char ch = tmp.charAt(0);
		ch = Character.toLowerCase(ch);
		tmp = ch+tmp.substring(1);
		return getProperty(tmp);
	}
	
}

ConcreteConfig.java

public class ConcreteConfig {
	private String zookeeperQuorum;
	private String zookeeperPort;
	/**
	 * @param zookeeperQuorum the zookeeperQuorum to set
	 */
	public void setZookeeperQuorum(String zookeeperQuorum) {
		this.zookeeperQuorum = zookeeperQuorum;
	}
	/**
	 * @return the zookeeperQuorum
	 */
	public String getZookeeperQuorum() {
		return zookeeperQuorum;
	}
	/**
	 * @param zookeeperPort the zookeeperPort to set
	 */
	public void setZookeeperPort(String zookeeperPort) {
		this.zookeeperPort = zookeeperPort;
	}
	/**
	 * @return the zookeeperPort
	 */
	public String getZookeeperPort() {
		return zookeeperPort;
	}
	
}

Main.java

import org.springframework.context.support.FileSystemXmlApplicationContext;


public class Main {
	public static void main(String[] args) throws InterruptedException {
		FileSystemXmlApplicationContext context = new FileSystemXmlApplicationContext(
                new String[]{
                        "classpath:monitorContext.xml"
                });
		ConcreteConfig config = (ConcreteConfig)context.getBean("concreteConfig");
		while(true) {
			System.out.println(config.getZookeeperQuorum());
			System.out.println(config.getZookeeperPort());
			Thread.sleep(5000);
		}
	}
}

monitor.properties

zookeeperQuorum = host1:2181,host2:2181,host3:2181
zookeeperPort = 2181

monitorContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans default-lazy-init="false">

	<bean id="configManager" class="ConfigManager"/>
	
	<bean id="concreteConfig" class="ConcreteConfig">
  		<replaced-method name="getZookeeperQuorum" replacer="configManager"/>
  		<replaced-method name="getZookeeperPort" replacer="configManager"/>
  	</bean>
	
</beans>

测试过程：

在Eclipse里面以Main做主类运行，观察控制台输出。

然后改动monitor.properties，再看控制台输出，可以发现改动很快生效。