利用Spring实现配置文件动态替换
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。