配置源
配置源定义和实现了获取配置文件的方式。有两种配置源，一种是主动拉去方式获取配置，一种是被动监听方式获取配置
类图结构：
接口PolledConfigurationSource定义了获取配置的方法
public PollResult poll(boolean initial, Object checkPoint) throws Exception;
initial是否是初次获取，checkPoint上次获取的检查点。
JDBCConfigurationSource 从数据库中获取配置信息。从指定的DataSource中读取指定的key和value字段。
public PollResult poll(boolean initial, Object checkPoint) throws Exception {
Map<String, Object> map = new HashMap<String, Object>();
...
conn = getConnection();
pstmt = conn.prepareStatement(query.toString());
rs = pstmt.executeQuery();
while (rs.next()) {
String key = (String) rs.getObject(keyColumnName);
Object value = rs.getObject(valueColumnName);
map.put(key, value);
}
...
return PollResult.createFull(map);
}
URLConfigurationSource从指定url中获取配置信息。从指定的url中读取配置文件。
public PollResult poll(boolean initial, Object checkPoint)
throws IOException {
if (configUrls == null || configUrls.length == 0) {
return PollResult.createFull(null);
}
Map<String, Object> map = new HashMap<String, Object>();
for (URL url: configUrls) {
InputStream fin = url.openStream();
Properties props = ConfigurationUtils.loadPropertiesFromInputStream(fin);
for (Entry<Object, Object> entry: props.entrySet()) {
map.put((String) entry.getKey(), entry.getValue());
}
}
return PollResult.createFull(map);
}
WatchedConfigurationSource定义了监听器，当配置发生变化时，调用这些监听器。
public void addUpdateListener(WatchedUpdateListener l);
public void removeUpdateListener(WatchedUpdateListener l);
public Map<String, Object> getCurrentData() throws Exception;