Seata Configuration解析

seata-core Configuration
Configuration配置接口类
此接口类作用：获取配置文件，注册属性监听事件；

通过spi机制实现第三方配置中心，或本地File文件实现seata配置。

拿Zookeeper举例
ZookeeperConfiguration配置类详解：

spi机制创建ZookeeperConfigurationProvider类，类中provide() 实例化 ZookeeperConfiguration类

public interface Configuration {
//省略了部分接口

/**
 * Gets config.
 *
 * @param dataId       the data id
 * @param defaultValue the default value
 * @param timeoutMills the timeout mills
 * @return the config
 */
String getConfig(String dataId, String defaultValue, long timeoutMills);

String getConfig(String dataId);

boolean putConfig(String dataId, String content, long timeoutMills);

String getLatestConfig(String dataId, String defaultValue, long timeoutMills);

boolean removeConfig(String dataId, long timeoutMills);

/**
 * Add config listener.
 *
 * @param dataId   the data id
 * @param listener the listener
 */
void addConfigListener(String dataId, ConfigurationChangeListener listener);

void removeConfigListener(String dataId, ConfigurationChangeListener listener);

Set<ConfigurationChangeListener> getConfigListeners(String dataId);

}

AbstractConfiguration 实现接口类 Configuration
//zk配置类
public class ZookeeperConfiguration extends AbstractConfiguration {

//1. 先执行静态成员变量
见下图 ConfigurationFactory 和 FileConfiguration 类
Configuration FILE_CONFIG = ConfigurationFactory.CURRENT_FILE_INSTANCE;
...    

//2. 无参构造函数创建zkClient实例
public ZookeeperConfiguration() {
    if (zkClient == null) {
        synchronized (ZookeeperConfiguration.class) {
            if (zkClient == null) {
                //省略部分代码

                //获取配置文件中属性，传入zkClient
                String serverAddr = FILE_CONFIG.getConfig(FILE_CONFIG_KEY_PREFIX + SERVER_ADDR_KEY);
                zkClient = new ZkClient(serverAddr, sessionTimeout, connectTimeout, zkSerializer);
            }
        }
        if (!zkClient.exists(ROOT_PATH)) {
            zkClient.createPersistent(ROOT_PATH, true);
        }
    }
}

ConfigurationFactory类：

public final class ConfigurationFactory {

public static Configuration CURRENT_FILE_INSTANCE;

static {
    load();
}

private static void load() {
    //省略部分获取系统参数代码
    String seataConfigName = "registry";
    //创建FileConfiguration对象
    Configuration configuration = new FileConfiguration(seataConfigName, false);

    CURRENT_FILE_INSTANCE = configuration;
}

FileConfiguration类：

public class FileConfiguration extends AbstractConfiguration{
private FileConfig fileConfig;

public FileConfiguration(String name, boolean allowDynamicRefresh) {
    //getConfigFile方法获取classpath根目录资源文件, 此处name用默认配置，创建registry.conf文件
    File file = getConfigFile(name);
    if (file == null) {
        targetFilePath = null;
    } else {
        targetFilePath = file.getPath();
        //默认创建SimpleFileConfig对象，类中有参构造函数创建配置管理库typesafe.config
        fileConfig = FileConfigFactory.load(file, name);
    }
    /**
     * For seata-server side the conf file should always exists.
     * For application(or client) side,conf file may not exists when using seata-spring-boot-starter
     */
    if (targetFilePath == null) {
        fileConfig = FileConfigFactory.load();
        this.allowDynamicRefresh = false;
    } else {
        targetFileLastModified = new File(targetFilePath).lastModified();
        this.allowDynamicRefresh = allowDynamicRefresh;
    }
}

}
配置监听类ConfigurationChangeListener解析
作用：针对需要监听的配置属性，加入监听事件，属性修改后收到变更事件；

       如后文GlobalTransactionalInterceptor 重写 onChangeEvent 处理相关逻辑

Zookeeper怎么写入监听？

ZKListener 实现 zk数据监听接口，需要监听的子节点写入zk监听器，如果有变更则回调方法通知

public class ZookeeperConfiguration extends AbstractConfiguration {

private ConcurrentMap<String, ConcurrentMap<ConfigurationChangeListener, ZKListener>> configListenersMap = new ConcurrentHashMap<>(MAP_INITIAL_CAPACITY);

//相关属性加入监听
@Override
public void addConfigListener(String dataId, ConfigurationChangeListener listener) {
    if (StringUtils.isBlank(dataId) || listener == null) {
        return;
    }
    String path = ROOT_PATH + ZK_PATH_SPLIT_CHAR + dataId;
    if (zkClient.exists(path)) {
        ZKListener zkListener = new ZKListener(path, listener);
        configListenersMap.computeIfAbsent(dataId, key -> new ConcurrentHashMap<>())
                .put(listener, zkListener);
        zkClient.subscribeDataChanges(path, zkListener);
    }
}

@Override
public void removeConfigListener(String dataId, ConfigurationChangeListener listener)         

{
//…省略部分代码

    //移除监听事件
    zkClient.unsubscribeDataChanges(path, zkListener);
}

public static class ZKListener implements IZkDataListener {

    private String path;
    private ConfigurationChangeListener listener;

    public ZKListener(String path, ConfigurationChangeListener listener) {
        this.path = path;
        this.listener = listener;
    }

    @Override
    public void handleDataChange(String s, Object o) throws Exception {
        //创建监听的属性对象，作为参数传入自定义的监听类中
        ConfigurationChangeEvent event = new ConfigurationChangeEvent().setDataId(s).setNewValue(o.toString())
                .setChangeType(ConfigurationChangeType.MODIFY);
        //处理定义的监听事件
        listener.onProcessEvent(event);
    }

    @Override
    public void handleDataDeleted(String s) throws Exception {
        ConfigurationChangeEvent event = new ConfigurationChangeEvent().setDataId(s).setChangeType(
                ConfigurationChangeType.DELETE);
        listener.onProcessEvent(event);
    }
}

}

总结
seata通过定义Configuration接口，第三方配置中心如zk, nacos需要集成，则实现其接口、重写方法完成配置的读取。