[zebra源码]JdbcFilter过滤器和SPI扩展

一、 JdbcFilter 过滤器

zebra 定义了 JdbcFilter 过滤器，它包含的方法覆盖了 zebra 执行生命周期的各个环节（如各层数据源的初始化/刷新、分组连接的获取/关闭、sql的执行等）；那么就方便在各个环节进行监控上报等操作了

public interface JdbcFilter {
    int DEFAULT_ORDER = 0;

    int MAX_ORDER = Integer.MAX_VALUE;

    int MIN_ORDER = Integer.MIN_VALUE;

    /**
     * filter ordering <br>
     * filter_with_order_3_start filter_with_order_2_start
     * filter_with_order_1_start targer_start filter_with_order_1_finish
     * filter_with_order_2_finish filter_with_order_3_finish
     *
     * @return the order of execute
     */
    int getOrder();

    /**
     * init filter
     */
    void init();

    /** GroupDataSource Filter **/
    void initGroupDataSource(GroupDataSource source, JdbcFilter chain);

    void refreshGroupDataSource(GroupDataSource source, String propertiesName, JdbcFilter chain);

    GroupConnection getGroupConnection(GroupDataSource source, JdbcFilter chain) throws SQLException;

    FailOverDataSource.FindMasterDataSourceResult findMasterFailOverDataSource(
            FailOverDataSource.MasterDataSourceMonitor source, JdbcFilter chain);

    void closeGroupConnection(GroupConnection source, JdbcFilter chain) throws SQLException;

    void closeGroupDataSource(GroupDataSource source, JdbcFilter chain) throws SQLException;

    void switchFailOverDataSource(FailOverDataSource source, JdbcFilter chain);

    /** SingleDataSource Filter **/
    DataSource initSingleDataSource(SingleDataSource source, JdbcFilter chain);

    SingleConnection getSingleConnection(SingleDataSource source, JdbcFilter chain) throws SQLException;

    String processSQL(DataSourceConfig dsConfig, SQLProcessContext ctx, JdbcFilter chain) throws SQLException;

    <T> T executeSingleStatement(SingleStatement source, SingleConnection conn, String sql, List<String> batchedSql,
            boolean isBatched, boolean autoCommit, Object params, JdbcFilter chain) throws SQLException;

    void closeSingleConnection(SingleConnection source, JdbcFilter chain) throws SQLException;

    void closeSingleDataSource(SingleDataSource source, JdbcFilter chain) throws SQLException;

    void closeSingleResultSet(SingleResultSet source, JdbcFilter chain) throws SQLException;

    /** ShardDataSource Filter **/
    void initShardDataSource(ShardDataSource source, JdbcFilter chain);

    ResultSet executeShardQuery(ShardStatement source, String sql, JdbcFilter chain) throws SQLException;

    int executeShardUpdate(ShardStatement source, String sql, int autoGeneratedKeys, int[] columnIndexes,
            String[] columnNames, JdbcFilter chain) throws SQLException;

    void shardRouting(RouterResult rr, JdbcFilter chain) throws SQLException;

    void shardMerge(ShardResultSet rs, JdbcFilter chain) throws SQLException;

    void configChanged(PropertyChangeEvent evt, JdbcFilter chain);
}

都是些 void 的无害方法，在zebra数据源、配置及sql代理执行过程的各个点，会执行 JdbcFilter 的对应方法；如在GroupDataSource 初始化的时候，会调用 JdbcFilter#initGroupDataSource 方法

JdbcFilter chain = new DefaultJdbcFilterChain(filters) {
      @Override
      public void initGroupDataSource(GroupDataSource source, JdbcFilter chain) {
          if (index < filters.size()) {
              filters.get(index++).initGroupDataSource(source, chain);
          } else {
              // 开始初始化
              source.initInternal();
          }
      }
  };

zebra 里边的 JdbcFilter 由 DefaultFilterManager 类负责管理，只要是实现了 JdbcFilter 接口的类就会被它通过类加载的方式加载到，多个filter的执行是加入到责任链 DefaultJdbcFilterChain 里执行的

自带的 JdbcFilter有

CatFilter上报监控信息到cat
WallFilter 流控

如何扩展 Filter？

实现Filter接口一般继承DefaultJdbcFilter 即可，Zebra默认提供wallFilter和CatFilter，开发者可以进行参考

public class WallFilter extends DefaultJdbcFilter
注册 Filter

Filter的类加载文件放置在 META-INF/zebra-filter.properties 目录下,格式为

文件名：zebra.filter.${filterName}=类路径
内容： zebra.filter.wall=com.dianping.zebra.filter.wall.WallFilter

二、SPI扩展

ZebraSpi扩展说明

zebra 的 SPI 注解

@Target({ ElementType.METHOD, ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Inherited
public @interface Spi {
    String name() default "";

    Scope scope() default Scope.SINGLETON;
}

它针对的是配置获取方式 ConfigService

自定义的 ConfigService Spi 类加载文件可以放置在 META-INF/services/com.dianping.zebra.config.ConfigService 文件中进行注册，如

com.dianping.zebra.config.ZookeeperConfigService

com.dianping.zebra.config.PropertyConfigService

如 zk 配置的定义：

@Spi(name = "zookeeper", scope = Scope.SINGLETON)
public class ZookeeperConfigService implements ConfigService

他们会被 ExtensionLoader 加载并创建对象，用于配置拉取