/** * Hint manager holder. * <p>Use thread-local to manage hint.</p> * @author zhangliang */@NoArgsConstructor(access = AccessLevel.PRIVATE)public final class HintManagerHolder {    // hint特性保存数据的核心变量，即保存一个HintManager类型对象到ThreadLocal中    private static final ThreadLocal<HintManager> HINT_MANAGER_HOLDER = new ThreadLocal<>();    /**     * Set hint manager.     * @param hintManager hint manager instance     */    public static void setHintManager(final HintManager hintManager) {        Preconditions.checkState(null == HINT_MANAGER_HOLDER.get(), "HintManagerHolder has previous value, please clear first.");        HINT_MANAGER_HOLDER.set(hintManager);    }    public static boolean isUseShardingHint() {        // 判断当前线程中是否使用了sharding hint--即HintManager中的shardingHint为true        return null != HINT_MANAGER_HOLDER.get() && HINT_MANAGER_HOLDER.get().isShardingHint();    }    public static Optional<ShardingValue<?>> getDatabaseShardingValue(final ShardingKey shardingKey) {        // 如果使用了sharding hint，那么从ThreadLocal中取数据库的sharding值        return isUseShardingHint() ? Optional.<ShardingValue<?>>fromNullable(HINT_MANAGER_HOLDER.get().getDatabaseShardingValue(shardingKey)) : Optional.<ShardingValue<?>>absent();    }    public static Optional<ShardingValue<?>> getTableShardingValue(final ShardingKey shardingKey) {        // 如果使用了sharding hint，那么从ThreadLocal中取表的sharding值        return isUseShardingHint() ? Optional.<ShardingValue<?>>fromNullable(HINT_MANAGER_HOLDER.get().getTableShardingValue(shardingKey)) : Optional.<ShardingValue<?>>absent();    }    public static boolean isMasterRouteOnly() {        // 是否强制路由主库--sharding-jdbc的特性之一：强制路由        return null != HINT_MANAGER_HOLDER.get() && HINT_MANAGER_HOLDER.get().isMasterRouteOnly();    }    public static boolean isDatabaseShardingOnly() {        // 是否只是数据库sharding        return null != HINT_MANAGER_HOLDER.get() && HINT_MANAGER_HOLDER.get().isDatabaseShardingOnly();    }    /**     * Clear hint manager for current thread-local.     */    public static void clear() {        // ThreadLocal用完需要清理        HINT_MANAGER_HOLDER.remove();    }}

@NoArgsConstructor(access = AccessLevel.PRIVATE)public final class HintManager implements AutoCloseable {    // 数据库强制路由的值    private final Map<ShardingKey, ShardingValue<?>> databaseShardingValues = new HashMap<>();    // 表强制路由的值    private final Map<ShardingKey, ShardingValue<?>> tableShardingValues = new HashMap<>();    // 即是否使用了强制路由特性    @Getter    private boolean shardingHint;    // 是否强制路由到主数据库    @Getter    private boolean masterRouteOnly;    @Getter    private boolean databaseShardingOnly;    ... ...    @Override    public void close() {        HintManagerHolder.clear();    }}

private static ShardingDataSource getShardingDataSource() throws SQLException {    DataSourceRule dataSourceRule = new DataSourceRule(createDataSourceMap());    TableRule orderTableRule = TableRule            .builder("t_order")            .actualTables(Arrays.asList("t_order_0", "t_order_1"))            .dataSourceRule(dataSourceRule)            .build();    TableRule orderItemTableRule = TableRule            .builder("t_order_item")            .actualTables(Arrays.asList("t_order_item_0", "t_order_item_1"))            .dataSourceRule(dataSourceRule)            .build();    ShardingRule shardingRule = ShardingRule.builder()            .dataSourceRule(dataSourceRule)            .tableRules(Arrays.asList(orderTableRule, orderItemTableRule))            .bindingTableRules(Collections.singletonList(new BindingTableRule(Arrays.asList(orderTableRule, orderItemTableRule))))            .databaseShardingStrategy(new DatabaseShardingStrategy("user_id", new ModuloDatabaseShardingAlgorithm()))            .tableShardingStrategy(new TableShardingStrategy("order_id", new ModuloTableShardingAlgorithm())).build();    return new ShardingDataSource(shardingRule);}

private static void printHintSimpleSelect(final DataSource dataSource) throws SQLException {    // SQL语句并不涉及任何数据库路由和表路由信息（即where语句中没有user_id条件和order_id条件）    String sql = "SELECT i.* FROM t_order o JOIN t_order_item i ON o.order_id=i.order_id";    try (            HintManager hintManager = HintManager.getInstance();            Connection conn = dataSource.getConnection();            PreparedStatement preparedStatement = conn.prepareStatement(sql)) {        // 强制路由：数据库路由sharding column即user_id的值为10        hintManager.addDatabaseShardingValue("t_order", "user_id", 10);        try (ResultSet rs = preparedStatement.executeQuery()) {            //todo do something        }    }}

private Collection<String> routeDataSources(final TableRule tableRule) {    // 首先得到数据库sharding策略，例如：数据库按照列user_id进行sharding    DatabaseShardingStrategy strategy = shardingRule.getDatabaseShardingStrategy(tableRule);    // 然后从ThreadLocal中取出sharding的值    List<ShardingValue<?>> shardingValues = HintManagerHolder.isUseShardingHint() ? getDatabaseShardingValuesFromHint(strategy.getShardingColumns())            : getShardingValues(strategy.getShardingColumns());    Collection<String> result = strategy.doStaticSharding(tableRule.getActualDatasourceNames(), shardingValues);    Preconditions.checkState(!result.isEmpty(), "no database route info");    return result;}

private static void printHintSimpleSelect(final DataSource dataSource) throws SQLException {    // SQL语句并不涉及任何数据库路由和表路由信息（即where语句中没有user_id条件和order_id条件）    String sql = "SELECT i.* FROM t_order o JOIN t_order_item i ON o.order_id=i.order_id";    try (            HintManager hintManager = HintManager.getInstance();            Connection conn = dataSource.getConnection();            PreparedStatement preparedStatement = conn.prepareStatement(sql)) {        // 强制路由：表路由sharding column即order_id的值为1000        hintManager.addTableShardingValue("t_order", "order_id", 1000);        try (ResultSet rs = preparedStatement.executeQuery()) {            //todo do something        }    }}

private Collection<String> routeTables(final TableRule tableRule, final String routedDataSource) {    // 首先得到表的sharding策略，例如：表按照列order_id进行sharding    TableShardingStrategy strategy = shardingRule.getTableShardingStrategy(tableRule);    // 然后从ThreadLocal中取出sharding的值    List<ShardingValue<?>> shardingValues = HintManagerHolder.isUseShardingHint() ? getTableShardingValuesFromHint(strategy.getShardingColumns())            : getShardingValues(strategy.getShardingColumns());    Collection<String> result = tableRule.isDynamic() ? strategy.doDynamicSharding(shardingValues) : strategy.doStaticSharding(tableRule.getActualTableNames(routedDataSource), shardingValues);    Preconditions.checkState(!result.isEmpty(), "no table route info");    return result;}

HintManager hintManager = HintManager.getInstance();hintManager.setMasterRouteOnly();