Sharding-JDBC核心概念。

LogicTable

数据分片的逻辑表，对于水平拆分的数据库(表)，同一类表的总称。
例：上一篇文章为基础，用户信息表拆分为2张表,分别是t_order_0、t_order_1，他们的逻辑表名为t_order。

ActualTable

在分片的数据库中真实存在的物理表。即上个示例中的t_order_0、t_order_1。

DataNode

数据分片的最小单元。由数据源名称和数据表组成，例：test_msg0.t_order_0。配置时默认各个分片数据库的表结构均相同，直接配置逻辑表和真实表对应关系即可。

ShardingColumn

分片字段。用于将数据库(表)水平拆分的关键字段。SQL中如果无分片字段，将执行全路由，性能较差。Sharding-JDBC支持多分片字段。

ShardingAlgorithm

分片算法。Sharding-JDBC通过分片算法将数据分片，支持通过等号、BETWEEN和IN分片。分片算法目前需要业务方开发者自行实现，可实现的灵活度非常高。未来Sharding-JDBC也将会实现常用分片算法，如range，hash和tag等。

分库分表配置

分表分库配置会涉及如下类：

TableRule 表规则配置对象
ShardingRule 分库分表规则配置对象
ShardingStrategy 分片策略
ShardingAlgorithm 分片算法

举例：安装上一篇文章讲过的demo，分库分表策略配置方法进行debug：

配置分表策略代码图.png

    public static TableRule.TableRuleBuilder builder(String logicTable) {
        return new TableRule.TableRuleBuilder(logicTable);
    }

方法实现一个tableRule调用内部类；

 public static class TableRuleBuilder {
        private final String logicTable;
        private boolean dynamic;
        private List<String> actualTables;
        private DataSourceRule dataSourceRule;
        private Collection<String> dataSourceNames;
        private DatabaseShardingStrategy databaseShardingStrategy;
        private TableShardingStrategy tableShardingStrategy;
        private String generateKeyColumn;
        private Class<? extends KeyGenerator> keyGeneratorClass;

        public TableRule.TableRuleBuilder dynamic(boolean dynamic) {
            this.dynamic = dynamic;
            return this;
        }

        public TableRule.TableRuleBuilder actualTables(List<String> actualTables) {
            this.actualTables = actualTables;
            return this;
        }

        public TableRule.TableRuleBuilder dataSourceRule(DataSourceRule dataSourceRule) {
            this.dataSourceRule = dataSourceRule;
            return this;
        }

        public TableRule.TableRuleBuilder dataSourceNames(Collection<String> dataSourceNames) {
            this.dataSourceNames = dataSourceNames;
            return this;
        }

        public TableRule.TableRuleBuilder databaseShardingStrategy(DatabaseShardingStrategy databaseShardingStrategy) {
            this.databaseShardingStrategy = databaseShardingStrategy;
            return this;
        }

        public TableRule.TableRuleBuilder tableShardingStrategy(TableShardingStrategy tableShardingStrategy) {
            this.tableShardingStrategy = tableShardingStrategy;
            return this;
        }

        public TableRule.TableRuleBuilder generateKeyColumn(String generateKeyColumn) {
            this.generateKeyColumn = generateKeyColumn;
            return this;
        }

        public TableRule.TableRuleBuilder generateKeyColumn(String generateKeyColumn, Class<? extends KeyGenerator> keyGeneratorClass) {
            this.generateKeyColumn = generateKeyColumn;
            this.keyGeneratorClass = keyGeneratorClass;
            return this;
        }

        public TableRule build() {
            KeyGenerator keyGenerator = null;
            if(null != this.generateKeyColumn && null != this.keyGeneratorClass) {
                keyGenerator = KeyGeneratorFactory.createKeyGenerator(this.keyGeneratorClass);
            }

            return new TableRule(this.logicTable, this.dynamic, this.actualTables, this.dataSourceRule, this.dataSourceNames, this.databaseShardingStrategy, this.tableShardingStrategy, this.generateKeyColumn, keyGenerator);
        }

        @ConstructorProperties({"logicTable"})
        public TableRuleBuilder(String logicTable) {
            this.logicTable = logicTable;
        }
    }

从内部类来看，类初始化时，将图中代码传入配置参数，进行初始化赋值，此时this的各个参数如下图

TableRuleBuilder各个变量字段值.png

最终会调用build方法：

      public TableRule build() {
            KeyGenerator keyGenerator = null;
            if(null != this.generateKeyColumn && null != this.keyGeneratorClass) {
                keyGenerator = KeyGeneratorFactory.createKeyGenerator(this.keyGeneratorClass);
            }

            return new TableRule(this.logicTable, this.dynamic, this.actualTables, this.dataSourceRule, this.dataSourceNames, this.databaseShardingStrategy, this.tableShardingStrategy, this.generateKeyColumn, keyGenerator);
        }

最终初始化TableRule：

TableRule实例化.png

大多数业务场景下，我们使用静态分库分表数据单元，即 DataNode。如上文注释处 静态表的分库分表数据单元 处所见，分成两种判断，实质上第一种是将logicTable作为 actualTable，即在库里不进行分表，是第二种的一种特例。

我们来看看 generateDataNodes()方法：
参数说明：

/**
* 生成静态数据分片节点
*
* @param actualTables 真实表
* @param dataSourceRule 数据源配置对象
* @param actualDataSourceNames 数据源名集合
* @return 静态数据分片节点
*/

先看getDataSourceNames方法; 根据 数据源配置对象 和 数据源名集合 获得 最终的数据源名集合

    private Collection<String> getDataSourceNames(DataSourceRule dataSourceRule, Collection<String> actualDataSourceNames) {
        return (Collection)(null == dataSourceRule?Collections.emptyList():(null != actualDataSourceNames && !actualDataSourceNames.isEmpty()?actualDataSourceNames:dataSourceRule.getDataSourceNames()));
    }

 private List<DataNode> generateDataNodes(List<String> actualTables, DataSourceRule dataSourceRule, Collection<String> actualDataSourceNames) {
        Collection dataSourceNames = this.getDataSourceNames(dataSourceRule, actualDataSourceNames);
        ArrayList result = new ArrayList(actualTables.size() * (dataSourceNames.isEmpty()?1:dataSourceNames.size()));
        Iterator i$ = actualTables.iterator();

        while(true) {
            while(i$.hasNext()) {
                String actualTable = (String)i$.next();
                if(DataNode.isValidDataNode(actualTable)) {
                    result.add(new DataNode(actualTable));
                } else {
                    Iterator i$1 = dataSourceNames.iterator();

                    while(i$1.hasNext()) {
                        String dataSourceName = (String)i$1.next();
                        result.add(new DataNode(dataSourceName, actualTable));
                    }
                }
            }

            return result;
        }
    }

最终返回dataNode列表如下图所示：

dataNode列表.png

分库ShardingRule与分表结构相同；

ShardingAlgorithm

我们定义的策略类，继承了一下接口：

public class ModuloDatabaseShardingAlgorithm implements SingleKeyDatabaseShardingAlgorithm<Long>

SingleKeyDatabaseShardingAlgorithm接口的定义如下：

public interface SingleKeyDatabaseShardingAlgorithm<T extends Comparable<?>> extends SingleKeyShardingAlgorithm<T>, DatabaseShardingAlgorithm {
}

可知继承了DatabaseShardingAlgorithm，此时

public interface DatabaseShardingAlgorithm extends ShardingAlgorithm {
}

SingleKeyShardingAlgorithm``接口同样继承了ShardingAlgorithm ```

public interface SingleKeyShardingAlgorithm<T extends Comparable<?>> extends ShardingAlgorithm {
    
    /**
     * Sharding with equal operator.
     * 
     * @param availableTargetNames available data sources or tables's names
     * @param shardingValue sharding value
     * @return sharding results for data sources or tables's names
     */
    String doEqualSharding(Collection<String> availableTargetNames, ShardingValue<T> shardingValue);
    
    /**
     * Sharding with in operator.
     * 
     * @param availableTargetNames available data sources or tables's names
     * @param shardingValue sharding value
     * @return sharding results for data sources or tables's names
     */
    Collection<String> doInSharding(Collection<String> availableTargetNames, ShardingValue<T> shardingValue);
    
    /**
     * Sharding with between operator.
     * 
     * @param availableTargetNames available data sources or tables's names
     * @param shardingValue sharding value
     * @return sharding results for data sources or tables's names
     */
    Collection<String> doBetweenSharding(Collection<String> availableTargetNames, ShardingValue<T> shardingValue);
}

此时关系类图如图所示：

image.png

debug后，进入ShardingStrategy.java中的doSharding方法：

    private Collection<String> doSharding(final Collection<ShardingValue<?>> shardingValues, final Collection<String> availableTargetNames) {
        if (shardingAlgorithm instanceof NoneKeyShardingAlgorithm) {
            return Collections.singletonList(((NoneKeyShardingAlgorithm) shardingAlgorithm).doSharding(availableTargetNames, shardingValues.iterator().next()));
        }
        if (shardingAlgorithm instanceof SingleKeyShardingAlgorithm) {
            SingleKeyShardingAlgorithm<?> singleKeyShardingAlgorithm = (SingleKeyShardingAlgorithm<?>) shardingAlgorithm;
            ShardingValue shardingValue = shardingValues.iterator().next();
            switch (shardingValue.getType()) {
                case SINGLE:
                    return Collections.singletonList(singleKeyShardingAlgorithm.doEqualSharding(availableTargetNames, shardingValue));
                case LIST:
                    return singleKeyShardingAlgorithm.doInSharding(availableTargetNames, shardingValue);
                case RANGE:
                    return singleKeyShardingAlgorithm.doBetweenSharding(availableTargetNames, shardingValue);
                default:
                    throw new UnsupportedOperationException(shardingValue.getType().getClass().getName());
            }
        }
        if (shardingAlgorithm instanceof MultipleKeysShardingAlgorithm) {
            return ((MultipleKeysShardingAlgorithm) shardingAlgorithm).doSharding(availableTargetNames, shardingValues);
        }
        throw new UnsupportedOperationException(shardingAlgorithm.getClass().getName());
    }

按照上一篇文章demo进行debug，当请求接口进行数据插入时，首先调用ModuloDatabaseShardingAlgorithm类中的doEqualSharding进行分库策略的使用。

分库策略.png

参数.png