Sharding JDBC自動配置的原理

與所有starter一樣，shardingsphere-jdbc-core-spring-boot-starter也是通過SPI自動配置的原理實現(xiàn)分庫分表配置加載，spring.factories文件中的自動配置類shardingsphere-jdbc-core-spring-boot-starter功不可沒，他主要是自動創(chuàng)建了模式bean、事務(wù)類型bean和數(shù)據(jù)源bean，配置加載的過程可以歸納如下：

其中，創(chuàng)建數(shù)據(jù)源bean時會根據(jù)不同的模式創(chuàng)建不同的bean，本地模式直接從配置文件中加載，配置中心模式就從配置中心加載。ShardingSphereAutoConfiguration的實現(xiàn)如下：

@Configuration
@ComponentScan("org.apache.shardingsphere.spring.boot.converter")
@EnableConfigurationProperties(SpringBootPropertiesConfiguration.class)
@AutoConfigureBefore(DataSourceAutoConfiguration.class)
@RequiredArgsConstructor
public class ShardingSphereAutoConfiguration implements EnvironmentAware {
    
    private String databaseName;
    
    private final SpringBootPropertiesConfiguration props;
    
    private final Map<String, DataSource> dataSourceMap = new LinkedHashMap<>();
    
    /**
     * 模式配置
     *
     * @return mode configuration
     */
    @Bean
    public ModeConfiguration modeConfiguration() {
        return null == props.getMode() ? null : new YamlModeConfigurationSwapper().swapToObject(props.getMode());
    }
    
    /**
     * 單機(jī)模式：從本地配置中加載DataSource
     *
     * @param rules rules configuration
     * @param modeConfig mode configuration
     * @return data source bean
     * @throws SQLException SQL exception
     */
    @Bean
    @Conditional(LocalRulesCondition.class)
    @Autowired(required = false)
    public DataSource shardingSphereDataSource(final ObjectProvider<List<RuleConfiguration>> rules, final ObjectProvider<ModeConfiguration> modeConfig) throws SQLException {
        Collection<RuleConfiguration> ruleConfigs = Optional.ofNullable(rules.getIfAvailable()).orElseGet(Collections::emptyList);
        return ShardingSphereDataSourceFactory.createDataSource(databaseName, modeConfig.getIfAvailable(), dataSourceMap, ruleConfigs, props.getProps());
    }
    
    /**
     * 集群模式：從配置中心中加載DataSource
     *
     * @param modeConfig mode configuration
     * @return data source bean
     * @throws SQLException SQL exception
     */
    @Bean
    @ConditionalOnMissingBean(DataSource.class)
    public DataSource dataSource(final ModeConfiguration modeConfig) throws SQLException {
        return !dataSourceMap.isEmpty() ? ShardingSphereDataSourceFactory.createDataSource(databaseName, modeConfig, dataSourceMap, Collections.emptyList(), props.getProps())
                : ShardingSphereDataSourceFactory.createDataSource(databaseName, modeConfig);
    }
    
    /**
     * 事務(wù)類型掃描bean
     *
     * @return transaction type scanner
     */
    @Bean
    public TransactionTypeScanner transactionTypeScanner() {
        return new TransactionTypeScanner();
    }
    
    @Override
    public final void setEnvironment(final Environment environment) {
        dataSourceMap.putAll(DataSourceMapSetter.getDataSourceMap(environment));
        databaseName = DatabaseNameSetter.getDatabaseName(environment);
    }
}

下面以單機(jī)模式出發(fā)點，理一下加載的過程。

@Bean
@Conditional(LocalRulesCondition.class)
@Autowired(required = false)
public DataSource shardingSphereDataSource(final ObjectProvider<List<RuleConfiguration>> rules, final ObjectProvider<ModeConfiguration> modeConfig) throws SQLException {
    Collection<RuleConfiguration> ruleConfigs = Optional.ofNullable(rules.getIfAvailable()).orElseGet(Collections::emptyList);
    // 通過ShardingSphereDataSourceFactory工廠創(chuàng)建數(shù)據(jù)源
    return ShardingSphereDataSourceFactory.createDataSource(databaseName, modeConfig.getIfAvailable(), dataSourceMap, ruleConfigs, props.getProps());
}

通過對源碼的跟蹤，可以發(fā)現(xiàn)，ShardingSphereDataSourceFactory.createDataSource創(chuàng)建數(shù)據(jù)源經(jīng)歷了如下的過程

分片規(guī)則加載原理

分片規(guī)則、審計規(guī)則、key生成規(guī)則都是通過SPI的方式加載，自動配置類ShardingSphereAutoConfiguration中創(chuàng)建ShardingSphereDataSource的時候，會加載配置的分片規(guī)則，創(chuàng)建核心配置類ShardingRule，在ShardingRule的創(chuàng)建中會通過SPI的方式加載分片規(guī)則。加載的過程如下：

SPI核心實現(xiàn)類ShardingSphereServiceLoader中會將SPI接口進(jìn)行Map緩存管理，需要時直接獲取。如果Map中不存在，就通過反射的方式新建服務(wù)實例，具體實現(xiàn)源碼如下：文章來源地址http://www.zghlxwxcb.cn/news/detail-693990.html

public final class ShardingSphereServiceLoader {
    
    // 緩存service實例，
    // 緩存的Key,如：
    //  org.apache.shardingsphere.sharding.spi.ShardingAlgorithm
    //  org.apache.shardingsphere.sharding.spi.KeyGenerateAlgorithm
    //  org.apache.shardingsphere.transaction.spi.ShardingSphereTransactionManager
    private static final Map<Class<?>, Collection<Object>> SERVICES = new ConcurrentHashMap<>();
    
    /**
     * 注冊服務(wù)實例
     *
     * @param 服務(wù)接口
     */
    public static void register(final Class<?> serviceInterface) {
        if (!SERVICES.containsKey(serviceInterface)) {
            SERVICES.put(serviceInterface, load(serviceInterface));
        }
    }
    
    private static <T> Collection<Object> load(final Class<T> serviceInterface) {
        Collection<Object> result = new LinkedList<>();
        for (T each : ServiceLoader.load(serviceInterface)) {
            result.add(each);
        }
        return result;
    }
    
    /**
     * 獲取服務(wù)實例
     * 
     * @param 服務(wù)接口
     * @param <T> 服務(wù)類型
     * @return 服務(wù)實例
     */
    public static <T> Collection<T> getServiceInstances(final Class<T> serviceInterface) {
        return null == serviceInterface.getAnnotation(SingletonSPI.class) ? createNewServiceInstances(serviceInterface) : getSingletonServiceInstances(serviceInterface);
    }
    
    @SneakyThrows(ReflectiveOperationException.class)
    @SuppressWarnings("unchecked")
    private static <T> Collection<T> createNewServiceInstances(final Class<T> serviceInterface) {
        if (!SERVICES.containsKey(serviceInterface)) {
            return Collections.emptyList();
        }
        Collection<Object> services = SERVICES.get(serviceInterface);
        if (services.isEmpty()) {
            return Collections.emptyList();
        }
        Collection<T> result = new LinkedList<>();
        for (Object each : services) {
            // 通過反射新建實例
            result.add((T) each.getClass().getDeclaredConstructor().newInstance());
        }
        return result;
    }
    
    @SuppressWarnings("unchecked")
    private static <T> Collection<T> getSingletonServiceInstances(final Class<T> serviceInterface) {
        return (Collection<T>) SERVICES.getOrDefault(serviceInterface, Collections.emptyList());
    }
}

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