相当于MyBatis Guice中的MyBatis XML多环境

Question

我正在编写一个需要根据上下文使用不同数据库的服务（一个简单的字符串标签）。每个数据库都具有完全相同的模式。数据库列表是动态的。

通过MyBatis-Guice documentation on multiple data sources查看，示例是预先知道数据源列表的位置，每个数据源都有不同的映射器。同样，找到的问题here on SO也有相同的要求。

如上所述，我的要求更加动态和流畅。我们的想法是将所有当前已知的数据库（及其连接信息）放在配置中，并在服务启动时进行解析。然后，根据任何传入请求的上下文，代码应该为正确的数据库提取SqlSessionFactory。使用该SqlSessionFactory的所有下游代码完全相同 - 即不依赖于请求上下文。这意味着无论使用何种数据库，都会使用相同的映射器。

我的MyBatis和Guice知识无疑是新的和有限的。但是，我无法谷歌任何显示MyBatis-Guice等同于MyBatis的multiple environment approach supported by the XML configuration的内容。

Answer 1

我设法提出了一个适合我的解决方案，所以我想在这里分享一下。使用Guice的决定已经完成，所以那里没有蠕动的空间。

首先，我编写了一个MyBatis Guice模块，用于注册单个数据源。它是PrivateModule，因此为一个数据源注册的所有MyBatis类都不会与其他数据源的其他注册冲突。它使用内部MyBatisModule实现，因为Java不支持多继承。这意味着我们无法做public class MyMyBatisModule extends PrivateModule, MyBatisModule {...}。

public class MyMyBatisModule extends PrivateModule {

    private final String     datasourceLabel;
    private final Properies  datasourceProperties;
    private       List< Key<?> > exposedKeys = new ArrayList< Key<?> >();

    public MyMyBatisModule( String datasourceLabel, Properties datasourceProperties ) {

        this.datasourceLabel = datasourceLabel;
        this.datasourceProperties = datasourceProperties;
    }

    @Override
    protected void configure() {

        install( new InternalMyMyBatisModule( ) );

        for( Key<?> key: keys ) {
            expose( key );
        }
    }

    private class InternalMyMyBatisModule extends MyBatisModule {

        @Override
        protected void initialize( ) {

            environmentId( datasourceLabel );
            Names.bindProperties( binder(), properties );

            install( JdbcHelper.MySQL ); // See JDBC Helper commentary below

            bindDataSourceProviderType( C3p0DataSourceProvider.class ); // Choose whichever one you want
            bindTransactionFactoryType( JdbcTransactionFactory.class );

            // Register your mapper classes here.  These mapper classes will have their
            // keys exposed from the PrivateModule
            //
            // i.e.
            // 
            // keys.add( registerMapper( FredMapper.class );
            // kets.add( registerMapper( GingerMapper.class );
        }

        private <T> Key<T> registerMapper( Class<T> mapperClass ) {
            Key<T> key = Key.get( mapperClass, Names.named( datasourceLabel ) );
            bind( key ).to( mapperClass );
            addMapperClass( mapperClass );
            return key;
        }
    }
}

JdbcHeler.MySQL ：我使用JdbcHelper.MySQL作为将属性映射到连接字符串的快捷方式，并使用com.mysql.jdbc.Driver作为JDBC驱动程序。它被声明为：

MySQL("jdbc:mysql://${JDBC.host|localhost}:${JDBC.port|3306}/${JDBC.schema}", "com.mysql.jdbc.Driver"),

现在是时候注册所有数据源了。 MyBatisModules为我们处理此问题。它需要datasourceLabel到jdbc属性的映射。

public class MyBatisModules extends AbstractModule {

    private Map< String, Properties > connectionsProperties;

    public MyBatisModules( Map< String, Properties > = new HashMap< String, Properties > connectionsProperties ) {
        this.connectionsProperties = connectionsProperties; // consider deep copy if appropriate
    }

    @Override
    protected void configure( ) {

        for( Entry< String, Properties > datasourceConnectionProperties : this.connectionsProperties.entrySet() ) {
            install( new MyMyBatisModule( datasourceConnectionProperties.getKey(), datasourceConnectionProperties.getValue() ) );
        }

        bind( MapperRetriever.class ); // See MapperRetriever later

        // bind your DAO classes here.  By wrapping MyBatis Mapper use in DAO implementations, theoretically we
        // can fairly easily change from MyBatis to any other database library just by changing the DAO implementation.
        // The rest of our codebase would remain the same.
        //
        // i.e.
        //
        // bind( FredDao.class ).to( FredDaoMyBatis.class );
        // bind( GingerDao.class).to( GingerDaoMyBatis.class );
    }
}

现在我们只需要一些方法来获得正确的Mapper类（它本身与正确的数据源相关联）。为此，我们实际上需要在Guice Injector上调用一个方法。我真的不喜欢传递它的想法，所以我将它包装在MapperRetriever中。您需要为每个Mapper实现检索方法。

public class MapperRetriever {

    private final Injector injector;

    @Inject
    public MapperRetriver( Injector injector ) {
        this.injector = injector;
    }

    // The follwing two methods use the example Mappers referenced in the MyMyBatisModule implementation above

    public FredMapper getFredMapper( String datasourceLabel ) {
        return this.injector.getInstance( Key.get( FredMapper.class, Names.named( datasourceLabel ) ) );
    }

    public GingerMapper getGingerMapper( String datasourceLabel ) {
        return this.injector.getInstance( Key.get( GingerMapper.class, Names.named( datasourceLabel ) ) );
    }
}

DAO实施示例......

public interface FredDao {
    Fred selectFred( String datasourceLable, String fredId );
}    

public class FredDaoMyBatis implements FredDao {

    private MapperRetriever mapperRetriever;

    @Inject
    public FredDaoMyBatis( MapperRetriever mapperRetriever ) {
        this.mapperRetriever = mapperRetriever;
    }

    @Override
    public Fred selectFred( String datasourceLabel, String fredId ) {
        FredMapper fredMapper = this.mapperRetriever.getFredMapper( datasourceLabel );
        return fredMapper.getFred( fredId );
    }
}

Answer 2

您还可以创建一个自定义SqlSessionFactoryProvider，它返回一个SqlSessionFactory，它委托给正确的DataSource的SqlSessionFactory。使用ThreadLocal确定底层的SqlSessionFactory。

public class DelegatingSqlSessionFactory implements SqlSessionFactory {
    private final Map<String, SqlSessionFactory> factories = new HashMap<>();

    public DelegatingSqlSessionFactory(Map<String, DataSource> dataSources) throws ClassNotFoundException {
        dataSources.forEach((key, ds) -> {
            factories.put(key, createSqlSessionFactory(ds));
        });
    }

    private SqlSessionFactory delegate() {
        // Read from a ThreadLocal to determine correct SqlSessionFactory key
        String key = findKey();
        return factories.get(key);
    }

    @Override
    public SqlSession openSession() {
        return delegate().openSession();
    }

    @Override
    public SqlSession openSession(boolean autoCommit) {
        return delegate().openSession(autoCommit);
    }

    @Override
    public SqlSession openSession(Connection connection) {
        return delegate().openSession(connection);
    }

    @Override
    public SqlSession openSession(TransactionIsolationLevel level) {
        return delegate().openSession(level);
    }

    @Override
    public SqlSession openSession(ExecutorType execType) {
        return delegate().openSession(execType);
    }

    @Override
    public SqlSession openSession(ExecutorType execType, boolean autoCommit) {
        return delegate().openSession(execType, autoCommit);
    }

    @Override
    public SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level) {
        return delegate().openSession(execType, level);
    }

    @Override
    public SqlSession openSession(ExecutorType execType, Connection connection) {
        return delegate().openSession(execType, connection);
    }

    @Override
    public Configuration getConfiguration() {
        return delegate().getConfiguration();
    }
}