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mybatis-SqlSession

而本文解析的类，都在 session 包下，整体类图如下：

老艿艿：省略了一部分前面已经解析过的类。

技术图片

  • 核心是 SqlSession 。
  • SqlSessionFactory ，负责创建 SqlSession 对象的工厂。
  • SqlSessionFactoryBuilder ，是 SqlSessionFactory 的构建器。

下面，我们按照 SqlSessionFactoryBuilder => SqlSessionFactory => SqlSession 来详细解析。

2. SqlSessionFactoryBuilder

org.apache.ibatis.session.SqlSessionFactoryBuilder ，SqlSessionFactory 构造器。代码如下：

// SqlSessionFactory.java

public class SqlSessionFactoryBuilder {

    public SqlSessionFactory build(Reader reader) {
        return build(reader, null, null);
    }

    public SqlSessionFactory build(Reader reader, String environment) {
        return build(reader, environment, null);
    }

    public SqlSessionFactory build(Reader reader, Properties properties) {
        return build(reader, null, properties);
    }

    /**
     * 构造 SqlSessionFactory 对象
     *
     * @param reader Reader 对象
     * @param environment 环境
     * @param properties Properties 变量
     * @return SqlSessionFactory 对象
     */
    @SuppressWarnings("Duplicates")
    public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
        try {
            // 创建 XMLConfigBuilder 对象
            XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
            // 执行 XML 解析
            // 创建 DefaultSqlSessionFactory 对象
            return build(parser.parse());
        } catch (Exception e) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", e);
        } finally {
            ErrorContext.instance().reset();
            try {
                reader.close();
            } catch (IOException e) {
                // Intentionally ignore. Prefer previous error.
            }
        }
    }

    public SqlSessionFactory build(InputStream inputStream) {
        return build(inputStream, null, null);
    }

    public SqlSessionFactory build(InputStream inputStream, String environment) {
        return build(inputStream, environment, null);
    }

    public SqlSessionFactory build(InputStream inputStream, Properties properties) {
        return build(inputStream, null, properties);
    }

    public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
        try {
            // 创建 XMLConfigBuilder 对象
            XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
            // 执行 XML 解析
            // 创建 DefaultSqlSessionFactory 对象
            return build(parser.parse());
        } catch (Exception e) {
            throw ExceptionFactory.wrapException("Error building SqlSession.", e);
        } finally {
            ErrorContext.instance().reset();
            try {
                inputStream.close();
            } catch (IOException e) {
                // Intentionally ignore. Prefer previous error.
            }
        }
    }

    /**
     * 创建 DefaultSqlSessionFactory 对象
     *
     * @param config Configuration 对象
     * @return DefaultSqlSessionFactory 对象
     */
    public SqlSessionFactory build(Configuration config) {
        return new DefaultSqlSessionFactory(config);
    }

}
  • 提供了各种 build 的重载方法，核心的套路都是解析出 Configuration 配置对象，从而创建出 DefaultSqlSessionFactory 对象。

3. SqlSessionFactory

org.apache.ibatis.session.SqlSessionFactory ，SqlSession 工厂接口。代码如下：

// SqlSessionFactory.java

public interface SqlSessionFactory {

    SqlSession openSession();

    SqlSession openSession(boolean autoCommit);

    SqlSession openSession(Connection connection);

    SqlSession openSession(TransactionIsolationLevel level);

    SqlSession openSession(ExecutorType execType);

    SqlSession openSession(ExecutorType execType, boolean autoCommit);

    SqlSession openSession(ExecutorType execType, TransactionIsolationLevel level);

    SqlSession openSession(ExecutorType execType, Connection connection);

    Configuration getConfiguration();

}
  • 定义了 #openSession(...) 和 #getConfiguration() 两类方法。

3.1 DefaultSqlSessionFactory

org.apache.ibatis.session.defaults.DefaultSqlSessionFactory ，实现 SqlSessionFactory 接口，默认的 SqlSessionFactory 实现类。

3.1.1 构造方法

// DefaultSqlSessionFactory.java

private final Configuration configuration;

public DefaultSqlSessionFactory(Configuration configuration) {
    this.configuration = configuration;
}

@Override
public Configuration getConfiguration() {
    return configuration;
}

3.1.2 openSession

// DefaultSqlSessionFactory.java

@Override
public SqlSession openSession() {
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
}

@Override
public SqlSession openSession(boolean autoCommit) {
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, autoCommit);
}

@Override
public SqlSession openSession(ExecutorType execType) {
    return openSessionFromDataSource(execType, null, false);
}

@Override
public SqlSession openSession(TransactionIsolationLevel level) {
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), level, false);
}

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

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

@Override
public SqlSession openSession(Connection connection) {
    return openSessionFromConnection(configuration.getDefaultExecutorType(), connection);
}

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

  • 调用 #openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) 方法，获得 SqlSession 对象。代码如下：

    // DefaultSqlSessionFactory.java

    private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
        Transaction tx = null;
        try {
            // 获得 Environment 对象
            final Environment environment = configuration.getEnvironment();
            // 创建 Transaction 对象
            final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
            tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
            // 创建 Executor 对象
            final Executor executor = configuration.newExecutor(tx, execType);
            // 创建 DefaultSqlSession 对象
            return new DefaultSqlSession(configuration, executor, autoCommit);
        } catch (Exception e) {
            // 如果发生异常，则关闭 Transaction 对象
            closeTransaction(tx); // may have fetched a connection so lets call close()
            throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
        } finally {
            ErrorContext.instance().reset();
        }
    }
    • DefaultSqlSession 的创建，需要 configuration、executor、autoCommit 三个参数。

  • #openSessionFromConnection(ExecutorType execType, Connection connection) 方法，获得 SqlSession 对象。代码如下：

    // DefaultSqlSessionFactory.java

    private SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {
        try {
            // 获得是否可以自动提交
            boolean autoCommit;
            try {
                autoCommit = connection.getAutoCommit();
            } catch (SQLException e) {
                // Failover to true, as most poor drivers
                // or databases won‘t support transactions
                autoCommit = true;
            }
            // 获得 Environment 对象
            final Environment environment = configuration.getEnvironment();
            // 创建 Transaction 对象
            final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
            final Transaction tx = transactionFactory.newTransaction(connection);
            // 创建 Executor 对象
            final Executor executor = configuration.newExecutor(tx, execType);
            // 创建 DefaultSqlSession 对象
            return new DefaultSqlSession(configuration, executor, autoCommit);
        } catch (Exception e) {
            throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
        } finally {
            ErrorContext.instance().reset();
        }
    }

3.1.3 getTransactionFactoryFromEnvironment

// DefaultSqlSessionFactory.java

private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
    // 情况一，创建 ManagedTransactionFactory 对象
    if (environment == null || environment.getTransactionFactory() == null) {
        return new ManagedTransactionFactory();
    }
    // 情况二，使用 `environment` 中的
    return environment.getTransactionFactory();
}

3.1.4 closeTransaction

// DefaultSqlSessionFactory.java

private void closeTransaction(Transaction tx) {
    if (tx != null) {
        try {
            tx.close();
        } catch (SQLException ignore) {
            // Intentionally ignore. Prefer previous error.
        }
    }
}

4. SqlSession

org.apache.ibatis.session.SqlSession ，SQL Session 接口。代码如下：

// SqlSession.java

public interface SqlSession extends Closeable {

    <T> T selectOne(String statement);
    <T> T selectOne(String statement, Object parameter);

    <E> List<E> selectList(String statement);
    <E> List<E> selectList(String statement, Object parameter);
    <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds);

    <K, V> Map<K, V> selectMap(String statement, String mapKey);
    <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey);
    <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds);

    <T> Cursor<T> selectCursor(String statement);
    <T> Cursor<T> selectCursor(String statement, Object parameter);
    <T> Cursor<T> selectCursor(String statement, Object parameter, RowBounds rowBounds);

    void select(String statement, Object parameter, ResultHandler handler);
    void select(String statement, ResultHandler handler);
    void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler);

    int insert(String statement);
    int insert(String statement, Object parameter);

    int update(String statement);
    int update(String statement, Object parameter);

    int delete(String statement);
    int delete(String statement, Object parameter);

    void commit();
    void commit(boolean force);
    void rollback();
    void rollback(boolean force);

    List<BatchResult> flushStatements();

    @Override
    void close();

    void clearCache();

    Configuration getConfiguration();

    /**
     * Retrieves a mapper.
     * @param <T> the mapper type
     * @param type Mapper interface class
     * @return a mapper bound to this SqlSession
     */
    <T> T getMapper(Class<T> type);

    /**
     * Retrieves inner database connection
     * @return Connection
     */
    Connection getConnection();

}
  • 大体接口上，和 Executor 接口是相似的。

4.1 DefaultSqlSession

org.apache.ibatis.session.defaults.DefaultSqlSession ，实现 SqlSession 接口，默认的 SqlSession 实现类。

4.1.1 构造方法

// DefaultSqlSession.java

private final Configuration configuration;
private final Executor executor;

/**
 * 是否自动提交事务
 */
private final boolean autoCommit;
/**
 * 是否发生数据变更
 */
private boolean dirty;
/**
 * Cursor 数组
 */
private List<Cursor<?>> cursorList;

public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
    this.configuration = configuration;
    this.executor = executor;
    this.dirty = false;
    this.autoCommit = autoCommit;
}

public DefaultSqlSession(Configuration configuration, Executor executor) {
    this(configuration, executor, false);
}

4.1.2 selectList

// DefaultSqlSession.java

@Override
public <E> List<E> selectList(String statement) {
    return this.selectList(statement, null);
}

@Override
public <E> List<E> selectList(String statement, Object parameter) {
    return this.selectList(statement, parameter, RowBounds.DEFAULT);
}

@Override
public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
    try {
        // <1> 获得 MappedStatement 对象
        MappedStatement ms = configuration.getMappedStatement(statement);
        // <2> 执行查询
        return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
    } catch (Exception e) {
        throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
        ErrorContext.instance().reset();
    }
}

  • <1> 处，调用 Configuration#getMappedStatement(String id) 方法，获得 MappedStatement 对象。代码如下：

    // DefaultSqlSession.java

    /**
     * MappedStatement 映射
     *
     * KEY：`${namespace}.${id}`
     */
    protected final Map<String, MappedStatement> mappedStatements = new StrictMap<>("Mapped Statements collection");

    public MappedStatement getMappedStatement(String id, boolean validateIncompleteStatements) {
        // 校验，保证所有 MappedStatement 已经构造完毕
        if (validateIncompleteStatements) {
            buildAllStatements();
        }
        // 获取 MappedStatement 对象
        return mappedStatements.get(id);
    }

    protected void buildAllStatements() {
        if (!incompleteResultMaps.isEmpty()) {
            synchronized (incompleteResultMaps) { // 保证 incompleteResultMaps 被解析完
                // This always throws a BuilderException.
                incompleteResultMaps.iterator().next().resolve();
            }
        }
        if (!incompleteCacheRefs.isEmpty()) {
            synchronized (incompleteCacheRefs) { // 保证 incompleteCacheRefs 被解析完
                // This always throws a BuilderException.
                incompleteCacheRefs.iterator().next().resolveCacheRef();
            }
        }
        if (!incompleteStatements.isEmpty()) {
            synchronized (incompleteStatements) { // 保证 incompleteStatements 被解析完
                // This always throws a BuilderException.
                incompleteStatements.iterator().next().parseStatementNode();
            }
        }
        if (!incompleteMethods.isEmpty()) {
            synchronized (incompleteMethods) { // 保证 incompleteMethods 被解析完
                // This always throws a BuilderException.
                incompleteMethods.iterator().next().resolve();
            }
        }
    }
    • 其中，#buildAllStatements() 方法，是用来保证所有 MappedStatement 已经构造完毕。不过艿艿，暂时没想到，什么情况下，会出现 MappedStatement 没被正确构建的情况。猜测有可能是防御性编程。
  • <2> 处，调用 Executor#query(...) 方法，执行查询。

4.1.3 selectOne

// DefaultSqlSession.java

@Override
public <T> T selectOne(String statement) {
    return this.selectOne(statement, null);
}

@Override
public <T> T selectOne(String statement, Object parameter) {
    // Popular vote was to return null on 0 results and throw exception on too many.
    List<T> list = this.selectList(statement, parameter);
    if (list.size() == 1) {
        return list.get(0);
    } else if (list.size() > 1) {
        throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
    } else {
        return null;
    }
}
  • 内部调用 #selectList(String statement, Object parameter) 方法，进行实现。

4.1.4 selectMap

#selectMap(...) 方法，查询结果，并基于 Map 聚合结果。代码如下：

// DefaultSqlSession.java

@Override
public <K, V> Map<K, V> selectMap(String statement, String mapKey) {
    return this.selectMap(statement, null, mapKey, RowBounds.DEFAULT);
}

@Override
public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey) {
    return this.selectMap(statement, parameter, mapKey, RowBounds.DEFAULT);
}

@Override
public <K, V> Map<K, V> selectMap(String statement, Object parameter, String mapKey, RowBounds rowBounds) {
    // <1> 执行查询
    final List<? extends V> list = selectList(statement, parameter, rowBounds);
    // <2> 创建 DefaultMapResultHandler 对象
    final DefaultMapResultHandler<K, V> mapResultHandler = new DefaultMapResultHandler<>(mapKey,
            configuration.getObjectFactory(), configuration.getObjectWrapperFactory(), configuration.getReflectorFactory());
    // <3> 创建 DefaultResultContext 对象
    final DefaultResultContext<V> context = new DefaultResultContext<>();
    // <4> 遍历查询结果
    for (V o : list) {
        // 设置 DefaultResultContext 中
        context.nextResultObject(o);
        // 使用 DefaultMapResultHandler 处理结果的当前元素
        mapResultHandler.handleResult(context);
    }
    // <5> 返回结果
    return mapResultHandler.getMappedResults();
}
  • <1> 处，调用 #selectList(String statement, Object parameter, RowBounds rowBounds) 方法，执行查询。
  • <2> 处，创建 DefaultMapResultHandler 对象。
  • <3> 处，创建 DefaultResultContext 对象。

  • <4> 处，遍历查询结果，并调用 DefaultMapResultHandler#handleResult(context) 方法，将结果的当前元素，聚合成 Map 。代码如下：

    // DefaultMapResultHandler.java

    public class DefaultMapResultHandler<K, V> implements ResultHandler<V> {

        /**
         * 结果，基于 Map 聚合
         */
        private final Map<K, V> mappedResults;
        /**
         * {@link #mappedResults} 的 KEY 属性名
         */
        private final String mapKey;
        private final ObjectFactory objectFactory;
        private final ObjectWrapperFactory objectWrapperFactory;
        private final ReflectorFactory reflectorFactory;

        @SuppressWarnings("unchecked")
        public DefaultMapResultHandler(String mapKey, ObjectFactory objectFactory, ObjectWrapperFactory objectWrapperFactory, ReflectorFactory reflectorFactory) {
            this.objectFactory = objectFactory;
            this.objectWrapperFactory = objectWrapperFactory;
            this.reflectorFactory = reflectorFactory;
            // 创建 Map 对象
            this.mappedResults = objectFactory.create(Map.class);
            this.mapKey = mapKey;
        }

        @Override
        public void handleResult(ResultContext<? extends V> context) {
            // 获得 KEY 对应的属性
            final V value = context.getResultObject();
            final MetaObject mo = MetaObject.forObject(value, objectFactory, objectWrapperFactory, reflectorFactory);
            // TODO is that assignment always true?
            final K key = (K) mo.getValue(mapKey);
            // 添加到 mappedResults 中
            mappedResults.put(key, value);
        }

        public Map<K, V> getMappedResults() {
            return mappedResults;
        }

    }

  • <5> 处，返回结果。

4.1.5 selectCursor

// DefaultSqlSession.java

@Override
public <T> Cursor<T> selectCursor(String statement) {
    return selectCursor(statement, null);
}

@Override
public <T> Cursor<T> selectCursor(String statement, Object parameter) {
    return selectCursor(statement, parameter, RowBounds.DEFAULT);
}

@Override
public <T> Cursor<T> selectCursor(String statement, Object parameter, RowBounds rowBounds) {
    try {
        // <1> 获得 MappedStatement 对象
        MappedStatement ms = configuration.getMappedStatement(statement);
        // <2> 执行查询
        Cursor<T> cursor = executor.queryCursor(ms, wrapCollection(parameter), rowBounds);
        // <3> 添加 cursor 到 cursorList 中
        registerCursor(cursor);
        return cursor;
    } catch (Exception e) {
        throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
        ErrorContext.instance().reset();
    }
}
  • <1> 处，调用 Configuration#getMappedStatement(String id) 方法，获得 MappedStatement 对象。
  • <2> 处，调用 Executor#queryCursor(...) 方法，执行查询。

  • <3> 处，调用 #registerCursor(Cursor<T> cursor) 方法，添加 cursor 到 cursorList 中。代码如下：

    // DefaultSqlSession.java

    private <T> void registerCursor(Cursor<T> cursor) {
        if (cursorList == null) {
            cursorList = new ArrayList<>();
        }
        cursorList.add(cursor);
    }

4.1.6 select

#select(..., ResultHandler handler) 方法，执行查询，使用传入的 handler 方法参数，对结果进行处理。代码如下：

// DefaultSqlSession.java

@Override
public void select(String statement, Object parameter, ResultHandler handler) {
    select(statement, parameter, RowBounds.DEFAULT, handler);
}

@Override
public void select(String statement, ResultHandler handler) {
    select(statement, null, RowBounds.DEFAULT, handler);
}

@Override
public void select(String statement, Object parameter, RowBounds rowBounds, ResultHandler handler) {
    try {
        // 获得 MappedStatement 对象
        MappedStatement ms = configuration.getMappedStatement(statement);
        // 执行查询
        executor.query(ms, wrapCollection(parameter), rowBounds, handler);
    } catch (Exception e) {
        throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
        ErrorContext.instance().reset();
    }
}

4.1.7 wrapCollection

在上述的查询方法中，我们都可以看到一个 #wrapCollection(final Object object) 方法，若参数 object 是 Collection、Array、Map 参数类型的情况下，包装成 Map 返回。代码如下：

// DefaultSqlSession.java

private Object wrapCollection(final Object object) {
    if (object instanceof Collection) {
        // 如果是集合，则添加到 collection 中
        StrictMap<Object> map = new StrictMap<>();
        map.put("collection", object);
        // 如果是 List ，则添加到 list 中
        if (object instanceof List) {
            map.put("list", object);
        }
        return map;
    } else if (object != null && object.getClass().isArray()) {
        // 如果是 Array ，则添加到 array 中
        StrictMap<Object> map = new StrictMap<>();
        map.put("array", object);
        return map;
    }
    return object;
}

4.1.8 update

// DefaultSqlSession.java

@Override
public int update(String statement) {
    return update(statement, null);
}

@Override