入门：入门程序代码追踪

【2020/10/08 01:28:55】

入口代码

public class Mybatis_first {
	
	//会话工厂
	private SqlSessionFactory sqlSessionFactory;

	@Before
	public void createSqlSessionFactory() throws IOException {
		// mybatis配置文件
		String resource = "SqlMapConfig.xml";
		// 得到配置文件流
		InputStream inputStream = Resources.getResourceAsStream(resource);

		// 使用SqlSessionFactoryBuilder从xml配置文件中创建SqlSessionFactory
		sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
	}

	public void testFindUserById() {
		// 数据库会话实例
		SqlSession sqlSession = null;
		try {
			// 创建数据库会话实例sqlSession
			sqlSession = sqlSessionFactory.openSession();
            
			// selectOne查询出一条记录
			User user = sqlSession.selectOne("test.findUserById", 1);

SqlSessionFactoryBuilder代码

由入口：sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);：

package org.apache.ibatis.session;

public class SqlSessionFactoryBuilder {

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

  ...
  public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
    try {
      XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
      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.
      }
    }
  }
	
  ...
  public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

得到sqlSessionFactory为DefaultSqlSessionFactory；

• SqlSessionFactoryBuilder().build返回值均为DefaultSqlSessionFactory类型

sqlSessionFactory代码

由入口：sqlSession = sqlSessionFactory.openSession();：（由sqlSessionFactory可知，即“DefaultSqlSessionFactory.openSession()”）

package org.apache.ibatis.session.defaults;

public class DefaultSqlSessionFactory implements SqlSessionFactory {

  private final Configuration configuration;

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

  public SqlSession openSession() {
    return openSessionFromDataSource(configuration.getDefaultExecutorType(), null, false);
  }
    
  ...
  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      closeTransaction(tx); // may have fetched a connection so lets call close()
      throw ExceptionFactory.wrapException("Error opening session.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }
 
  ...
  private TransactionFactory getTransactionFactoryFromEnvironment(Environment environment) {
    if (environment == null || environment.getTransactionFactory() == null) {
      return new ManagedTransactionFactory();
    }
    return environment.getTransactionFactory();
  }

1. 根据configuration得到当前环境实例environment；
2. 根据environment中的Transaction配置得到TransactionFactory；
3. 并由transactionFactory根据environment数据源配置等，创建Transaction实例（tx）；
   1. “TransactionIsolationLevel level”：事务隔离级别
   2. “boolean autoCommit”：事务自动提交【？？？】
4. 由configuration根据tx实例和execType，创建executor实例；
   1. “ExecutorType execType”：executor类型（如：BatchExecutor、ReuseExecutor、SimpleExecutor）
5. 根据configuration, executor生成DefaultSqlSession对象，并返回；

得到sqlSession为DefaultSqlSession；

• DefaultSqlSessionFactory.openSession返回值均为DefaultSqlSession类型
• 如果SqlMapConfig.xml中没有Transaction，则返回默认的ManagedTransactionFactory
• tx（Transaction）作为参数，用于构造Executor
• 其中Environment、TransactionFactory、Executor均被final修饰

Executor

由DefaultSqlSessionFactory中configuration.getDefaultExecutorType()、final Executor executor = configuration.newExecutor(tx, execType);：

package org.apache.ibatis.session;

public class Configuration {
  ...
  protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;

  ...
  public ExecutorType getDefaultExecutorType() {
    return defaultExecutorType;
  }
  ...
  public Executor newExecutor(Transaction transaction, ExecutorType executorType) {
    executorType = executorType == null ? defaultExecutorType : executorType;
    executorType = executorType == null ? ExecutorType.SIMPLE : executorType;
    Executor executor;
    if (ExecutorType.BATCH == executorType) {
      executor = new BatchExecutor(this, transaction);
    } else if (ExecutorType.REUSE == executorType) {
      executor = new ReuseExecutor(this, transaction);
    } else {
      executor = new SimpleExecutor(this, transaction);
    }
    if (cacheEnabled) {
      executor = new CachingExecutor(executor);
    }
    executor = (Executor) interceptorChain.pluginAll(executor);
    return executor;
  }

得到executor = new SimpleExecutor；

SimpleExecutor

SimpleExecutor源码如下（继承了抽象类BaseExecutor）：

package org.apache.ibatis.executor;
...
public class SimpleExecutor extends BaseExecutor {

  public SimpleExecutor(Configuration configuration, Transaction transaction) {
    super(configuration, transaction);
  }

  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Statement stmt = null;
    try {
      Configuration configuration = ms.getConfiguration();
      StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
      stmt = prepareStatement(handler, ms.getStatementLog());
      return handler.update(stmt);
    } finally {
      closeStatement(stmt);
    }
  }

  public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
    Statement stmt = null;
    try {
      Configuration configuration = ms.getConfiguration();
      StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
      stmt = prepareStatement(handler, ms.getStatementLog());
      return handler.<E>query(stmt, resultHandler);
    } finally {
      closeStatement(stmt);
    }
  }

  public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException {
    return Collections.emptyList();
  }

  private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
    Statement stmt;
    Connection connection = getConnection(statementLog);
    stmt = handler.prepare(connection);
    handler.parameterize(stmt);
    return stmt;
  }
}

BaseExecutor

抽象类BaseExecutor源码如下：

package org.apache.ibatis.executor;

...
public abstract class BaseExecutor implements Executor {

  ...
  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
    BoundSql boundSql = ms.getBoundSql(parameter);
    CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);
    return query(ms, parameter, rowBounds, resultHandler, key, boundSql);
 }

  @SuppressWarnings("unchecked")
  public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
    ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
    if (closed) throw new ExecutorException("Executor was closed.");
    if (queryStack == 0 && ms.isFlushCacheRequired()) {
      clearLocalCache();
    }
    List<E> list;
    try {
      queryStack++;
      list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
      if (list != null) {
        handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
      } else {
        list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
      }
    } finally {
      queryStack--;
    }
    if (queryStack == 0) {
      for (DeferredLoad deferredLoad : deferredLoads) {
        deferredLoad.load();
      }
      deferredLoads.clear(); // issue #601
      if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
        clearLocalCache(); // issue #482
      }
    }
    return list;
  }
  
  ...
  protected abstract int doUpdate(MappedStatement ms, Object parameter)
      throws SQLException;

  protected abstract List<BatchResult> doFlushStatements(boolean isRollback)
      throws SQLException;

  protected abstract <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql)
      throws SQLException;

  protected void closeStatement(Statement statement) {
    if (statement != null) {
      try {
        statement.close();
      } catch (SQLException e) {
        // ignore
      }
    }
  }
  
  ...
  private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
    List<E> list;
    localCache.putObject(key, EXECUTION_PLACEHOLDER);
    try {
      list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
    } finally {
      localCache.removeObject(key);
    }
    localCache.putObject(key, list);
    if (ms.getStatementType() == StatementType.CALLABLE) {
      localOutputParameterCache.putObject(key, parameter);
    }
    return list;
  }

  protected Connection getConnection(Log statementLog) throws SQLException {
    Connection connection = transaction.getConnection();
    if (statementLog.isDebugEnabled()) {
      return ConnectionLogger.newInstance(connection, statementLog, queryStack);
    } else {
      return connection;
    }
  }

1. “doQuery(ms, parameter, rowBounds, resultHandler, boundSql)”等方法在实现类中实现（如：BatchExecutor、ReuseExecutor、SimpleExecutor）；
2. “getConnection(Log statementLog)”用于（使用transaction）获取链接，在SimpleExecutor的 prepareStatement 方法中调用；
3. “closeStatement(Statement statement)”用于关闭链接：在在SimpleExecutor的 doQuery 等方法中调用；

• Mybatis源码：BaseExecutor解析

Transaction

由sqlSession中final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);、return new ManagedTransactionFactory();有：
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);即“ManagedTransactionFactory.newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit)”：

package org.apache.ibatis.transaction.managed;

public class ManagedTransactionFactory implements TransactionFactory {

  ...
  public Transaction newTransaction(DataSource ds, TransactionIsolationLevel level, boolean autoCommit) {
    // Silently ignores autocommit and isolation level, as managed transactions are entirely
    // controlled by an external manager.  It's silently ignored so that
    // code remains portable between managed and unmanaged configurations.
    return new ManagedTransaction(ds, level, closeConnection);
  }
}

得到Transaction tx = new ManagedTransaction，其源码如下：

package org.apache.ibatis.transaction.managed;
...
public class ManagedTransaction implements Transaction {

  private static final Log log = LogFactory.getLog(ManagedTransaction.class);

  private DataSource dataSource;
  private TransactionIsolationLevel level;
  private Connection connection;
  private boolean closeConnection;

  public ManagedTransaction(Connection connection, boolean closeConnection) {
    this.connection = connection;
    this.closeConnection = closeConnection;
  }

  public ManagedTransaction(DataSource ds, TransactionIsolationLevel level, boolean closeConnection) {
    this.dataSource = ds;
    this.level = level;
    this.closeConnection = closeConnection;
  }

  public Connection getConnection() throws SQLException {
    if (this.connection == null) {
      openConnection();
    }
    return this.connection;
  }

  public void commit() throws SQLException {
    // Does nothing
  }

  public void rollback() throws SQLException {
    // Does nothing
  }

  public void close() throws SQLException {
    if (this.closeConnection && this.connection != null) {
      if (log.isDebugEnabled()) {
        log.debug("Closing JDBC Connection [" + this.connection + "]");
      }
      this.connection.close();
    }
  }

  protected void openConnection() throws SQLException {
    if (log.isDebugEnabled()) {
      log.debug("Opening JDBC Connection");
    }
    this.connection = this.dataSource.getConnection();
    if (this.level != null) {
      this.connection.setTransactionIsolation(this.level.getLevel());
    }
  }
}

1. “getConnection()”在BaseExecutor的“getConnection(Log statementLog)”方法中调用；

sqlSession代码

以入口“User user = sqlSession.selectOne("test.findUserById", 1);”为例：
由DefaultSqlSessionFactory代码，User user = sqlSession.selectOne("test.findUserById", 1);即“DefaultSqlSession.selectOne(String statement, Object parameter)”：

package org.apache.ibatis.session.defaults;

public class DefaultSqlSession implements SqlSession {
  ...
  public DefaultSqlSession(Configuration configuration, Executor executor, boolean autoCommit) {
    this.configuration = configuration;
    this.executor = executor;
    this.dirty = false;
    this.autoCommit = autoCommit;
  }
  
  ...
  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.<T>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;
    }
  }
  
  ...
  public <E> List<E> selectList(String statement, Object parameter) {
    return this.selectList(statement, parameter, RowBounds.DEFAULT);
  }
  
  ...
  public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
    try {
      MappedStatement ms = configuration.getMappedStatement(statement);
      List<E> result = executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
      return result;
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

• selectOne也是由selectList实现，“list.size() > 1”则抛出异常
• 操作数据库由executor实现
• 默认的executor是“SimpleExecutor”

  （继承自抽象类BaseExecutor）：