入门：入门程序代码追踪

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【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;
  }
}
  1. 由configuration对象获取StatementHandler实例（handler）；
    （StatementHandler 是四大组件中最重要的一个对象，负责操作 Statement 对象与数据库进行交流）
  2. 调用prepareStatement方法，初始化StatementHandler对象（handler.prepare()方法），并进行参数设置（handler.parameterize(stmt)方法）；
  3. 调用StatementHandler的执行方法（query等），并返回结果；
  • doFlushStatements：刷新Statement对象（SimpleExecutor的doFlushStatements不做实质性操作）
其中configuration.newStatementHandler(...)如下：
package org.apache.ibatis.session;
...
public class Configuration {

  ...
  public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);
    statementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);
    return statementHandler;
  }
可知handler为“RoutingStatementHandler”类型，其源代码如下： 
package org.apache.ibatis.executor.statement;
...
public class RoutingStatementHandler implements StatementHandler {

  private final StatementHandler delegate;

  public RoutingStatementHandler(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {

    switch (ms.getStatementType()) {
      case STATEMENT:
        delegate = new SimpleStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case PREPARED:
        delegate = new PreparedStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      case CALLABLE:
        delegate = new CallableStatementHandler(executor, ms, parameter, rowBounds, resultHandler, boundSql);
        break;
      default:
        throw new ExecutorException("Unknown statement type: " + ms.getStatementType());
    }

  }

  public Statement prepare(Connection connection) throws SQLException {
    return delegate.prepare(connection);
  }

  public void parameterize(Statement statement) throws SQLException {
    delegate.parameterize(statement);
  }

  public void batch(Statement statement) throws SQLException {
    delegate.batch(statement);
  }

  public int update(Statement statement) throws SQLException {
    return delegate.update(statement);
  }

  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    return delegate.<E>query(statement, resultHandler);
  }

  public BoundSql getBoundSql() {
    return delegate.getBoundSql();
  }

  public ParameterHandler getParameterHandler() {
    return delegate.getParameterHandler();
  }
}
如同其名称一样，起到路由功能，根据Statement类型不同，使用不同的StatementHandler是实例对象去操作【？？？代表模式】；
如，“PreparedStatementHandler”其源码如下： 
package org.apache.ibatis.executor.statement;
...
public class PreparedStatementHandler extends BaseStatementHandler {

  public PreparedStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {
    super(executor, mappedStatement, parameter, rowBounds, resultHandler, boundSql);
  }

  public int update(Statement statement) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    int rows = ps.getUpdateCount();
    Object parameterObject = boundSql.getParameterObject();
    KeyGenerator keyGenerator = mappedStatement.getKeyGenerator();
    keyGenerator.processAfter(executor, mappedStatement, ps, parameterObject);
    return rows;
  }

  public void batch(Statement statement) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.addBatch();
  }

  public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException {
    PreparedStatement ps = (PreparedStatement) statement;
    ps.execute();
    return resultSetHandler.<E> handleResultSets(ps);
  }

  protected Statement instantiateStatement(Connection connection) throws SQLException {
    String sql = boundSql.getSql();
    if (mappedStatement.getKeyGenerator() instanceof Jdbc3KeyGenerator) {
      String[] keyColumnNames = mappedStatement.getKeyColumns();
      if (keyColumnNames == null) {
        return connection.prepareStatement(sql, PreparedStatement.RETURN_GENERATED_KEYS);
      } else {
        return connection.prepareStatement(sql, keyColumnNames);
      }
    } else if (mappedStatement.getResultSetType() != null) {
      return connection.prepareStatement(sql, mappedStatement.getResultSetType().getValue(), ResultSet.CONCUR_READ_ONLY);
    } else {
      return connection.prepareStatement(sql);
    }
  }

  public void parameterize(Statement statement) throws SQLException {
    parameterHandler.setParameters((PreparedStatement) statement);
  }
}
  1. 与数据库的交互仍然是JDBC的API（java.sql包中）；
  2. 返回“resultSetHandler.<E> handleResultSets()”方法结果到，结果类型为List<Object>；
    1. 返回到RoutingStatementHandler中，最终返回到BaseExecutor的List，并进行结果处理；
    2. 其源代码为：
package org.apache.ibatis.executor.resultset;
...
public class DefaultResultSetHandler implements ResultSetHandler {

  public List<Object> handleResultSets(Statement stmt) throws SQLException {
    final List<Object> multipleResults = new ArrayList<Object>();

    int resultSetCount = 0;
    ResultSetWrapper rsw = getFirstResultSet(stmt);

    List<ResultMap> resultMaps = mappedStatement.getResultMaps();
    int resultMapCount = resultMaps.size();
    validateResultMapsCount(rsw, resultMapCount);
    while (rsw != null && resultMapCount > resultSetCount) {
      ResultMap resultMap = resultMaps.get(resultSetCount);
      handleResultSet(rsw, resultMap, multipleResults, null);
      rsw = getNextResultSet(stmt);
      cleanUpAfterHandlingResultSet();
      resultSetCount++;
    }

    String[] resultSets = mappedStatement.getResulSets();
    if (resultSets != null) {
      while (rsw != null && resultSetCount < resultSets.length) {
        ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]);
        if (parentMapping != null) {
          String nestedResultMapId = parentMapping.getNestedResultMapId();
          ResultMap resultMap = configuration.getResultMap(nestedResultMapId);
          handleResultSet(rsw, resultMap, null, parentMapping);
        }
        rsw = getNextResultSet(stmt);
        cleanUpAfterHandlingResultSet();
        resultSetCount++;
      }
    }

    return collapseSingleResultList(multipleResults);
  }

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；

Transaction

由DefaultSqlSessionFactory中final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);及getTransactionFactoryFromEnvironment(Environment environment)方法可知：
tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);，
即“tx = 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）：
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