Mybatis系列(三)深入理解Mybatis執行流程及底層代碼分析(一)

mybatis基於xml配置文件的執行過程大體如下：

1.加載配置文件，初始化配置，創建Configuration對象。

2.創建SqlSessionFactory

3.根據SqlSessionFactory獲得SqlSession

4.SqlSession執行操作(增刪改查)

通過一個簡單的demo來實現一次數據庫操作（單獨使用mybatis框架時）

String resource = "mybatis-config.xml";
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
SqlSession sqlSession = sqlSessionFactory.openSession();
List list = sqlSession.selectList("com.xie.dao.BlogMapper.queryAllInfo");

介紹：上述代碼中mybatis-config.xml時mybatis的配置文件，加載配置文件後創建SqlSessionFactory，創建的過程採用builder設計模式。然後通過SqlSessionFactory獲得SqlSession

根據上面的demo代碼看源碼

1.SqlSessionFactoryBuilder源碼，獲得DefaultSqlSessionFactory對象。DefaultSqlSessionFactory是SqlSessionFactory的一個實現類

package org.apache.ibatis.session;

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);
  }
  
  public SqlSessionFactory build(Reader reader, String environment, Properties properties) {
    try {
      //加載配置文件生成對應的XMLConfigBuilder對象,通過XMLConfigBuilder可獲得Configuration
      XMLConfigBuilder parser = new XMLConfigBuilder(reader, environment, properties);
      //parser.parse()獲得Configuration對象，Configuration對象包含mybatis-config.xml文件中所有mybatis配置信息
      //然後調用build()
      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 {
      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.
      }
    }
  }
  //根據Configuration對象創建DefaultSqlSessionFactory
  public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }

}

2.DefaultSqlSessionFactory源碼。DefaultSqlSessionFactory爲SqlSessionFactory的一個實現類，通過DefaultSqlSessionFactory獲得DefaultSqlSession(DefaultSqlSession是SqlSession的實現類)

package org.apache.ibatis.session.defaults;
//實現了SqlSessionFactory接口
public class DefaultSqlSessionFactory implements SqlSessionFactory {

  private final Configuration configuration;//配置類

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

  @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);
  }

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

  //真正創建DefaultSqlSession的方法
  private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
    Transaction tx = null;
    try {
      //解析配置對象
      final Environment environment = configuration.getEnvironment();
      //創建事務管理器
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
      //創建Executor對象，Executor爲真正執行sql的對象，在此處創建傳入DefaultSqlSession
      final Executor executor = configuration.newExecutor(tx, execType);
      //創建DefaultSqlSession對象並返回
      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 SqlSession openSessionFromConnection(ExecutorType execType, Connection connection) {
    try {
      boolean autoCommit;
      try {
        autoCommit = connection.getAutoCommit();
      } catch (SQLException e) {
        // Failover to true, as most poor drivers
        // or databases won't support transactions
        autoCommit = true;
      }      
      final Environment environment = configuration.getEnvironment();
      final TransactionFactory transactionFactory = getTransactionFactoryFromEnvironment(environment);
      final Transaction tx = transactionFactory.newTransaction(connection);
      final Executor executor = configuration.newExecutor(tx, execType);
      return new DefaultSqlSession(configuration, executor, autoCommit);
    } catch (Exception e) {
      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();
  }

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

}

3.DefaultSqlSession源碼，DefaultSqlSession是SqlSession的實現類。包含一些操作數據的方法

package org.apache.ibatis.session.defaults;


public class DefaultSqlSession implements SqlSession {

  private final Configuration configuration;
  private final Executor executor;

  private final boolean autoCommit;
  private boolean dirty;
  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);
  }

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

  @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) {
    final List<? extends V> list = selectList(statement, parameter, rowBounds);
    final DefaultMapResultHandler<K, V> mapResultHandler = new DefaultMapResultHandler<K, V>(mapKey,
        configuration.getObjectFactory(), configuration.getObjectWrapperFactory(), configuration.getReflectorFactory());
    final DefaultResultContext<V> context = new DefaultResultContext<V>();
    for (V o : list) {
      context.nextResultObject(o);
      mapResultHandler.handleResult(context);
    }
    return mapResultHandler.getMappedResults();
  }

  @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 {
      MappedStatement ms = configuration.getMappedStatement(statement);
      Cursor<T> cursor = executor.queryCursor(ms, wrapCollection(parameter), rowBounds);
      registerCursor(cursor);
      return cursor;
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

  @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);
  }
  //statement參數爲Mapper.xml文件中一個數據操作的接口名稱
  @Override
  public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
    try {
      //根據statement獲取到MappedStatement，MappedStatement爲Mybatis框架中用於表示XML文件中一個sql語句節點
      MappedStatement ms = configuration.getMappedStatement(statement);
      //通過executor執行sql操作
      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();
    }
  }

  @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 {
      MappedStatement ms = configuration.getMappedStatement(statement);
      executor.query(ms, wrapCollection(parameter), rowBounds, handler);
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

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

  @Override
  public int insert(String statement, Object parameter) {
    return update(statement, parameter);
  }

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

  @Override
  public int update(String statement, Object parameter) {
    try {
      dirty = true;
      MappedStatement ms = configuration.getMappedStatement(statement);
      return executor.update(ms, wrapCollection(parameter));
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error updating database.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

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

  @Override
  public int delete(String statement, Object parameter) {
    return update(statement, parameter);
  }

  @Override
  public void commit() {
    commit(false);
  }

  @Override
  public void commit(boolean force) {
    try {
      executor.commit(isCommitOrRollbackRequired(force));
      dirty = false;
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error committing transaction.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

  @Override
  public void rollback() {
    rollback(false);
  }

  @Override
  public void rollback(boolean force) {
    try {
      executor.rollback(isCommitOrRollbackRequired(force));
      dirty = false;
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error rolling back transaction.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

  @Override
  public List<BatchResult> flushStatements() {
    try {
      return executor.flushStatements();
    } catch (Exception e) {
      throw ExceptionFactory.wrapException("Error flushing statements.  Cause: " + e, e);
    } finally {
      ErrorContext.instance().reset();
    }
  }

  @Override
  public void close() {
    try {
      executor.close(isCommitOrRollbackRequired(false));
      closeCursors();
      dirty = false;
    } finally {
      ErrorContext.instance().reset();
    }
  }

  private void closeCursors() {
    if (cursorList != null && cursorList.size() != 0) {
      for (Cursor<?> cursor : cursorList) {
        try {
          cursor.close();
        } catch (IOException e) {
          throw ExceptionFactory.wrapException("Error closing cursor.  Cause: " + e, e);
        }
      }
      cursorList.clear();
    }
  }

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

  @Override
  public <T> T getMapper(Class<T> type) {
    return configuration.<T>getMapper(type, this);
  }

  @Override
  public Connection getConnection() {
    try {
      return executor.getTransaction().getConnection();
    } catch (SQLException e) {
      throw ExceptionFactory.wrapException("Error getting a new connection.  Cause: " + e, e);
    }
  }

  @Override
  public void clearCache() {
    executor.clearLocalCache();
  }

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

  private boolean isCommitOrRollbackRequired(boolean force) {
    return (!autoCommit && dirty) || force;
  }

  private Object wrapCollection(final Object object) {
    if (object instanceof Collection) {
      StrictMap<Object> map = new StrictMap<Object>();
      map.put("collection", object);
      if (object instanceof List) {
        map.put("list", object);
      }
      return map;
    } else if (object != null && object.getClass().isArray()) {
      StrictMap<Object> map = new StrictMap<Object>();
      map.put("array", object);
      return map;
    }
    return object;
  }

  public static class StrictMap<V> extends HashMap<String, V> {

    private static final long serialVersionUID = -5741767162221585340L;

    @Override
    public V get(Object key) {
      if (!super.containsKey(key)) {
        throw new BindingException("Parameter '" + key + "' not found. Available parameters are " + this.keySet());
      }
      return super.get(key);
    }

  }

}

幾個類總結解釋：

SqlSessionFactoryBuilder ： SqlSessionFactory的構造器，用於創建SqlSessionFactory，採用了Builder設計模式

Configuration ：該對象是mybatis-config.xml文件中所有mybatis配置信息

SqlSessionFactory：SqlSession工廠類，以工廠形式創建SqlSession對象，採用了Factory工廠設計模式

XmlConfigParser ：負責將mybatis-config.xml配置文件解析成Configuration對象，供SqlSessonFactoryBuilder使用，創建SqlSessionFactory

MappedStatement：Mybatis框架中用於表示XML文件中一個sql語句節點，即一個、或者標籤。Mybatis框架在初始化階段會對XML配置文件進行讀取，將其中的sql語句節點對象化爲一個個MappedStatement對象

 

 

。。。。。。。。。先學到這，之後再補充。