ibatis部分源码窥探

ibatis2.3.4部分类结构图

[img]http://dl.iteye.com/upload/attachment/607817/2a8babd7-06c9-3085-a437-4bf6d370dde8.jpg[/img]

SqlMapClientImpl拥有SqlMapExecutorDelegate，ThreadLocal两个对象。还有getLocalSqlMapSession(),openSession()和insert(),update,delete(),queryForObject()几个方法。代码：

  public SqlMapExecutorDelegate delegate;

  protected ThreadLocal localSqlMapSession = new ThreadLocal();

  public SqlMapSession openSession() {
    SqlMapSessionImpl sqlMapSession = new SqlMapSessionImpl(this);
    sqlMapSession.open();
    return sqlMapSession;
  }

  public SqlMapSession openSession(Connection conn) {
    try {
      SqlMapSessionImpl sqlMapSession = new SqlMapSessionImpl(this);
      sqlMapSession.open();
      sqlMapSession.setUserConnection(conn);
      return sqlMapSession;
    } catch (SQLException e) {
      throw new SqlMapException("Error setting user provided connection.  Cause: " + e, e);
    }
  }

  protected SqlMapSessionImpl getLocalSqlMapSession() {
    SqlMapSessionImpl sqlMapSession = (SqlMapSessionImpl)      localSqlMapSession.get();
    if (sqlMapSession == null || sqlMapSession.isClosed()) {
      sqlMapSession = new SqlMapSessionImpl(this);
      localSqlMapSession.set(sqlMapSession);
    }
    return sqlMapSession;
  }

  public Object insert(String id, Object param) throws SQLException {
    return getLocalSqlMapSession().insert(id, param);
  }

  public int update(String id, Object param) throws SQLException {
    return getLocalSqlMapSession().update(id, param);
  }

  public int delete(String id, Object param) throws SQLException {
    return getLocalSqlMapSession().delete(id, param);
  }

  public Object queryForObject(String id, Object paramObject) throws SQLException {
    return getLocalSqlMapSession().queryForObject(id, paramObject);
  }

不难看出SqlMapClientImpl拥有多个SqlMapSessionImpl(它们隶属于不同线程,通过localSqlMapSession 来管理)。
而其中的insert(),update(),delete(),queryForObject()将委托给SqlMapSessionImpl。
那在看看SqlMapSessionImpl部分代码：

 protected SqlMapExecutorDelegate delegate;
 protected SessionScope sessionScope;
 public SqlMapSessionImpl(SqlMapClientImpl client) {
    this.delegate = client.getDelegate();
    this.sessionScope = this.delegate.beginSessionScope();
    this.sessionScope.setSqlMapClient(client);
    this.sessionScope.setSqlMapExecutor(client);
    this.sessionScope.setSqlMapTxMgr(client);
    this.closed = false;
 }
 public Object insert(String id, Object param) throws SQLException {
    return delegate.insert(sessionScope, id, param);
 }
 public int update(String id, Object param) throws SQLException {
    return delegate.update(sessionScope, id, param);
 }
 public int delete(String id, Object param) throws SQLException {
    return delegate.delete(sessionScope, id, param);
 }
 public Object queryForObject(String id, Object paramObject) throws SQLException {
    return delegate.queryForObject(sessionScope, id, paramObject);
 }

首先是构造函数，它将初始化一些信息，注意this.delegate = client.getDelegate();说明SqlMapClientImpl,SqlMapSessionImpl所使用的是同一个SqlMapExecutorDelegate。
而它的insert(),update,delete(),queryForObject()这几个方法将委托给SqlMapExecutorDelegate。
看看SqlMapExecutorDelegate代码(只是部分代码，没有贴全)：

protected SqlExecutor sqlExecutor;
public int update(SessionScope sessionScope, String id, Object param) throws SQLException {
    int rows = 0;

    MappedStatement ms = getMappedStatement(id);
    Transaction trans = getTransaction(sessionScope);
    boolean autoStart = trans == null;

    try {
      trans = autoStartTransaction(sessionScope, autoStart, trans);

      StatementScope statementScope = beginStatementScope(sessionScope, ms);
      try {
        rows = ms.executeUpdate(statementScope, trans, param);
      } finally {
        endStatementScope(statementScope);
      }

      autoCommitTransaction(sessionScope, autoStart);
    } finally {
      autoEndTransaction(sessionScope, autoStart);
    }

    return rows;
  }

SqlMapExecutorDelegate将做些事务控制,从代码rows = ms.executeUpdate(statementScope, trans, param);可以看出之后将具体操作委托给MappedStatement。
继续跟下去，看下MappedStatement的相关代码:

  public int executeUpdate(StatementScope statementScope, Transaction trans, Object parameterObject)
      throws SQLException {
    ErrorContext errorContext = statementScope.getErrorContext();
    errorContext.setActivity("preparing the mapped statement for execution");
    errorContext.setObjectId(this.getId());
    errorContext.setResource(this.getResource());

    statementScope.getSession().setCommitRequired(true);

    try {
      parameterObject = validateParameter(parameterObject);

      Sql sql = getSql();

      errorContext.setMoreInfo("Check the parameter map.");
      ParameterMap parameterMap = sql.getParameterMap(statementScope, parameterObject);

      errorContext.setMoreInfo("Check the result map.");
      ResultMap resultMap = sql.getResultMap(statementScope, parameterObject);

      statementScope.setResultMap(resultMap);
      statementScope.setParameterMap(parameterMap);

      int rows = 0;

      errorContext.setMoreInfo("Check the parameter map.");
      Object[] parameters = parameterMap.getParameterObjectValues(statementScope, parameterObject);

      errorContext.setMoreInfo("Check the SQL statement.");
      String sqlString = sql.getSql(statementScope, parameterObject);

      errorContext.setActivity("executing mapped statement");
      errorContext.setMoreInfo("Check the statement or the result map.");
      rows = sqlExecuteUpdate(statementScope, trans.getConnection(), sqlString, parameters);// important

      errorContext.setMoreInfo("Check the output parameters.");
      if (parameterObject != null) {
        postProcessParameterObject(statementScope, parameterObject, parameters);
      }

      errorContext.reset();
      sql.cleanup(statementScope);
      notifyListeners();
      return rows;
    } catch (SQLException e) {
      errorContext.setCause(e);
      throw new NestedSQLException(errorContext.toString(), e.getSQLState(), e.getErrorCode(), e);
    } catch (Exception e) {
      errorContext.setCause(e);
      throw new NestedSQLException(errorContext.toString(), e);
    }
  }

  protected int sqlExecuteUpdate(StatementScope statementScope, Connection conn, String sqlString, Object[] parameters) throws SQLException {
    if (statementScope.getSession().isInBatch()) {
      getSqlExecutor().addBatch(statementScope, conn, sqlString, parameters);
      return 0;
    } else {
      return getSqlExecutor().executeUpdate(statementScope, conn, sqlString, parameters);
    }
  }

  public SqlExecutor getSqlExecutor() {
    return sqlMapClient.getSqlExecutor();
  }

哦，executeUpdate(StatementScope statementScope, Transaction trans, Object parameterObject)中的
rows = sqlExecuteUpdate(statementScope, trans.getConnection(), sqlString, parameters);将调用
sqlExecuteUpdate(StatementScope statementScope, Connection conn, String sqlString, Object[] parameters)，
而sqlExecuteUpdate(StatementScope statementScope, Connection conn, String sqlString, Object[] parameters)
将调用SqlExecutor的executeUpdate来进行具体操作。而这个SqlExecutor是来自SqlMapExecutorDelegate的。
所以我们在做ibatis分页的时候可以通过反射向SqlMapExecutorDelegate强制注入自定义的SqlExecutor来达到分页效果。