ReuseExecutor.java

/*
 *    Copyright 2009-2014 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.apache.ibatis.executor;

import java.sql.Connection;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.apache.ibatis.executor.statement.StatementHandler;
import org.apache.ibatis.logging.Log;
import org.apache.ibatis.mapping.BoundSql;
import org.apache.ibatis.mapping.MappedStatement;
import org.apache.ibatis.session.Configuration;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;
import org.apache.ibatis.transaction.Transaction;

/**
 * @author Clinton Begin
 */
/**
 * 可重用的执行器
 */
public class ReuseExecutor extends BaseExecutor {

  //可重用的执行器内部用了一个map，用来缓存SQL语句对应的Statement
  private final Map<String, Statement> statementMap = new HashMap<String, Statement>();

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

  @Override
  public int doUpdate(MappedStatement ms, Object parameter) throws SQLException {
    Configuration configuration = ms.getConfiguration();
    //和SimpleExecutor一样，新建一个StatementHandler
    //这里看到ResultHandler传入的是null
    StatementHandler handler = configuration.newStatementHandler(this, ms, parameter, RowBounds.DEFAULT, null, null);
    //准备语句
    Statement stmt = prepareStatement(handler, ms.getStatementLog());
    return handler.update(stmt);
  }

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

  @Override
  public List<BatchResult> doFlushStatements(boolean isRollback) throws SQLException {
    for (Statement stmt : statementMap.values()) {
      closeStatement(stmt);
    }
    statementMap.clear();
    return Collections.emptyList();
  }

  private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException {
    Statement stmt;
    //得到绑定的SQL语句
    BoundSql boundSql = handler.getBoundSql();
    String sql = boundSql.getSql();
    //如果缓存中已经有了，直接得到Statement
    if (hasStatementFor(sql)) {
      stmt = getStatement(sql);
    } else {
      //如果缓存没有找到，则和SimpleExecutor处理完全一样，然后加入缓存
      Connection connection = getConnection(statementLog);
      stmt = handler.prepare(connection);
      putStatement(sql, stmt);
    }
    handler.parameterize(stmt);
    return stmt;
  }

  private boolean hasStatementFor(String sql) {
    try {
      return statementMap.keySet().contains(sql) && !statementMap.get(sql).getConnection().isClosed();
    } catch (SQLException e) {
      return false;
    }
  }

  private Statement getStatement(String s) {
    return statementMap.get(s);
  }

  private void putStatement(String sql, Statement stmt) {
    statementMap.put(sql, stmt);
  }

}