002 - executeQuery方法执行过程

// executeQuery()方法调用方式
String sql = "select id, name, password, is_delete, create_by, create_time, modify_by, modify_time from user where name like concat_ws('', '%', ?,'%')";
log.info("== sql = " + sql);
Connection conn = jdbcUtil.getConnection();
PreparedStatement ps = conn.prepareStatement(sql);
ps.setString(1, username);
ResultSet rs = ps.executeQuery();

/**
 * Executes the SQL query in this <code>PreparedStatement</code> object
 * and returns the <code>ResultSet</code> object generated by the query.
 *
 * -- 在PreparedStatement对象中执行SQL查询，并返回查询生成的ResultSet对象
 *
 * @return a <code>ResultSet</code> object that contains the data produced by the
 *         query; never <code>null</code>
 * @exception SQLException if a database access error occurs;
 * this method is called on a closed  <code>PreparedStatement</code> or the SQL
 *            statement does not return a <code>ResultSet</code> object
 * @throws SQLTimeoutException when the driver has determined that the
 * timeout value that was specified by the {@code setQueryTimeout}
 * method has been exceeded and has at least attempted to cancel
 * the currently running {@code Statement}
 */
@Override
public java.sql.ResultSet executeQuery() throws SQLException {
  // bobo 进入同步代码块中，
  // connection 是否已经关闭
    synchronized (checkClosed().getConnectionMutex()) {
        // bobo 本方法中connection对象
        JdbcConnection locallyScopedConn = this.connection;


        // bobo 校验是否是dml的sql语句
        /**
         * - 校验是否是dml的sql语句
         * - 先判断首字母是否是由I,U,D,A,C,T,R字母开始，即
         * I - INSERT - 插入
         * U - UPDATE - 更新
         * D - DELETE、DROP - 删除数据、删除表
         * A - ALTER - 修改表
         * C - CREATE - 创建表、数据库
         * T - TRUNCATE - 删除表所有记录
         * R - RENAME - 重命名
         * - 如果是以上任意一种，抛异常 SQLException
         */
        checkForDml(((PreparedQuery<?>) this.query).getOriginalSql(), ((PreparedQuery<?>) this.query).getParseInfo().getFirstStmtChar());


        // bobo 初始化批量生成主键key
        this.batchedGeneratedKeys = null;


        // bobo 重置取消状态
        resetCancelledState();


        // bobo 立刻关闭所有结果集
        /**
         * Close all result sets in this statement. This includes multi-results
         * - 关闭此语句中的所有结果集。这包括multi-results
         * @throws SQLException
         */
        implicitlyCloseAllOpenResults();


        // bobo 清除所有警告
        clearWarnings();


        // bobo ping 服务器，是否可以了解
        /**
         * Detect if the connection is still good by sending a ping command to the server.
         * - 通过向服务器发送ping命令来检测连接是否仍然有效
         */
        if (this.doPingInstead) {
            doPingInstead();


            return this.results;
        }


        // bobo 设置流的超时时间
        setupStreamingTimeout(locallyScopedConn);


        // bobo 拼接sql语句，将参数匹配到对应？位置处
        Message sendPacket = ((PreparedQuery<?>) this.query).fillSendPacket();


        // bobo 初始化数据库
        String oldDb = null;


        if (!locallyScopedConn.getDatabase().equals(this.getCurrentDatabase())) {
            oldDb = locallyScopedConn.getDatabase();
            locallyScopedConn.setDatabase(this.getCurrentDatabase());
        }


        //
        // Check if we have cached metadata for this query...
        //
        // bobo 检查是否缓存了此查询的元数据
        // bobo 缓存的结果集
        CachedResultSetMetaData cachedMetadata = null;
        boolean cacheResultSetMetadata = locallyScopedConn.getPropertySet().getBooleanProperty(PropertyKey.cacheResultSetMetadata).getValue();


        // bobo select id, name, password, is_delete, create_by, create_time, modify_by, modify_time from user where name like concat_ws('', '%', ?,'%')
        // bobo 源sql语句，即带有占位符的sql语句
        String origSql = ((PreparedQuery<?>) this.query).getOriginalSql();


        // bobo 是否缓存了数据
        if (cacheResultSetMetadata) {
          // bobo 获取缓存的数据
            cachedMetadata = locallyScopedConn.getCachedMetaData(origSql);
        }


        // bobo 初始化行数
        locallyScopedConn.setSessionMaxRows(this.maxRows);


        // bobo 执行sql语句，返回执行后的结果集
        /**
         * - 获取结果集
         * - 存放在 result.rowData.rows字节数组中
         */
        this.results = executeInternal(this.maxRows, sendPacket, createStreamingResultSet(), true, cachedMetadata, false);


        if (oldDb != null) {
            locallyScopedConn.setDatabase(oldDb);
        }


        // bobo 缓存中有数据，则将缓存中数据赋值给结果集
        if (cachedMetadata != null) {
            locallyScopedConn.initializeResultsMetadataFromCache(origSql, cachedMetadata, this.results);
        } else {
          // bobo 是否创建缓存数据，将得到的结果集数据添加到缓存中
            if (cacheResultSetMetadata) {
                locallyScopedConn.initializeResultsMetadataFromCache(origSql, null /* will be created */, this.results);
            }
        }


        // bobo 这个结果集返回的auto_increment的值，即自增主键的值
        this.lastInsertId = this.results.getUpdateID();


        // bobo 返回获取的结果集
        return this.results;
    }
}

/**
 * -- 在PreparedStatement对象中执行SQL查询，并返回查询生成的ResultSet对象
 */
@Override
public java.sql.ResultSet executeQuery() throws SQLException {
  // bobo 进入同步代码块中，
  // connection 是否已经关闭
    synchronized (checkClosed().getConnectionMutex()) {
        
         ··· ···
         
        // bobo 拼接sql语句，将参数匹配到对应？位置处
        Message sendPacket = ((PreparedQuery<?>) this.query).fillSendPacket();


        ··· ···
        
        // bobo 执行sql语句，返回执行后的结果集
        /**
         * - 获取结果集
         * - 存放在 result.rowData.rows字节数组中
         */
        this.results = executeInternal(this.maxRows, sendPacket, createStreamingResultSet(), true, cachedMetadata, false);


        ··· ···


        // bobo 返回获取的结果集
        return this.results;
    }
}