Mysql JDBC驱动源码分析(处理结果集)五

一，现在已经返回了结果集，接下来是对返回数据的分析

ResultSet.next()只不过是对rowData集合的操作

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if (!this.isBinaryEncoded) {                       //先通getString获取String stringVal = getString(columnIndex);if (this.wasNullFlag || (stringVal == null)) {return 0;}return getByteFromString(stringVal, columnIndex);}return getNativeByte(columnIndex);}//===========//通过索引位置获取字符串值public String getString(int columnIndex) throws SQLException {String stringVal = getStringInternal(columnIndex, true);if (this.padCharsWithSpace && stringVal != null) {Field f = this.fields[columnIndex - 1];if (f.getMysqlType() == MysqlDefs.FIELD_TYPE_STRING ) {int fieldLength = (int)f.getLength() /* safe, bytes in a CHAR <= 1024 */ / f.getMaxBytesPerCharacter(); /* safe, this will never be 0 */int currentLength = stringVal.length();if (currentLength < fieldLength) {StringBuffer paddedBuf = new StringBuffer(fieldLength);paddedBuf.append(stringVal);int difference = fieldLength - currentLength;paddedBuf.append(EMPTY_SPACE, 0, difference);stringVal = paddedBuf.toString();}}}return stringVal;}//==================protected String getStringInternal(int columnIndex, boolean checkDateTypes)throws SQLException {if (!this.isBinaryEncoded) {checkRowPos();checkColumnBounds(columnIndex);if (this.fields == null) {throw SQLError.createSQLException(Messages.getString("ResultSet.Query_generated_no_fields_for_ResultSet_99"), //$NON-NLS-1$SQLError.SQL_STATE_INVALID_COLUMN_NUMBER, getExceptionInterceptor());}// JDBC is 1-based, Java is not !?int internalColumnIndex = columnIndex - 1;if (this.thisRow.isNull(internalColumnIndex)) {this.wasNullFlag = true;return null;}this.wasNullFlag = false;//获取到相应的字段属性类Field metadata = this.fields[internalColumnIndex];String stringVal = null;if (metadata.getMysqlType() == MysqlDefs.FIELD_TYPE_BIT) {if (metadata.isSingleBit()) {byte[] value = this.thisRow.getColumnValue(internalColumnIndex);if (value.length == 0) {return String.valueOf(convertToZeroWithEmptyCheck());}return String.valueOf(value[0]);}return String.valueOf(getNumericRepresentationOfSQLBitType(columnIndex));}String encoding = metadata.getCharacterSet();                                          //在根据next()操作时指定的thisRow中获取相应的数据(BufferRow)stringVal = this.thisRow.getString(internalColumnIndex, encoding, this.connection);//// Special handling for YEAR type from mysql, some people// want it as a DATE, others want to treat it as a SHORT//if (metadata.getMysqlType() == MysqlDefs.FIELD_TYPE_YEAR) {if (!this.connection.getYearIsDateType()) {return stringVal;}Date dt = getDateFromString(stringVal, columnIndex, null);if (dt == null) {this.wasNullFlag = true;return null;}this.wasNullFlag = false;return dt.toString();}// Handles timezone conversion and zero-date behaviorif (checkDateTypes && !this.connection.getNoDatetimeStringSync()) {                                //所获取到的String值，根据metadata中的类型再进行相应的转换switch (metadata.getSQLType()) {case Types.TIME:Time tm = getTimeFromString(stringVal, null, columnIndex,this.getDefaultTimeZone(), false);if (tm == null) {this.wasNullFlag = true;return null;}this.wasNullFlag = false;return tm.toString();case Types.DATE:Date dt = getDateFromString(stringVal, columnIndex, null);if (dt == null) {this.wasNullFlag = true;return null;}this.wasNullFlag = false;return dt.toString();case Types.TIMESTAMP:Timestamp ts = getTimestampFromString(columnIndex,null, stringVal, this.getDefaultTimeZone(), false);if (ts == null) {this.wasNullFlag = true;return null;}this.wasNullFlag = false;return ts.toString();default:break;}}return stringVal;}return getNativeString(columnIndex);}////BufferRow继承了ResultSetRow下获取相应的值 public String getString(int columnIndex, String encoding, MySQLConnection conn)throws SQLException {if (this.isBinaryEncoded) {if (isNull(columnIndex)) {return null;}}                //指针指向到相应的列findAndSeekToOffset(columnIndex);long length = this.rowFromServer.readFieldLength();if (length == Buffer.NULL_LENGTH) {return null;}if (length == 0) {return "";}// TODO: I don't like this, would like to push functionality back// to the buffer class somehowint offset = this.rowFromServer.getPosition();                //获取到值，后对string进行相应的转换return getString(encoding, conn, this.rowFromServer.getByteBuffer(),offset, (int) length);}       //BufferRowprotected String getString(String encoding, MySQLConnection conn,byte[] value, int offset, int length) throws SQLException {String stringVal = null;if ((conn != null) && conn.getUseUnicode()) {try {if (encoding == null) {stringVal = StringUtils.toString(value);} else {SingleByteCharsetConverter converter = conn.getCharsetConverter(encoding);if (converter != null) {                                                //对编码的一些转换stringVal = converter.toString(value, offset, length);} else {                                                //或者常用类中的转换stringVal = StringUtils.toString(value, offset, length, encoding);}}} catch (java.io.UnsupportedEncodingException E) {throw SQLError.createSQLException(Messages.getString("ResultSet.Unsupported_character_encoding____101") //$NON-NLS-1$+ encoding + "'.", "0S100", this.exceptionInterceptor);}} else {stringVal = StringUtils.toAsciiString(value, offset, length);}return stringVal;}

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