Sharding-JDBC 源码分析 —— SQL 解析（二）之SQL解析

// SQLParsingEngine.java
public SQLStatement parse() {
   // 获取 SQL解析器
   SQLParser sqlParser = getSQLParser();
   //
   sqlParser.skipIfEqual(Symbol.SEMI); // 跳过 ";"
   if (sqlParser.equalAny(DefaultKeyword.WITH)) { // WITH Syntax
       skipWith(sqlParser);
   }
   // 获取对应 SQL语句解析器 解析SQL
   if (sqlParser.equalAny(DefaultKeyword.SELECT)) {
       return SelectParserFactory.newInstance(sqlParser).parse();
   }
   if (sqlParser.equalAny(DefaultKeyword.INSERT)) {
       return InsertParserFactory.newInstance(shardingRule, sqlParser).parse();
   }
   if (sqlParser.equalAny(DefaultKeyword.UPDATE)) {
       return UpdateParserFactory.newInstance(sqlParser).parse();
   }
   if (sqlParser.equalAny(DefaultKeyword.DELETE)) {
       return DeleteParserFactory.newInstance(sqlParser).parse();
   }
   throw new SQLParsingUnsupportedException(sqlParser.getLexer().getCurrentToken().getType());
}

// SQLParsingEngine.java#parse()片段
if (sqlParser.equalAny(DefaultKeyword.SELECT)) {
    return SelectParserFactory.newInstance(sqlParser).parse();
}

// AbstractParser.java
public final boolean equalAny(final TokenType... tokenTypes) {
   for (TokenType each : tokenTypes) {
       if (each == lexer.getCurrentToken().getType()) {
           return true;
       }
   }
   return false;
}

// AbstractParser.java
/**
* 跳过小括号内所有的词法标记.
*
* @return 小括号内所有的词法标记
*/
public final String skipParentheses() {
   StringBuilder result = new StringBuilder("");
   int count = 0;
   if (Symbol.LEFT_PAREN == getLexer().getCurrentToken().getType()) {
       final int beginPosition = getLexer().getCurrentToken().getEndPosition();
       result.append(Symbol.LEFT_PAREN.getLiterals());
       getLexer().nextToken();
       while (true) {
           if (equalAny(Symbol.QUESTION)) {
               increaseParametersIndex();
           }
           // 到达结尾 或者 匹配合适数的)右括号
           if (Assist.END == getLexer().getCurrentToken().getType() || (Symbol.RIGHT_PAREN == getLexer().getCurrentToken().getType() && 0 == count)) {
               break;
           }
           // 处理里面有多个括号的情况，例如：SELECT COUNT(DISTINCT(order_id) FROM t_order
           if (Symbol.LEFT_PAREN == getLexer().getCurrentToken().getType()) {
               count++;
           } else if (Symbol.RIGHT_PAREN == getLexer().getCurrentToken().getType()) {
               count--;
           }
           // 下一个词法
           getLexer().nextToken();
       }
       // 获得括号内的内容
       result.append(getLexer().getInput().substring(beginPosition, getLexer().getCurrentToken().getEndPosition()));
       // 下一个词法
       getLexer().nextToken();
   }
   return result.toString();
}

// SQLParser.java
/**
* 解析表达式.
*
* @return 表达式
*/
// TODO 完善Expression解析的各种场景
public final SQLExpression parseExpression() {
   // 解析表达式
   String literals = getLexer().getCurrentToken().getLiterals();
   final SQLExpression expression = getExpression(literals);
   // SQLIdentifierExpression 需要特殊处理。考虑自定义函数，表名.属性情况。
   if (skipIfEqual(Literals.IDENTIFIER)) {
       if (skipIfEqual(Symbol.DOT)) { // 例如，ORDER BY o.uid 中的 "o.uid"
           String property = getLexer().getCurrentToken().getLiterals();
           getLexer().nextToken();
           return skipIfCompositeExpression() ? new SQLIgnoreExpression() : new SQLPropertyExpression(new SQLIdentifierExpression(literals), property);
       }
       if (equalAny(Symbol.LEFT_PAREN)) { // 例如，GROUP BY DATE(create_time) 中的 "DATE(create_time)"
           skipParentheses();
           skipRestCompositeExpression();
           return new SQLIgnoreExpression();
       }
       return skipIfCompositeExpression() ? new SQLIgnoreExpression() : expression;
   }
   getLexer().nextToken();
   return skipIfCompositeExpression() ? new SQLIgnoreExpression() : expression;
}
/**
* 获得 词法Token 对应的 SQLExpression
*
* @param literals 词法字面量标记
* @return SQLExpression
*/
private SQLExpression getExpression(final String literals) {
   if (equalAny(Symbol.QUESTION)) {
       increaseParametersIndex();
       return new SQLPlaceholderExpression(getParametersIndex() - 1);
   }
   if (equalAny(Literals.CHARS)) {
       return new SQLTextExpression(literals);
   }
   // TODO 考虑long的情况
   if (equalAny(Literals.INT)) {
       return new SQLNumberExpression(Integer.parseInt(literals));
   }
   if (equalAny(Literals.FLOAT)) {
       return new SQLNumberExpression(Double.parseDouble(literals));
   }
   // TODO 考虑long的情况
   if (equalAny(Literals.HEX)) {
       return new SQLNumberExpression(Integer.parseInt(literals, 16));
   }
   if (equalAny(Literals.IDENTIFIER)) {
       return new SQLIdentifierExpression(SQLUtil.getExactlyValue(literals));
   }
   return new SQLIgnoreExpression();
}
/**
* 如果是 复合表达式，跳过。
*
* @return 是否跳过
*/
private boolean skipIfCompositeExpression() {
   if (equalAny(Symbol.PLUS, Symbol.SUB, Symbol.STAR, Symbol.SLASH, Symbol.PERCENT, Symbol.AMP, Symbol.BAR, Symbol.DOUBLE_AMP, Symbol.DOUBLE_BAR, Symbol.CARET, Symbol.DOT, Symbol.LEFT_PAREN)) {
       skipParentheses();
       skipRestCompositeExpression();
       return true;
   }
   return false;
}
/**
* 跳过剩余复合表达式
*/
private void skipRestCompositeExpression() {
   while (skipIfEqual(Symbol.PLUS, Symbol.SUB, Symbol.STAR, Symbol.SLASH, Symbol.PERCENT, Symbol.AMP, Symbol.BAR, Symbol.DOUBLE_AMP, Symbol.DOUBLE_BAR, Symbol.CARET, Symbol.DOT)) {
       if (equalAny(Symbol.QUESTION)) {
           increaseParametersIndex();
       }
       getLexer().nextToken();
       skipParentheses();
   }
}

/**
* 解析别名.不仅仅是字段的别名，也可以是表的别名。
*
* @return 别名
*/
public Optional<String> parseAlias() {
   // 解析带 AS 情况
   if (skipIfEqual(DefaultKeyword.AS)) {
       if (equalAny(Symbol.values())) {
           return Optional.absent();
       }
       String result = SQLUtil.getExactlyValue(getLexer().getCurrentToken().getLiterals());
       getLexer().nextToken();
       return Optional.of(result);
   }
   // 解析别名
   // TODO 增加哪些数据库识别哪些关键字作为别名的配置
   if (equalAny(Literals.IDENTIFIER, Literals.CHARS, DefaultKeyword.USER, DefaultKeyword.END, DefaultKeyword.CASE, DefaultKeyword.KEY, DefaultKeyword.INTERVAL, DefaultKeyword.CONSTRAINT)) {
       String result = SQLUtil.getExactlyValue(getLexer().getCurrentToken().getLiterals());
       getLexer().nextToken();
       return Optional.of(result);
   }
   return Optional.absent();
}

/**
* 解析单表.
*
* @param sqlStatement SQL语句对象
*/
public final void parseSingleTable(final SQLStatement sqlStatement) {
   boolean hasParentheses = false;
   if (skipIfEqual(Symbol.LEFT_PAREN)) {
       if (equalAny(DefaultKeyword.SELECT)) { // multiple-update 或者 multiple-delete
           throw new UnsupportedOperationException("Cannot support subquery");
       }
       hasParentheses = true;
   }
   Table table;
   final int beginPosition = getLexer().getCurrentToken().getEndPosition() - getLexer().getCurrentToken().getLiterals().length();
   String literals = getLexer().getCurrentToken().getLiterals();
   getLexer().nextToken();
   if (skipIfEqual(Symbol.DOT)) {
       getLexer().nextToken();
       if (hasParentheses) {
           accept(Symbol.RIGHT_PAREN);
       }
       table = new Table(SQLUtil.getExactlyValue(literals), parseAlias());
   } else {
       if (hasParentheses) {
           accept(Symbol.RIGHT_PAREN);
       }
       table = new Table(SQLUtil.getExactlyValue(literals), parseAlias());
   }
   if (skipJoin()) { // multiple-update 或者 multiple-delete
       throw new UnsupportedOperationException("Cannot support Multiple-Table.");
   }
   sqlStatement.getSqlTokens().add(new TableToken(beginPosition, literals));
   sqlStatement.getTables().add(table);
}

// SQLParser.java
/**
* 跳过表关联词法.
*
* @return 是否表关联.
*/
public final boolean skipJoin() {
   if (skipIfEqual(DefaultKeyword.LEFT, DefaultKeyword.RIGHT, DefaultKeyword.FULL)) {
       skipIfEqual(DefaultKeyword.OUTER);
       accept(DefaultKeyword.JOIN);
       return true;
   } else if (skipIfEqual(DefaultKeyword.INNER)) {
       accept(DefaultKeyword.JOIN);
       return true;
   } else if (skipIfEqual(DefaultKeyword.JOIN, Symbol.COMMA, DefaultKeyword.STRAIGHT_JOIN)) {
       return true;
   } else if (skipIfEqual(DefaultKeyword.CROSS)) {
       if (skipIfEqual(DefaultKeyword.JOIN, DefaultKeyword.APPLY)) {
           return true;
       }
   } else if (skipIfEqual(DefaultKeyword.OUTER)) {
       if (skipIfEqual(DefaultKeyword.APPLY)) {
           return true;
       }
   }
   return false;
}

// SQLParser.java
/**
* 解析所有查询条件。
* 目前不支持 OR 条件。
*
* @param sqlStatement SQL
*/
private void parseConditions(final SQLStatement sqlStatement) {
   // AND 查询
   do {
       parseComparisonCondition(sqlStatement);
   } while (skipIfEqual(DefaultKeyword.AND));
   // 目前不支持 OR 条件
   if (equalAny(DefaultKeyword.OR)) {
       throw new SQLParsingUnsupportedException(getLexer().getCurrentToken().getType());
   }
} 
// TODO 解析组合expr
/**
* 解析单个查询条件
*
* @param sqlStatement SQL
*/
public final void parseComparisonCondition(final SQLStatement sqlStatement) {
   skipIfEqual(Symbol.LEFT_PAREN);
   SQLExpression left = parseExpression(sqlStatement);
   if (equalAny(Symbol.EQ)) {
       parseEqualCondition(sqlStatement, left);
       skipIfEqual(Symbol.RIGHT_PAREN);
       return;
   }
   if (equalAny(DefaultKeyword.IN)) {
       parseInCondition(sqlStatement, left);
       skipIfEqual(Symbol.RIGHT_PAREN);
       return;
   }
   if (equalAny(DefaultKeyword.BETWEEN)) {
       parseBetweenCondition(sqlStatement, left);
       skipIfEqual(Symbol.RIGHT_PAREN);
       return;
   }
   if (equalAny(Symbol.LT, Symbol.GT, Symbol.LT_EQ, Symbol.GT_EQ)) {
       if (left instanceof SQLIdentifierExpression && sqlStatement instanceof SelectStatement
               && isRowNumberCondition((SelectStatement) sqlStatement, ((SQLIdentifierExpression) left).getName())) {
           parseRowNumberCondition((SelectStatement) sqlStatement);
       } else if (left instanceof SQLPropertyExpression && sqlStatement instanceof SelectStatement
               && isRowNumberCondition((SelectStatement) sqlStatement, ((SQLPropertyExpression) left).getName())) {
           parseRowNumberCondition((SelectStatement) sqlStatement);
       } else {
           parseOtherCondition(sqlStatement);
       }
   } else if (equalAny(DefaultKeyword.LIKE)) {
       parseOtherCondition(sqlStatement);
   }
   skipIfEqual(Symbol.RIGHT_PAREN);
}

// SQLParser.java
/**
* 解析 = 条件
*
* @param sqlStatement SQL
* @param left 左SQLExpression
*/
private void parseEqualCondition(final SQLStatement sqlStatement, final SQLExpression left) {
   getLexer().nextToken();
   SQLExpression right = parseExpression(sqlStatement);
   // 添加列
   // TODO 如果有多表,且找不到column是哪个表的,则不加入condition,以后需要解析binding table
   if ((sqlStatement.getTables().isSingleTable() || left instanceof SQLPropertyExpression)
           // 只有对路由结果有影响的才会添加到 conditions。SQLPropertyExpression 和 SQLIdentifierExpression 无法判断，所以未加入 conditions
           && (right instanceof SQLNumberExpression || right instanceof SQLTextExpression || right instanceof SQLPlaceholderExpression)) {
       Optional<Column> column = find(sqlStatement.getTables(), left);
       if (column.isPresent()) {
           sqlStatement.getConditions().add(new Condition(column.get(), right), shardingRule);
       }
   }
}

public final class SelectParserFactory {

    /**
     * 创建Select语句解析器.
     * 
     * @param sqlParser SQL解析器
     * @return Select语句解析器
     */
    public static AbstractSelectParser newInstance(final SQLParser sqlParser) {
        if (sqlParser instanceof MySQLParser) {
            return new MySQLSelectParser(sqlParser);
        }
        if (sqlParser instanceof OracleParser) {
            return new OracleSelectParser(sqlParser);
        }
        if (sqlParser instanceof SQLServerParser) {
            return new SQLServerSelectParser(sqlParser);
        }
        if (sqlParser instanceof PostgreSQLParser) {
            return new PostgreSQLSelectParser(sqlParser);
        }
        throw new UnsupportedOperationException(String.format("Cannot support sqlParser class [%s].", sqlParser.getClass()));
    } 
}