问如何从解析树获取Java类文件

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/**
001     * Parses the query to see if there's already a top-level limit clause. If none was found, the query is
002     * rewritten to include a limit clause with the given values.
003     *
004     * @param query The query to check and modify.
005     * @param serverVersion The version of MySQL to use for checking.
006     * @param sqlMode The current SQL mode in the server.
007     * @param offset The limit offset to add.
008     * @param count The row count value to add.
009     *
010     * @returns The rewritten query if the original query is error free and contained no top-level LIMIT clause.
011     *          Otherwise the original query is returned.
012     */
013    public checkAndApplyLimits(query: string, serverVersion: number, sqlMode: string, offset: number,
014        count: number): [string, boolean] {
015
016        this.applyServerDetails(serverVersion, sqlMode);
017        const tree = this.startParsing(query, false, MySQLParseUnit.Generic);
018        if (!tree || this.errors.length > 0) {
019            return [query, false];
020        }
021
022        const rewriter = new TokenStreamRewriter(this.tokenStream);
023        const expressions = XPath.findAll(tree, "/query/simpleStatement//queryExpression", this.parser);
024        let changed = false;
025        if (expressions.size > 0) {
026            // There can only be one top-level query expression where we can add a LIMIT clause.
027            const candidate: ParseTree = expressions.values().next().value;
028
029            // Check if the candidate comes from a subquery.
030            let run: ParseTree | undefined = candidate;
031            let invalid = false;
032            while (run) {
033                if (run instanceof SubqueryContext) {
034                    invalid = true;
035                    break;
036                }
037
038                run = run.parent;
039            }
040
041            if (!invalid) {
042                // Top level query expression here. Check if there's already a LIMIT clause before adding one.
043                const context = candidate as QueryExpressionContext;
044                if (!context.limitClause() && context.stop) {
045                    // OK, ready to add an own limit clause.
046                    rewriter.insertAfter(context.stop, ` LIMIT ${offset}, ${count}`);
047                    changed = true;
048                }
049            }
040        }
051
052        return [rewriter.getText(), changed];
053    }