使用druid的工具包改sql的库名，实现单实例分库

 /**
     * 自定义Visitor ,这里是MySQL，其他数据库请自行更换
     **/
    public static class MyReplaceTableVisitor extends MySqlASTVisitorAdapter {

        private final String databaseName;

        public MyReplaceTableVisitor(String databaseName) {
            this.databaseName = databaseName;
        }

        @Override
        public boolean visit(SQLExprTableSource x) {
            String originTableName = x.getExpr().toString();
            if (databaseName != null) {
                if (originTableName.contains(".")) {
                    return true;
                }
                //修改表名
                x.setExpr(databaseName + "." + originTableName);
                logger.info(" replace table:" + originTableName + " -> " + databaseName + "." + originTableName);
            }
            return true;
        }
    }

    public static String replaceTableName(String sql, String tableName) {
        if (tableName == null) {
            return sql;
        }
        List<SQLStatement> statements = SQLUtils.parseStatements(sql, JdbcConstants.MYSQL);
        MyReplaceTableVisitor visitor = new MyReplaceTableVisitor(tableName);
        for (SQLStatement stmt : statements) {
            stmt.accept(visitor);
        }
        return SQLUtils.toSQLString(statements, JdbcConstants.MYSQL);
    }

    public static void main(String[] args) {
        String sql = "select c.*, (select a.name as province_name from portal_area a where a.id = c.province_id) as province_name, (select a.name as city_name from portal_area a where a.id = c.city_id) as city_name, (CASE WHEN c.area_id IS NULL THEN NULL ELSE (select a.name as area_name from portal_area a where a.id = c.area_id)  END )as area_name  from portal.portal_company c where no = ?";
        String s = replaceTableName(sql, "abc");
        System.out.println(s);
    }