Dump Oracle database into a textual SQL script

Does it exist on Oracle?

Similar utility exists in Oracle environment called Data Pump.

How can it be done?

Use expdp command line tool to perform full database export.

Example:

expdp hr DIRECTORY=dpump_dir2 DUMPFILE=expfull.dmp FULL=YES NOLOGFILE=YES

Then can use impdp to import it in another database.

Example:

impdp hr DUMPFILE=dpump_dir1:expfull.dmp FULL=YES LOGFILE=dpump_dir2:full_imp.log

If you specify DUMPFILE parameter it writes a binary file called dump file. With the SQLFILE parameter(SQLFILE=/my/file/name.sql) you can get all of the SQL DDL that Import would have executed.

More on it depends upon the requirements.

Oracle Documentation explains more than I can here.

Overview of Oracle Data Pump

There is no such thing in the database itself.

You can perform something similar in SQL Developer, with the Database Export tool.

How to Export Data using SQL Developer

With the Tools / Database Export tool, you can specify the objects you want to export, then SQL Developer generates an SQL file for recreating them, with the data as insert statements.