Oracle: source text for the view, package and other objects

The best method is to use dbms_metadata package:

SELECT dbms_metadata.get_ddl(UPPER('&OBJ_TYPE'),UPPER('&OBJ_NAME'),UPPER('&OWNER'))
FROM dual;

Additional methods could be also used:
Source text of the package

SELECT text
FROM dba_source
WHERE UPPER(name) LIKE UPPER('&which_object')
ORDER BY line ;

Use $ORACLE_HOME/bin/wrap utility to encrypt the package (there is no unwrap)
(Well, actually, there is unwrap – just look in the search machine for the words unwrap10 or rewrap…)

Source text of the views

SET LONG 5000
col text FOR a80

SELECT text FROM dba_views WHERE view_name = UPPER('&which_view');
SELECT query FROM DBA_mviews WHERE mview_name = UPPER('&which_view');
SELECT view_definition FROM v$fixed_view_definition WHERE view_name='&which_view';

Source text of the synonym

SELECT
TABLE_OWNER || '.' || TABLE_NAME
|| DECODE ( db_link , NULL , '' , '@' || db_link ) SYNONYM_OBJECT
FROM dba_synonyms
WHERE SYNONYM_NAME = UPPER('&which_synonym');

Source text of the trigger

SELECT
 'create or replace trigger "' || trigger_name || '"'
  || CHR(10)|| DECODE( SUBSTR( trigger_type, 1, 1 ), 'A', 'AFTER', 'B', 'BEFORE', 'I', 'INSTEAD OF' )
  || CHR(10) || triggering_event || CHR(10) || 'ON "' || table_owner || '"."' || table_name
  || '"' || CHR(10) || DECODE( INSTR( trigger_type, 'EACH ROW' ), 0, NULL, 'FOR EACH ROW' )
  || CHR(10) ,
  trigger_body
FROM dba_triggers
WHERE trigger_name = UPPER('&which_trigger')  AND owner=UPPER('&trigger_owner');