Apex - Change a Button to a Link

Firstly, You need a copy "text" button template as "link".

And then you can use your new template on a button. 

Creation of JSON object with APEX_JSON package

BEGIN
    APEX_JSON.initialize_clob_output;
    apex_json.open_object;        -- {
    apex_json.write('a', 1);    --   "a":1
    apex_json.open_array('b');  --  ,"b":[
    apex_json.open_object;    --    {
    apex_json.write('c',2); --      "c":2
    apex_json.close_object;   --    }
    apex_json.write('hello'); --   ,"hello"
    apex_json.write('world'); --   ,"world"
    apex_json.close_all;          --  ]
                          -- }
    DBMS_OUTPUT.put_line(APEX_JSON.get_clob_output);
    APEX_JSON.free_output;                     
END; 

Email validation for Apex

You can use below regexp expression for email validation in your apex applications.

^[A-Za-z_-]+[A-Za-z0-9._-]+@[A-Za-z0-9._-]+\.[A-Za-z]{2,4}$

Oracle Apex Standart Report Download Link Problem

Problem was related with download link and 

somehow download link's checksum was missing.
When I removed "Page Item to Submit" property value, it solved.

I faced with this problem at Apex Version 5.1.3.00.05.
 

Oracle sleep func in Apex

APEX_UTIL.PAUSE(5); --sleep for 5 second

Setting Session State with PL/SQL

APEX_UTIL.set_session_state(p_name => 'PX_MY_ITEM', p_value => 'wibble');

Implement a busy modal indicator in Oracle Apex

At the start of your processing, execute (javascript):

    apex.widget.waitPopup()

And when done, just remove the elements (again, javascript): 

    $(".u-Processing,#apex_wait_overlay").remove();