Page headers/footers in Excel are generated using a string which is a combination of plain text and control characters.

The available control characters are:

Control	Category	Description
`&L`	Justification	Left
`&C`		Center
`&R`		Right
`&P`	Information	Page number
`&N`		Total number of pages
`&D`		Date
`&T`		Time
`&F`		File name
`&A`		Worksheet name
`&Z`		Workbook path
`&fontsize`	Font	Font size
`&"font,style"`		Font name and style
`&U`		Single underline
`&E`		Double underline
`&S`		Strikethrough
`&X`		Superscript
`&Y`		Subscript

Text in headers and footers can be justified (aligned) to the left, center and right by prefixing the text with the control characters &L, &C and &R.

For example (with ASCII art representation of the results):

worksheet1.setHeader("&LHello");
//     ---------------------------------------------------------------
//    |                                                               |
//    | Hello                                                         |
//    |                                                               |

For simple text, if you do not specify any justification the text will be centered. However, you must prefix the text with &C if you specify a font name or any other formatting:

You can have text in each of the justification regions:

worksheet1.setHeader("&LCiao&CBello&RCielo");
//     ---------------------------------------------------------------
//    |                                                               |
//    | Ciao                     Bello                          Cielo |
//    |                                                               |

The information control characters act as variables that Excel will update as the Excel file or worksheet changes. Times and dates are in the users default format:

worksheet1.setHeader("&CPage &P of &N");
//     ---------------------------------------------------------------
//    |                                                               |
//    |                        Page 1 of 6                            |
//    |                                                               |
worksheet1.setHeader("&CUpdated at &T");
//     ---------------------------------------------------------------
//    |                                                               |
//    |                    Updated at 12:30 PM                        |
//    |                                                               |

You can specify the font size of a section of the text by prefixing it with the control character &n where n is the font size:

worksheet1.setHeader("&C&30Hello Big");

worksheet2.setHeader("&C&10Hello Small");

You can specify the font of a section of the text by prefixing it with the control sequence &"font,style" where font is a font name such as "Courier New" or "Times New Roman" and style is one of the standard Windows font styles: "Regular", "Italic", "Bold" or "Bold Italic".

worksheet1.setHeader("&C&\"Courier New,Italic\"Hello");
worksheet2.setHeader("&C&\"Courier New,Bold Italic\"Hello");
worksheet3.setHeader("&C&\"Times New Roman,Regular\"Hello");

To include a single literal ampersand & in a header or footer you should use a double ampersand &&:

worksheet1.setHeader("&CCuriouser && Curiouser - Attorneys at Law");

Note:

The header or footer string must be less than 255 characters. Strings longer than this will not be written.