Excelling in Excel with Java

Whether you have balance sheets, account information downloads, tax calculations, or pay slips, they all tend to come in Microsoft Excel. Non-IT professionals feel comfortable using Microsoft Excel as a data exchange technology. The Jakarta POI (Poor Obfuscation Implementation) API is a fantastic way for Java programmers to access Microsoft document formats. The most mature API from Jakarta POI is the HSSF (Horrible Spreadsheet Format) API, which accesses Microsoft Excel documents.

In this article, I walk you through the steps for creating and reading Excel documents, and for using fonts and cell styling—all using Java.

Note: You can download the source code for all the examples in this article from Resources.

POI terminology

The key terms associated with Jakarta POI are as follows:

• POIFS (Poor Obfuscation Implementation File System): Java APIs for reading and writing OLE (Object Linking and Embedding) 2 compound document formats
• HSSF (Horrible Spreadsheet Format): Java API to read Microsoft Excel
• HDF (Horrible Document Format): Java API to read and write Microsoft Word 97
• HPSF (Horrible Property Set Format): Java API for reading property sets using (only) Java

Create an Excel document

The Jakarta POI API can be used to create an Excel document programmatically. The important steps involved are:

• Create a workbook: HSSFWorkbook workbook = new HSSFWorkbook();
• Create a new worksheet in the workbook and name the worksheet “Java Excels”: HSSFSheet sheet = workbook.createSheet("Java Excels");
• Create a new row in the sheet: HSSFRow row = sheet.createRow((short)0);
• Create a cell in the row: HSSFCell cell = row.createCell((short) 0);
• Put some content in the cell: cell.setCellValue("Have a Cup of XL");
• Write the workbook into the filesystem: workbook.write(fileOutputStream);

Read data from the Excel document

In this example, you’ll see how to read values from an Excel document.

Let’s assume this is our Excel sheet:

The key steps in reading the Excel sheet are as follows:

• Create a new Excel document reference: HSFWorkbook workbook = new HSSFWorkbook(new FileInputStream(fileToBeRead));.
• Refer to the sheet: By default, the first sheet in the Excel document is at reference 0: HSSFSheet sheet = workbook.getSheetAt(0);. A sheet can also be referred to by name. Let’s assume that the Excel sheet has the default name “Sheet1”. It can be referred to as follows: HSSFSheet sheet = workbook.getSheet("Sheet1");.
• Refer to a row: HSSFRow row = sheet.getRow(0);.
• Refer to a cell in the row: HSSFCell cell = row.getCell((short)0);.
• Get the values in that cell: cell.getStringCellValue();.

A practical example

Now let’s assume that we want to see the list of all declared methods and member variables in a jar file. It would be ideal to have a consolidated list of all information in one single file. We would like to view the information so that the class names are in the first column, declared fields in the second column, and declared methods in the third column, with the column headings appearing in red.

The program will have to complete the following activities:

• Unzip the jar file
• Read all classfiles in the jar file
• Load the classes in the jar file
• Using reflection, get the declared methods and fields
• Write the class information into an Excel sheet using Jakarta POI

Let’s concentrate on just the interesting steps of Jakarta POI usage:

• Create a new Excel document: workbook = new HSSFWorkbook();
• Make a worksheet in that document and give the worksheet a name: sheet = workbook.createSheet("Java Class Info");
• Set the first three columns’ widths: sheet.setColumnWidth((short)0,(short)10000 );
• Create the header line: HSSFRow row = sheet.createRow((short)0);
• Create and set font and cell style:

     HSSFFont font = workbook.createFont();
     font.setColor(HSSFFont.COLOR_RED);
     font.setBoldweight(HSSFFont.BOLDWEIGHT_BOLD);
     // Create the style
        HSSFCellStyle cellStyle= workbook.createCellStyle();
        cellStyle.setFont(font);
  

• Use the cell style:

        HSSFCell cell = row.createCell((short) 0);
        cell.setCellStyle(cellStyle);
        cell.setCellType(HSSFCell.CELL_TYPE_STRING);
        cell.setCellValue("Class Name ");
  

• Write the output file:

        FileOutputStream fOut = new FileOutputStream(outputFile);
        // Write the Excel sheet
        workbook.write(fOut);
        fOut.flush();
        // Done deal. Close it.
        fOut.close();
  

Summary

As demonstrated in this article, Java developers no longer need to wince at data in Excel sheets. We can programmatically access Excel documents. Have a cup of Java, and excel in Excel!