JSF exporting excel data from another page

Question

I am new to jsf and I am setting up a basic reporting tool (sql queries) which shows a list of reports in the home page. I want to put an excel export commandbutton in the home page and export the report selected by the user or drive the user to a different execution page to show results in a datatable for the selected report. How can I achieve that? datatable with query results, of course, is visible only in the execution page and is dynamically created during query execution (this part works fine). Am I going crazy for nothing? Thanks in advance for any suggestion.

Answer 1

If you want to export data to Excel you need to use a third party library. There are free ones like JExcelApi and Apache POI. Also, there are commercial libraries like Aspose. If you're going to choose an open source library check this question: Choosing an excel java api.

When you export data to Excel, you must create the Excel file and download the content for the client. You can check how to download a file using JSF by @BalusC (JSF expert).

One more advice, when you're downloading a file don't add ajax functionality to the command link/button.

Answer 2

You can use under code this code block provide excel export as genericly way. You can send any List and send any fileName

public class ExcelUtils {

public static <T> void writeToExcel(String fileName, List<T> data) {

    FacesContext context = FacesContext.getCurrentInstance();

    HttpServletResponse response = (HttpServletResponse) context.getExternalContext().getResponse();

    response.setContentType("application/vnd.ms-excel");
    response.setHeader("Content-Disposition", "attachment;filename=" + fileName + ".xls");
    response.setHeader("Pragma", "no-cache");

    OutputStream fos = null;
    try {
        fos = response.getOutputStream();
    } catch (IOException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
    XSSFWorkbook workbook = null;
    try {
        // File file = new File(fileName);
        workbook = new XSSFWorkbook();
        Sheet sheet = workbook.createSheet();
        List<String> fieldNames = getFieldNamesForClass(data.get(0).getClass());
        int rowCount = 0;
        int columnCount = 0;
        Row row = sheet.createRow(rowCount++);
        for (String fieldName : fieldNames) {
            if (!fieldName.equals("serialVersionUID")) {
                Cell cell = row.createCell(columnCount++);
                cell.setCellValue(fieldName);
            }
        }
        Class<? extends Object> classz = data.get(0).getClass();
        for (T t : data) {
            row = sheet.createRow(rowCount++);
            columnCount = 0;
            for (String fieldName : fieldNames) {
                if (!fieldName.equals("serialVersionUID")) {
                    Cell cell = row.createCell(columnCount);
                    Method method = null;
                    try {
                        method = classz.getMethod("get" + capitalize(fieldName));
                    } catch (NoSuchMethodException nme) {
                        method = classz.getMethod("get" + fieldName);
                    }

                    Object value = method.invoke(t, (Object[]) null);
                    if (value != null) {
                        if (value instanceof String) {
                            cell.setCellValue((String) value);
                        } else if (value instanceof Long) {
                            cell.setCellValue((Long) value);
                        } else if (value instanceof Integer) {
                            cell.setCellValue((Integer) value);
                        } else if (value instanceof Double) {
                            cell.setCellValue((Double) value);
                        }
                    }
                    columnCount++;
                }
            }
        }
        workbook.write(fos);
        fos.flush();
    } catch (Exception e) {
        e.printStackTrace();
    } finally {
        try {
            if (fos != null) {
                fos.close();
                context.responseComplete();
                context.renderResponse();
            }
        } catch (IOException e) {
        }
        try {
            if (workbook != null) {
                workbook.close();
            }
        } catch (IOException e) {
        }
    }
}

// retrieve field names from a POJO class
private static List<String> getFieldNamesForClass(Class<?> clazz) throws Exception {
    List<String> fieldNames = new ArrayList<String>();
    Field[] fields = clazz.getDeclaredFields();
    for (int i = 0; i < fields.length; i++) {
        fieldNames.add(fields[i].getName());
    }
    return fieldNames;
}

// capitalize the first letter of the field name for retriving value of the
// field later
private static String capitalize(String s) {
    if (s.length() == 0)
        return s;
    return s.substring(0, 1).toUpperCase() + s.substring(1);
}

}