// Style the cell with borders all around.
CellStyle style = wb.createCellStyle();
style.setBorderBottom(CellStyle.BORDER_THIN);
style.setBottomBorderColor(IndexedColors.BLACK.getIndex());

style.setBorderLeft(CellStyle.BORDER_THIN);
style.setLeftBorderColor(IndexedColors.GREEN.getIndex());

style.setBorderRight(CellStyle.BORDER_THIN);
style.setRightBorderColor(IndexedColors.BLUE.getIndex());

style.setBorderTop(CellStyle.BORDER_MEDIUM_DASHED);
style.setTopBorderColor(IndexedColors.BLACK.getIndex());

cell.setCellStyle(style);

//Setting the line of the top border
style.setBorder(BorderType.TOP_BORDER,CellBorderType.THICK,Color.getBlack());

//Setting the line of the bottom border
style.setBorder(BorderType.BOTTOM_BORDER,CellBorderType.THICK,Color.getBlack());

//Setting the line of the left border
style.setBorder(BorderType.LEFT_BORDER,CellBorderType.THICK,Color.getBlack());

//Setting the line of the right border
style.setBorder(BorderType.RIGHT_BORDER,CellBorderType.THICK,Color.getBlack());

//Saving the modified style to the "A1" cell.
cell.setStyle(style);