header overlapping with data in generated pdf document

I have written a method to generate pdf document as a report. Report is generated fine. But in the report, the header is being overlapped by the data.
Below is the code :

public ByteArrayOutputStream generateStockDetailsMasterReport(
			List<StockDetails> stockList) {
		ByteArrayOutputStream baosPDF = null;
		try {
			baosPDF = new ByteArrayOutputStream();
                        Document doc = new Document();
			PdfWriter docWriter = null;
			docWriter = PdfWriter.getInstance(doc, baosPDF);
			doc = addHeaderDetails(doc);
			doc.open();
                        
			Font f = FontFactory.getFont("Verdana", 7);
			FontSelector fontselector = new FontSelector();
			fontselector.addFont(f);
			PdfPCell cell = null;

PdfPTable headerLabelTable = new PdfPTable(4);
			cell = new PdfPCell(new Paragraph(fontselector.process("Stock Details Report")));
			cell.setBorderWidth(0);
			cell.setHorizontalAlignment(Paragraph.ALIGN_CENTER);
			cell.setColspan(4);
			headerLabelTable.addCell(cell);
			doc.add(headerLabelTable);

PdfPTable headTable = new PdfPTable(8);
			headTable.setWidthPercentage(100);

cell = new PdfPCell(new Paragraph(fontselector.process("MSISDN")));
			cell.setBackgroundColor(new Color(0xFF, 0x69, 0xB4));
			headTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector.process("SIM")));
			cell.setBackgroundColor(new Color(0xFF, 0x69, 0xB4));
			headTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector.process("Category")));
			cell.setBackgroundColor(new Color(0xFF, 0x69, 0xB4));
			headTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector.process("Category Type")));
			cell.setBackgroundColor(new Color(0xFF, 0x69, 0xB4));
			headTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector.process("Allocated Date")));
			cell.setBackgroundColor(new Color(0xFF, 0x69, 0xB4));
			headTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector.process("Allocated To")));
			cell.setBackgroundColor(new Color(0xFF, 0x69, 0xB4));
			headTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector.process("Activated Date")));
			cell.setBackgroundColor(new Color(0xFF, 0x69, 0xB4));
			headTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector.process("Status")));
			cell.setBackgroundColor(new Color(0xFF, 0x69, 0xB4));
			headTable.addCell(cell);

doc.add(headTable);

PdfPTable StockDetailsMasterTable = new PdfPTable(8);
			StockDetailsMasterTable.setWidthPercentage(100);

int size = stockList.size();
			for (int i = 0; i < size; i++) {
				StockDetails stockDetails = stockList.get(i);
				cell = new PdfPCell(new Paragraph(fontselector.process(String.valueOf(stockDetails
								.getMsisdnNumber() != null ? stockDetails.getMsisdnNumber().getRawString() : ""))));
				StockDetailsMasterTable.addCell(cell);

cell = new PdfPCell(new Paragraph(
						fontselector.process(String.valueOf(stockDetails
								.getSimNumber() != null ? stockDetails	.getSimNumber().getRawString() : ""))));
				StockDetailsMasterTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector
						.process(String.valueOf(stockDetails
								.getPremiumCategory() != null ? stockDetails.getPremiumCategory().getRawString() : ""))));
				StockDetailsMasterTable.addCell(cell);

cell = new PdfPCell(new Paragraph(
						fontselector.process(String.valueOf(stockDetails
								.getCategoryType() != null ? stockDetails.getCategoryType().getRawString() : ""))));
				StockDetailsMasterTable.addCell(cell);

cell = new PdfPCell(new Paragraph(
						fontselector.process(String.valueOf(stockDetails
								.getAllocatedDate() != null ? stockDetails.getAllocatedDate().getRawString() : ""))));
				StockDetailsMasterTable.addCell(cell);

cell = new PdfPCell(new Paragraph(
						fontselector.process(String.valueOf(stockDetails
								.getAllocatedTo() != null ? stockDetails.getAllocatedTo().getRawString() : ""))));
				StockDetailsMasterTable.addCell(cell);

cell = new PdfPCell(new Paragraph(
						fontselector.process(String.valueOf(stockDetails
								.getActivatedDate() != null ? stockDetails.getActivatedDate().getRawString() : ""))));
				StockDetailsMasterTable.addCell(cell);

cell = new PdfPCell(new Paragraph(fontselector
						.process(String.valueOf(stockDetails
								.getCustomerStatus() != null ? stockDetails.getCustomerStatus().getRawString() : ""))));
				StockDetailsMasterTable.addCell(cell);
			}

doc.add(StockDetailsMasterTable);
			doc.close();
			docWriter.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		return baosPDF;
	}

method addHeaderDetails is below

private Document addHeaderDetails(Document doc) throws Exception {

PdfPTable headerTable = new PdfPTable(2);
		headerTable.setWidthPercentage(100);

Image img = Image.getInstance(servletContext
				.getRealPath(File.separator)
				+ File.separator + "img" + File.separator + "zain.jpeg");
		img.scalePercent(40);
		PdfPCell cell1 = new PdfPCell(img);
		cell1.setBackgroundColor(new Color(0xFF, 0xFF, 0xFF));
		cell1.setBorderColor(new Color(255, 255, 255));

headerTable.addCell(cell1);

PdfPCell cell2 = new PdfPCell();
		cell2.setBackgroundColor(new Color(0xFF, 0xFF, 0xFF));
		cell2.setBorderColor(new Color(255, 255, 255));
		cell2.setHorizontalAlignment(Paragraph.ALIGN_RIGHT);
		headerTable.addCell(cell2);

Phrase p = new Phrase();
		p.add(headerTable);

HeaderFooter header = new HeaderFooter(p, false);
		header.setBackgroundColor(new Color(0x41, 0x69, 0xE1));
		header.setAlignment(Paragraph.ALIGN_TOP);
                
		header.disableBorderSide(HeaderFooter.TOP);

HeaderFooter footer = new HeaderFooter(new Phrase(""), true);
		footer.setBackgroundColor(new Color(0x41, 0x69, 0xE1));
		footer.disableBorderSide(HeaderFooter.TOP);
		footer.disableBorderSide(HeaderFooter.BOTTOM);

doc.setHeader(header);
		doc.setFooter(footer);

return doc;
	}

The pdf generation is fine, but overlapping is being done.

Please let me know what I have missed to avoid that overlapping.

Thanks in advance.

Welcome to Javaranch Krishna!