This code will help you to take the screenshot of the complete scrollable page.

CaptureBrowserScreenShot.java

package com.mobile.equinox.util;

import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import javax.imageio.ImageIO;

import org.apache.commons.io.FileUtils;
import org.openqa.selenium.JavascriptExecutor;
import org.openqa.selenium.OutputType;
import org.openqa.selenium.TakesScreenshot;
import org.openqa.selenium.WebDriver;
import org.openqa.selenium.WebDriverException;
import org.openqa.selenium.remote.Augmenter;
import org.openqa.selenium.support.events.EventFiringWebDriver;
public class CaptureBrowserScreenShot {
	List<ArrayList<BufferedImage>> imageslist;
	
	public void seleniumCaptureBrowserScreenShot(EventFiringWebDriver driver,String ImgPath) throws InterruptedException, IOException {
		int height_covered=0,width_covered=0,pageHeightLeft=0,pageWidthLeft=0;
		JavascriptExecutor js = (JavascriptExecutor)driver;
		//scrolling to top before taking the full screenshot.
		js.executeScript("window.scrollTo(0,0)");
		
		Long pageheight1=(Long)js.executeScript("return window.innerHeight");
		Long maxPageHeight1=(Long)js.executeScript("return Math.max(document.documentElement.scrollHeight, document.body.scrollHeight," +
				"document.documentElement.clientHeight, window.innerHeight)");
		float sections=(float)maxPageHeight1/pageheight1;
		int numberOfRows=(int)Math.ceil(sections);						//denotes the number of rows.

		imageslist=new ArrayList<ArrayList<BufferedImage>>(numberOfRows);

		Long pageWidth1=(Long)js.executeScript("return window.innerWidth");
		Long maxPageWidth1=(Long)js.executeScript("return Math.max(document.documentElement.scrollWidth, document.body.scrollWidth," +
				"document.documentElement.clientWidth, window.innerWidth)");
		sections=(float)maxPageWidth1/pageWidth1;
		int numberOfCols=(int)Math.ceil(sections);							//denotes the number of columns.

		int pageheight=pageheight1.intValue();
		int maxPageHeight=maxPageHeight1.intValue();
		int pageWidth=pageWidth1.intValue();
		int maxPageWidth=maxPageWidth1.intValue();

//		System.out.println("HTML Page height="+pageheight+"   Max Page Height="+maxPageHeight+"   Rows="+numberOfRows);
//		System.out.println("HTML Page Width="+pageWidth+"   Max Page Width="+maxPageWidth+"   Columns="+numberOfCols);

		for (int row=0; row<numberOfRows ; row++) {

			ArrayList<BufferedImage> rowArr=new ArrayList<BufferedImage>(numberOfCols);
			imageslist.add(rowArr);
			width_covered=0;
			pageHeightLeft=maxPageHeight-height_covered;

			for(int col=0; col<numberOfCols;col++){
				pageWidthLeft=maxPageWidth-width_covered;
				takeScreenshot(driver,row,col,ImgPath);
//				System.out.println("\nRow="+row+"  Col="+col+"  PageWidthLeft="+pageWidthLeft+"  PageHeightLeft="+pageHeightLeft);

				if((pageHeightLeft < pageheight) && (pageWidthLeft < pageWidth )){
//					System.out.println("Page Width and Height both are at extreme!");
				}
				else if(pageHeightLeft < pageheight ){

//					System.out.println("....Page Height needs cropping...");
					/*Crops the Image*/
					BufferedImage lastScreenShot=rowArr.get(rowArr.size()-1);
					int lastScreenShotHeight=lastScreenShot.getHeight();
//					System.out.println("Last Image height="+lastScreenShotHeight);

					double pagePercent=((double)(pageheight-pageHeightLeft)/pageheight)*100;
//					System.out.println("Page Remove Percent from top="+pagePercent);	

					double imageToBeCropped=Math.round(((double)(pagePercent/100))*lastScreenShotHeight);
//					System.out.println("Height of Image to be cropped from top="+imageToBeCropped);
//					System.out.println("Height of resultant image="+(lastScreenShotHeight-imageToBeCropped));

					BufferedImage subImage=lastScreenShot.getSubimage(0, (int)imageToBeCropped, lastScreenShot.getWidth(), (int) (lastScreenShotHeight-imageToBeCropped));
//					ImageIO.write(subImage, "jpg", new File(ImgPath + row+"_"+col+"_1.jpg"));
					rowArr.set(rowArr.size()-1, subImage);

				}
				else if(pageWidthLeft < pageWidth ){

//					System.out.println("Page Width needs cropping...Size of Images array: "+rowArr.size());
					/*Crops the Image*/
					BufferedImage lastScreenShot=rowArr.get(rowArr.size()-1);
					int lastScreenShotWidth=lastScreenShot.getWidth();
//					System.out.println("Last Image Width="+lastScreenShotWidth);

					double pagePercent=((double)(pageWidth-pageWidthLeft)/pageWidth)*100;
//					System.out.println("Percent of UnUseful Page="+pagePercent);	

					double imageToBeCropped=Math.round(((double)(pagePercent/100))*lastScreenShotWidth);
//					System.out.println("Width of Image to be cropped from Left="+imageToBeCropped);
//					System.out.println("Width of resultant image="+(lastScreenShotWidth-imageToBeCropped));

					BufferedImage subImage=lastScreenShot.getSubimage((int)imageToBeCropped, 0, (int) (lastScreenShotWidth-imageToBeCropped),lastScreenShot.getHeight());
//					ImageIO.write(subImage, "jpg", new File(ImgPath + row+"_"+col+".jpg"));
					rowArr.set(rowArr.size()-1, subImage);

				}else{
					if(maxPageWidth==pageWidth)	{	//No action on width has to be taken.
						break;
					}
					js.executeScript("window.scrollBy("+pageWidth+",0)");
					width_covered=width_covered+pageWidth;

//					System.out.println("Horizontally Scrolled window by now "+pageWidth+"  pixels. Row="+row);
				}
				Thread.sleep(700);
			}

//			js.executeScript("window.scrollBy(0,"+pageheight+")");
			height_covered=height_covered+pageheight;
			js.executeScript("window.scrollTo(0,"+height_covered+")");


//			System.out.println("Vertically Scrolled window by now "+height_covered+"  pixels.");
			Thread.sleep(500);
		}
		try {
			joinImages(ImgPath);
		} catch (IOException e) {
			e.printStackTrace();
		}

	}
	
	private void takeScreenshot(EventFiringWebDriver driver, int row, int col,String ImgPath) {
		File screenshot = null;
		if(ConfigManager.getProperties().getProperty("seleniumGrid").trim().equalsIgnoreCase("true")){
			org.openqa.selenium.WebDriver augmentedDriver = new Augmenter().augment(driver.getWrappedDriver());
			try {
				screenshot = ((TakesScreenshot) augmentedDriver).getScreenshotAs(OutputType.FILE);
			} catch (WebDriverException e) {
				e.printStackTrace();
			}
		}
		else if(driver.getWrappedDriver().getClass().toString().toLowerCase().contains("chromedriver")
				||driver.getWrappedDriver().getClass().toString().toLowerCase().contains("safari")
				||driver.getWrappedDriver().getClass().toString().toLowerCase().contains("firefox")||
				driver.getWrappedDriver().getClass().toString().toLowerCase().contains("remotewebdriver")){
			screenshot = ((TakesScreenshot) driver.getWrappedDriver()).getScreenshotAs(OutputType.FILE);
		}
/*		File screenshotfile = new File(ImgPath);
		try {
			FileUtils.copyFile(screenshot, screenshotfile);
		} catch (IOException e) {
			e.printStackTrace();
		}
		*/
		
//		WebDriver augmentedDriver = new Augmenter().augment(driver);
//		TakesScreenshot driver_secreenshot=(TakesScreenshot)augmentedDriver;

		//If you are executing the test case using only ChromeDriver then use the below code instead. You dont need Augmenter.
//		TakesScreenshot driver_secreenshot=(TakesScreenshot)driver;

//		File file=driver_secreenshot.getScreenshotAs(OutputType.FILE);
		if(screenshot!=null)
		try {
			BufferedImage image=ImageIO.read(screenshot);
			imageslist.get(row).add(image);
//			ImageIO.write(image, "jpg", new File("D:\\Github\\QACompetencyCenter\\AppiumAndroidTest\\snapshots\\screenshot"+row+"_"+col+".jpg"));
//			ImageIO.write(image, "jpg", new File(ImgPath + row+"_"+col+".jpg"));

		} catch (IOException e) {
			e.printStackTrace();
		}		
	}
		
		private void joinImages(String ImgPath) throws IOException{
		
			int resultImageHeight=0, resultImageWidth=0;
		
//			System.out.println("Height of all Images are:");
		    for(ArrayList<BufferedImage> arr:imageslist){
		    	 	 BufferedImage image=arr.get(0);
//		    		 System.out.println(image.getHeight());
		    		 resultImageHeight=resultImageHeight+image.getHeight();
		    }
//		    System.out.println("Width of all Images are:"); 
		    ArrayList<BufferedImage> arrImage=imageslist.get(0); 
			for(BufferedImage image: arrImage){
//				System.out.println(image.getWidth());
				resultImageWidth=resultImageWidth+image.getWidth();
			}
//		     System.out.println("Final Image Height="+resultImageHeight+"  Width="+resultImageWidth);
		
		     BufferedImage resultImage = new BufferedImage(resultImageWidth,resultImageHeight ,BufferedImage.TYPE_INT_RGB);
			 Graphics g = resultImage.createGraphics();
		
			 int imageBelow=0;
			 for(ArrayList<BufferedImage> arr:imageslist){
				 int imageSide=0;
				 for(BufferedImage screenshot : arr){
		
					 g.drawImage(screenshot, imageSide, imageBelow, null);
					 imageSide=imageSide+screenshot.getWidth();
				 }
				imageBelow=imageBelow+arr.get(0).getHeight();
			 }
			 ImageIO.write(resultImage, "jpg", new File(ImgPath));
		}

		private void setMaximizeBrowser(WebDriver driver){
			JavascriptExecutor js = (JavascriptExecutor)driver;
			js.executeScript("var oldY = document.documentElement.clientHeight;" +
					"window.resizeTo(800, 600);" +
					"var padX = 800 - document.documentElement.clientWidth; var padY = 600 - document.documentElement.clientHeight;" +
					"window.resizeTo(padX, oldY + padY);");
//			System.out.println("Sets the Browser Size");
		
		}

}