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getting a bufferedImage from a bytearray

I am trying to get back a bufferedImage from array of bytes, but I am getting an error saying bufferedimage is null. I actually tried several ways, everything ended up in the same way. Here goes my code:
1)
byte[] arr = Base64.decode(base64String);
BufferedImage bImageFromConvert =ImageIO.read(new ByteArrayInputStream(arr));
2)
InputStream in = new ByteArrayInputStream(arr);
BufferedImage bImageFromConvert = ImageIO.read(in);
I am pretty sure my byte array contains data and I think ImageIO.read() is where my code goes wrong.

The error is in your BufferedImage to Base64 encode method as you have posted in the comments.
You are never writing the BufferedImage to the ByteArrayOutputStream. Therefore the Base64 string is empty, and reading the empty string produces a null BufferedImage.
You should use this code to encode your image:
BufferedImage originalImage = ImageIO.read(new File("G:\\a.jpg"));
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write( originalImage, "jpg", baos );
String base64String=Base64.encode(baos.toByteArray());
To decode the image use this code:
byte[] arr = Base64.decode(base64String);
BufferedImage bImageFromConvert =ImageIO.read(new ByteArrayInputStream(arr));
System.out.println(bImageFromConvert.getWidth());

Try this code.Maybe it works. It worked for me.
byte[] aByteArray = {};
int width = ;
int height = ;
DataBuffer buffer = new DataBufferByte(aByteArray, aByteArray.length);
WritableRaster raster = Raster.createInterleavedRaster(buffer, width, height, 3 * width, 3, new int[] {0, 1, 2}, (Point)null);
ColorModel cm = new ComponentColorModel(ColorModel.getRGBdefault().getColorSpace(), false, true, Transparency.OPAQUE, DataBuffer.TYPE_BYTE);
BufferedImage image = new BufferedImage(cm, raster, true, null);
Just add the byte, width and height to code and customize it.

8 bit gray scale image byte array to jpg

I am trying to convert a 8 bit gray scale image byte array to jpg image format in java.
static byte[] bytes = new byte[]{126, 126, 127, -128};
public static void main(String[] args) throws IOException {
ByteArrayInputStream bis = new ByteArrayInputStream(bytes);
Iterator<?> readers = ImageIO.getImageReadersByFormatName("jpg");
ImageReader reader = (ImageReader) readers.next();
Object source = bis;
ImageInputStream iis = ImageIO.createImageInputStream(source);
reader.setInput(iis, true);
ImageReadParam param = reader.getDefaultReadParam();
Image image = reader.read(0, param);
BufferedImage bufferedImage = new BufferedImage(image.getWidth(null), image.getHeight(null), BufferedImage.TYPE_BYTE_GRAY);
Graphics2D g2 = bufferedImage.createGraphics();
g2.drawImage(image, null, null);
File imageFile = new File("C:\\newrose3.jpg");
ImageIO.write(bufferedImage, "jpg", imageFile);
System.out.println(imageFile.getPath());
}
I have bytes having image data and I want to convert it into readable image format in java.

Assuming bytes is supposed to be pixel data, you should create an image from those bytes, then write it out as JPEG.
Something like:
// Create an image type grayscale
BufferedImage image = new BufferedImage(2, 2, BufferedImage.TYPE_BYTE_GRAY);
// Get the backing pixels, and copy into it
byte[] data = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
System.arraycopy(bytes, 0, data, 0, bytes.length);
// Write it out:
ImageIO.write(image, "jpg", new File("yourPathHere");

JAVA : How to create .PNG image from a byte[]?

I have seen some code source, but I do not understand...
I use Java 7
Please, how to convert a RGB (Red,Green,Blue) Byte Array (or something similar) to a .PNG file format ?
Example from an array that could represent "a RGB pixel" :
byte[] aByteArray={0xa,0x2,0xf};
Important Aspect :
I try to generate a .PNG file only from a byte[] "not from a previous existing file"
is it possible with an existing API? ;)
Here my first code :
byte[] aByteArray={0xa,0x2,0xf};
ByteArrayInputStream bais = new ByteArrayInputStream(aByteArray);
File outputfile = new File("image.png");
ImageIO.write(bais, "png", outputfile);
....Error : No suitable Method Found
Here the other version modified from Jeremy but look similar :
byte[] aByteArray={0xa,0x2,0xf};
ByteArrayInputStream bais = new ByteArrayInputStream(aByteArray);
final BufferedImage bufferedImage = ImageIO.read(newByteArrayInputStream(aByteArray));
ImageIO.write(bufferedImage, "png", new File("image.png"));
....multiple Errors : image == null! ...... Sure ? Note : I do not search to use a source file

The Image I/O API deals with images, so you need to make an image from your byte array first before you write it out.
byte[] aByteArray = {0xa,0x2,0xf,(byte)0xff,(byte)0xff,(byte)0xff};
int width = 1;
int height = 2;
DataBuffer buffer = new DataBufferByte(aByteArray, aByteArray.length);
//3 bytes per pixel: red, green, blue
WritableRaster raster = Raster.createInterleavedRaster(buffer, width, height, 3 * width, 3, new int[] {0, 1, 2}, (Point)null);
ColorModel cm = new ComponentColorModel(ColorModel.getRGBdefault().getColorSpace(), false, true, Transparency.OPAQUE, DataBuffer.TYPE_BYTE);
BufferedImage image = new BufferedImage(cm, raster, true, null);
ImageIO.write(image, "png", new File("image.png"));
This assumes the byte array has three bytes per pixel (red, green then blue) and the range of values is 0-255.

Java: How To Convert Image to Byte[]

I'm having an image in Database in bytearray format. I want to display on browser. I don't know how to write Image using OutputStream. Here is my code.
byte[] imageInBytes = (byte[]) obj; // from Database
InputStream in = new ByteArrayInputStream(imageInBytes);
Image img = ImageIO.read(in).getScaledInstance(50, -1, Image.SCALE_SMOOTH);
OutputStream o = resp.getOutputStream(); // HttpServletResponse
o.write(imgByte);

You may try something like this:
File f=new File("image.jpg");
BufferedImage o=ImageIO.read(f);
ByteArrayOutputStream b=new ByteArrayOutputStream();
ImageIO.write(o, "jpg", b);
byte[] img=b.toByteArray();

You have to set the content type of the response to be an image type that you are sending.
Suppose your image was stored when it was a jpeg. then,
OutputStream o = resp.getOutputStream(); // HttpServletResponse
o.setContentType("image/jpeg");
o.write(img.getBytes() /* imgByte */);
would send the browser an image. ( The browser understands from the header information that the following information you just sent it, is a jpeg image. )

You could try using ImageIO.write...
ImageIO.write(img, "jpg", o);
But this will require you to use BufferedImage when reading...
BufferedImage img = ImageIO.read(in);
You could then use AffineTransform to scale the image...
BufferedImage scaled = new BufferedImage(img.getWidth() / 2, img.getHeight() / 2, img.getType());
Graphics2D g2d = scaled.createGraphics();
g2d.setTransform(AffineTransform.getScaledInstance(0.5, 0.5));
g2d.drawImage(img, 0, 0, null);
g2d.dispose();
img = scaled;
This, obviously, only scales the image by 50%, so you'll need to calculate the required scaling factor based on the original size of the image against your desired size...
Take a look at Java: maintaining aspect ratio of JPanel background image for some ideas on scaling images...

encoding and decoding in JPG images in Android

I am creating an application over Android where I need to manipulate my JPG files. I am not getting much of header information for JPG format so for that I am converting it to Bitmap, manipulated the pixel values in bitmap and then again convert it back to JPG.
Here what problem I am facing is- after manipulating only some pixels of bitmap and
converting it back to JPG, I do not get the same set of pixels I got earlier (for those pixels which I did not manipulate). I am getting the same image as the original in the new image. But when I check new image pixels values for decoding, the untouched pixels are different...
File imagefile = new File(filepath);
FileInputStream fis = new FileInputStream(imagefile);
Bitmap bi = BitmapFactory.decodeStream(fis);
int intArray[];
bi=bi.copy(Bitmap.Config.ARGB_8888,true);
intArray = new int[bi.getWidth()*bi.getHeight()];
bi.getPixels(intArray, 0, bi.getWidth(), 0, 0, bi.getWidth(), bi.getHeight());
int newArray[] = encodeImage(msgbytes,intArray,mbytes); // method where i am manipulating my pixel values
// converting the bitmap data back to JPG file
bi = Bitmap.createBitmap(newArray, bi.getWidth(), bi.getHeight(), Bitmap.Config.ARGB_8888);
ByteArrayOutputStream baos = new ByteArrayOutputStream();
bi.compress(Bitmap.CompressFormat.JPEG, 100, baos);
byte[] data = baos.toByteArray();
Bitmap bitmapimage = BitmapFactory.decodeByteArray(data, 0, data.length);
String filepath = "/sdcard/image/new2.jpg";
File imagefile = new File(filepath);
FileOutputStream fos = new FileOutputStream(imagefile);
bitmapimage.compress(CompressFormat.JPEG, 100, fos);
Help me if I am wrong somewhere or whether I should use some other method to manipulate JPG pixel values...

JPEG is an image format that is usually based on lossy compression. That means that some information that is not important for the human eye is thrown away to further shrink the file size. Try to save your image as a PNG (a lossless format).

Be careful with using
Bitmap bi = BitmapFactory.decodeStream(fis);
bi = bi.copy(Bitmap.Config.ARGB_8888, true);
At the point where you have the first bi you may have already lost a lot of information, instead try using BitmapFactory.Options to force 8888 (which is the default too):
BitmapFactory.Options options = new BitmapFactory.Options();
options.inPreferredConfig = Bitmap.Config.ARGB_8888;
options.inDither = false;
Bitmap bi = BitmapFactory.decodeStream(fis, options);
If you stay with copy you should still recycle() the one that you throw away.