Convert image to byte array and viceversa

Question

I'm trying to send an image as byte array through android, and convert it back to png file on server side, I'm getting IllegalArgumentException on server side.

This is my android code which converts image to byte array and sends it as request to server:

 GestureOverlayView gestureView = (GestureOverlayView) findViewById(R.id.signaturePad);

            Bitmap bm = Bitmap.createBitmap(gestureView.getGesture().toBitmap(100, 100, 8, Color.WHITE));

            FileOutputStream fos = openFileOutput("signature.png", Context.MODE_PRIVATE);
            bm.compress(Bitmap.CompressFormat.PNG, 100, fos);

            byte[] image_byte = fos.toString().getBytes();//Base64.encode(fos.toString().getBytes(), 0);

            String strImage = image_byte.toString();

This is my server side program:

String imageString = request.getParameter("SignatureImage");
    byte[] imageByte = imageString.getBytes();
    try {
        InputStream in = new ByteArrayInputStream(imageByte);
        BufferedImage bImageFromConvert = ImageIO.read(in);

        //Getting exception at this line
        ImageIO.write(bImageFromConvert, "png", new File(
                "E:/signature/signature.png"));
        /*BufferedImage bufferedImage = ImageIO.read(new ByteArrayInputStream(imageByte));
        ImageIO.write(bufferedImage, "jpg", new File("E:/signature/signature.jpg"));*/
    } catch (IOException e) {
        e.printStackTrace();
    }

Exception on server is:

12:39:40,990 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[localhost].[/APDTest].[ImageRetrieve]] Servlet.service() for servlet ImageRetrieve threw exception: java.lang.IllegalArgumentException: im == null!
    at javax.imageio.ImageIO.write(ImageIO.java:1457) [:1.6.0_32]
    at javax.imageio.ImageIO.write(ImageIO.java:1521) [:1.6.0_32]
    at com.apd.test.ImageRetrieve.doPost(ImageRetrieve.java:52) [:]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:754) [:1.0.0.Final]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [:1.0.0.Final]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:324) [:6.1.0.Final]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:242) [:6.1.0.Final]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [:6.1.0.Final]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161) [:6.1.0.Final]
    at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:181) [:6.1.0.Final]
    at org.jboss.modcluster.catalina.CatalinaContext$RequestListenerValve.event(CatalinaContext.java:285) [:1.1.0.Final]
    at org.jboss.modcluster.catalina.CatalinaContext$RequestListenerValve.invoke(CatalinaContext.java:261) [:1.1.0.Final]
    at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:88) [:6.1.0.Final]
    at org.jboss.web.tomcat.security.SecurityContextEstablishmentValve.invoke(SecurityContextEstablishmentValve.java:100) [:6.1.0.Final]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:159) [:6.1.0.Final]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [:6.1.0.Final]
    at org.jboss.web.tomcat.service.jca.CachedConnectionValve.invoke(CachedConnectionValve.java:158) [:6.1.0.Final]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [:6.1.0.Final]
    at org.jboss.web.tomcat.service.request.ActiveRequestResponseCacheValve.invoke(ActiveRequestResponseCacheValve.java:53) [:6.1.0.Final]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:362) [:6.1.0.Final]
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [:6.1.0.Final]
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:654) [:6.1.0.Final]
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:951) [:6.1.0.Final]

Answer 1

Your writing the image to a file output stream on your client side, which will store the contents into a physical file. You are then trying to convert the toString representation of FileOutputStream as the image content. This won't work, the toString method of that class doesn't give you the contents that were written to the stream, it just prints a barely helpful message like this:

java.io.FileOutputStream@761eec35

I believe what you intended to do was use a ByteArrayOutputStream - this class does allow you to retrieve the actual contents written via its toString method.

On Android side (snippet):

Bitmap bm = Bitmap.createBitmap(gestureView.getGesture().toBitmap(100,
        100, 8, Color.WHITE));

ByteArrayOutputStream baos = new ByteArrayOutputStream(2056);
bm.compress(Bitmap.CompressFormat.PNG, 100, baos);

byte[] imageBytes = baos.toByteArray();
String encodedString = Base64.encodeToString(imageBytes, Base64.DEFAULT);

On server side (snippet):

String imageString = request.getParameter("SignatureImage");
byte[] decodedBytes = Base64.decode(imageString, Base64.DEFAULT);

try {
    InputStream in = new ByteArrayInputStream(decodedBytes);
    BufferedImage bImageFromConvert = ImageIO.read(in);

    ImageIO.write(bImageFromConvert, "png", new File(
            "E:/signature/signature.png"));
} catch (IOException e) {
    e.printStackTrace();
}

Answer 2

Try this code.

Converting image into Byte: For reference

                  yourSelectedImage = BitmapFactory.decodeFile(galleryFilePath);     
              ByteArrayOutputStream baos = new ByteArrayOutputStream();  
              yourSelectedImage.compress(Bitmap.CompressFormat.PNG, 100, baos); 
              byte[] b = baos.toByteArray(); 

Converting Byte into image: For reference

                         final String encodedImage = response.toString();
           byte[] decodedString = Base64.decode(encodedImage, Base64.DEFAULT);
         decodedByte = BitmapFactory.decodeByteArray(decodedString, 0, decodedString.length);

Hope this will give you some solution.