在Java中将base64字符串转换为Image

Question

I have an image being sent to me through a JSON string. I want to convert that string into an image in my android app and then display that image.

The JSON string looks like this:

"data:image\/png;base64,iVBORw0KGgoAAAANSUhEUgAAAVI..."

Note: I truncated the string with a ...

I've got a function that (I think) converts the string into an image. Am I doing this right?

public Bitmap ConvertToImage(String image){
    try{
        InputStream stream = new ByteArrayInputStream(image.getBytes());
        Bitmap bitmap = BitmapFactory.decodeStream(stream);                 
        return bitmap;  
    }
    catch (Exception e) {
        return null;            
    }
}

Then I try to display it on my android activity like this

String image = jsonObject.getString("barcode_img");         
Bitmap myBitmap = this.ConvertToImage(image);
ImageView cimg = (ImageView)findViewById(R.id.imageView1);

//Now try setting dynamic image
cimg.setImageBitmap(myBitmap);

However, when I do this, nothing shows up. I don't get any errors in the logcat. What am I doing wrong?

Thanks

Answer 1

I'm worried about that you need to decode only the base64 string to get the image bytes, so in your

"data:image\/png;base64,iVBORw0KGgoAAAANSUhEUgAAAVI..."

string, you must get the data after data:image\\/png;base64, , so you get only the image bytes and then decode them:

String imageDataBytes = completeImageData.substring(completeImageData.indexOf(",")+1);

InputStream stream = new ByteArrayInputStream(Base64.decode(imageDataBytes.getBytes(), Base64.DEFAULT));

This is a code so you understand how it works, but if you receive a JSON object it should be done the correct way:

• Converting the JSON string to a JSON object.
• Extract the String under data key.
• Make sure that starts with image/png so you know is a png image.
• Make sure that contains base64 string, so you know that data must be decoded.
• Decode the data after base64 string to get the image.

Answer 2

InputStream stream = new ByteArrayInputStream(image.getBytes());

should be changed to

InputStream stream = new ByteArrayInputStream(Base64.decode(image.getBytes(), Base64.DEFAULT));

Refer http://developer.android.com/reference/android/util/Base64.html for details on how to do Base64 decoding.

Disclaimer: I have not checked for syntax, but this is how you should do it.

Answer 3

Here is the working code that converts the Base64 encoded inputStream and writes it to the disk. I spent a few time to make it work correctly. So I hope this helps other developers.

public boolean writeImageToDisk(FileItem item, File imageFile) {
    // clear error message
    errorMessage = null;
    FileOutputStream out = null;
    boolean ret = false;
    try {
        // write thumbnail to output folder
        out = createOutputStream(imageFile);

        // Copy input stream to output stream
        byte[] headerBytes = new byte[22];
        InputStream imageStream = item.getInputStream();
        imageStream.read(headerBytes);

        String header = new String(headerBytes);
        // System.out.println(header);

        byte[] b = new byte[4 * 1024];
        byte[] decoded;
        int read = 0;
        while ((read = imageStream.read(b)) != -1) {
            // System.out.println();
            if (Base64.isArrayByteBase64(b)) {
                decoded = Base64.decodeBase64(b);
                out.write(decoded);
            }
        }

        ret = true;
    } catch (IOException e) {
        StringWriter sw = new StringWriter();
        e.printStackTrace(new PrintWriter(sw));
        errorMessage = "error: " + sw;

    } finally {
        if (out != null) {
            try {
                out.close();
            } catch (Exception e) {
                StringWriter sw = new StringWriter();
                e.printStackTrace(new PrintWriter(sw));
                System.out.println("Cannot close outputStream after writing file to disk!" + sw.toString());
            }
        }

    }

    return ret;
}

/**
 * Helper method for the creation of a file output stream.
 * 
 * @param imageFolder
 *            : folder where images are to be saved.
 * @param id
 *            : id of spcefic image file.
 * @return FileOutputStream object prepared to store images.
 * @throws FileNotFoundException
 */
protected FileOutputStream createOutputStream(File imageFile) throws FileNotFoundException {

    imageFile.getParentFile().mkdirs();

    return new FileOutputStream(imageFile);
}