Base64 encoding a image in Java wrong apparently,

问题:

I am attempting to POST a Base64 encoded image from my Java code to a website. I have tested encoding and decoding the file locally and it works great! However when it gets to the website, I am told the image is blank.

Here is how I am POST'ing. If I used another action instead of upload, I get the correct response!

ready = new java.net.URL(url);
        WebRequest request = new WebRequest(ready, HttpMethod.POST);
        request.setAdditionalHeader("Content-Type", "application/x-www-form-urlencoded");

        String requestBody = "action=upload"
                +"&key=ABCDEFG123456"
                + "&file=" + encodedFile
                + "&gen_task_id=" + SQL.getNextID();

encodedFile comes from the following code:

    File file = new File("temp.jpg");

    FileInputStream fin = new FileInputStream(file);

    byte fileContent[] = new byte[(int)file.length()];
    fin.read(fileContent);

    //all chars in encoded are guaranteed to be 7-bit ASCII
    byte[] encoded = Base64.encodeBase64(fileContent);
    String encodedFile = new String(encoded);

Seriously, what am I doing wrong?? I've been beating my head against the wall for hours now!

回答1:

I finally figured it out. Here is what I did for anyone else having this issue.

BufferedImage img = ImageIO.read(new File("temp.jpg"));             
ByteArrayOutputStream baos = new ByteArrayOutputStream();
ImageIO.write(img, "jpg", baos);
baos.flush();
Base64 base = new Base64(false);
String encodedImage = base.encodeToString(baos.toByteArray());
baos.close();
encodedImage = java.net.URLEncoder.encode(encodedImage, "ISO-8859-1");
request.setRequestBody(encodedImage);

回答2:

FileInputStream.read(byte[] b) does not guarantee that the byte array buffer b will be completely filled even if the data is available. The following code ensures the buffer is completely full.

File file = new File("temp.jpg");

FileInputStream fin = new FileInputStream(file);

byte fileContent[] = new byte[(int)file.length()];
int offset = 0;

while ( offset < fileContent.length ) {
    int count = fin.read(fileContent, offset, fileContent.length - offset);
    offset += count;
}

//all chars in encoded are guaranteed to be 7-bit ASCII
byte[] encoded = Base64.encodeBase64(fileContent);
String encodedFile = new String(encoded);

Alternatively, you could use ByteArrayOutputStream like this:

File file = new File("temp.jpg");

FileInputStream fin = new FileInputStream(file);
ByteArrayOutputStream baos = new ByteArrayOutputStream();

byte [] buffer = new byte[1024];
int count = 0;

while ( (count = fin.read(buffer)) != -1 ) {
    baos.write(buffer, 0, count);
}

byte [] fileContent = baos.toByteArray();

//all chars in encoded are guaranteed to be 7-bit ASCII
byte[] encoded = Base64.encodeBase64(fileContent);
String encodedFile = new String(encoded);

Or, you could wrap your FileInputStream object in a DataInputStream object like this:

File file = new File("temp.jpg");

FileInputStream fin = new FileInputStream(file);
DataInputStream dis = new DataInputStream(fin);

byte fileContent[] = new byte[(int)file.length()];
dis.readFully(fileContent);

//all chars in encoded are guaranteed to be 7-bit ASCII
byte[] encoded = Base64.encodeBase64(fileContent);
String encodedFile = new String(encoded);

I'm sure there are more ways to get this done.