从MySQL获取Blob图片转JSON后，在Android中转为Bitmap求助

Alright, let's get this sorted out for you. The main issue here is that raw Blob data can't be directly sent via JSON (since JSON only handles text-based data), so we need to adjust your PHP code first, then handle the conversion on the Android side.

Step 1: Fix Your PHP Code to Send Image Data Correctly #

When you pull the image Blob from your database, you need to convert it to a Base64-encoded string before adding it to your JSON response. This ensures the binary data is safely transmitted as text. Here's the updated PHP code:

$sql = "SELECT * FROM bim WHERE category = '$category'";
$r = mysqli_query($conn,$sql);
$result = array();
while($res = mysqli_fetch_array($r)){
    array_push($result,array(
        "signText"=>$res['signText'],
        "image"=>base64_encode($res['image']) // Convert Blob to Base64 string for JSON compatibility
    ));
}
echo json_encode(array("result"=>$result));
mysqli_close($conn);

Quick security note: Your current SQL query is vulnerable to SQL injection. For better security, use prepared statements instead:

$stmt = $conn->prepare("SELECT * FROM bim WHERE category = ?");
$stmt->bind_param("s", $category);
$stmt->execute();
$result = $stmt->get_result();

$responseArray = array();
while($res = $result->fetch_assoc()){
    array_push($responseArray,array(
        "signText"=>$res['signText'],
        "image"=>base64_encode($res['image'])
    ));
}
echo json_encode(array("result"=>$responseArray));
$stmt->close();
mysqli_close($conn);

Step 2: Convert Base64 String to Bitmap in Android #

Once your PHP API is sending the Base64-encoded image, you can parse the JSON response and convert the string to a Bitmap in your Android app. Here's how to do it:

1. Parse the JSON Response #

First, extract the Base64 image string from the JSON result array. This example uses native Android JSON parsing:

// Assume you've already fetched the JSON response into a String called jsonResponse
try {
    JSONObject rootObject = new JSONObject(jsonResponse);
    JSONArray resultArray = rootObject.getJSONArray("result");

    for (int i = 0; i < resultArray.length(); i++) {
        JSONObject item = resultArray.getJSONObject(i);
        String signText = item.getString("signText");
        String imageBase64 = item.getString("image");

        // Convert the Base64 string to a Bitmap
        Bitmap imageBitmap = convertBase64ToBitmap(imageBase64);

        // Use the bitmap (e.g., set it to an ImageView)
        // yourImageView.setImageBitmap(imageBitmap);
    }
} catch (JSONException e) {
    e.printStackTrace();
}

2. Implement the Conversion Function #

Create a helper method to handle the Base64-to-Bitmap conversion. This also accounts for any optional data URI prefixes (like data:image/png;base64,) that might be present:

private Bitmap convertBase64ToBitmap(String base64String) {
    try {
        // Remove data URI prefix if present
        if (base64String.contains(",")) {
            base64String = base64String.split(",")[1];
        }

        // Decode Base64 string to byte array
        byte[] imageBytes = Base64.decode(base64String, Base64.DEFAULT);

        // Convert byte array to Bitmap
        return BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.length);
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}

3. Handle Large Images (Avoid OOM Errors) #

If your images are large, you might run into OutOfMemoryError. To fix this, use BitmapFactory.Options to downscale the image:

private Bitmap convertBase64ToBitmap(String base64String) {
    try {
        if (base64String.contains(",")) {
            base64String = base64String.split(",")[1];
        }

        byte[] imageBytes = Base64.decode(base64String, Base64.DEFAULT);

        BitmapFactory.Options options = new BitmapFactory.Options();
        options.inSampleSize = 2; // Reduce image dimensions by 50% (adjust as needed)
        options.inPreferredConfig = Bitmap.Config.RGB_565; // Uses less memory than ARGB_8888

        return BitmapFactory.decodeByteArray(imageBytes, 0, imageBytes.length, options);
    } catch (Exception e) {
        e.printStackTrace();
        return null;
    }
}

内容的提问来源于stack exchange，提问作者pienapeace