Example of Uploading and Downloading Function Implemented in Android Programming

This article illustrates the implementation of image upload and download functions in Android programming. Share it with everyone for reference, as follows:

When implementing an Android web service client, such as a microblog or forum client, the upload and download of images are often used. Here, we introduce how to use HttpClient to implement the image upload and download function.

1 Image uploadWhen uploading an image, first obtain the image path, create a file, and convert the image to a byte stream and write it to the request, then send the request.

Client-side code:

File file = new File(imageUrl);
String httpUrl = httpDomain+"AddImageServlet"+"?gid="+gid;
HttpPost request = new HttpPost(httpUrl);
HttpClient httpClient = new DefaultHttpClient();
FileEntity entity = new FileEntity(file,"binary",/octet-stream");
HttpResponse response;
try {
  request.setEntity(entity);
  entity.setContentEncoding("binary"/octet-stream");
  response = httpClient.execute(request);
//If the return status is200, get the returned result
if(response.getStatusLine().getStatusCode()==HttpStatus.SC_OK){
……//Image upload successful
}
}
catch(Exception e){
}

The work done by the server-side is to receive the byte stream, write it into the file, and save the file in the corresponding folder on the server, and record the path of the file, and write the path of the image file into the database for saving.

Server-side code:

//Get the news id
String gid = request.getParameter("gid");
String filePath = getRealPath(request) + "\\userpic\\";
//   Define the maximum bytes of the uploaded file
int MAX_SIZE = 102400 * 102400;
//   Declare the file reading class
DataInputStream in = null;
FileOutputStream fileOut = null;
//   Get the data type of the uploaded data from the client
String contentType = request.getContentType();
if(contentType.indexOf("binary"/octet-(stream") >= 0){
  //   Read in the uploaded data
  in = new DataInputStream(request.getInputStream());
  int formDataLength = request.getContentLength();
  // If the image is too large
  if(formDataLength > MAX_SIZE){
    String errormsg=("The number of bytes of the uploaded file cannot exceed" + MAX_SIZE);
    out.println(errormsg);
    return ;
  }
//   Save the data of the uploaded file
byte dataBytes[] = new byte[formDataLength];
int byteRead = 0;
int totalBytesRead = 0;
//   The data uploaded is stored in a byte array
while(totalBytesRead < formDataLength){
byteRead = in.read(dataBytes,totalBytesRead,formDataLength);
totalBytesRead += byteRead;
 }
String fileName = filePath + gid+.png
 //   Check if the directory of the uploaded file exists
File fileDir = new File(filePath);
if(!fileDir.exists()){
fileDir.mkdirs();
}
//   Create the writing class of the file
fileOut = new FileOutputStream(fileName);
//   Data to save the file
fileOut.write(dataBytes);
fileOut.close();
//The path name of the file to be saved
……

2 Image downloadFirstly, obtain the image address of the network picture, send the request, and the server will return the byte stream of the picture. Use the BitmapFactory.decodeStream() method to convert the byte stream into an image and return it. The specific code is as follows:

//Obtain pictures from the network
public Bitmap getGossipImage(String gid){
    String httpUrl = httpDomain+"userpic/"+gid+.png
    Bitmap bitmap = null;
    HttpGet httpRequest = new HttpGet(httpUrl);
    //Obtain HttpClient object
    HttpClient httpclient = new DefaultHttpClient();
    try {
      //Request httpClient, obtain HttpRestponse
      HttpResponse httpResponse = httpclient.execute(httpRequest);
      if(httpResponse.getStatusLine().getStatusCode() == HttpStatus.SC_OK){
        //Obtain relevant information Obtain HttpEntiy
        HttpEntity httpEntity = httpResponse.getEntity();
        InputStream is = httpEntity.getContent();
        bitmap = BitmapFactory.decodeStream(is);
        is.close();
      } else {
         Toast.makeText(context, "Connection failed!", Toast.LENGTH_SHORT).show();
      }
    } catch (ClientProtocolException e) {
      e.printStackTrace();
    } catch (IOException e) {
      e.printStackTrace();
    }
    return bitmap;
}

Readers who are interested in more content related to Android can check the special topics on this site: 'Summary of Android Graphics and Image Processing Techniques', 'Android Development Tutorial for Beginners and Advanced', 'Summary of Android Debugging Techniques and Common Problem Solving Methods', 'Summary of Android Multimedia Operation Techniques (audio, video, recording, etc.)', 'Summary of Android Basic Component Usage', 'Summary of Android View View Techniques', 'Summary of Android Layout Layout Techniques', and 'Summary of Android Widget Usage'.

I hope the content described in this article will be helpful to everyone's Android program design.

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