How to implement breakpoint continuous transmission function in Android

1. Project Introduction

As mobile users become increasingly dependent on video, file downloads and large file transfers, breakpoint continuous transmission has emerged as a technology that effectively saves bandwidth and improves user experience. The so-called breakpoint continuous transmission means that if the network interrupts or the user cancels the download during the download process, the download can continue from the last end when it starts again, without starting from the beginning, saving download time and data traffic. This project aims to implement a breakpoint continuous transmission function based on Android, download files through HTTP Range requests, and store and manage some downloaded data to achieve the breakpoint continuous transmission effect. The project can be applied to video, software updates, image file downloads and other scenarios.

2. Background and demand analysis

2.1 Project background

In actual development, problems such as network fluctuations and connection interruptions often occur when downloading large files. If you download them from scratch, the user experience will be greatly reduced. Implementing the breakpoint continuous transmission function can:

• Improve the efficiency of file download;

• Save user data traffic;

• Improve user experience, especially in unstable network environments.

Common implementation methods usually use the Range header field in the HTTP protocol to request the download of data at the specified location, and then merge the data downloaded in segments into a complete file. At the same time, it is necessary to process errors that may occur during the download process and save the current download status to facilitate the next time.

2.2 Requirements Analysis

This project mainly needs to meet the following functional requirements:

1. Breakpoint continuous transmission download

   • Supports that when the download is interrupted, the next startup can continue from the end of the previous download;

   • Use HTTP Range request method to specify the starting location of the requested data;

   • The response returned by the server is parsed, the integrity of the downloaded data is verified, and the segmented data is merged into a complete file.

2. Download Status Management

   • Save the current download location and downloaded data size to local storage (such as SharedPreferences or database);

   • When you restart the download, continue downloading from the saved breakpoint.

3. Exception handling

   • Handle abnormal situations such as network interruption and timeout;

   • Ability to perform multiple retry and error prompts;

   • Avoid file corruption due to abnormalities during downloading.

4. User interface and feedback

   • Provides a simple and intuitive user interface to display download progress and breakpoint status;

   • Give clear prompt information when the download is completed or failed;

   • Supports pause, resume, and cancel download operations.

5. Performance and scalability

   • Try to execute the download process in the child thread to avoid blocking the UI thread;

   • Modular design, easy to reuse in different projects (such as video downloads, file updates, etc.);

   • Provides expansion solutions for connecting third-party network libraries (such as OkHttp, Retrofit).

3. Key technologies and implementation principles

3.1 The principle of breakpoint continuous transmission

Breakpoint continuous pass depends on the Range request header in the HTTP protocol, which allows the client to request a part of the resource, such as "Range: bytes=xxx-" to indicate downloading starts from the specified byte. After receiving the request, the server will return the status code 206 (Partial Content), and the response header contains Content-Range information. After receiving the data, the client only saves this part of the data and specifies the next starting point in subsequent requests, thereby realizing segmented download and merging of the file.

3.2 HTTP Range header and response resolution

• Range head
  Format:Range: bytes=start position-end position。
  In breakpoint continuous transmission, only the starting position is usually specified, and the server automatically returns subsequent data according to the file size.

• Content-Range response header
  Format:Content-Range: bytes Start position-end position/total file size。
  Through this header information, the client can check whether the download data is complete and calculate the starting position of the next request.

3.3 File Reading, Write and State Management

• File writing
  Use RandomAccessFile to specify the write location, which is ideal for breakpoint continuous transmission.
  After opening the file, the downloaded data is written from the current breakpoint and the write location is constantly updated.

• Status Management
  Save the current download location and total file size with SharedPreferences, database, or local files to ensure that the last download status can be correctly read when the breakpoint is continued.

3.4 Network request and exception handling

• Network request library
  You can use network libraries such as OkHttp to send GET requests and add a Range field to the request header.

• Exception handling
  Design the capture and retry strategy for network interrupts, HTTP status code exceptions, file write exceptions, etc. to ensure the robustness of the download process.

4. Project implementation ideas and architecture design

4.1 Overall architecture design

The project is roughly divided into the following modules:

1. Network request module

   • Responsible for constructing HTTP requests and setting Range in the request header;

   • Receives the 206 part of the content response returned by the server and passes the data to the file to the write module.

2. File Management Module

   • Use RandomAccessFile to write downloaded files;

   • Record the current write location every time it is downloaded and saved to local persistent storage;

   • File merging and verification to ensure that the download data is complete.

3. Status Management Module

   • Save and read the status of breakpoint continuous transmission (download progress, total file size, etc.) to facilitate the implementation of breakpoint continuous transmission;

   • Provides functional interfaces such as pause, recovery, and cancellation.

4. User interface module

   • Show download progress, remaining time and status prompts;

   • Provide interactive buttons such as pause, resume, and cancel to facilitate users to control the download process.

4.2 Download process and breakpoint continuous transmission implementation

1. initialization

   • Get the total file size (can be obtained via HEAD request or the first full request);

   • Check whether there are partial download files locally and read the number of bytes that have been downloaded.

2. Start downloading

   • Send a Range request through a network request, with the starting position being the number of downloaded bytes;

   • Write the returned data to the file and update the current downloaded bytes in real time;

   • Update UI to display progress.

3. Exception and retry

   • When a network interruption or other abnormality occurs, the current progress is saved through state management;

   • After the user resumes the network, he can start the download again and continue from the breakpoint.

4. Complete processing

   • After the download is completed, perform file verification (such as MD5 verification) to ensure the data is correct;

   • Update the status, notify the user that the download is completed, and clear the saved breakpoint status.

4.3 Breakpoint continuous transmission status management

• Use SharedPreferences or local database to store the progress information of the current download;

• Update the number of currently downloaded bytes each time a file is written, so that it is convenient for continued downloading at the next startup;

• Provides an interface to facilitate users to manually reset or cancel breakpoint status.

5. Detailed code examples and comments

The following is a sample code for breakpoint continuation based on OkHttp. The code uses HTTP Range requests, RandomAccessFile writes, and SharedPreferences to save progress. A complete comment is provided to explain each step in detail.

5.1 Sample code for implementing breakpoint continuous transmission based on OkHttp

package ;
 
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
import ;
 
public class DownloadManager {
 
    private static final String TAG = "DownloadManager";
    private static final String PREFS_NAME = "download_prefs";
    private static final String KEY_DOWNLOAD_PROGRESS = "download_progress";
 
    private OkHttpClient client;
    private Context context;
 
    public DownloadManager(Context context) {
         = context;
        client = new OkHttpClient();
    }
 
    /**
      * Start downloading the file and implement breakpoint continuous transmission.
      *
      * @param fileUrl file download address
      * @param destFilePath Local file saving path
      */
    public void downloadFile(String fileUrl, String destFilePath) {
        // Read the number of downloaded bytes        SharedPreferences prefs = (PREFS_NAME, Context.MODE_PRIVATE);
        long downloadedBytes = (KEY_DOWNLOAD_PROGRESS, 0);
 
        Request request = new ()
                .url(fileUrl)
                // Set the Range request header and start downloading from the breakpoint position                .addHeader("Range", "bytes=" + downloadedBytes + "-")
                .build();
 
        (request).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {
                (TAG, "Download failed:" + ());
            }
 
            @Override
            public void onResponse(Call call, Response response) throws IOException {
                // Write to the file after downloading successfully                if (() == 206 || () == 200) {
                    File file = new File(destFilePath);
                    // Use RandomAccessFile to write data from the specified location                    RandomAccessFile raf = new RandomAccessFile(file, "rw");
                    (downloadedBytes);
                    
                    byte[] buffer = new byte[1024 * 4];
                    int len;
                    long currentBytes = downloadedBytes;
                    
                    while ((len = ().byteStream().read(buffer)) != -1) {
                        (buffer, 0, len);
                        currentBytes += len;
                        // Save the current download progress                        saveProgress(currentBytes);
                    }
                    
                    ();
                    (TAG, "Download Completed:" + currentBytes + " byte");
                } else {
                    (TAG, "Server response exception:" + ());
                }
            }
        });
    }
 
    /**
      * Save the current download progress into SharedPreferences
      *
      * @param bytes The number of bytes currently downloaded
      */
    private void saveProgress(long bytes) {
        SharedPreferences prefs = (PREFS_NAME, Context.MODE_PRIVATE);
        ().putLong(KEY_DOWNLOAD_PROGRESS, bytes).apply();
    }
 
    /**
      * Reset download progress (for example, when canceling or restarting download)
      */
    public void resetProgress() {
        SharedPreferences prefs = (PREFS_NAME, Context.MODE_PRIVATE);
        ().putLong(KEY_DOWNLOAD_PROGRESS, 0).apply();
    }
}

5.2 Examples of usage Activity

package ;
 
import ;
import ;
import ;
import ;
import ;
 
public class DownloadActivity extends AppCompatActivity {
 
    private DownloadManager downloadManager;
    // Download the target file URL (sample URL, please replace it with the actual file address)    private String fileUrl = "/path/to/your/";
    // Local save path    private String destFilePath = ().getAbsolutePath() + "/download/";
    private Button btnDownload;
    private Button btnReset;
 
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        (savedInstanceState);
        setContentView(.activity_download);
        downloadManager = new DownloadManager(this);
 
        btnDownload = findViewById(.btn_download);
        btnReset = findViewById(.btn_reset);
 
        (new () {
            @Override
            public void onClick(View v) {
                (fileUrl, destFilePath);
            }
        });
 
        (new () {
            @Override
            public void onClick(View v) {
                ();
            }
        });
    }
}

5.3 XML layout file example

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:andro
    android:
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:gravity="center"
    android:orientation="vertical"
    android:padding="24dp">
 
    <Button
        android:
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Start Download" />
 
    <Button
        android:
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Reset Breakpoint"
        android:layout_marginTop="16dp" />
</LinearLayout>

6. Code parsing and explanation

6.1 Detailed explanation of core modules and key methods

• DownloadManager class
  This class encapsulates the core logic of breakpoint continuous transmission.

  • Before the download begins, get the number of downloaded bytes through SharedPreferences.

  • When constructing an HTTP request, add a Range field in the request header to achieve continuous transmission from a breakpoint.

  • Use OkHttp to send a network request, and the response status code 206 (Partial Content) indicates that the server supports breakpoint continuous transmission.

  • Use RandomAccessFile to write download data to a specified location, and continuously update the number of downloaded bytes to save it in SharedPreferences.

  • If the download is interrupted and restarts the download, you can read the last progress from SharedPreferences and continue to download the remaining data.

• DownloadActivity class
  As the UI layer, two buttons are provided to trigger the "Start Download" and "Reset Breakpoint" operations respectively, demonstrating the breakpoint continuous transmission function. After the user clicks "Start Download", DownloadManager starts the download task; if you need to download again, you can click the reset button.

6.2 Data segmented reading and file merging logic

• Random file access
  By adjusting the write position by adjusting the () method, the data downloaded can be spliced ​​at the end of the file to achieve breakpoint continuous transmission.

• Data update and persistence
  After each write operation, call the saveProgress() method to update the download progress stored in SharedPreferences to ensure that data downloads can be accurately restored in the event of an interrupt.

7. Project testing and operation results

7.1 Testing scheme and process

1. Functional testing

   • Test the download function on a real device to check whether you can continue from the last breakpoint when the download is interrupted (such as network disconnection) and start the download again.

   • Verify that the HTTP Range request returns part of the content correctly and that the downloaded file is fully spliced.

2. Stability test

   • Simulate network exceptions and server response exceptions, detect whether DownloadManager can catch exceptions and prompt errors.

   • Check whether there are I/O exceptions during file writing, and ensure that relevant resources are released in a timely manner.

3. User Experience Test

   • Check whether the "Reset Breakpoint" button can correctly clear the downloaded status and ensure that the next download starts from scratch;

   • Observe the log output during the download process and confirm that the breakpoint data is correctly recorded and restored.

7.2 Performance and compatibility testing

• Network testing：
  Test the download speed and breakpoint continuous transmission effect in different network environments to ensure that it can work normally under high latency, weak signals, etc.

• Device compatibility：
  Testing on different Android system versions and device models ensures that file operations and SharedPreferences read and write performance are consistent and there is no compatibility issue.

8. Project summary and experience sharing

8.1 Analysis of project advantages and disadvantages

Project Advantages

• Through HTTP Range requests and RandomAccessFile, we achieve breakpoint continuous transmission effect, making full use of standard protocols and APIs;

• Use SharedPreferences to store download progress, which is simple and easy to use;

• Supports common download scenarios such as pause and breakpoint recovery, and is highly scalable.

Insufficient projects

• Only breakpoint continuous transmission is performed for a single file, and no multi-tasking concurrent download is involved;

• For large file downloads, more efficient I/O caching mechanisms may be required;

• The exception handling and error retry mechanism can be further improved, adding logging and user-friendly prompts.

8.2 Development experience and improvement suggestions

• The principle of breakpoint continuation
  The key is to correctly use the HTTP Range header and RandomAccessFile to realize file segmentation and state saving. Make sure to position the pointer at the appropriate offset before each write.

• Resource Management
  During the download task, be careful to turn off network flow and RandomAccessFile to prevent memory leakage.

• Exception and retry mechanism
  It is necessary to add a retry mechanism based on the actual network conditions to increase robustness and feedback error messages to users in real time.

• Extended application
  In the future, multi-threading and block-based downloading can be combined to further improve the download speed of large files, and at the same time, a download management interface will be added to display the progress of multi-task downloading.

9. Thinking about follow-up optimization and expansion

1. Multi-threaded chunked download

   • Divide the file into multiple blocks, and use the thread pool to download different blocks at the same time, and finally merge them into a complete file.

   • Improve download speed and network utilization efficiency, suitable for large-scale resource downloads.

2. Progress prompts and notification functions

   • Use the notification bar to display download progress to improve user experience;

   • Supports comprehensive download management of pause, continue and cancel downloads.

3. Improved breakpoint continuous transmission status saving

   • Store download status into the database, suitable for multi-task downloads, easy to manage and display status.

   • Provide download records to facilitate users to query historical download records.

4. Expand to multimedia files such as videos and pictures

   • Optimize the cache processing mechanism for different types of files.

   • Make sure the downloaded file is lossless with MD5 verification or other integrity verification methods.

5. Integrate with network library

   • Combined with Retrofit or OkHttp-based packaging, the breakpoint continuous transmission function is independent as a download module to improve code reusability.

in conclusion

This article explains in detail how to implement the breakpoint continuous transmission function in Android. Starting from project background and requirements analysis, we introduce the basic principles of breakpoint continuous transmission and the use of HTTP Range requests. File segmented writing and merging are implemented through RandomAccessFile, and download progress is saved using SharedPreferences. The entire solution has been designed and coding examples from network requests, file operations, status management and exception handling.

The project test results show that this solution can effectively realize the breakpoint continuous transmission function and is suitable for file download, video, software update and other scenarios. At the same time, this article also discusses future optimization directions such as multi-threaded download, progress prompts, and expansion to multi-task download, providing developers with rich implementation ideas and reference materials.

I hope this article can provide Android developers with sufficient technical guidance and practical experience to help you achieve efficient and stable breakpoint continuous transmission function in actual projects.

The above is the detailed content of how to implement the breakpoint continuous transmission function in Android. For more information about Android breakpoint continuous transmission, please follow my other related articles!

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