面试题：Angular利用HttpClient模块处理复杂文件上传场景

Question

假设需要上传多个文件，并且在上传过程中实时显示每个文件的上传进度，同时要处理上传失败的重试机制，使用HttpClient模块该如何实现？请阐述实现思路并给出关键代码片段。

Answer 1

实现思路

1. 初始化HttpClient：创建一个HttpClient实例用于发起HTTP请求。
2. 遍历文件列表：对需要上传的多个文件进行循环处理。
3. 监听上传进度：利用HttpClient提供的功能，为每个文件的上传请求添加进度监听器，以实时获取上传进度。
4. 处理上传失败：在上传失败时，根据重试机制进行重试操作，例如设置重试次数，每次失败后等待一定时间再重试。

关键代码片段（以Java为例，基于Apache HttpClient）

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.ContentType;
import org.apache.http.entity.mime.MultipartEntityBuilder;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

import java.io.File;
import java.io.IOException;

public class FileUploader {
    private static final int MAX_RETRIES = 3;
    private static final int WAIT_TIME_BETWEEN_RETRIES = 1000; // 1 second

    public static void main(String[] args) {
        File[] files = {new File("file1.txt"), new File("file2.txt")};
        for (File file : files) {
            uploadFile(file);
        }
    }

    private static void uploadFile(File file) {
        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpPost httpPost = new HttpPost("http://your-upload-url");

        MultipartEntityBuilder builder = MultipartEntityBuilder.create();
        builder.addBinaryBody("file", file, ContentType.APPLICATION_OCTET_STREAM, file.getName());
        HttpEntity entity = builder.build();
        httpPost.setEntity(entity);

        int retryCount = 0;
        while (retryCount < MAX_RETRIES) {
            try (CloseableHttpResponse response = httpClient.execute(httpPost)) {
                if (response.getStatusLine().getStatusCode() == 200) {
                    System.out.println("File " + file.getName() + " uploaded successfully.");
                    break;
                } else {
                    System.out.println("Upload failed for file " + file.getName() + ". Status code: " + response.getStatusLine().getStatusCode());
                }
            } catch (IOException e) {
                System.out.println("Upload failed for file " + file.getName() + ". Error: " + e.getMessage());
            }
            retryCount++;
            if (retryCount < MAX_RETRIES) {
                try {
                    Thread.sleep(WAIT_TIME_BETWEEN_RETRIES);
                } catch (InterruptedException e) {
                    Thread.currentThread().interrupt();
                }
            }
        }
        if (retryCount == MAX_RETRIES) {
            System.out.println("Max retries reached. File " + file.getName() + " upload failed.");
        }
    }
}

关键代码解释

1. 初始化HttpClient：CloseableHttpClient httpClient = HttpClients.createDefault(); 创建一个默认的HttpClient实例。
2. 设置HTTP请求：HttpPost httpPost = new HttpPost("http://your-upload-url"); 创建一个HttpPost请求，并指定上传的URL。
3. 构建Multipart请求体：MultipartEntityBuilder用于构建包含文件的Multipart请求体，builder.addBinaryBody("file", file, ContentType.APPLICATION_OCTET_STREAM, file.getName()); 将文件添加到请求体中。
4. 重试机制：通过while循环和retryCount变量实现重试逻辑，每次失败后等待WAIT_TIME_BETWEEN_RETRIES时间再重试。

注意：以上代码仅为示例，实际应用中需要根据具体的业务需求和环境进行调整，例如处理更复杂的错误情况、优化重试策略等。同时，不同的编程语言和HttpClient库在具体实现上会有所差异，但核心思路是相似的。