java httpClient 下载文件

Java httpClient 下载文件实现流程

1. 确定下载文件的URL和保存路径

在开始编写代码之前，首先需要确定需要下载文件的URL和保存文件的路径。可以通过以下代码指定URL和保存路径：

String url = "
String savePath = "C:/path/to/save/file.txt";

2. 创建HttpClient实例

使用Apache HttpClient库来实现文件下载功能。首先需要创建一个HttpClient实例，可以通过以下代码创建：

CloseableHttpClient httpClient = HttpClients.createDefault();

3. 创建HttpGet请求

接下来，需要创建一个HttpGet请求对象，并设置请求的URL。代码如下：

HttpGet httpGet = new HttpGet(url);

4. 执行请求并获取响应

执行HttpGet请求并获取服务器的响应。可以通过以下代码实现：

CloseableHttpResponse response = httpClient.execute(httpGet);

5. 检查响应状态码

检查服务器的响应状态码，确保请求成功。通常情况下，状态码为200表示请求成功。可以通过以下代码检查状态码：

int statusCode = response.getStatusLine().getStatusCode();
if (statusCode == 200) {
    // 请求成功
} else {
    // 请求失败，处理错误情况
}

6. 获取响应实体并保存文件

如果响应状态码为200，表示请求成功，可以获取响应实体，并将实体保存到本地文件。以下是实现代码：

HttpEntity entity = response.getEntity();
try (InputStream inputStream = entity.getContent();
     FileOutputStream outputStream = new FileOutputStream(savePath)) {
    byte[] buffer = new byte[1024];
    int bytesRead;
    while ((bytesRead = inputStream.read(buffer)) != -1) {
        outputStream.write(buffer, 0, bytesRead);
    }
    outputStream.flush();
} catch (IOException e) {
    e.printStackTrace();
}

7. 关闭HttpClient和响应

下载完成后，需要关闭HttpClient和响应实例，以释放资源。以下是代码示例：

response.close();
httpClient.close();

完整代码示例

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;

public class FileDownloader {

    public static void main(String[] args) {
        String url = "
        String savePath = "C:/path/to/save/file.txt";

        CloseableHttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet(url);
        try (CloseableHttpResponse response = httpClient.execute(httpGet)) {
            int statusCode = response.getStatusLine().getStatusCode();
            if (statusCode == 200) {
                HttpEntity entity = response.getEntity();
                try (InputStream inputStream = entity.getContent();
                     FileOutputStream outputStream = new FileOutputStream(savePath)) {
                    byte[] buffer = new byte[1024];
                    int bytesRead;
                    while ((bytesRead = inputStream.read(buffer)) != -1) {
                        outputStream.write(buffer, 0, bytesRead);
                    }
                    outputStream.flush();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            } else {
                System.out.println("File download failed. Status code: " + statusCode);
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                httpClient.close();
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
}

关系图示例

erDiagram
    DOWNLOAD_FILE --> HTTP_CLIENT: 使用HttpClient下载文件
    HTTP_CLIENT --> CLOSEABLE_HTTP_CLIENT: 创建CloseableHttpClient实例
    DOWNLOAD_FILE --> HTTP_GET: 创建HttpGet请求
    HTTP_GET --> URL: 设置请求URL
    DOWNLOAD_FILE --> EXECUTE_REQUEST: 执行请求并获取响应
    EXECUTE_REQUEST --> RESPONSE: 获取服务器响应
    EXECUTE_REQUEST --> STATUS_CODE: 检查响应状态码
    RESPONSE --> ENTITY: 获取响应实体
    STATUS_CODE --> FILE: 状态码为200则保存文件
    ENTITY --> INPUT_STREAM: 获取输入流
    ENTITY --> CLOSEABLE_HTTP_RESPONSE: 关闭响应
    INPUT_STREAM --> OUTPUT_STREAM: 将文件内容写入输出流
    CLOSEABLE_HTTP_RESPONSE --> CLOSEABLE_HTTP_CLIENT: 关闭HttpClient实例

以上是实现Java httpClient下载文件的完整流程和代码示例。通过步骤的详细说明和代码注释，希望能够帮助新手开发者顺利实现文件下载功能。