使用 java HTTP POST 连接发送图像文件

Question

我正在尝试使用 Java HTTP POST 请求将图像发送到网站。

我正在使用此处使用的基本代码将 文件从 Java 客户端上传到 HTTP 服务器：

这是我的修改：

 String urlToConnect = "http://localhost:9000/upload";
File fileToUpload = new File("C:\\Users\\joao\\Pictures\\bla.jpg");
String boundary = Long.toHexString(System.currentTimeMillis()); // Just generate some unique random value.

URLConnection connection = new URL(urlToConnect).openConnection();
connection.setDoOutput(true); // This sets request method to POST.
connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + boundary);
PrintWriter writer = null;
try {
    writer = new PrintWriter(new OutputStreamWriter(connection.getOutputStream()));
    writer.println("--" + boundary);
    writer.println("Content-Disposition: form-data; name=\"picture\"; filename=\"bla.jpg\"");
    writer.println("Content-Type: image/jpeg");
    writer.println();
    BufferedReader reader = null;
    try {
        reader = new BufferedReader(new InputStreamReader(new FileInputStream(fileToUpload)));
        for (String line; (line = reader.readLine()) != null;) {
            writer.println(line);
        }
    } finally {
        if (reader != null) try { reader.close(); } catch (IOException logOrIgnore) {}
    }
    writer.println("--" + boundary + "--");
} finally {
    if (writer != null) writer.close();
}

// Connection is lazily executed whenever you request any status.
int responseCode = ((HttpURLConnection) connection).getResponseCode();
System.out.println(responseCode); // Should be 200

最后我得到了一个 200 的响应代码，但图像有问题，例如随机颜色，这让我认为这是字符编码错误。我尝试像在原始示例中那样使用 UTF-8，但这只会创建损坏的图像。

我也 100% 确定这不是服务器端问题，因为我可以使用其他客户端，例如 Advanced Rest Client/Postman，它们可以毫无问题地发送图像。

你能帮我查明哪里出了问题吗？谢谢你。

原文由 asdt11 发布，翻译遵循 CC BY-SA 4.0 许可协议

Answer 1

import java.io.File;
import org.apache.http.HttpEntity;
import org.apache.http.HttpResponse;
import org.apache.http.HttpVersion;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.mime.MultipartEntity;
import org.apache.http.entity.mime.content.ContentBody;
import org.apache.http.entity.mime.content.FileBody;
import org.apache.http.impl.client.DefaultHttpClient;
import org.apache.http.params.CoreProtocolPNames;
import org.apache.http.util.EntityUtils;

public class PostFile {
  public static void main(String[] args) throws Exception {
    HttpClient httpclient = new DefaultHttpClient();
    httpclient.getParams().setParameter(CoreProtocolPNames.PROTOCOL_VERSION, HttpVersion.HTTP_1_1);

    HttpPost httppost = new HttpPost("http://localhost:9000/upload");
    File file = new File("C:\\Users\\joao\\Pictures\\bla.jpg");

    MultipartEntity mpEntity = new MultipartEntity();
    ContentBody cbFile = new FileBody(file, "image/jpeg");
    mpEntity.addPart("userfile", cbFile);

    httppost.setEntity(mpEntity);
    System.out.println("executing request " + httppost.getRequestLine());
    HttpResponse response = httpclient.execute(httppost);
    HttpEntity resEntity = response.getEntity();

    System.out.println(response.getStatusLine());
    if (resEntity != null) {
      System.out.println(EntityUtils.toString(resEntity));
    }
    if (resEntity != null) {
      resEntity.consumeContent();
    }

    httpclient.getConnectionManager().shutdown();
  }
}

使用 HttpClient 来计算这段代码。使用稳定的库总是比从头开始处理更好，除非有一些东西需要以自定义方式处理。

原文由 Kris 发布，翻译遵循 CC BY-SA 4.0 许可协议