如何在没有第三方库的情况下使用'multipart/form-data”编码从 Java 客户端上传带有附加参数的文件？

将带有附加参数的文件从 Java 客户端上传到 HTTP 服务器

为了将带有附加参数的文件从 Java 客户端上传到 HTTP 服务器，让我们探索一下一个场景及其解决方案。

假设您想要将一个文件和一个名为“用户名”的参数传递到服务器。如何使用带有 multipart/form-data 编码的 POST 请求来实现此目的？

为了让事情简单明了，让我们避开第三方库并依赖 Java 的内置工具。

<code class="java">import java.io.File;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.URLConnection;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Scanner;

public class HttpFileUploadWithParameters {

    private static final String BOUNDARY = Long.toHexString(System.currentTimeMillis());
    private static final String CRLF = "\r\n";
    private static final String CHARSET = "UTF-8";

    public static void main(String[] args) throws Exception {
        String url = "http://example.com/upload";

        File file = new File("/path/to/file.txt");
        String parameter = "value";

        URLConnection connection = new URL(url).openConnection();
        connection.setDoOutput(true);
        connection.setRequestProperty("Content-Type", "multipart/form-data; boundary=" + BOUNDARY);

        try (OutputStream output = connection.getOutputStream();
             PrintWriter writer = new PrintWriter(new OutputStreamWriter(output, CHARSET), true)) {

            // Write parameter
            writer.append("--" + BOUNDARY).append(CRLF);
            writer.append("Content-Disposition: form-data; name=\"parameter\"").append(CRLF);
            writer.append("Content-Type: text/plain; charset=" + CHARSET).append(CRLF);
            writer.append(CRLF).append(parameter).append(CRLF).flush();

            // Write file
            writer.append("--" + BOUNDARY).append(CRLF);
            writer.append("Content-Disposition: form-data; name=\"file\"; filename=\"" + file.getName() + "\"").append(CRLF);
            writer.append("Content-Type: application/octet-stream").append(CRLF);
            writer.append(CRLF).flush();
            Files.copy(file.toPath(), output);
            output.flush(); // Important before continuing with writer!
            writer.append(CRLF).flush(); // CRLF is important! It indicates end of boundary.

            // End of multipart/form-data.
            writer.append("--" + BOUNDARY + "--").append(CRLF).flush();
        }

        // Request is lazily fired whenever you need to obtain information about response.
        int responseCode = ((java.net.HttpURLConnection) connection).getResponseCode();
        System.out.println(responseCode); // Should be 200
    }
}</code>

以上是如何在没有第三方库的情况下使用'multipart/form-data”编码从 Java 客户端上传带有附加参数的文件？的详细内容。更多信息请关注PHP中文网其他相关文章！