java往服务器上传文件

要在Java中将文件上传到服务器，可以使用Java的HTTPURLConnection类或Apache的HTTPClient类。这里提供HTTPURLConnection类的示例代码：

import java.io.File;
import java.io.FileInputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class FileUploader {

    public static void main(String[] args) {
        String serverUrl = "http://example.com/upload";
        String filePath = "/path/to/file.jpg";
        String fileName = "file.jpg";

        try {
            File file = new File(filePath);
            URL url = new URL(serverUrl);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setDoOutput(true);
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=----WebKitFormBoundary7MA4YWxkTrZu0gW");

            OutputStream outputStream = conn.getOutputStream();
            String header = "------WebKitFormBoundary7MA4YWxkTrZu0gW\r\n" +
                    "Content-Disposition: form-data; name=\"file\"; filename=\"" + fileName + "\"\r\n" +
                    "Content-Type: image/jpeg\r\n" +
                    "\r\n";
            outputStream.write(header.getBytes());

            FileInputStream fileInputStream = new FileInputStream(file);
            byte[] buffer = new byte[4096];
            int bytesRead = -1;
            while ((bytesRead = fileInputStream.read(buffer)) != -1) {
                outputStream.write(buffer, 0, bytesRead);
            }
            outputStream.flush();
            fileInputStream.close();

            String footer = "\r\n------WebKitFormBoundary7MA4YWxkTrZu0gW--\r\n";
            outputStream.write(footer.getBytes());
            outputStream.flush();
            outputStream.close();

            System.out.println("File uploaded successfully!");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

这个示例代码中，我们将文件上传到了指定的服务器URL，使用了POST方法，指定了Content-Type为multipart/form-data，同时指定了文件的Content-Disposition和Content-Type。其中，boundary为自定义的分隔符，可以随意指定。在输出流中先写入header，再写入文件内容，最后写入footer。注意，这里的文件名需要与服务器端的处理代码中的参数名一致，才能正确接收并处理上传的文件。