用java写一个文件上传方法

好的，以下是一个简单的Java文件上传方法的示例代码：

import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URL;
import java.net.URLConnection;

public class FileUploader {
    public static void uploadFile(String urlString, String filePath) throws IOException {
        URL url = new URL(urlString);
        URLConnection conn = url.openConnection();
        conn.setDoOutput(true);
        conn.setDoInput(true);
        conn.setRequestProperty("Content-Type", "multipart/form-data; boundary=---------------------------7d33a816d302b6");

        OutputStream out = conn.getOutputStream();
        File file = new File(filePath);
        String fileName = file.getName();
        String boundary = "-----------------------------7d33a816d302b6";
        String header = "--" + boundary + "\r\nContent-Disposition: form-data; name=\"file\"; filename=\"" + fileName + "\"\r\nContent-Type: application/octet-stream\r\n\r\n";
        out.write(header.getBytes());

        InputStream in = FileUploader.class.getResourceAsStream(filePath);
        byte[] buffer = new byte[1024];
        int len;
        while ((len = in.read(buffer)) != -1) {
            out.write(buffer, 0, len);
        }
        in.close();

        String footer = "\r\n--" + boundary + "--\r\n";
        out.write(footer.getBytes());
        out.flush();
        out.close();

        InputStream responseIn = conn.getInputStream();
        byte[] responseBuffer = new byte[1024];
        int responseLen;
        while ((responseLen = responseIn.read(responseBuffer)) != -1) {
            System.out.println(new String(responseBuffer, 0, responseLen));
        }
        responseIn.close();
    }
}

你可以将上面的代码保存为一个名为 FileUploader.java 的文件，然后在你的 Java 项目中使用它来上传文件。调用 uploadFile 方法时，需要传入两个参数：文件上传的 URL 和要上传的文件的本地路径。例如：

FileUploader.uploadFile("http://example.com/upload", "/path/to/file.txt");

这将会把本地的 /path/to/file.txt 文件上传到 http://example.com/upload。