java 一个完整的文件下载接口代码

下面是一个基于 Java 的简单文件下载接口代码示例：

import java.io.*;
import javax.servlet.*;
import javax.servlet.http.*;

public class FileDownloadServlet extends HttpServlet {
    private static final int BYTES_DOWNLOAD = 1024;

    public void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
        String fileName = request.getParameter("fileName");
        String filePath = "/path/to/files/" + fileName;

        File file = new File(filePath);
        InputStream inputStream = new BufferedInputStream(new FileInputStream(file));

        response.setContentType("application/octet-stream");
        response.setHeader("Content-Disposition", "attachment; filename=\"" + fileName + "\"");
        response.setHeader("Content-Length", String.valueOf(file.length()));

        OutputStream outputStream = response.getOutputStream();
        byte[] buffer = new byte[BYTES_DOWNLOAD];
        int bytesRead = -1;
        while ((bytesRead = inputStream.read(buffer)) != -1) {
            outputStream.write(buffer, 0, bytesRead);
        }

        inputStream.close();
        outputStream.close();
    }
}

这个代码示例通过 GET 请求方式获取文件名，然后读取文件并将其作为附件下载。需要将 `/path/to/files/` 替换为实际文件存储路径。注意在处理完请求后需要关闭输入输出流。