java通过post请求下载文件

可以通过以下步骤通过POST请求下载文件：

1. 创建一个URL对象，用于连接下载文件的地址。

URL url = new URL("http://example.com/download");

2. 创建一个HttpURLConnection对象，用于发送POST请求。

HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("POST");
connection.setDoOutput(true);

3. 设置POST请求的参数，例如文件名和其他参数。

String fileName = "example.txt";
String postData = "filename=" + fileName;
OutputStream outputStream = connection.getOutputStream();
outputStream.write(postData.getBytes());

4. 发送请求并获取响应流。

InputStream inputStream = connection.getInputStream();

5. 将响应流写入文件。

FileOutputStream fileOutputStream = new FileOutputStream(fileName);
byte[] buffer = new byte[1024];
int len;
while ((len = inputStream.read(buffer)) != -1) {
    fileOutputStream.write(buffer, 0, len);
}
fileOutputStream.close();

完整代码示例：

import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;

public class FileDownloader {
    public static void main(String[] args) throws Exception {
        URL url = new URL("http://example.com/download");
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("POST");
        connection.setDoOutput(true);

        String fileName = "example.txt";
        String postData = "filename=" + fileName;
        OutputStream outputStream = connection.getOutputStream();
        outputStream.write(postData.getBytes());

        InputStream inputStream = connection.getInputStream();
        FileOutputStream fileOutputStream = new FileOutputStream(fileName);
        byte[] buffer = new byte[1024];
        int len;
        while ((len = inputStream.read(buffer)) != -1) {
            fileOutputStream.write(buffer, 0, len);
        }
        fileOutputStream.close();
    }
}