java 如何使用 transfer-encoding模式进行http post请求

在Java中，发送HTTP POST请求通常通过`HttpURLConnection`、`HttpClient`或者第三方库如`Apache HttpClient`或`OkHttp`来实现。如果你想使用`transfer-encoding`模式，通常意味着你想处理大文件上传或者分块传输编码（Chunked Encoding）。这里我会展示如何使用`HttpURLConnection`的一个例子，假设你想要分块上传数据：

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

public class ChunkedEncodingPostRequest {
    private static final int BUFFER_SIZE = 4096; // 分块大小

    public void uploadFile(String url, byte[] data) throws Exception {
        URL urlObject = new URL(url);
        HttpURLConnection connection = (HttpURLConnection) urlObject.openConnection();
        
        // 设置POST请求并允许输出流
        connection.setRequestMethod("POST");
        connection.setRequestProperty("Transfer-Encoding", "chunked");
        connection.setDoOutput(true);

        try (OutputStream outputStream = connection.getOutputStream()) {
            long totalSize = data.length;
            for (long remaining = totalSize; remaining > 0; ) {
                long chunkSize = Math.min(BUFFER_SIZE, remaining);
                outputStream.write(chunkSize & 0xff); // 写入长度（包括前缀'\r\n')
                outputStream.write(data, (int) (remaining - chunkSize), (int) chunkSize);
                outputStream.write('\r');
                outputStream.write('\n');
                remaining -= chunkSize;
            }

            // 结束分块
            outputStream.write('0');
            outputStream.write('\r');
            outputStream.write('\n');

            outputStream.flush(); // 确保所有数据已发送
        }
        connection.disconnect();
    }
}

在这个示例中，首先创建`HttpURLConnection`连接，然后设置请求方法为POST，并添加`Transfer-Encoding`头为"chunked"。接着使用循环将数据分成小块（默认`BUFFER_SIZE`），每一块写入输出流，并按照HTTP的chunked encoding格式进行。