拉卡拉商户进件java实现合同下载

拉卡拉商户进件接口文档中提供了合同下载的接口，Java代码实现如下：

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

public class LKLContractDownload {
    public static void main(String[] args) {
        String urlStr = "http://xxx.xxx.xxx.xxx:xxxx/lkl/file/download";
        String token = "your_token_here";
        String contractNo = "your_contract_no_here";

        try {
            URL url = new URL(urlStr);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setRequestMethod("POST");
            conn.setRequestProperty("Content-Type", "application/json");
            conn.setRequestProperty("Authorization", token);
            conn.setDoOutput(true);

            String input = "{\"contractNo\":\"" + contractNo + "\"}";

            OutputStream os = conn.getOutputStream();
            os.write(input.getBytes());
            os.flush();

            if (conn.getResponseCode() != HttpURLConnection.HTTP_OK) {
                throw new RuntimeException("Failed : HTTP error code : " + conn.getResponseCode());
            }

            InputStream is = conn.getInputStream();
            BufferedReader br = new BufferedReader(new InputStreamReader(is));

            String output;
            while ((output = br.readLine()) != null) {
                System.out.println(output);
            }

            conn.disconnect();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

其中，`urlStr` 是合同下载接口的 URL，`token` 是接口认证所需的 token，`contractNo` 是要下载合同的编号。根据实际情况修改这三个参数即可。