Java HttpClient改变内容类型？

Java HttpClient 改变内容类型（Content-Type）的方法是通过设置请求头（request header）中的 "Content-Type" 属性。以下是一个使用 Java HttpClient 发送 POST 请求并更改内容类型的示例：

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;

public class Main {
    public static void main(String[] args) throws IOException {
        String url = "https://example.com/api";
        String json = "{\"key\": \"value\"}";

        URL obj = new URL(url);
        HttpURLConnection connection = (HttpURLConnection) obj.openConnection();

        connection.setRequestMethod("POST");
        connection.setRequestProperty("Content-Type", "application/json;charset=UTF-8");
        connection.setRequestProperty("Accept", "application/json");
        connection.setDoOutput(true);

        connection.getOutputStream().write(json.getBytes(StandardCharsets.UTF_8));
        int responseCode = connection.getResponseCode();

        if (responseCode == HttpURLConnection.HTTP_OK) {
            BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String inputLine;
            StringBuilder response = new StringBuilder();

            while ((inputLine = in.readLine()) != null) {
                response.append(inputLine);
            }
            in.close();

            System.out.println(response.toString());
        } else {
            System.out.println("Request failed. Response code: " + responseCode);
        }
    }
}

在这个示例中，我们使用 HttpURLConnection 发送一个 POST 请求，并设置请求头中的 "Content-Type" 为 "application/json;charset=UTF-8"。这将告诉服务器我们发送的数据是 JSON 格式的。同时，我们还设置了 "Accept" 请求头，表示我们期望服务器返回的数据类型是 JSON。