如何用Java发送HTTP POST请求

在Java中发送HTTP POST请求，你可以使用多种方法。以下是两种常见的方法：

1. 使用HttpURLConnection类（Java标准库）
2. 使用第三方库，如Apache HttpClient

方法1：使用HttpURLConnection类

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

public class HttpPostRequest {
    public static void main(String[] args) {
        try {
            // 创建URL对象
            URL url = new URL("https://example.com/post");

            // 打开连接
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();

            // 设置请求方法为POST
            connection.setRequestMethod("POST");

            // 设置请求头
            connection.setRequestProperty("Content-Type", "application/json;charset=UTF-8");
            connection.setRequestProperty("Accept", "application/json");

            // 允许输出
            connection.setDoOutput(true);

            // 创建JSON数据
            String jsonInputString = "{\"param1\": \"value1\", \"param2\": \"value2\"}";

            // 获取输出流并写入JSON数据
            try (OutputStream os = connection.getOutputStream()) {
                byte[] input = jsonInputString.getBytes("utf-8");
                os.write(input, 0, input.length);
            }

            // 获取响应码
            int responseCode = connection.getResponseCode();
            System.out.println("POST Response Code :  " + responseCode);

            // 读取响应
            // ...

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

方法2：使用Apache HttpClient

首先，你需要将Apache HttpClient库添加到项目的依赖中。如果你使用Maven，可以在pom.xml文件中添加以下依赖：

<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.13</version>
</dependency>

然后，你可以使用以下代码发送HTTP POST请求：

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class HttpPostRequest {
    public static void main(String[] args) {
        try {
            // 创建HttpClient对象
            HttpClient httpClient = HttpClients.createDefault();

            // 创建HttpPost对象
            HttpPost httpPost = new HttpPost("https://example.com/post");

            // 创建JSON数据
            String jsonInputString = "{\"param1\": \"value1\", \"param2\": \"value2\"}";

            // 设置请求体
            httpPost.setEntity(new StringEntity(jsonInputString, "UTF-8"));

            // 设置请求头
            httpPost.setHeader("Content-Type", "application/json;charset=UTF-8");
            httpPost.setHeader("Accept", "application/json");

            // 执行请求并获取响应
            HttpResponse response = httpClient.execute(httpPost);

            // 获取响应码
            int responseCode = response.getStatusLine().getStatusCode();
            System.out.println("POST Response Code :  " + responseCode);

            // 读取响应内容
            String responseBody = EntityUtils.toString(response.getEntity());
            System.out.println("Response Content: " + responseBody);

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

这两种方法都可以用来发送HTTP POST请求。根据你的需求和项目环境，你可以选择使用Java标准库中的HttpURLConnection类，或者使用第三方库Apache HttpClient来简化操作。