java怎么post一个json

Java中如何发送POST请求并传递JSON数据

在Java开发中，经常需要通过HTTP POST请求发送JSON数据到服务器，本文将详细介绍几种在Java中实现POST JSON请求的方法，包括使用原生HttpURLConnection、第三方库如Apache HttpClient和OkHttp,以及Spring框架中的RestTemplate。

使用原生HttpURLConnection

Java标准库中的HttpURLConnection是最基础的方式,无需额外依赖：

import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.nio.charset.StandardCharsets;
public class PostJsonWithHttpUrlConnection {
    public static void main(String[] args) throws Exception {
        // 目标URL
        String urlString = "https://example.com/api";
        String jsonInputString = "{\"name\":\"John\", \"age\":30}";
        URL url = new URL(urlString);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Content-Type", "application/json; utf-8");
        conn.setRequestProperty("Accept", "application/json");
        conn.setDoOutput(true);
        try (OutputStream os = conn.getOutputStream()) {
            byte[] input = jsonInputString.getBytes(StandardCharsets.UTF_8);
            os.write(input, 0, input.length);
        }
        int responseCode = conn.getResponseCode();
        System.out.println("Response Code: " + responseCode);
        // 读取响应...
    }
}

使用Apache HttpClient

Apache HttpClient提供了更强大和灵活的HTTP客户端功能：

首先添加Maven依赖：

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

然后使用以下代码发送POST请求：

import org.apache.http.HttpEntity;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpPost;
import org.apache.http.entity.StringEntity;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;
public class PostJsonWithHttpClient {
    public static void main(String[] args) throws Exception {
        String url = "https://example.com/api";
        String jsonPayload = "{\"name\":\"John\", \"age\":30}";
        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            HttpPost httpPost = new HttpPost(url);
            httpPost.setHeader("Accept", "application/json");
            httpPost.setHeader("Content-Type", "application/json");
            httpPost.setEntity(new StringEntity(jsonPayload));
            try (CloseableHttpResponse response = httpClient.execute(httpPost)) {
                HttpEntity entity = response.getEntity();
                String responseString = EntityUtils.toString(entity);
                System.out.println("Response: " + responseString);
            }
        }
    }
}

使用OkHttp

OkHttp是一个现代、高效的HTTP客户端：

添加Maven依赖：

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.9.3</version>
</dependency>

使用示例：

import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
public class PostJsonWithOkHttp {
    public static void main(String[] args) throws Exception {
        String url = "https://example.com/api";
        String jsonPayload = "{\"name\":\"John\", \"age\":30}";
        OkHttpClient client = new OkHttpClient();
        MediaType JSON = MediaType.get("application/json; charset=utf-8");
        RequestBody body = RequestBody.create(jsonPayload, JSON);
        Request request = new Request.Builder()
                .url(url)
                .post(body)
                .build();
        try (Response response = client.newCall(request).execute()) {
            if (!response.isSuccessful()) {
                throw new IOException("Unexpected code " + response);
            }
            System.out.println(response.body().string());
        }
    }
}

使用Spring RestTemplate

如果项目已经使用Spring框架,RestTemplate是一个便捷的选择：

import org.springframework.http.*;
import org.springframework.web.client.RestTemplate;
public class PostJsonWithRestTemplate {
    public static void main(String[] args) {
        String url = "https://example.com/api";
        String jsonPayload = "{\"name\":\"John\", \"age\":30}";
        RestTemplate restTemplate = new RestTemplate();
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_JSON);
        HttpEntity<String> entity = new HttpEntity<>(jsonPayload, headers);
        ResponseEntity<String> response = restTemplate.postForEntity(url, entity, String.class);
        System.out.println("Response: " + response.getBody());
    }
}