java如何实现post请求

在Java中实现POST请求，可以使用HttpURLConnection或者HttpClient两种方式。下面分别介绍这两种方式：

1. 使用HttpURLConnection实现POST请求：

import java.net.HttpURLConnection;
import java.net.URL;

public class HttpUrlConnectionPostDemo {
    public static void main(String[] args) throws Exception {
        URL url = new URL("http://example.com/api");
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("POST");
        conn.setRequestProperty("Content-Type", "application/json;charset=UTF-8");
        conn.setDoOutput(true);
        String jsonInputString = "{\"username\": \"admin\",\"password\": \"password\"}";
        try (OutputStream os = conn.getOutputStream()) {
            byte[] input = jsonInputString.getBytes("utf-8");
            os.write(input, 0, input.length);
        }
        try (BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream(), "utf-8"))) {
            StringBuilder response = new StringBuilder();
            String responseLine = null;
            while ((responseLine = br.readLine()) != null) {
                response.append(responseLine.trim());
            }
            System.out.println(response.toString());
        }
    }
}

2. 使用HttpClient实现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.HttpClientBuilder;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class HttpClientPostDemo {
    public static void main(String[] args) throws Exception {
        HttpClient httpClient = HttpClientBuilder.create().build();
        HttpPost request = new HttpPost("http://example.com/api");
        String jsonInputString = "{\"username\": \"admin\",\"password\": \"password\"}";
        StringEntity params = new StringEntity(jsonInputString);
        request.addHeader("content-type", "application/json");
        request.setEntity(params);
        HttpResponse response = httpClient.execute(request);
        BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
        StringBuilder result = new StringBuilder();
        String line = "";
        while ((line = reader.readLine()) != null) {
            result.append(line);
        }
        System.out.println(result.toString());
    }
}

这两种方式都可以实现POST请求，具体使用哪种方式取决于具体场景和个人喜好。