Java HTTP客户端如何发送请求

在Java中，你可以使用多种方式来发送HTTP请求。以下是一些常用的方法：

1. 使用java.net.HttpURLConnection（Java标准库）

import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpClientExample {
    public static void main(String[] args) {
        try {
            URL url = new URL("https://api.example.com/data");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");
            connection.setRequestProperty("Accept", "application/json");

            int responseCode = connection.getResponseCode();
            System.out.println("Response Code: " + responseCode);

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

2. 使用Apache HttpClient库 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请求：

import org.apache.http.HttpResponse;
import org.apache.http.client.HttpClient;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;

public class HttpClientExample {
    public static void main(String[] args) {
        try {
            HttpClient httpClient = HttpClients.createDefault();
            HttpGet request = new HttpGet("https://api.example.com/data");
            request.addHeader("Accept", "application/json");

            HttpResponse response = httpClient.execute(request);
            String responseBody = EntityUtils.toString(response.getEntity());

            System.out.println(responseBody);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

3. 使用OkHttp库 首先，你需要将OkHttp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>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.9.1</version>
</dependency>

然后，你可以使用以下代码发送HTTP请求：

import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;

public class HttpClientExample {
    public static void main(String[] args) {
        OkHttpClient client = new OkHttpClient();

        Request request = new Request.Builder()
                .url("https://api.example.com/data")
                .addHeader("Accept", "application/json")
                .build();

        try (Response response = client.newCall(request).execute()) {
            if (response.isSuccessful()) {
                System.out.println(response.body().string());
            } else {
                System.out.println("Error: " + response.code());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

这些示例展示了如何使用Java发送HTTP GET请求。如果你需要发送POST请求或其他类型的HTTP请求，你可以根据需要修改这些示例。