Java中HTTP请求怎么发

在Java中发送HTTP请求，你可以使用多种方法。以下是一些常用的方法：

1. 使用java.net.HttpURLConnection类（适用于Java 1.1及以上版本）：

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

public class HttpGetRequest {
    public static void main(String[] args) {
        try {
            URL url = new URL("http://example.com");
            HttpURLConnection connection = (HttpURLConnection) url.openConnection();
            connection.setRequestMethod("GET");

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

            BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
            String inputLine;
            StringBuffer response = new StringBuffer();

            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（需要添加依赖）： 首先，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，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 HttpGetRequest {
    public static void main(String[] args) {
        HttpClient httpClient = HttpClients.createDefault();
        HttpGet httpGet = new HttpGet("http://example.com");

        try {
            HttpResponse httpResponse = httpClient.execute(httpGet);
            String responseContent = EntityUtils.toString(httpResponse.getEntity());

            System.out.println(responseContent);

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

3. 使用OkHttp库（需要添加依赖）： 首先，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，使用以下代码发送HTTP请求：

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

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

        Request request = new Request.Builder()
                .url("http://example.com")
                .build();

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

以上是三种常用的在Java中发送HTTP请求的方法。你可以根据自己的需求选择合适的方法。