在 Java 中使用 GET 和 POST 请求

最新推荐文章于 2025-02-10 23:15:00 发布

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最新推荐文章于 2025-02-10 23:15:00 发布

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在 Java 中，我们通常使用 HttpURLConnection 或第三方库（如 Apache HttpClient 或 OkHttp）来发送 GET 和 POST 请求。本文将通过示例讲解如何实现这两种 HTTP 请求。

1. 使用 `HttpURLConnection` 实现 GET 和 POST 请求

HttpURLConnection 是 Java 原生类库中提供的工具，可以用来发送 HTTP 请求。

1.1 GET 请求示例

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

public class GetRequestExample {
    public static void main(String[] args) {
        try {
            // 创建 URL 对象
            URL url = new URL("https://jsonplaceholder.typicode.com/posts/1");

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

            // 设置请求头（可选）
            connection.setRequestProperty("User-Agent", "Mozilla/5.0");

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

            // 读取响应
            if (responseCode == HttpURLConnection.HTTP_OK) { // 200
                BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String inputLine;
                StringBuilder response = new StringBuilder();

                while ((inputLine = in.readLine()) != null) {
                    response.append(inputLine);
                }
                in.close();

                // 打印响应内容
                System.out.println("Response: " + response.toString());
            } else {
                System.out.println("GET request failed.");
            }

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

1.2 POST 请求示例

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

public class PostRequestExample {
    public static void main(String[] args) {
        try {
            // 创建 URL 对象
            URL url = new URL("https://jsonplaceholder.typicode.com/posts");

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

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

            // 启用写入数据到请求体
            connection.setDoOutput(true);

            // JSON 数据
            String jsonInputString = "{ \"title\": \"foo\", \"body\": \"bar\", \"userId\": 1 }";

            // 写入数据
            try (OutputStream os = connection.getOutputStream()) {
                byte[] input = jsonInputString.getBytes("utf-8");
                os.write(input, 0, input.length);
            }

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

            // 读取响应
            if (responseCode == HttpURLConnection.HTTP_CREATED) { // 201
                BufferedReader in = new BufferedReader(new InputStreamReader(connection.getInputStream()));
                String inputLine;
                StringBuilder response = new StringBuilder();

                while ((inputLine = in.readLine()) != null) {
                    response.append(inputLine);
                }
                in.close();

                // 打印响应内容
                System.out.println("Response: " + response.toString());
            } else {
                System.out.println("POST request failed.");
            }

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

2. 使用 `Apache HttpClient` 实现 GET 和 POST 请求

Apache HttpClient 是一个强大的第三方库，适合处理复杂的 HTTP 请求。

2.1 添加 Maven 依赖

在 pom.xml 文件中添加以下依赖：

<dependency>
    <groupId>org.apache.httpcomponents.client5</groupId>
    <artifactId>httpclient5</artifactId>
    <version>5.2</version>
</dependency>

2.2 GET 请求示例

import org.apache.hc.client5.http.classic.methods.HttpGet;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.HttpClients;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ApacheHttpClientGetExample {
    public static void main(String[] args) {
        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            HttpGet request = new HttpGet("https://jsonplaceholder.typicode.com/posts/1");

            try (CloseableHttpResponse response = httpClient.execute(request)) {
                System.out.println("Response Code: " + response.getCode());

                BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
                String line;
                StringBuilder responseContent = new StringBuilder();

                while ((line = reader.readLine()) != null) {
                    responseContent.append(line);
                }

                System.out.println("Response: " + responseContent.toString());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

2.3 POST 请求示例

import org.apache.hc.client5.http.classic.methods.HttpPost;
import org.apache.hc.client5.http.entity.StringEntity;
import org.apache.hc.client5.http.impl.classic.CloseableHttpClient;
import org.apache.hc.client5.http.impl.classic.CloseableHttpResponse;
import org.apache.hc.client5.http.impl.classic.HttpClients;

import java.io.BufferedReader;
import java.io.InputStreamReader;

public class ApacheHttpClientPostExample {
    public static void main(String[] args) {
        try (CloseableHttpClient httpClient = HttpClients.createDefault()) {
            HttpPost post = new HttpPost("https://jsonplaceholder.typicode.com/posts");

            // 设置请求头
            post.setHeader("Content-Type", "application/json");

            // 设置请求体
            String json = "{ \"title\": \"foo\", \"body\": \"bar\", \"userId\": 1 }";
            post.setEntity(new StringEntity(json));

            try (CloseableHttpResponse response = httpClient.execute(post)) {
                System.out.println("Response Code: " + response.getCode());

                BufferedReader reader = new BufferedReader(new InputStreamReader(response.getEntity().getContent()));
                String line;
                StringBuilder responseContent = new StringBuilder();

                while ((line = reader.readLine()) != null) {
                    responseContent.append(line);
                }

                System.out.println("Response: " + responseContent.toString());
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

3. 使用 `OkHttp` 实现 GET 和 POST 请求

OkHttp 是另一个流行的 HTTP 客户端库，轻量且易用。

3.1 添加 Maven 依赖

在 pom.xml 文件中添加以下依赖：

<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>4.11.0</version>
</dependency>

3.2 GET 请求示例

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

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

        Request request = new Request.Builder()
                .url("https://jsonplaceholder.typicode.com/posts/1")
                .build();

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

3.3 POST 请求示例

import okhttp3.MediaType;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;

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

        String json = "{ \"title\": \"foo\", \"body\": \"bar\", \"userId\": 1 }";
        RequestBody body = RequestBody.create(json, MediaType.get("application/json; charset=utf-8"));

        Request request = new Request.Builder()
                .url("https://jsonplaceholder.typicode.com/posts")
                .post(body)
                .build();

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