Java调用外部接口有哪些方式

1.有哪些？

1.HttpURLConnection

1.介绍

1.这是Java标准库提供的一个类，用于发送HTTP请求和接收响应

2.它不需要额外的依赖，但是API相对底层，编写代码时需要处理很多细节，如设置请求头、处理连接和流等

2.代码示例

import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;public class HttpURLConnectionExample {public static void main(String[] args) throws Exception {URL url = new URL("http://example.com/api");HttpURLConnection conn = (HttpURLConnection) url.openConnection();conn.setRequestMethod("GET");// 设置请求头（如果需要）conn.setRequestProperty("User-Agent", "Java-HttpClient/1.0");int responseCode = conn.getResponseCode();System.out.println("Response Code: " + responseCode);// 处理响应...conn.disconnect();}
}

2.Apache HttpClient

1.介绍

1.Apache HttpClient是一个功能强大的HTTP客户端库，提供了比HttpURLConnection更高级别的抽象

2.它支持复杂的HTTP操作，包括持久连接、认证、重定向处理等，并且API设计更加友好

3.需要引入外部依赖，但它是开源社区广泛使用的解决方案之一

2.依赖

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

3.代码示例

import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.HttpClients;
import org.apache.http.util.EntityUtils;public class ApacheHttpClientExample {public static void main(String[] args) throws Exception {try (CloseableHttpClient httpClient = HttpClients.createDefault()) {HttpGet request = new HttpGet("http://example.com/api");try (CloseableHttpResponse response = httpClient.execute(request)) {String responseBody = EntityUtils.toString(response.getEntity());System.out.println("Response Body: " + responseBody);}}}
}

3.OkHttp

1.介绍

1.OkHttp是一个现代的HTTP & HTTP/2客户端，适用于Android和Java应用程序

2.它提供了一种简洁的API来构建请求和处理响应，同时也内置了缓存、连接池等功能以优化性能

3.广泛应用于移动开发领域，但同样适用于一般的Java应用

2.依赖

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

3.代码示例

import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.Response;public class OkHttpExample {public static void main(String[] args) throws Exception {OkHttpClient client = new OkHttpClient();Request request = new Request.Builder().url("http://example.com/api").build();try (Response response = client.newCall(request).execute()) {if (!response.isSuccessful()) throw new RuntimeException("Unexpected code " + response);System.out.println("Response Body: " + response.body().string());}}
}

4.Retrofit

1.介绍

1.Retrofit是一个类型安全的HTTP客户端，专门为Android和Java设计

2.它基于OkHttp构建，并添加了对RESTful服务的支持，使得定义和调用API变得非常简单

3.你可以通过注解定义API端点，并自动生成实现代码，从而简化了与远程服务交互的过程

2.依赖

<dependency><groupId>com.squareup.retrofit2</groupId><artifactId>retrofit</artifactId>
</dependency><dependency><groupId>com.squareup.retrofit2</groupId><artifactId>converter-gson</artifactId>
</dependency>

3.代码示例

import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
import retrofit2.Call;
import retrofit2.http.GET;interface ApiService {@GET("api")Call<String> getData();
}public class RetrofitExample {public static void main(String[] args) {Retrofit retrofit = new Retrofit.Builder().baseUrl("http://example.com/").addConverterFactory(GsonConverterFactory.create()).build();ApiService apiService = retrofit.create(ApiService.class);Call<String> call = apiService.getData();try {retrofit2.Response<String> response = call.execute();System.out.println("Response Body: " + response.body());} catch (Exception e) {e.printStackTrace();}}
}

5.Spring RestTemplate或WebClient

1.介绍

1.如果你在使用Spring框架，那么RestTemplate或新的响应式WebClient是很好的选择

2.RestTemplate是同步的，而WebClient支持非阻塞式的异步调用，适合于响应式编程模型

3.它们集成了Spring生态系统的许多特性，如消息转换器、异常处理等，可以极大地简化HTTP通信的代码

3.代码示例

// RestTemplate Example (Synchronous)
import org.springframework.web.client.RestTemplate;public class RestTemplateExample {public static void main(String[] args) {RestTemplate restTemplate = new RestTemplate();String result = restTemplate.getForObject("http://example.com/api", String.class);System.out.println("Response Body: " + result);}
}// WebClient Example (Reactive)
import org.springframework.web.reactive.function.client.WebClient;
import reactor.core.publisher.Mono;public class WebClientExample {public static void main(String[] args) {WebClient webClient = WebClient.create("http://example.com");Mono<String> result = webClient.get().uri("/api").retrieve().bodyToMono(String.class);result.subscribe(System.out::println);}
}

6.Feign

1.介绍

1.Feign是一个声明式的HTTP客户端，它让开发者可以通过简单的注解来定义HTTP请求，类似于Retrofit

2.它通常与Spring Cloud一起使用，以便在微服务架构中进行服务间通信

3.支持可插拔的编码器和解码器，便于集成不同的数据格式

2.依赖

<dependencyManagement><dependencies><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-dependencies</artifactId><version>Hoxton.SR9</version> <!-- 请根据需要选择最新的版本 --><type>pom</type><scope>import</scope></dependency></dependencies>
</dependencyManagement><dependencies><!-- Spring Boot Starter Web for building web, including RESTful, applications --><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><!-- Feign Client for declarative REST clients --><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-openfeign</artifactId></dependency><!-- Optional: If you are using Eureka for service discovery --><dependency><groupId>org.springframework.cloud</groupId><artifactId>spring-cloud-starter-netflix-eureka-client</artifactId></dependency>
</dependencies>

3.代码示例

import org.springframework.cloud.openfeign.FeignClient;
import org.springframework.web.bind.annotation.GetMapping;@FeignClient(name = "example-api", url = "http://example.com")
public interface ExampleClient {@GetMapping("/api")String getApiData();
}public class FeignExample {private final ExampleClient exampleClient;public FeignExample(ExampleClient exampleClient) {this.exampleClient = exampleClient;}public void fetchData() {String data = exampleClient.getApiData();System.out.println("Fetched Data: " + data);}
}