使用Spring Boot和Apache HttpClient构建REST客户端

本文介绍: 在本教程中，我们将学习如何使用Spring Boot和Apache HttpClient创建一个REST客户端。我们将探讨如何与远程服务器进行通信、处理JSON响应，并为Web应用程序配置跨源资源共享（CORS）。让我们深入代码吧！

介绍：
在本文中，我们将学习如何使用Spring Boot和Apache HttpClient创建一个REST客户端。我们将探讨如何与远程服务器进行通信、处理JSON响应，并为Web应用程序配置跨源资源共享（CORS）。让我们深入代码吧！

ClientService 类负责发起HTTP请求并处理响应。它使用 @Service 注解表示它应该由Spring容器进行管理。

@Service
public class ClientService {
    @Autowired
    private CloseableHttpClient httpClient;
    @Autowired
    private ObjectMapper objectMapper;
    
    // 发起GET请求并将响应作为Map返回的方法
    public Map ResponseMap(String url) throws IOException {
        // 创建GET请求，并使用提供的URL
        HttpGet request = new HttpGet(url);

        // 发送请求并获取响应
        HttpResponse response = httpClient.execute(request);
        HttpEntity entity = response.getEntity();

        // 处理响应体
        Map responseBody = null;
        if (entity != null) {
            String jsonString = EntityUtils.toString(entity);
            responseBody = objectMapper.readValue(jsonString, Map.class);
        }

        // 关闭连接
        EntityUtils.consume(entity);

        return responseBody;
    }

    // 发起GET请求并将响应作为String返回的方法
    public String ResponString(String url) throws IOException {
        // 创建GET请求，并使用提供的URL
        HttpGet request = new HttpGet(url);

        // 发送请求并获取响应
        HttpResponse response = httpClient.execute(request);
        HttpEntity entity = response.getEntity();

        // 处理响应体
        String responseBody = "";
        if (entity != null) {
            responseBody = EntityUtils.toString(entity);
        }

        // 关闭连接
        EntityUtils.consume(entity);

        return responseBody;
    }
}

MyClientController 类是控制器层，负责处理HTTP请求并返回响应。

@RestController
@RequestMapping("/api")
public class MyClientController {
    private final ObjectMapper objectMapper;
    private final CloseableHttpClient httpClient;
    private final ClientService clientService;

    @Autowired
    public MyClientController(CloseableHttpClient httpClient, ObjectMapper objectMapper, ClientService clientService) {
        this.httpClient = httpClient;
        this.objectMapper = objectMapper;
        this.clientService = clientService;
    }

    @GetMapping("/example")
    public ResponseEntity<String> ResponString() throws IOException {
        String s = clientService.ResponString("http://localhost:8081/api/test");
        return ResponseEntity.ok(s);
    }

    @GetMapping("/mapreq")
    public ResponseEntity<Map> ResponseMap() throws IOException {
        Map map1 = clientService.ResponseMap("http://localhost:8081/flux/testmap");
        System.out.println("map1 = " + map1);
        Object key1 = map1.get("key1");
        System.out.println("key1.toString() = " + key1.toString());
        return ResponseEntity.ok(map1);
    }

    @GetMapping("/test")
    public String testEndpoint() {
        return "test";
    }
}

HttpClientConfiguration 类是一个配置类，用于自动装配到Bean中。

@Configuration
public class HttpClientConfiguration {

    @Bean
    public CloseableHttpClient httpClient() {
        HttpClientBuilder httpClientBuilder = HttpClientBuilder.create();

        // 设置请求头
        httpClientBuilder.setDefaultHeaders(Arrays.asList(createDefaultHeaders()));

        // 设置基础配置
        httpClientBuilder.setDefaultRequestConfig(createRequestConfig());

        // 创建HttpClient对象
        CloseableHttpClient httpClient = httpClientBuilder.build();
        return httpClient;
    }

    private RequestConfig createRequestConfig() {
        // 设置连接超时时间
        int connectionTimeout = 5000;
        // 设置读取超时时间
        int socketTimeout = 5000;

        return RequestConfig.custom()
                .setConnectTimeout(connectionTimeout)
                .setSocketTimeout(socketTimeout)
                .build();
    }

    private Header[] createDefaultHeaders() {
        Header[] headers = {
                new BasicHeader(HttpHeaders.CONTENT_TYPE, "application/json"),
                // 可以添加其他请求头
        };
        return headers;
    }
}

MyCorsConfiguration 类是一个配置类，用于配置WebFlux的跨域。

@Configuration
public class MyCorsConfiguration extends org.springframework.web.cors.CorsConfiguration {

    @Bean
    public CorsWebFilter corsWebFilter() {
        CorsConfiguration corsConfig = new CorsConfiguration();
        corsConfig.addAllowedOrigin("*");
        corsConfig.addAllowedMethod("*");
        corsConfig.addAllowedHeader("*");

        UrlBasedCorsConfigurationSource source = new UrlBasedCorsConfigurationSource();
        source.registerCorsConfiguration("/**", corsConfig);

        return new CorsWebFilter(source);
    }
}

在本示例中，我们创建了一个包含服务层、控制器层和配置类的Spring Boot应用程序。服务层的 ClientService 类负责通过Apache HttpClient发起HTTP请求，并处理响应。控制器层的 MyClientController 类负责处理HTTP请求并返回响应。我们还创建了一个配置类 HttpClientConfiguration，用于配置Apache HttpClient，并将其作为Bean注入到应用程序中。另外，我们还创建了一个配置类 MyCorsConfiguration，用于配置WebFlux的跨域资源共享（CORS）。