应用场景：主要是为了在java代码中去调用第三方的接口。
1.OkHttp
1.1引入okhtpp依赖
<dependency><groupId>com.squareup.okhttp3</groupId><artifactId>okhttp</artifactId><version>4.9.1</version></dependency>1.2封装一个请求的方法
private <T> T requestBase(Object object, String tag, Class<T> resultClass) {T result = null;OkHttpClient client = new OkHttpClient().newBuilder().connectTimeout(90, TimeUnit.SECONDS).writeTimeout(90, TimeUnit.SECONDS).readTimeout(90, TimeUnit.SECONDS).build();okhttp3.MediaType mediaType = okhttp3.MediaType.parse("text/plain");RequestBody body = RequestBody.create(mediaType, JSON.toJSONString(object));Request request = new Request.Builder().url("https://www.xxx.xxx./xxx/" + tag).method("POST", body).addHeader("Content-Type", "text/plain").build();Response response = null;try {response = client.newCall(request).execute();String originResult = response.body().string();result = JSON.parseObject(originResult, resultClass);} catch (IOException e) {e.printStackTrace();}return result;}其实就两步，构建客户端client，构建请求request，客户端client去调用newCall(request)发起请求
2.RestTemplate
这个是由我们Spring框架中的web依赖提供的，不用额外引入，但需要一个配置类。
2.1 添加配置类RestTemplateConfig
@Configuration
public class RestTemplateConfig {@Beanpublic RestTemplate restTemplate(ClientHttpRequestFactory factory) {RestTemplate restTemplate = new RestTemplate(factory);restTemplate.getMessageConverters().add(0, new StringHttpMessageConverter(Charset.forName("UTF-8")));return restTemplate;}@Beanpublic ClientHttpRequestFactory simpleClientHttpRequestFactory() {SimpleClientHttpRequestFactory factory = new SimpleClientHttpRequestFactory();factory.setConnectTimeout(180000);factory.setReadTimeout(180000);return factory;}}2.2封装一个通用的方法
public <T> T requestBase(Object requestBody, String tag, Class<T> resultClass) {HttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_JSON);HttpEntity httpEntity = new HttpEntity(requestBody, headers);ResponseEntity<T> response = restTemplate.postForEntity("https://www.xxx.xxx./xxx/" + tag, httpEntity, resultClass);return response.getBody();}写法相对简单一些
总结：上述两种方法没有限制，想使用哪个用哪个，其实实际运用中最好是封装一个工具类。不想自己封装的，上网搜一下，最好还是自己封装，理解更深一些，再搜搜别的稍加补充。
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