HttpClient和RestTemplate

java请求网络资源通常用HttpClient等，Spring封装了库，提供更为简洁的资源请求方式RestTemplate
RestTemplate默认使用的是SimpleClientHttpRequestFactory工厂
默认它是以java.net下的HttpURLConnection方式发起的请求
所以RestTemplate是支持多种方式发起请求的
查看该工程的实现类可知，支持包括HttpClient, OkHttp等方式

HttpClient：代码复杂，还得操心资源回收等,代码很复杂，冗余代码多，不建议直接使用，一般是封装为 HttpUtils工具类使用
RestTemplate： 是 Spring 提供的用于访问Rest服务的客户端， RestTemplate 提供了多种便捷访问远程Http服务的方法,能够大大提高客户端的编写效率

一、HttpClient

1、发起get无参请求

@Test //get 无参public void doGet() {	String uri = "https://openapi.chanjet.com/auth/refreshToken?grantType=refresh_token&appKey=K2vIOn4m&refreshToken=1";// 1.创建Http客户端CloseableHttpClient httpClient = HttpClientBuilder.create().build();// 2.创建Get请求HttpGet request = new HttpGet(uri);// 3.响应模型CloseableHttpResponse response = null;try {// 3.执行Get请求response = httpClient.execute(request);// 4.从响应模型中获取响应实体HttpEntity responseEntity = response.getEntity();System.out.println("响应状态为:" + response.getStatusLine());if (responseEntity != null) {System.out.println("响应内容长度为:" + responseEntity.getContentLength());System.out.println("响应内容为:" + EntityUtils.toString(responseEntity, StandardCharsets.UTF_8));}} catch (IOException e) {e.printStackTrace();} finally {try {if (httpClient != null) {httpClient.close();}if (response != null) {response.close();}} catch (IOException e) {e.printStackTrace();}}}

2、发起post无参请求

@Test //post 对象public void postObject() {	// 如果有普通参数，uri 改成 URIBuilderString uri = "http://localhost:8080/people/addPeople";// 创建Http客户端CloseableHttpClient httpClient = HttpClientBuilder.create().build();		// 创建Post请求HttpPost request = new HttpPost(uri);request.setHeader("Content-Type", "application/json;charset=utf8");		// 添加json对象People people = new People();people.setName("张飞");people.setCreateTime(LocalDateTime.now());String jsonString = JSON.toJSONString(people);StringEntity entity = new StringEntity(jsonString, "UTF-8");httpPost.setEntity(entity);// 响应模型CloseableHttpResponse response = null;try {// 执行Post请求response = httpClient.execute(request);// 从响应模型中获取响应实体HttpEntity responseEntity = response.getEntity();System.out.println("响应状态为:" + response.getStatusLine());if (responseEntity != null) {System.out.println("响应内容长度为:" + responseEntity.getContentLength());System.out.println("响应内容为:" + EntityUtils.toString(responseEntity, StandardCharsets.UTF_8));}} catch (IOException e) {e.printStackTrace();} finally {try {if (httpClient != null) {httpClient.close();}if (response != null) {response.close();}} catch (IOException e) {e.printStackTrace();}}}

二、RestTemplate

1、发起get请求请求

发送一个HTTP GET请求，返回的请求体将映射为一个对象
getForObject()

发送一个HTTP GET请求，返回的ResponseEntity包含了响应体所映射成的对象
getForEntity()

RestTemplate restTemplate = new RestTemplate();ResponseEntity<String> entity = restTemplate.getForEntity(uri, String.class);// TODO 处理响应

2、发起Post请求方式

postForEntity()
POST 数据到一个URL，返回包含一个对象的ResponseEntity，这个对象是从响应体中映射得到的。

postForObject()
POST 数据到一个URL，返回根据响应体匹配形成的对象。

postForLocation()
POST 数据到一个URL，返回新创建资源的URL

RestTemplate restTemplate = new RestTemplate();// headersHttpHeaders headers = new HttpHeaders();headers.setContentType(MediaType.APPLICATION_JSON_UTF8);HttpEntity<Object> objectHttpEntity = new HttpEntity<>(headers);// TODO 处理响应ResponseEntity<String> entity = restTemplate.postForEntity(uri, request, String.class);