Spring_RestTemplate的使用

RestTemplate

简介

• 现如今的 IT 项目，由服务端向外发起网络请求的场景，基本上处处可见！

• RestTemplate是由Spring框架提供的一个可用于应用中调用rest服务的类它简化了与http服务的通信方式，统一了RESTFul的标准，封装了http连接，我们只需要传入url及其返回值类型即可。相较于之前常用的HttpClient，RestTemplate是一种更为优雅的调用RESTFul服务的方式。

• 在Spring应用程序中访问第三方REST服务与使用Spring RestTemplate类有关。RestTemplate类的设计原则与许多其他Spring的模板类(例如JdbcTemplate)相同，为执行复杂任务提供了一种具有默认行为的简化方法。

• RestTemplate默认依赖JDK提供了http连接的能力（HttpURLConnection），如果有需要的话也可以通过setRequestFactory方法替换为例如Apache HttpCompoent、Netty或OKHttp等其他Http libaray。

• 考虑到了RestTemplate类是为了调用REST服务而设计的，因此它的主要方法与REST的基础紧密相连就不足为奇了，后者时HTTP协议的方法：HEAD、GET、POST、PUT、DELETE、OPTIONS例如，RestTemplate类具有headForHeaders()、getForObject()、putForObject()，put()和delete()等方法。

创建RestTemplate

因为RestTemplate是Spirng框架提供的所以只要是一个Springboot项目就不用考虑导包的问题，这些都是提供好的。

但是Spring并没有将其加入SpringBean容器中，需要我们手动加入，因为我们首先创建一个Springboot配置类，再在配置类中将我们的RestTemlate注册到Bean容器中

方法一

使用Springboot提供的RestTemplateBuilder构造类来构造一个RestTemplate，可以自定义一些连接参数，如：连接超时时间，读取超时时间，还有认证信息等

@Configuration
public class WebConfiguration {
    @Bean
    public RestTemplate restTemplate(RestTemplateBuilder builder){
        return builder
                //设置连接超时时间
                .setConnectTimeout(Duration.ofSeconds(5000))
                //设置读取超时时间
                .setReadTimeout(Duration.ofSeconds(5000))
                //设置认证信息
                .basicAuthentication("username","password")
                //设置根路径
                .rootUri("https://api.test.com/")
                //构建
                .build();
    }
}

添加自定义的拦截器

自定义拦截器示例

• @Slf4j public class CustomClientHttpRequestInterceptor implements ClientHttpRequestInterceptor {     @Override     public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {      <span class="token comment">//打印请求明细</span>     <span class="token function">logRequestDetails</span><span class="token punctuation">(</span>request<span class="token punctuation">,</span>body<span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">ClientHttpResponse</span> response <span class="token operator">=</span> execution<span class="token punctuation">.</span><span class="token function">execute</span><span class="token punctuation">(</span>request<span class="token punctuation">,</span> body<span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token comment">//打印响应明细</span>     <span class="token function">logResponseDetails</span><span class="token punctuation">(</span>response<span class="token punctuation">)</span><span class="token punctuation">;</span>      <span class="token keyword">return</span> response<span class="token punctuation">;</span> <span class="token punctuation">}</span>  <span class="token keyword">private</span> <span class="token keyword">void</span> <span class="token function">logRequestDetails</span><span class="token punctuation">(</span><span class="token class-name">HttpRequest</span> request<span class="token punctuation">,</span> <span class="token keyword">byte</span><span class="token punctuation">[</span><span class="token punctuation">]</span> body<span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>     log<span class="token punctuation">.</span><span class="token function">debug</span><span class="token punctuation">(</span><span class="token string">"Headers:{}"</span><span class="token punctuation">,</span>request<span class="token punctuation">.</span><span class="token function">getHeaders</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     log<span class="token punctuation">.</span><span class="token function">debug</span><span class="token punctuation">(</span><span class="token string">"body:{}"</span><span class="token punctuation">,</span><span class="token keyword">new</span> <span class="token class-name">String</span><span class="token punctuation">(</span>body<span class="token punctuation">,</span> <span class="token class-name">StandardCharsets</span><span class="token punctuation">.</span>UTF_8<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     log<span class="token punctuation">.</span><span class="token function">debug</span><span class="token punctuation">(</span><span class="token string">"{}:{}"</span><span class="token punctuation">,</span>request<span class="token punctuation">.</span><span class="token function">getMethod</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span>request<span class="token punctuation">.</span><span class="token function">getMethodValue</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>  <span class="token keyword">private</span> <span class="token keyword">void</span> <span class="token function">logResponseDetails</span><span class="token punctuation">(</span><span class="token class-name">ClientHttpResponse</span> response<span class="token punctuation">)</span> <span class="token keyword">throws</span> <span class="token class-name">IOException</span> <span class="token punctuation">{<!-- --></span>     log<span class="token punctuation">.</span><span class="token function">debug</span><span class="token punctuation">(</span><span class="token string">"Status code : {}"</span><span class="token punctuation">,</span>response<span class="token punctuation">.</span><span class="token function">getStatusCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     log<span class="token punctuation">.</span><span class="token function">debug</span><span class="token punctuation">(</span><span class="token string">"Status text : {}"</span><span class="token punctuation">,</span>response<span class="token punctuation">.</span><span class="token function">getStatusText</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     log<span class="token punctuation">.</span><span class="token function">debug</span><span class="token punctuation">(</span><span class="token string">"Headers : {}"</span><span class="token punctuation">,</span>response<span class="token punctuation">.</span><span class="token function">getHeaders</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     log<span class="token punctuation">.</span><span class="token function">debug</span><span class="token punctuation">(</span><span class="token string">"Response body: {}"</span><span class="token punctuation">,</span> <span class="token class-name">StreamUtils</span><span class="token punctuation">.</span><span class="token function">copyToString</span><span class="token punctuation">(</span>response<span class="token punctuation">.</span><span class="token function">getBody</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">,</span><span class="token class-name">StandardCharsets</span><span class="token punctuation">.</span>UTF_8<span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>}
   使用`RestTemplateBuilder`构造类，添加自定义拦截器，构造带有自定义拦截器的`RestTemplate`实例
  
  @Configuration public class WebConfiguration {  <span class="token annotation punctuation">@Bean</span> <span class="token keyword">public</span> <span class="token class-name">RestTemplate</span> <span class="token function">restTemplate</span><span class="token punctuation">(</span><span class="token class-name">RestTemplateBuilder</span> builder<span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>     <span class="token keyword">return</span> builder             <span class="token punctuation">.</span><span class="token function">additionalInterceptors</span><span class="token punctuation">(</span><span class="token keyword">new</span> <span class="token class-name">CustomClientHttpRequestInterceptor</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span>             <span class="token comment">//构建</span>             <span class="token punctuation">.</span><span class="token function">build</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>    }
  
  - 11
  
   测试请求确实经过了拦截器，注册成功（注意请求和响应的流只会被读取一次，这里我们读取了response后返回的response就读取不到刚刚读过的内容了）
  
   ![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/a56513281ea8934d77357484a87f3532.png)
  
  ------
  
  #### 方法二
  
   使用`RestTemplate`构造方法构造一个`RestTemlate`，虽然不能像`RestTemplate`构造类那样更详细、更多样的配置参数，但是`RestTemplate`构造方法在一般情况是够用的。
  
  ![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/91ad85473e90723be1d0d927398bf495.png)
  
  - 无参构造 全部参数默认
  
  - 指定
  ClientHttpRequestFactory
   
  
  的构造方法可以指定自己实现的
  ClientHttpRequestFactory
  （客户端
  http
    请求工厂）其他的与无参构造相同。
  
    - `ClientHttpRequestFactory`
  
  - 指定`List<HttpMessageConverter<?>>`的构造方法可以指定自己是实现的`HttpMessageConverter`（`Http`消息转换器）传入其他与无参构造相同。
  
  @Configuration public class WebConfiguration {  <span class="token annotation punctuation">@Bean</span> <span class="token keyword">public</span> <span class="token class-name">RestTemplate</span> <span class="token function">restTemplate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{<!-- --></span>     <span class="token keyword">return</span> <span class="token keyword">new</span> <span class="token class-name">RestTemplate</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>}
  
  ------
  
   两者方法都可使用，前者提供了多样的自定义参数的选择，可以将`RestTemplate`配置的更为完善，后者则简化了配置虽然配置多样性不如前者，但是日常使用调用些`API`还是足以使用
  
  ### `RestTemplate API`使用
  
   在使用`RestTemplate`前先让我们看看`RestTemplate`有哪些`API`
  
  ![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/99611aa7f0e2775b470ec35701bf9b90.png)![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/6ff76f2d0a9f01cb9986069f307b0fcf.png)
  
   相信大家看到这么多方法，一定很头大，但是我们仔细看上述的方法，我们可以提取出主要的几种方法是(这里只讨论Http请求的)：
  
  - **`GET`**
  - **`POST`**
  - **`PUT`**
  - **`DELETE`**
  - **`HEAD`**
  - **`OPTIONS`**
  - **`EXCHANGE`**
  - **`EXECUTE`**
  
   **这里我给大家安利一个一个网站，它提供免费的RESTFul api的样例测试。**[httpbin A simple HTTP Request & Response Service.](http://httpbin.org/)
  
  ------
  
  #### GET
  
   通过上图我们可以发现`RestTemlate`发送`GET`请求的方法有两种
  
  > - `public <T> T getForObject(...)`
  > - `public <T> ResponseEntity<T> getForEntity(...)`
  
  ##### `getForEntity()`
  
   后缀带有`Entity`的方法都代表返回一个`ResponseEntity<T>`，`ResponseEntity<T>`是Spring对`HTTP`请求响应的封装，包括了几个重要的元素，如响应码，`contentType、contentLength`、响应消息体等
  
  ![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/9ed533f6f639df2da3f34587f44b865a.png)
  
   通过它继承父类(`HttpEntity<T>`)的`getHeader()`方法我们可以获取`contentType、contentLength`、响应消息体等。比如下面这个例子。
  
  public void queryWeather() {      <span class="token class-name">ResponseEntity</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">Object</span><span class="token punctuation">&gt;</span></span> forEntity <span class="token operator">=</span> restTemplate<span class="token punctuation">.</span><span class="token function">getForEntity</span><span class="token punctuation">(</span><span class="token string">"https://restapi.amap.com/v3/weather/weatherInfo?city=510100&amp;key=e7a5fa943f706602033b6b329c49fbc6"</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"状态码:"</span><span class="token operator">+</span>forEntity<span class="token punctuation">.</span><span class="token function">getStatusCode</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"状态码内容:"</span><span class="token operator">+</span>forEntity<span class="token punctuation">.</span><span class="token function">getStatusCodeValue</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">HttpHeaders</span> headers <span class="token operator">=</span> forEntity<span class="token punctuation">.</span><span class="token function">getHeaders</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"响应头:"</span><span class="token operator">+</span>headers<span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">Object</span> body <span class="token operator">=</span> forEntity<span class="token punctuation">.</span><span class="token function">getBody</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span><span class="token string">"响应内容:"</span><span class="token operator">+</span>body<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>
  
  - 
  
   该例子中`getForEntity()`方法的第一个参数为我要调用服务的`URL`，第二个参数则为响应内容的类的类型（Java嘛 万物皆对象）还可以添加第三个参数，第三个参数为一个可变参数 代表着调用服务时的传参。
  
  ![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/35bcf9bd26d4d7ff748139299a99cf0a.png) **第三个参数可以使用key-value的map来传入参数**
  
   **get请求也可通过向在url上添加查询参数来发送带有请求的参数**
  
  ------
  
  ##### `getForObject()`
  
   相比于前者`getForEntity()`该方法则是，更偏向于直接获取响应内容的，因为他直接返回响应实体的`body`（响应内容），。比如下面这个例子
  
  public void queryWeather() {      <span class="token class-name">Object</span> body <span class="token operator">=</span> restTemplate<span class="token punctuation">.</span><span class="token function">getForObject</span><span class="token punctuation">(</span><span class="token string">"https://restapi.amap.com/v3/weather/weatherInfo?city=510100&amp;key=e7a5fa943f706602033b6b329c49fbc6"</span><span class="token punctuation">,</span> <span class="token class-name">Object</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>body<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>
  方法参数签名与`getForEntity()`基本一致。
  1
  ------
  
   当你只需要返回的响应内容时，使用`getForObject()`是一个很好的选择，但当你需要获得更详细的响应信息，如响应头中的信息，你就只能选择`getForEntity()`了。
  
  ------
  
  #### POST
  
   `POST`请求有如下三种方法
  
  > - `public URI postForLocation(...)`
  > - `public <T> T postForObject(...)`
  > - `public <T> ResponseEntity<T> postForEntity(...)`
  
   后两种用法与`GET`基本一致不做详细介绍，这里着重介绍`postForLocation()`
  
  ------
  
  ##### `postForEntity()`
  
   该方法有三个参数，第一个为调用服务的地址（URL）
  
   第二个参数表示上传的参数(json格式提交)
  
   第三个表示返回响应内容的具体类型
  
   第四个参数也用于指定参数（在URL中添加）
  @Override
    public void queryWeather() {
        User user = new User();
        user.setName("鲁大师");
        ResponseEntity<Object> objectResponseEntity = restTemplate.postForEntity("https://restapi.amap.com/v3/weather/weatherInfo?city=510100&key=e7a5fa943f706602033b6b329c49fbc6", user, Object.class);
        System.out.println("消息响应内容:"+objectResponseEntity.getBody());
    }
  1234567
  ------
  
  ##### `postForObject()`
  
   使用方法与`getForObject`类似只是多了一个传入对象参数（传入方式与`postForEntity()`相同）
  public void queryWeather() {
        User user = new User();
        user.setName("鲁大师");
        ResponseEntity<Object> objectResponseEntity = restTemplate.postForEntity("https://httpbin.org/post", user, Object.class);
        MediaType contentType = objectResponseEntity.getHeaders().getContentType();
        System.out.println(contentType);
        System.out.println("消息响应内容:"+objectResponseEntity.getBody());
    }
  12345678
  ------
  
  ##### `postForLocation()`
  
   `postForLocation`传参用法与前两者一致，只不过返回从实体变成了一个`URL`，因此它不需要指定返回响应内容的类型。
  public void queryWeather() {
        User user = new User();
        user.setName("鲁大师");
        URI uri = restTemplate.postForLocation("https://httpbin.org/post", user);
        System.out.println(uri);
    }
  123456
  这个只需要服务提供者返回一个 URI 即可，该`URI`返回值体现的是：用于提交完成数据之后的页面跳转，或数据提交完成之后的下一步数据操作`URI`。
  
  ##### 使用POST以表单方式提交
  
   这里我们着重说一下，如何自己封装一个请求体。
  
   我们需要用到如下几个类
  
  > - `HttpHeaders`
  > - `MultiValueMap<K,V>`
  > - `HttpEntity<T>`
  
  ###### `HttpHeaders`
  
   故名思意，就是用来封装Http请求的请求头的，这里我们要设置他的`ContentType`为**`MediaType.APPLICATION_FORM_URLENCODED`**以使得我们提交的参数是以Form(表单)的形式提交。
  //设置请求头, x-www-form-urlencoded格式的数据
        HttpHeaders httpHeaders = new HttpHeaders();
        //这里指定参数以UTF-8编码格式传输
        MediaType mediaType = new MediaType(MediaType.APPLICATION_FORM_URLENCODED, UTF_8);
        httpHeaders.setContentType(mediaType);
        //提交参数设置
        MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
        map.add("name","鲁大师");
  

12345678

------

###### `MultiValueMap<K,V>`

 该类是用来封装请求参数的，是以`key-value`的形式封装但是以单个key对应多个value的格式传输(也就是是以单个`key:[value...]`的格式传输的)。

//提交参数设置
MultiValueMap<String, String> map = new LinkedMultiValueMap<>();
map.add(“name”,”鲁大师”);
123

 **如果像传输单个`key`对应单个`value`使用普通的`Map`传参即可**

------

###### `HttpEntity<T>`

 该类是用来封装请求的，主要作用就是将请求头和请求体封装在一起成为一个请求实体 T用来指定用来封装参数的容器的类型。

//组装请求体
HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(map, httpHeaders);
12

------

###### 测试

通过上述介绍后，我们就可以自己封装一个以form形式提交参数的`POST`请求了。

@Test     void contextLoads() {         //请求地址         String url = "https://httpbin.org/post";      <span class="token comment">//设置请求头, x-www-form-urlencoded格式的数据</span>     <span class="token class-name">HttpHeaders</span> httpHeaders <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HttpHeaders</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     httpHeaders<span class="token punctuation">.</span><span class="token function">setContentType</span><span class="token punctuation">(</span><span class="token class-name">MediaType</span><span class="token punctuation">.</span>APPLICATION_FORM_URLENCODED<span class="token punctuation">)</span><span class="token punctuation">;</span>      <span class="token comment">//提交参数设置</span>     <span class="token class-name">MultiValueMap</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">String</span><span class="token punctuation">&gt;</span></span> map <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">LinkedMultiValueMap</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     map<span class="token punctuation">.</span><span class="token function">add</span><span class="token punctuation">(</span><span class="token string">"name"</span><span class="token punctuation">,</span><span class="token string">"鲁大师"</span><span class="token punctuation">)</span><span class="token punctuation">;</span>      <span class="token comment">//组装请求体</span>     <span class="token class-name">HttpEntity</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token class-name">MultiValueMap</span><span class="token punctuation">&lt;</span><span class="token class-name">String</span><span class="token punctuation">,</span> <span class="token class-name">String</span><span class="token punctuation">&gt;</span><span class="token punctuation">&gt;</span></span> request <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token class-name">HttpEntity</span><span class="token generics"><span class="token punctuation">&lt;</span><span class="token punctuation">&gt;</span></span><span class="token punctuation">(</span>map<span class="token punctuation">,</span> httpHeaders<span class="token punctuation">)</span><span class="token punctuation">;</span>       <span class="token comment">//发送post请求并打印结果 以String类型接收响应结果JSON字符串</span>     <span class="token class-name">String</span> s <span class="token operator">=</span> restTemplate<span class="token punctuation">.</span><span class="token function">postForObject</span><span class="token punctuation">(</span>url<span class="token punctuation">,</span> request<span class="token punctuation">,</span> <span class="token class-name">String</span><span class="token punctuation">.</span><span class="token keyword">class</span><span class="token punctuation">)</span><span class="token punctuation">;</span>     <span class="token class-name">System</span><span class="token punctuation">.</span>out<span class="token punctuation">.</span><span class="token function">println</span><span class="token punctuation">(</span>s<span class="token punctuation">)</span><span class="token punctuation">;</span> <span class="token punctuation">}</span>

![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/6a5782b6482195903fcd0865b1fd5c17.png)

 通过拦截器拦截了请求并对请求头进行拆包，可以发现`ContentType`已经被修改成了`x-www-form-urlencoded`格式了。

#### PUT

 `PUT`请求的方法只有一类

> - `void put()`

##### `PUT()`

 使用方法与`postForEntity()`参数基本一致，只是`put`方法没有返回值（也就不必去设置响应内容的类型了）。

@Test
void contextLoads() {
//请求地址
String url = “http://httpbin.org/put“;
User user = new User();
user.setName(“鲁大师”);
restTemplate.put(url,user);
}

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------

#### DELETE

 与`PUT`一样，`DELETE`方法只有一类

> - `void delete()`

##### `delete()`

 `delete()`可以指定`url`中的中的参数，但是`RestTemplate`的`delete()`方法是不支持上传`requestBody`的。

void contextLoads() {
//请求地址
String url = “http://httpbin.org/delete“;
restTemplate.delete(url);
}
12345

------

#### HEADER

 `HEADER`也只有一类方法

> - `public HttpHeaders headForHeaders()`

 主要用来发送请求获取响应头部信息，但是像`DELETE`、`PUT`这类没有响应的方法，是不能使用该方法的（因为没有响应也就没有响应头了）。

@Test
void contextLoads() {
//请求地址
String url = “http://httpbin.org/get“;
HttpHeaders httpHeaders = restTemplate.headForHeaders(url);
System.out.println(httpHeaders);
}
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![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/2920645602cbb64f76f1197d4d0bd373.png)

------

#### OPTIONS

> - `public Set<HttpMethod> optionsForAllow()`

 该方法的主要用来判断该服务地址，能够使用那种方法去执行

@Test
void contextLoads() {
    //请求地址
    String url = "http://httpbin.org/get";
    Set<HttpMethod> httpMethods = restTemplate.optionsForAllow(url);
    System.out.println(httpMethods);
}

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![img](https://gitee.com/jacksonzhang1014/blog-image/raw/master/2da18056f390295ed8747d0a86770ced.png)

------

#### EXCHANGE

> - `<T> ResponseEntity<T> exchange()`

 该接口与其他接口不同

> - 该方法允许用户指定请求的方法（`get,post,put`等）
> - 可以在请求中增加body以及头信息，其内容通过参数`HttpEntity<?> requestEntity`描述
> - `exchange`支持’含参数的类型(即泛型)'作为返回类型，该特性通过`ParameterizedTypeReferenceresponseType` 描述

 该方法支持五个参数

> - 第一个是服务地址
> - 第二个是请求方法
> - 第三个是写入的请求实体
> - 第四个是响应内容的类型
> - 第五个是扩展模板的变量或包含`URI`模板变量的映射

@Test
void contextLoads() {
//请求地址
String url = “http://httpbin.org/post“;
User user = new User();
user.setName(“彭于晏”);
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.setContentType(MediaType.APPLICATION_JSON);
HttpEntity userHttpEntity = new HttpEntity<>(user, httpHeaders);
ResponseEntity