标签：请求 url spring restTemplate Dog ResponseEntity new throws

1，引言

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！
传统情况下，在服务端代码里访问 http 服务时，一般会使用 JDK 的 HttpURLConnection 或者 Apache 的 HttpClient，不过这种方法使用起来太过繁琐，而且 api 使用起来非常的复杂，还得操心资源回收。

RestTemplate是一个执行HTTP请求的同步阻塞式工具类，它仅仅只是在 HTTP 客户端库（例如 JDK HttpURLConnection，Apache HttpComponents，okHttp 等）基础上，封装了更加简单易用的模板方法 API，方便程序员利用已提供的模板方法发起网络请求和处理，能很大程度上提升我们的开发效率

2，环境配置

1，Spring 环境下

RestTemplate 在 spring-web 包中，需要引入

<dependency>
  <groupId>org.springframework</groupId>
  <artifactId>spring-web</artifactId>
  <version>5.2.6.RELEASE</version>
</dependency>

2，SpringBoot 环境下

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

从 spring 某个版本开始，默认不生成 RestTemplate bean，需要我们自己注入

@Configuration
public class RestTemplateConfig {
    /**
     * 没有实例化RestTemplate时，初始化RestTemplate
     * @return
     */
    @ConditionalOnMissingBean(RestTemplate.class)
    @Bean
    public RestTemplate restTemplate(){
        RestTemplate restTemplate = new RestTemplate();
        return restTemplate;
    }
}

3，RestTemplate 底层实现

1. 源码分析

RestTemplate 有一个非常重要的基类叫做 HttpAccessor，可以理解为用于HTTP接触访问的基础类。

总结：

RestTemplate 支持至少三种HTTP客户端库，也就是 ClientHttpRequestFactory 的子类。
- SimpleClientHttpRequestFactory。对应的HTTP库是java JDK自带的HttpURLConnection。
- HttpComponentsAsyncClientHttpRequestFactory。对应的HTTP库是Apache HttpComponents。
- OkHttp3ClientHttpRequestFactory。对应的HTTP库是OkHttp
java JDK自带的HttpURLConnection是默认的底层HTTP实现客户端
SimpleClientHttpRequestFactory，即java JDK自带的HttpURLConnection不支持HTTP协议的Patch方法，如果希望使用Patch方法，需要将底层HTTP客户端实现切换为Apache HttpComponents 或 OkHttp
可以通过设置 setRequestFactory 方法，来切换 RestTemplate 的底层HTTP客户端实现类库。

2. 切换底层实现方法

1. 切换为 OKHttp

<!-- https://mvnrepository.com/artifact/com.squareup.okhttp3/okhttp -->
<dependency>
    <groupId>com.squareup.okhttp3</groupId>
    <artifactId>okhttp</artifactId>
    <version>3.12.0</version>
</dependency>

@Bean
public RestTemplate restTemplate(){
    RestTemplate restTemplate = new RestTemplate(getClientHttpRequestFactory());
    return restTemplate;
}

private ClientHttpRequestFactory getClientHttpRequestFactory(){
    OkHttpClient okHttpClient = new OkHttpClient.Builder()
            .connectTimeout(5, TimeUnit.SECONDS)
            .writeTimeout(5, TimeUnit.SECONDS)
            .readTimeout(5, TimeUnit.SECONDS)
            .build();
    return new OkHttp3ClientHttpRequestFactory(okHttpClient);
}

要注意一下版本。

2. 切换为 Apache HttpClient

<!-- https://mvnrepository.com/artifact/org.apache.httpcomponents/httpclient -->
<dependency>
    <groupId>org.apache.httpcomponents</groupId>
    <artifactId>httpclient</artifactId>
    <version>4.5.10</version>
</dependency>

@Bean
public RestTemplate restTemplate(){
    RestTemplate restTemplate = new RestTemplate(getClientHttpRequestFactory());
    return restTemplate;
}

/**
 * 使用 appach 的 HttpClient 作为底层客户端
 * @return
 */
private ClientHttpRequestFactory getClientHttpRequestFactory() {
    int timeout = 1_000;
    RequestConfig config = RequestConfig.custom()
            .setConnectTimeout(timeout)
            .setConnectionRequestTimeout(timeout)
            .setSocketTimeout(timeout)
            .build();
    CloseableHttpClient client = HttpClientBuilder
            .create()
            .setDefaultRequestConfig(config)
            .build();
    return new HttpComponentsClientHttpRequestFactory(client);
}

据说 OkHttp > Apache HttpComponents > HttpURLConnection

4. 拦截器设置

1. 定义一个拦截器

public class RestTemplateInterceptor implements ClientHttpRequestInterceptor {
    @Override
    public ClientHttpResponse intercept(HttpRequest request, byte[] body, ClientHttpRequestExecution execution) throws IOException {
        System.out.println("拦截器！！！");
        ClientHttpResponse response = execution.execute(request, body);
        return response;
    }
}

2. 给 restTemplate 设置拦截器

@Bean
public RestTemplate restTemplate(){
    RestTemplate restTemplate = new RestTemplate(getClientHttpRequestFactory());

    restTemplate.setInterceptors(Collections.singletonList(new RestTemplateInterceptor()));

    return restTemplate;
}

5. RestTemplate Api

1. get 请求

getForObject()：返回值是HTTP协议的响应体内容
getForEntity()：返回的是ResponseEntity，ResponseEntity是对HTTP响应的封装，除了包含响应体，还包含HTTP状态码、contentType、contentLength、Header等信息

getForObject 方法

<T> T getForObject(URI url, Class<T> responseType) throws RestClientException;
/** url 请求路径，responseType 返回类型，uriVariables URL 上参数 */
<T> T getForObject(String url, Class<T> responseType, Object... uriVariables) throws RestClientException;
/** url 请求路径，responseType 返回类型，uriVariables 请求参数*/
<T> T getForObject(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;

/**
 * 无参
 * */
Dog dog = restTemplate.getForObject(url + "/get", Dog.class);
System.out.println(dog);

/**
 * path 参数
 * */
Dog dog1 = restTemplate.getForObject(url + "/get/path/{code}", Dog.class, "不太聪明");
System.out.println(dog1);

/**
 * restful 参数
 * */
Map<String, Object> map = new HashMap<>();
map.put("name", "张飞");
map.put("color", "green");
Dog dog2 = restTemplate.getForObject(url + "/get/restful?name={name}&color={color}", Dog.class, map);
System.out.println(dog2);

getForEntity 方法

//无参
<T> ResponseEntity<T> getForEntity(URI url, Class<T> responseType) throws RestClientException;
//路径参数
<T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... uriVariables) throws RestClientException;
//restful 参数
<T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;

/**
 * 无参
 * */
ResponseEntity<Dog> res = restTemplate.getForEntity(url + "/get", Dog.class);
System.out.println( res.getStatusCode());
System.out.println( res.getBody() );

/**
 * path 参数
 * */
ResponseEntity<Dog> res1 = restTemplate.getForEntity(url + "/get/path/{code}", Dog.class, "不太聪明");
System.out.println( res1.getStatusCode());
System.out.println( res1.getBody() );

/**
 * restful 参数
 * */
Map<String, Object> map = new HashMap<>();
map.put("name", "张飞");
map.put("color", "green");
ResponseEntity<Dog> res2 = restTemplate.getForEntity(url + "/get/restful?name={name}&color={color}", Dog.class, map);
System.out.println( res2.getStatusCode());
System.out.println( res2.getBody() );

2. post 请求

postForObject()：返回值是HTTP协议的响应体body内容
postForEntity()：返回的是ResponseEntity，ResponseEntity是对HTTP响应的封装，除了包含响应体，还包含HTTP状态码、contentType、contentLength、Header等信息
postForLocation：使用POST创建一个新资源，返回UTI对象，可以从响应中返回Location报头。

postForObject 方法

/** url 请求路径，request 请求体，responseType 返回类型 */
<T> T postForObject(URI url, @Nullable Object request, Class<T> responseType) throws RestClientException;
/** uriVariables 路劲里的参数 */
<T> T postForObject(String url, @Nullable Object request, Class<T> responseType,
			Object... uriVariables) throws RestClientException;
/** uriVariables 请求参数 */
<T> T postForObject(String url, @Nullable Object request, Class<T> responseType,
			Map<String, ?> uriVariables) throws RestClientException;

/**
 * 无参
 * */
Dog dog = restTemplate.postForObject(url + "/api", null, Dog.class);
System.out.println(dog);

/**
 * path 参数
 * */
Dog dog1 = restTemplate.postForObject(url + "/api/path/{code}", null, Dog.class, "不太聪明");
System.out.println(dog1);

/**
 * 表单 参数 表单参数(专用map)
 * */
MultiValueMap<String,String> map = new LinkedMultiValueMap<>();
map.add("name", "张飞");
map.add("color", "green");

HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.setContentType(MediaType.APPLICATION_FORM_URLENCODED);

HttpEntity<MultiValueMap<String,String>> requestEntity = new HttpEntity<>(map,httpHeaders);
Dog dog2 = restTemplate.postForObject(url + "/api/restful", requestEntity, Dog.class);
System.out.println(dog2);

/**
 * json
 * */
Dog d = new Dog("李白", "得瑟");
Dog dog3 = restTemplate.postForObject(url + "/api/json", d, Dog.class);
System.out.println(dog3);

postForEntity 方法

/** url 请求路径，request 请求体，responseType 返回类型 */
<T> ResponseEntity<T> postForEntity(URI url, @Nullable Object request, Class<T> responseType)
			throws RestClientException;
/** uriVariables 路劲里的参数 */
<T> ResponseEntity<T> postForEntity(String url, @Nullable Object request, Class<T> responseType,
			Object... uriVariables) throws RestClientException;
/** uriVariables 请求参数 */
<T> ResponseEntity<T> postForEntity(String url, @Nullable Object request, Class<T> responseType,
			Map<String, ?> uriVariables) throws RestClientException;

/**
 * 无参
 * */
ResponseEntity<Dog> entity = restTemplate.postForEntity(url + "/api", null, Dog.class);
System.out.println(entity.getBody());

/**
 * path 参数
 * */
ResponseEntity<Dog> entity1 = restTemplate.postForEntity(url + "/api/path/{code}", null, Dog.class, "不太聪明");
System.out.println(entity1.getBody());

/**
 * 表单 参数
 * */
//表单参数(专用map)
MultiValueMap<String,String> map = new LinkedMultiValueMap<String,String>();
map.add("name", "张飞");
map.add("color", "green");

HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
HttpEntity<MultiValueMap<String,String>> requestEntity = new HttpEntity<>(map,httpHeaders);
ResponseEntity<Dog> entity2 = restTemplate.postForEntity(url + "/api/restful", requestEntity, Dog.class);
System.out.println(entity2.getBody());

/**
 * json
 * */
Dog d = new Dog("李白", "得瑟");
ResponseEntity<Dog> entity3 = restTemplate.postForEntity(url + "/api/json", d, Dog.class);
System.out.println(entity3.getBody());

/**
 * json 封装请求体
 * */
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
ResponseEntity<Dog> entity4 = restTemplate.postForEntity(url + "/api/json", new HttpEntity<>(d,headers), Dog.class);
System.out.println(entity4.getBody());

3. exchange 请求

exchange 通用请求类型方法，可以自己组装各种各样的请求。

/**
 * url 请求地址
 * method 请求方式，get、post 等
 * requestEntity 请求体
 * responseType 返回类型
 * uriVariables 路径中的参数
 */
<T> ResponseEntity<T> exchange(String url, HttpMethod method, @Nullable HttpEntity<?> requestEntity,
            Class<T> responseType, Object... uriVariables) throws RestClientException;
/**
 * uriVariables 请求参数
 */
<T> ResponseEntity<T> exchange(String url, HttpMethod method, @Nullable HttpEntity<?> requestEntity,
            Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException;
<T> ResponseEntity<T> exchange(URI url, HttpMethod method, @Nullable HttpEntity<?> requestEntity,
            Class<T> responseType) throws RestClientException;
<T> ResponseEntity<T> exchange(String url,HttpMethod method, @Nullable HttpEntity<?> requestEntity,
            ParameterizedTypeReference<T> responseType, Object... uriVariables) throws RestClientException;
/**
 * responseType 返回 List<T> 这种类型的时候，要用这个， Class<T> 表示不了
 */
<T> ResponseEntity<T> exchange(String url, HttpMethod method, @Nullable HttpEntity<?> requestEntity,
            ParameterizedTypeReference<T> responseType, Map<String, ?> uriVariables) throws RestClientException;
<T> ResponseEntity<T> exchange(URI url, HttpMethod method, @Nullable HttpEntity<?> requestEntity,
            ParameterizedTypeReference<T> responseType) throws RestClientException;
<T> ResponseEntity<T> exchange(RequestEntity<?> requestEntity, Class<T> responseType)
            throws RestClientException;
<T> ResponseEntity<T> exchange(RequestEntity<?> requestEntity, ParameterizedTypeReference<T> responseType)
            throws RestClientException;

//无参
ResponseEntity<Dog> e1 = restTemplate.exchange(url + "/api", HttpMethod.GET, null, Dog.class);
System.out.println( e1.getBody() );

//path 参数
ResponseEntity<Dog> e2 = restTemplate.exchange(url + "/api/path/{code}", HttpMethod.GET, null, Dog.class, "啥子");
System.out.println( e2.getBody() );

//表单参数
MultiValueMap<String,String> map = new LinkedMultiValueMap<String,String>();
map.add("name", "张飞");
map.add("color", "green");
HttpHeaders httpHeaders = new HttpHeaders();
httpHeaders.setContentType(MediaType.APPLICATION_FORM_URLENCODED);
HttpEntity<MultiValueMap<String,String>> requestEntity = new HttpEntity<>(map,httpHeaders);
ResponseEntity<Dog> e3 = restTemplate.exchange(url + "/api/restful", HttpMethod.POST, requestEntity, Dog.class);
System.out.println(e3.getBody());

//json 参数
Dog d1 = new Dog("尸鬼", "李贺");
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
HttpEntity<Dog> dogHttpEntity = new HttpEntity<>(d1, headers);
ResponseEntity<Dog> e4 = restTemplate.exchange(url + "/api/json", HttpMethod.POST, dogHttpEntity, Dog.class);
System.out.println(e4.getBody());

//返回结果是 list<T> 这种格式
ResponseEntity<List<Dog>> e5 = restTemplate.exchange(url + "/api/list", HttpMethod.GET, null, new ParameterizedTypeReference<List<Dog>>() {
    @Override
    public Type getType() {
        return super.getType();
    }
});
System.out.println( e5.getBody() );

4. 文件上传下载

@RequestMapping("/file/upload")
public void fileDemo(){

    // 请求头设置,multipart/form-data格式的数据
    HttpHeaders headers = new HttpHeaders();
    headers.setContentType(MediaType.MULTIPART_FORM_DATA);

    //提交参数
    String path = "C:\\Users\\admin\\Desktop\\local-file\\jsStream.js";
    MultiValueMap<String, Object> param = new LinkedMultiValueMap<>();
    param.add("file", new FileSystemResource(new File(path)));
    param.add("name", "小三子");

    // 组装请求体
    HttpEntity<MultiValueMap<String, Object>> request = new HttpEntity<>(param, headers);

    ResponseEntity<Dog> exchange = restTemplate.postForEntity("http://localhost:8080/file/upload",  request, null);
    System.out.println(exchange.getStatusCode());

}

/**
 * 下载
 * */
@RequestMapping("/file/download")
public void fileDemo1() throws IOException {
    //发起请求（响应内容为字节文件）
    ResponseEntity<byte[]> response = restTemplate.getForEntity("http://localhost:8080/file/download", byte[].class);
    System.out.println( response.getStatusCode() );

    Files.write(Paths.get( "C:\\Users\\admin\\Desktop\\local-file\\dd"), response.getBody() );
}

上述文件下载的方式，是一次性将响应内容加载到客户端内存中，然后再从内存中将文件写入到磁盘中，这种方式适用于一些小文件的下载。如果遇到大的文件，可能会爆内存。之后我们使用 execute 方法处理。

5. execute 方法

其内部调用的 doExecute 方法，是几乎所有方法最终的走向

/** requestCallback 对请求的处理，responseExtractor 对响应的处理 */
<T> T execute(URI url, HttpMethod method, @Nullable RequestCallback requestCallback,
			@Nullable ResponseExtractor<T> responseExtractor) throws RestClientException;
<T> T execute(String url, HttpMethod method, @Nullable RequestCallback requestCallback,
			@Nullable ResponseExtractor<T> responseExtractor, Map<String, ?> uriVariables)
			throws RestClientException;
<T> T execute(String url, HttpMethod method, @Nullable RequestCallback requestCallback,
        	@Nullable ResponseExtractor<T> responseExtractor, Object... uriVariables)
			throws RestClientException;

doExecute 方法源码：

@Nullable
protected <T> T doExecute(URI url, @Nullable HttpMethod method, @Nullable RequestCallback requestCallback, @Nullable ResponseExtractor<T> responseExtractor) throws RestClientException {
    	Assert.notNull(url, "URI is required");
        Assert.notNull(method, "HttpMethod is required");
        ClientHttpResponse response = null;

        Object var14;
        try {
            //1.生成请求
            ClientHttpRequest request = this.createRequest(url, method);
            if (requestCallback != null) {
                //2.设置header
                requestCallback.doWithRequest(request);
            }
			//3.执行请求
            response = request.execute();
            //4.处理响应
            this.handleResponse(url, method, response);
            //5.返回执行结果
            var14 = responseExtractor != null ? responseExtractor.extractData(response) : null;
        } catch (IOException var12) {
            String resource = url.toString();
            String query = url.getRawQuery();
            resource = query != null ? resource.substring(0, resource.indexOf(63)) : resource;
            throw new ResourceAccessException("I/O error on " + method.name() + " request for \"" + resource + "\": " + var12.getMessage(), var12);
        } finally {
            if (response != null) {
                response.close();
            }

        }

        return var14;
}

此方法并没有对外暴露，只能通过继承调用。可以看到我们每次请求的时候内部会发生这几个步骤：

生成请求
设置header
执行请求
处理响应
返回执行结果

RequestCallback 接口官方介绍

RequestCallback用于操作ClientHttpRequest的代码的回调接口。允许操作请求头，并写入请求体。

在RestTemplate内部使用，但对应用程序代码也很有用。有以下两个实现类:

AcceptHeaderRequestCallback：只处理请求头回调，用于restTemplate.getXXX()方法；
HttpEntityRequestCallback：继承AcceptHeaderRequestCallback，可以处理请求头和body，用于restTemplate.putXXX()、restTemplate.postXXX()和restTemplate.exchange()等方法。

ResponseExtractor 接口

响应提取器，主要就是用来从Response中提取数据。RestTemplate请求完成后，都是通过它来从ClientHttpResponse提取出指定内容，比如：请求头、请求body等。

ResponseExtractor有三个实现类：

HeadersExtractor：用于提取请求头
HttpMessageConverterExtractor：用于提取响应body体内容
ResponseEntityResponseExtractor：内部借助HttpMessageConverterExtractor提取body体（委托模式），然后将body和响应头、状态封装成ResponseEntity对象返回调用者。

下载大文件

/**
 * 下载
 * */
@RequestMapping("/file/download")
public void fileDemo1() throws Exception {

    //请求地址
    String url = "http://localhost:8080/file/download";

    //定义请求头的接收类型
    RequestCallback requestCallback = clientHttpRequest
            -> clientHttpRequest.getHeaders()
            .setAccept(Arrays.asList(MediaType.APPLICATION_OCTET_STREAM,MediaType.ALL));

    //下载文件保存路径
    File savePath = new File("C:\\Users\\admin\\Desktop\\local-file\\");
    if (!savePath.isDirectory()){
        savePath.mkdirs();
    }
    Path path = Paths.get(savePath.getPath() + File.separator + "ssss.zip");

    try {
        //对响应结果进行流式处理，而不是一次性将响应结果全部加载到内存
        restTemplate.execute(url, HttpMethod.GET, requestCallback,clientHttpResponse
                -> {
            //每响应一次就写入磁盘一次，不在内存中逗留
            Files.copy(Objects.requireNonNull(clientHttpResponse.getBody(),"下载文件失败！"), path);
            return null;
        });
    }catch (Exception e){
        throw new Exception("文件下载异常或已经存在！");
    }

}

参考文献

https://zhuanlan.zhihu.com/p/166214440
https://blog.csdn.net/qq_52596258/article/details/127604909

标签：请求,url,spring,restTemplate,Dog,ResponseEntity,new,throws
From： https://www.cnblogs.com/cnff/p/17864428.html

spring-restTemplate-网络请求