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WebClient使用
引言
Spring Framework 5 包括一个新的 spring-webflux 模块。该模块包含对响应式 HTTP 和 WebSocket 客户端的支持，以及对REST，HTML浏览器和 WebSocket风格交互的响应式服务器Web应用程序的支持。本文主要介绍WebClient的使用，包括通过WebClient请求接口及实现接口的文件上传下载。
1.引入依赖
在pom.xml中引入WebClient所需的依赖
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>
<dependency>
    <groupId>org.projectreactor</groupId>
    <artifactId>reactor-spring</artifactId>
    <version>1.0.1.RELEASE</version>
</dependency>

2.一个简单的请求示例
请求百度首页示例
// 1.创建WebClient实例
WebClient webClient = WebClient
                .builder()
                .baseUrl("https://www.baidu.com")
                .build();

// 2.通过通过retrieve()请求并获得响应
Mono<String> bodyToMono = webClient
                .get()
                .retrieve()
                // 将请求结果处理为String类型
                .bodyToMono(String.class);

log.info("请求返回的数据内容：{}", bodyToMono.block());

3.WebClient配置
在创建WebClient时可对一些变量进行默认设置
WebClient client3 = WebClient
  .builder()
    .baseUrl("http://localhost:8080")
    .defaultCookie("cookieKey", "cookieValue")
    .defaultHeader(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE) 
    .defaultUriVariables(Collections.singletonMap("url", "http://localhost:8080"))
  .build();

也可在发起请求时填入cookie、header等参数
webClient
  .get()
  .uri("https://www.baidu.com")
  .cookie("cookieKey", "cookieValue")
  .header(HttpHeaders.CONTENT_TYPE, MediaType.APPLICATION_JSON_VALUE)
  .retrieve();

4.在请求中传参
在日常使用中传递参数的方法
WebClient webClient = WebClient.create();
Mono<String> bodyToMono = webClient.post()
  .uri(uriBuilder ->
       uriBuilder
       .scheme("https")
       .host("localhost:8080")
       .path("/api/test")
       .queryParam("id", "123")
       .queryParam("invalid", "invalid123")
       .build()
      )
  // requestbody，也可以使用MultiValueMap<String, String> map = new LinkedMultiValueMap<>()，传入参数，发起form提交。或直接使用HashMap传参
  .syncBody(new Student())
  .retrieve()
  .bodyToMono(String.class);

5.设置连接超时时间
设置请求超时时间
TcpClient tcpClient = TcpClient
              .create()
              .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 5000)
              .doOnConnected(connection -> {
	connection.addHandlerLast(new ReadTimeoutHandler(5000, TimeUnit.MILLISECONDS));
	connection.addHandlerLast(new WriteTimeoutHandler(5000, TimeUnit.MILLISECONDS));
                });

WebClient client = WebClient.builder()
                .clientConnector(new ReactorClientHttpConnector(HttpClient.from(tcpClient)))
                .build();

6.文件上传
上传文件代码
HttpHeaders headers = new HttpHeaders();
headers.add("content-type", "application/x-www-form-urlencoded");
HttpEntity<ClassPathResource> entity = new HttpEntity<>(new ClassPathResource("a.txt"), headers);
MultiValueMap<String, Object> parts = new LinkedMultiValueMap<>();
parts.add("file", entity);
Mono<String> bodyToMono = WebClient.create().post()
        .uri("http://localhost:8080/upload")
        .contentType(MediaType.MULTIPART_FORM_DATA)
        .body(BodyInserters.fromMultipartData(parts))
        .retrieve().bodyToMono(String.class);

7.文件下载
通过将.retrieve()方法换成.exchange()，可以获取到响应的头信息、Cookie等信息，与restTemplate相似。
Mono<ClientResponse> responseMono = WebClient.create().get()
                .uri("http://localhost:8080/file/download")
                .accept(MediaType.APPLICATION_OCTET_STREAM)
                .exchange(); 
ClientResponse response = responseMono.block();
// 可从headers中获取filename等信息 
ClientResponse.Headers headers = response.headers();
Resource resource = response.bodyToMono(Resource.class).block();
// 获取文件流
InputStream inputStream = resource.getInputStream();

8.WebTestClient
The WebTestClient is the main entry point for testing WebFlux server endpoints. It has a very similar API to the WebClient, and it delegates most of the work to an internal WebClient instance focusing mainly on providing a test context. The DefaultWebTestClient class is a

single interface implementation.
主要意思是WebTestClient用于测试WebFlux服务器端点，他和WebClient相似，且将大部分工作委托给了内部的WebClient，主要用于测试上下文，此部分后期在单独整理。

spring 5 webclient使用指南

序

之前写了一篇restTemplate使用实例，由于spring 5全面引入reactive，同时也有了restTemplate的reactive版webclient，本文就来对应展示下webclient的基本使用。

请求携带header

携带cookie
    @Test
    public void testWithCookie(){
        Mono<String> resp = WebClient.create()
                .method(HttpMethod.GET)
                .uri("http://baidu.com")
                .cookie("token","xxxx")
                .cookie("JSESSIONID","XXXX")
                .retrieve()
                .bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());
    }

携带basic auth
    @Test
    public void testWithBasicAuth(){
        String basicAuth = "Basic "+ Base64.getEncoder().encodeToString("user:pwd".getBytes(StandardCharsets.UTF_8));
        LOGGER.info(basicAuth);
        Mono<String> resp = WebClient.create()
                .get()
                .uri("http://baidu.com")
                .header(HttpHeaders.AUTHORIZATION,basicAuth)
                .retrieve()
                .bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());
    }

设置全局user-agent
    @Test
    public void testWithHeaderFilter(){
        WebClient webClient = WebClient.builder()
                .defaultHeader(HttpHeaders.USER_AGENT, "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/63.0.3239.132 Safari/537.36")
                .filter(ExchangeFilterFunctions
                        .basicAuthentication("user","password"))
                .filter((clientRequest, next) -> {
                    LOGGER.info("Request: {} {}", clientRequest.method(), clientRequest.url());
                    clientRequest.headers()
                            .forEach((name, values) -> values.forEach(value -> LOGGER.info("{}={}", name, value)));
                    return next.exchange(clientRequest);
                })
                .build();
        Mono<String> resp = webClient.get()
                .uri("https://baidu.com")
                .retrieve()
                .bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());
    }

get请求

使用placeholder传递参数
    @Test
    public void testUrlPlaceholder(){
        Mono<String> resp = WebClient.create()
                .get()
                //多个参数也可以直接放到map中,参数名与placeholder对应上即可
                .uri("http://www.baidu.com/s?wd={key}&other={another}","北京天气","test") //使用占位符
                .retrieve()
                .bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());

    }

使用uriBuilder传递参数
    @Test
    public void testUrlBiulder(){
        Mono<String> resp = WebClient.create()
                .get()
                .uri(uriBuilder -> uriBuilder
                        .scheme("http")
                        .host("www.baidu.com")
                        .path("/s")
                        .queryParam("wd", "北京天气")
                        .queryParam("other", "test")
                        .build())
                .retrieve()
                .bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());
    }

post表单

    @Test
    public void testFormParam(){
        MultiValueMap<String, String> formData = new LinkedMultiValueMap<>();
        formData.add("name1","value1");
        formData.add("name2","value2");
        Mono<String> resp = WebClient.create().post()
                .uri("http://www.w3school.com.cn/test/demo_form.asp")
                .contentType(MediaType.APPLICATION_FORM_URLENCODED)
                .body(BodyInserters.fromFormData(formData))
                .retrieve().bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());
    }

post json

使用bean来post
static class Book {
        String name;
        String title;

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public String getTitle() {
            return title;
        }

        public void setTitle(String title) {
            this.title = title;
        }
    }

    @Test
    public void testPostJson(){
        Book book = new Book();
        book.setName("name");
        book.setTitle("this is title");
        Mono<String> resp = WebClient.create().post()
                .uri("http://localhost:8080/demo/json")
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .body(Mono.just(book),Book.class)
                .retrieve().bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());
    }

直接post raw json
    @Test
    public void testPostRawJson(){
        Mono<String> resp = WebClient.create().post()
                .uri("http://localhost:8080/demo/json")
                .contentType(MediaType.APPLICATION_JSON_UTF8)
                .body(BodyInserters.fromObject("{\n" +
                        "  \"title\" : \"this is title\",\n" +
                        "  \"author\" : \"this is author\"\n" +
                        "}"))
                .retrieve().bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());
    }

post二进制--上传文件

    @Test
    public void testUploadFile(){
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.IMAGE_PNG);
        HttpEntity<ClassPathResource> entity = new HttpEntity<>(new ClassPathResource("parallel.png"), headers);
        MultiValueMap<String, Object> parts = new LinkedMultiValueMap<>();
        parts.add("file", entity);
        Mono<String> resp = WebClient.create().post()
                .uri("http://localhost:8080/upload")
                .contentType(MediaType.MULTIPART_FORM_DATA)
                .body(BodyInserters.fromMultipartData(parts))
                .retrieve().bodyToMono(String.class);
        LOGGER.info("result:{}",resp.block());
    }

下载二进制

下载图片
    @Test
    public void testDownloadImage() throws IOException {
        Mono<Resource> resp = WebClient.create().get()
                .uri("http://www.toolip.gr/captcha?complexity=99&size=60&length=9")
                .accept(MediaType.IMAGE_PNG)
                .retrieve().bodyToMono(Resource.class);
        Resource resource = resp.block();
        BufferedImage bufferedImage = ImageIO.read(resource.getInputStream());
        ImageIO.write(bufferedImage, "png", new File("captcha.png"));

    }

下载文件
    @Test
    public void testDownloadFile() throws IOException {
        Mono<ClientResponse> resp = WebClient.create().get()
                .uri("http://localhost:8080/file/download")
                .accept(MediaType.APPLICATION_OCTET_STREAM)
                .exchange();
        ClientResponse response = resp.block();
        String disposition = response.headers().asHttpHeaders().getFirst(HttpHeaders.CONTENT_DISPOSITION);
        String fileName = disposition.substring(disposition.indexOf("=")+1);
        Resource resource = response.bodyToMono(Resource.class).block();
        File out = new File(fileName);
        FileUtils.copyInputStreamToFile(resource.getInputStream(),out);
        LOGGER.info(out.getAbsolutePath());
    }

错误处理

    @Test
    public void testRetrieve4xx(){
        WebClient webClient = WebClient.builder()
                .baseUrl("https://api.github.com")
                .defaultHeader(HttpHeaders.CONTENT_TYPE, "application/vnd.github.v3+json")
                .defaultHeader(HttpHeaders.USER_AGENT, "Spring 5 WebClient")
                .build();
        WebClient.ResponseSpec responseSpec = webClient.method(HttpMethod.GET)
                .uri("/user/repos?sort={sortField}&direction={sortDirection}",
                        "updated", "desc")
                .retrieve();
        Mono<String> mono = responseSpec
                .onStatus(e -> e.is4xxClientError(),resp -> {
                    LOGGER.error("error:{},msg:{}",resp.statusCode().value(),resp.statusCode().getReasonPhrase());
                    return Mono.error(new RuntimeException(resp.statusCode().value() + " : " + resp.statusCode().getReasonPhrase()));
                })
                .bodyToMono(String.class)
                .doOnError(WebClientResponseException.class, err -> {
                    LOGGER.info("ERROR status:{},msg:{}",err.getRawStatusCode(),err.getResponseBodyAsString());
                    throw new RuntimeException(err.getMessage());
                })
                .onErrorReturn("fallback");
        String result = mono.block();
        LOGGER.info("result:{}",result);
    }

可以使用onStatus根据status code进行异常适配
	
可以使用doOnError异常适配
	
可以使用onErrorReturn返回默认值
小结

webclient是新一代的async rest template，api也相对简洁，而且是reactive的，非常值得使用。

doc

restTemplate使用实例
	
Decode ByteArray with spring 5 WebFlux framework

   
         

//这里触发代码
              using (WebClient wc = new WebClient())//防止内存泄漏
                {
                    wc.DownloadDataCompleted += new DownloadDataCompletedEventHandler(DownloadDataCallback);
                    Uri uri = new Uri(“图片的下载地址”);
                    wc.DownloadDataAsync(uri);
                }




//异步的事件
     public void DownloadDataCallback(object sender, DownloadDataCompletedEventArgs e)
        {
            try
            {
                if (e.Result.Length > 0 && e.Error == null && e.Cancelled == false)
                {
                    byte[] buffer = e.Result;
                    using (MemoryStream ms = new MemoryStream(buffer))
                    {
                        Bitmap bitmap = new Bitmap(ms);//得到数据
                     //   pbMain.Image = bitmap;
                    }
                }
            }
            catch
            {
            }
        }




WebClient使用DownloadDataCompleted异步下载图片  比同步的好处就是  如果你的URL出现出错 同步会卡住程序  而异步不会  减少等待时间