WebClient修仙指南：从HTTP小白到响应式请求大能的终极奥义

各位在Spring生态摸爬滚打的道友们！今天要解锁的是Spring 5的镇派绝学——WebClient！这货堪称响应式编程界的"御剑飞行术"，比老旧的RestTemplate快出三个境界，还能轻松处理高并发请求！准备好迎接"异步非阻塞"的修仙新时代了吗？ 🚀

一、筑基篇：初识WebClient

1.1 法宝祭炼（添加依赖）

<!-- Spring Boot WebFlux（已包含WebClient） -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-webflux</artifactId>
</dependency>

1.2 召唤本命法宝

// 基础召唤术（默认配置）
WebClient client = WebClient.create();

// 注入灵力版（推荐Bean方式）
@Bean
public WebClient webClient() {
    return WebClient.builder()
        .baseUrl("https://api.example.com")
        .defaultHeader("User-Agent", "WebClient-Discovery")
        .build();
}

二、金丹篇：基础请求术

2.1 GET请求（探查天地灵气）

Mono<String> response = webClient.get()
    .uri("/users/1")
    .retrieve()
    .bodyToMono(String.class);

// 同步获取结果（仅测试用，实际应该用响应式流）
System.out.println("响应内容：" + response.block());

2.2 POST请求（传送灵力）

User user = new User("张无忌", 25);

Mono<User> createdUser = webClient.post()
    .uri("/users")
    .contentType(MediaType.APPLICATION_JSON)
    .bodyValue(user)
    .retrieve()
    .bodyToMono(User.class);

createdUser.subscribe(user -> 
    System.out.println("创建用户成功，ID：" + user.getId())
);

三、元婴篇：高级神通

3.1 异步非阻塞（分身术）

Flux<User> users = webClient.get()
    .uri("/users")
    .retrieve()
    .bodyToFlux(User.class);

// 配合响应式流处理（不会阻塞主线程）
users.subscribe(
    user -> System.out.println("收到用户：" + user.getName()),
    error -> System.err.println("渡劫失败：" + error.getMessage()),
    () -> System.out.println("所有用户接收完毕！")
);

3.2 文件上传（乾坤大挪移）

MultipartBodyBuilder builder = new MultipartBodyBuilder();
builder.part("file", new FileSystemResource("avatar.jpg"));
builder.part("name", "张无忌");

Mono<String> result = webClient.post()
    .uri("/upload")
    .contentType(MediaType.MULTIPART_FORM_DATA)
    .body(BodyInserters.fromMultipartData(builder.build()))
    .retrieve()
    .bodyToMono(String.class);

四、化神篇：异常处理

4.1 错误状态码处理（渡劫护盾）

Mono<User> user = webClient.get()
    .uri("/users/99")
    .retrieve()
    .onStatus(HttpStatus::is4xxClientError, response -> 
        Mono.error(new RuntimeException("客户端错误: " + response.statusCode()))
    )
    .onStatus(HttpStatus::is5xxServerError, response ->
        Mono.error(new RuntimeException("服务器开小差了"))
    )
    .bodyToMono(User.class);

4.2 重试机制（不死之身）

Flux<User> users = webClient.get()
    .uri("/users")
    .retrieve()
    .bodyToFlux(User.class)
    .retryWhen(Retry.backoff(3, Duration.ofSeconds(1)) // 最多重试3次
    .doOnError(e -> System.err.println("最终失败：" + e.getMessage()));

五、大乘篇：性能调优

5.1 连接池配置（灵气循环）

@Bean
public WebClient webClient() {
    ConnectionProvider provider = ConnectionProvider.builder("myPool")
        .maxConnections(500)
        .pendingAcquireTimeout(Duration.ofSeconds(30))
        .build();

    HttpClient httpClient = HttpClient.create(provider)
        .responseTimeout(Duration.ofSeconds(10));

    return WebClient.builder()
        .clientConnector(new ReactorClientHttpConnector(httpClient))
        .build();
}

5.2 请求/响应日志（天眼通）

HttpClient httpClient = HttpClient.create()
    .wiretap("reactor.netty.http.client.HttpClient", 
        LogLevel.DEBUG, AdvancedByteBufFormat.TEXTUAL);

WebClient client = WebClient.builder()
    .clientConnector(new ReactorClientHttpConnector(httpClient))
    .build();

六、实战心法

6.1 与Spring Security集成（护山大阵）

@Bean
public WebClient securedWebClient(ReactiveClientRegistrationRepository repo) {
    ServerOAuth2AuthorizedClientExchangeFilterFunction oauth = 
        new ServerOAuth2AuthorizedClientExchangeFilterFunction(repo);
    oauth.setDefaultOAuth2AuthorizedClient(true);

    return WebClient.builder()
        .filter(oauth)
        .build();
}

// 使用自动携带令牌
Mono<String> data = securedWebClient.get()
    .uri("/protected-data")
    .retrieve()
    .bodyToMono(String.class);

6.2 SSE（服务器推送事件）处理

Flux<String> eventStream = webClient.get()
    .uri("/live-updates")
    .accept(MediaType.TEXT_EVENT_STREAM)
    .retrieve()
    .bodyToFlux(String.class);

eventStream.subscribe(event -> 
    System.out.println("收到事件：" + event)
);