[SpringBoot3]远程访问@HttpExchange

六、远程访问@HttpExchange[SpringBoot3]

远程访问是开发的常用技术，一个应用能够访问其他应用的功能。SpringBoot提供了多种远程访问的技术。基于HTTP协议的远程访问是最广泛的。
SpringBoot中定义接口提供HTTP服务。生成的代理对象实现此接口，代理对象实现HTTP的远程访问，需要理解：
- @HttpExchange
- WebClient

WebClient特性

我们想要调用其他系统提供的HTTP服务，通常可以使用Spring提供的RestTemplate来访问，RestTemplate是SpringBoot3中引入的同步阻塞式HTTP客户端，因此存在一定性能瓶颈。Spring官方在Spring5中引入了WebClient作为非阻塞式HTTP客户端。
- 非阻塞，异步请求
- 它的响应式编程基于Reactor
- 高并发，硬件资源少
- 支持Java 8 lambdas函数式编程

什么是异步非阻塞

异步和同步针对调用者，调用者发送请求，如果等待对方回应之后才去做其他事情，就是同步，如果发送请求之后不等着对方回应就去做其他事情就是异步
阻塞和非阻塞针对被调度者，被调度者收到请求后，做完请求任务之后才给出反馈就是阻塞，收到请求之后马上给出反馈然后去做事情，就是非阻塞。

6.1准备工作

安装GsonFormat插件，方便json和Bean的转换

6.2声明式HTTP远程服务

需求：访问https://jsonplaceholder.typicode.com/提供的todos服务。基于RESTful风格，增删改查。

1.Maven依赖pom.xml

<dependencies><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-web</artifactId></dependency><!--WebClient--><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-webflux</artifactId></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><optional>true</optional></dependency><dependency><groupId>org.springframework.boot</groupId><artifactId>spring-boot-starter-test</artifactId><scope>test</scope></dependency><dependency><groupId>io.projectreactor</groupId><artifactId>reactor-test</artifactId><scope>test</scope></dependency>
</dependencies>

2.声明Todo数据类

@Data
public class Todo {private Integer userId;private Integer id;private String title;private Boolean completed;
}

3.声明服务接口

public interface TodoService {// 一个方法就是一个远程服务（远程调用）@GetExchange("/todos/{id}")Todo getTodoById(@PathVariable("id") Integer id);//增加资源@PostExchange(value = "/todos/", accept = MediaType.APPLICATION_JSON_VALUE)Todo createTodo(@RequestBody Todo newTodo);//修改资源@PutExchange("/todos/{id}")ResponseEntity<Todo> modifyTodo(@PathVariable Integer id, @RequestBody Todo todo);//删除资源@DeleteExchange("/todos/{sid}")void removeTodo(@PathVariable("sid") Integer id);
}

4.创建HTTP服务代理对象

//proxyBeanMethods = false:多实例对象，无论被取出多少此都是不同的bean实例，在该模式下SpringBoot每次启动会跳过检查容器中是否存在该组件
@Configuration(proxyBeanMethods = false)
public class HttpConfiguration {//创建服务接口的代理对象，基于WebClient@Beanpublic TodoService requestService() {WebClient webClient =WebClient.builder().baseUrl("https://jsonplaceholder.typicode.com").build();//创建代理工厂,设置超时时间HttpServiceProxyFactory proxyFactory =HttpServiceProxyFactory.builder(WebClientAdapter.forClient(webClient)).blockTimeout(Duration.ofSeconds(60)).build();//创建某个接口的代理服务return proxyFactory.createClient(TodoService.class);}}

5.单元测试

@SpringBootTest
class Springboot18HttpServiceApplicationTests {//注入代理对象@Resourceprivate TodoService todoService;//测试访问todos/1@Testvoid testQuery() {Todo todo = todoService.getTodoById(1);System.out.println("todo = " + todo);System.out.println(todo.getTitle());}//创建资源@Testvoid testCreateTodo() {Todo todo = new Todo();todo.setId(1222);todo.setUserId(1223);todo.setTitle("事项1");todo.setCompleted(true);Todo res = todoService.createTodo(todo);System.out.println("res = " + res);}//修改资源@Testvoid testModify() {Todo todo = new Todo();todo.setId(1002);todo.setUserId(5002);todo.setTitle("事项2");todo.setCompleted(true);ResponseEntity<Todo> entity = todoService.modifyTodo(2, todo);HttpHeaders headers = entity.getHeaders();System.out.println("headers = " + headers);Todo body = entity.getBody();System.out.println("body = " + body);HttpStatusCode statusCode = entity.getStatusCode();System.out.println("statusCode = " + statusCode);}//删除资源@Testvoid testDelete() {todoService.removeTodo(10);}
}

6.3Http服务接口的方法定义

@HttpExchange注解用于声明接口作为HTTP远程服务。在方法、类级别使用。通过注解属性以及方法的参数设置HTTP请求的细节。
快捷注解简化不同的请求方式：
- GetExchange
- PostExchange
- PutExchange
- PatchExchange
- DeleteExchange
@GetExchange就是@HttpExchange表示的GET请求方式
作为HTTP服务接口中的方法允许使用的参数列表

接口中方法返回值

6.4组合使用注解

@HttpExchange、@GetExchange等可以组合使用。

1.创建Albums数据类

@Data
public class Albums {private Integer id;private Integer userId;private String title;
}

2.创建AlbumsService接口

接口声明方法，提供HTTP远程服务。

@HttpExchange(url = "https://jsonplaceholder.typicode.com/")
public interface AlbumsService {//查询专辑@HttpExchange(method = "GET",url = "/albums/{id}")Albums getById(@PathVariable Integer id);
}

3.声明代理

@Bean
//创建代理
public AlbumsService albumsService() {WebClient webClient = WebClient.create();HttpServiceProxyFactory proxyFactory = HttpServiceProxyFactory.builder(WebClientAdapter.forClient(webClient)).blockTimeout(Duration.ofSeconds(60)).build();return proxyFactory.createClient(AlbumsService.class);
}

4.单元测试

@SpringBootTest
public class AlbumsServiceTest {@Resourceprivate AlbumsService albumsService;@Testvoid testQuery() {Albums albums = albumsService.getById(5);System.out.println("albums = " + albums);}
}

6.5Java Record

测试Java Record作为返回类型。

创建Albums的Java Record

public record AlbumsRecord(Integer id, Integer userId, String title) {
}

其余步骤一样

6.6定制HTTP请求服务

设置HTTP远程的超时时间，异常处理
在创建接口代理对象前，先设置WebClient的有关配置。

1.设置超时，异常处理

//定制HTTP服务
@Bean
public AlbumsService albumsService() {//超时HttpClient httpClient = HttpClient.create().option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 30000)//连接时间.doOnConnected(conn -> {conn.addHandlerLast(new ReadTimeoutHandler(10));//读超时conn.addHandlerLast(new WriteTimeoutHandler(10));//写超时});//设置异常WebClient webClient = WebClient.builder().clientConnector(new ReactorClientHttpConnector(httpClient))//定制 4XX,5XX 的回调函数.defaultStatusHandler(HttpStatusCode::isError, clientResponse -> {System.out.println("WebClient请求异常");return Mono.error(new RuntimeException("请求异常" + clientResponse.statusCode().value()));}).build();HttpServiceProxyFactory proxyFactory = HttpServiceProxyFactory.builder(WebClientAdapter.forClient(webClient)).blockTimeout(Duration.ofSeconds(60)).build();return proxyFactory.createClient(AlbumsService.class);
}