Azure函数App的异步Java方法？

Question

我目前正在努力创建EventhubTrig在Java函数应用程序，它侦听IotHub的默认endpoint。目前按照教程，我没有看到任何用于Java函数应用程序的异步实现的示例代码，而建议对C#函数应用程序使用async/wait。

我是否应该考虑/是否可以在Java中为Function Apps添加异步实现？是否有任何示例代码可以参考？我是否应该考虑在函数应用中添加并行编程/多线程逻辑？

https://docs . Microsoft . com/en-us/azure/azure-functions/functions-binding-event-hubs-trigger？tabs = java #示例

https://docs . Microsoft . com/en-us/Java/API/com . Microsoft . azure . functions . annotation . eventhub trigger？view=azure-java-stable

Answer 1

我在java中发布了一个新项目JAsync实现异步等待方式，它使用Retor作为其低级框架。它处于alpha阶段。我需要更多的建议和测试用例。这个项目使开发人员的异步编程体验尽可能接近通常的同步编程，包括编码和调试。

下面是一个示例：

@RestController
@RequestMapping("/employees")
public class MyRestController {
    @Inject
    private EmployeeRepository employeeRepository;
    @Inject
    private SalaryRepository salaryRepository;

    // The standard JAsync async method must be annotated with the Async annotation, and return a JPromise object.
    @Async()
    private JPromise<Double> _getEmployeeTotalSalaryByDepartment(String department) {
        double money = 0.0;
        // A Mono object can be transformed to the JPromise object. So we get a Mono object first.
        Mono<List<Employee>> empsMono = employeeRepository.findEmployeeByDepartment(department);
        // Transformed the Mono object to the JPromise object.
        JPromise<List<Employee>> empsPromise = Promises.from(empsMono);
        // Use await just like es and c# to get the value of the JPromise without blocking the current thread.
        for (Employee employee : empsPromise.await()) {
            // The method findSalaryByEmployee also return a Mono object. We transform it to the JPromise just like above. And then await to get the result.
            Salary salary = Promises.from(salaryRepository.findSalaryByEmployee(employee.id)).await();
            money += salary.total;
        }
        // The async method must return a JPromise object, so we use just method to wrap the result to a JPromise.
        return JAsync.just(money);
    }

    // This is a normal webflux method.
    @GetMapping("/{department}/salary")
    public Mono<Double> getEmployeeTotalSalaryByDepartment(@PathVariable String department) { 
        // Use unwrap method to transform the JPromise object back to the Mono object.
        return _getEmployeeTotalSalaryByDepartment(department).unwrap(Mono.class);
    }
}

除了编码之外，JAsync 还大大改善了异步代码的调试体验。调试时，可以在监视窗口中查看所有变量，就像调试普通代码时一样。

Answer 2

Java没有async/wait，但它有reactive/webflow。

当您创建默认项目azure函数时，它应该与反应式打包，因此您只需要以反应式方式进行调用。

因此，假设您想对外部源进行一些调用，那么您的代码将如下所示：

public Mono<ResponseEntity<WishlistDto>> getList(String profileId, String listId) {
    return service.getWishList(profileId, listId)
            .map(w -> ResponseEntity.ok().body(DtoMapper.convertToDto(w, true)))
            .defaultIfEmpty(ResponseEntity.notFound().build());
}

但是我建议您尽可能多地使用输入/输出绑定

 @FunctionName("DocByIdFromQueryString")
    public HttpResponseMessage run(
            @HttpTrigger(name = "req",
              methods = {HttpMethod.GET, HttpMethod.POST},
              authLevel = AuthorizationLevel.ANONYMOUS)
            HttpRequestMessage<Optional<String>> request,
            @CosmosDBInput(name = "database",
              databaseName = "ToDoList",
              collectionName = "Items",
              id = "{Query.id}",
              partitionKey = "{Query.partitionKeyValue}",
              connectionStringSetting = "Cosmos_DB_Connection_String")
            Optional<String> item,
            final ExecutionContext context) 

在这种情况下，您不需要太担心reactive，因为您的函数会在一切准备就绪后立即启动，java sdk会处理它

另一个使用输出绑定的示例

@FunctionName("sbtopicsend")
    public HttpResponseMessage run(
            @HttpTrigger(name = "req", methods = {HttpMethod.GET, HttpMethod.POST}, authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Optional<String>> request,
            @ServiceBusTopicOutput(name = "message", topicName = "mytopicname", subscriptionName = "mysubscription", connection = "ServiceBusConnection") OutputBinding<String> message,
            final ExecutionContext context) {
        
        String name = request.getBody().orElse("Azure Functions");

        message.setValue(name);
        return request.createResponseBuilder(HttpStatus.OK).body("Hello, " + name).build();
        
    }