如何在Play Promise中使用Http.Context.current()? [英] How to use Http.Context.current() in a Promise in Play?

问题描述

在Play Framework 2.2.2中，我想返回一个Promise.但是，我正在调用一个函数，该函数需要访问存储在Http.Context.current()中的变量(当前登录的用户，JPA连接...).

In Play Framework 2.2.2, I'd like to return a Promise. However I'm calling a function which needs access to the variables stored in Http.Context.current() (the current logged in user, the JPA connection...).

当然，由于Promise是在另一个线程中执行的，因此它无权访问Http.Context.current().我可以将其保存在Promise中，还是应该手动还原?我应该使用另一种模式吗?

Of course, since the Promise is executed in another thread, it doesn't have access to Http.Context.current(). Can I preserve it in the Promise, or should I restore it manually? Is there another pattern I should use?

示例:

public static Promise<Result> getAvailableServices() {
    return new Promise.promise(new Function0<Result>(){
        @Override
        public Result apply() throws Throwable {
            // Long operation
            List<Services> data = buildResult();
            // Render the template
            // (The header of the template requires access to 
            // Http.Context.current().args.get("usermodel"))
            return Results.ok(services_template.render(services));
        }
    });
}

推荐答案

是的，HttpExecutionContext是您所需要的.

创建HttpExecutionContext时

When an HttpExecutionContext is created it gets the current thread's Http.Context and stores it. Then, when the HttpExecutionContext is later used to execute code it restores the Http.Context.

所有Promise方法都使用HttpExecutionContext

All Promise methods use an HttpExecutionContext wrapped around the default ExecutionContext so they should propagate the Http.Context correctly across threads.

例如，您的上面的示例代码应该可以正常工作.但是，您确实需要确保当您调用 getAvailableServices时，Http.Context在您从其进行调用的线程中可用.如果调用该方法时Http.Context不可用，则HttpExecutionContext将无法从该线程中捕获Http.Context，并且在应用promise的Function0时将其传播.

Your example code above should work fine, for example. However you do need to make sure that when you call getAvailableServices, that the Http.Context is available in the thread you're calling from. If the Http.Context isn't available when you call the method, then the HttpExecutionContext will be unable to capture the Http.Context from that thread and propagate it when the promise's Function0 is applied.

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