问题

在以下主题中：

• https://stackoverflow.com/questions/16299717/how-to-create-an-instance-of-an-annotation
• https://stackoverflow.com/questions/266903/create-annotation-instance-with-defaults-in-java

讨论了如何创建Java注解的实例。

我的问题是：拥有这样的注解实例，我可以用它做什么？特别地，我是否可以在方法的参数上以某种方式应用它？

动机：

我正在准备几个Azure函数，我不喜欢我需要重复多次类似以下代码的事实

 @HttpTrigger(name = "req", methods = {HttpMethod.GET}, route= "/api/mypath", authLevel = AuthorizationLevel.ANONYMOUS)

所以我想我可以创建一个方法 HttpTrigger createHttpTrigger(HttpMethod httpMethod) { ... }，然后代替

@FunctionName("MyFunction")
public HttpResponseMessage getModelNames(
   @HttpTrigger(name = "req", methods = {HttpMethod.GET}, route= "api/mypath", authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Optional<String>> request, 
   final ExecutionContext context) {
...
}

写类似于

@FunctionName("MyFunction")
public HttpResponseMessage getModelNames(
   @createHttpTrigger(HttpMethod.GET) HttpRequestMessage<Optional<String>> request, 
   final ExecutionContext context) {
}

(但是当然这段代码是不正确的)

 @HttpTrigger(name = "req", methods = {HttpMethod.GET}, route= "/api/mypath", authLevel = AuthorizationLevel.ANONYMOUS)

@FunctionName("MyFunction")
public HttpResponseMessage getModelNames(
   @HttpTrigger(name = "req", methods = {HttpMethod.GET}, route= "api/mypath", authLevel = AuthorizationLevel.ANONYMOUS) HttpRequestMessage<Optional<String>> request, 
   final ExecutionContext context) {
...
}

@FunctionName("MyFunction")
public HttpResponseMessage getModelNames(
   @createHttpTrigger(HttpMethod.GET) HttpRequestMessage<Optional<String>> request, 
   final ExecutionContext context) {
}

答案1

得分: 1

我查看了HttpTrigger源代码，并发现我只需要向注释的属性添加一些默认值。

```java
package com.microsoft.azure.functions.annotation;

import com.microsoft.azure.functions.HttpMethod;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PARAMETER})
public @interface HttpTrigger {
    String name();

    String dataType() default "";

    String route() default "";

    HttpMethod[] methods() default {};

    AuthorizationLevel authLevel() default AuthorizationLevel.FUNCTION;
}

创建一个新的注释。

import com.microsoft.azure.functions.HttpMethod;
import com.microsoft.azure.functions.annotation.AuthorizationLevel;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PARAMETER})
public @interface CreateHttpTrigger {
    String name() default "req";

    String dataType() default "";

    String route() default "/api/mypath";

    HttpMethod[] methods() default {};

    AuthorizationLevel authLevel() default AuthorizationLevel.ANONYMOUS;
}

代码可以重写如下。

    @FunctionName("HttpTrigger-Java")
    public HttpResponseMessage run(
            @CreateHttpTrigger(methods = {HttpMethod.GET}) HttpRequestMessage<Optional<String>> request,
            final ExecutionContext context) {

但当我运行它时，显示以下错误消息：

"HttpTrigger-Java" 函数错误：必须声明至少一个绑定。

我尝试了几种方法，但没有一种使其成功运行，所以我在官方文档中检查了有关绑定和触发的信息。

从上表中，我推断自定义的 CreateHttpTrigger 注释是 Azure 函数不支持的绑定。

总之，根据我推测，你的想法可能无法实现。如果你有更好的想法，欢迎告诉我。我愿意继续讨论这个问题。

<details>
<summary>英文:</summary>

I looked at the HttpTrigger source code and found that I just needed to add some default values to the properties of the annotation.

package com.microsoft.azure.functions.annotation;

import com.microsoft.azure.functions.HttpMethod;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PARAMETER})
public @interface HttpTrigger {
String name();

String dataType() default "";

String route() default "";

HttpMethod[] methods() default {};

AuthorizationLevel authLevel() default AuthorizationLevel.FUNCTION;

}

Create a new annotation.

import com.microsoft.azure.functions.HttpMethod;
import com.microsoft.azure.functions.annotation.AuthorizationLevel;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.PARAMETER})
public @interface CreateHttpTrigger {
String name() default "req";

String dataType() default "";

String route() default "/api/mypath";

HttpMethod[] methods() default {};

AuthorizationLevel authLevel() default AuthorizationLevel.ANONYMOUS;

}

The code can be rewritten like this.

@FunctionName("HttpTrigger-Java")
public HttpResponseMessage run(
        @CreateHttpTrigger(methods = {HttpMethod.GET}) HttpRequestMessage<Optional<String>> request,
        final ExecutionContext context) {

But when I run it, it shows the following error message:

>The 'HttpTrigger-Java' function is in error: At least one binding must be declared.

I tried several methods but none of them made it run successfully, so I checked the official [documentation][1] on binding and triggering.

[![enter image description here][2]][2]

From the above table, I infer that the custom `CreateHttpTrigger` annotation is a binding that is not supported by Azure function.

In summary, I guess your idea cannot be realized. If you have a better idea, you can tell me. I am willing to continue discussing this issue.


  [1]: https://learn.microsoft.com/en-us/azure/azure-functions/functions-triggers-bindings#supported-bindings
  [2]: https://i.stack.imgur.com/jvufu.png

</details>