Spring Proxy类和Kotlin中的Null指针异常 [英] Null Pointer Exception In Spring Proxy Class and Kotlin

问题描述

我在春天与kotlin一起遇到一些问题.

I am facing some problems with kotlin in conjunction with spring.

我有一个控制器bean(没有接口btw)，它具有通过主构造函数自动连接的服务bean.

I have a controller bean (without an interface btw) which has an auto-wired service bean via the primary constructor.

除非我对控制器使用了缓存注释，否则它会完美地工作.显然，spring缓存会在处理缓存的底层生成一个代理类.

It works perfectly unless I use caching annotations for the controller. Apparently springs caching generates a proxy class under the hood which deals with the caching.

我的代码如下:

@RestController
@RequestMapping("/regions/")
open class RegionController @Autowired constructor(val service: RegionService) {
    @RequestMapping("{id}", method = arrayOf(RequestMethod.GET))
    @Cacheable(cacheNames = arrayOf("regions"))
    fun get(@PathVariable id: Long): RegionResource {
        return this.service.get(id)
    }
}

现在的问题是执行该方法时出现空指针异常，实际上this.service是null，从技术上讲是不可能的，因为它是kotlin中的非空变量.

The problem now is a null pointer exception when the method is executed, actually this.service is null which technically is not possible as it is a nonnull variable in kotlin.

我认为由spring生成的类代理使用空值而不是自动装配的bean初始化类.这一定是使用kotlin和spring的常见陷阱.您是如何规避这个问题的?

I assume that class proxies generated by spring initialize the class with null values instead of the autowired bean. This must be a common pitfall using kotlin and spring. How did you circumvent this problem?

推荐答案

在科特林，两个对于代理库( CGLIB ，，因为这些库通过子类).将您的控制器方法更改为:

For the proxying library (CGLIB, javaassist) to be able to proxy a method it has to be declared non final and in a non final class (since those libraries implement proxying by subclassing). Change your controller method to:

@RequestMapping("{id}", method = arrayOf(RequestMethod.GET))
@Cacheable(cacheNames = arrayOf("regions"))
open fun get(@PathVariable id: Long): RegionResource {
    return this.service.get(id)
}

您可能会在控制台中看到有关RegionController方法不受代理约束的警告.

You probably see a warning in console regarding RegionController methods not being subject to proxying.

Kotlin团队已经意识到了这一困难，并创建了一个插件来标记标准AOP代理候选人，例如@Component和open.

The Kotlin team has acknowledged this difficulty and created a plugin that marks the standard AOP proxy candidates e.g. @Component with open.

您可以在build.gradle中启用插件:

plugins {
  id "org.jetbrains.kotlin.plugin.spring" version "1.1.60"
}

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