java 如何在运行时使用 spring 创建请求范围的 bean
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How to create a request scoped bean at runtime with spring
提问by flash
I have a spring application and want to create a bean at runtime per request to inject it into another class, just like @Producerfor CDI.
我有一个 spring 应用程序，想在每个请求运行时创建一个 bean 以将其注入另一个类，就像@ProducerCDI 一样。
My bean is just a simple POJO:
我的 bean 只是一个简单的 POJO：
public class UserDetails {
private String name;
// getter / setter ...
public UserDetails(String name) {
this.name = name;
}
}
My producer class looks like this:
我的生产者类看起来像这样：
@Configuration
public class UserFactory {
@Bean
@Scope("request")
public UserDetails createUserDetails() {
// this method should be called on every request
String name = SecurityContextHolder.getContext()
.getAuthentication().getPrincipal(); // get some user details, just an example (I am aware of Principal)
// construct a complex user details object here
return new UserDetails(name)
}
}
And this is the class where the UserDetailsinstance should be injected:
这是UserDetails应该注入实例的类：
@RestController
@RequestMapping(value = "/api/something")
public class MyResource {
@RequestMapping(method = RequestMethod.GET)
@ResponseBody
public List<String> getSomething(UserDetails userDetails) {
// the userdetails should be injected here per request, some annotations missing?
// do something
}
}
The problem is that Spring complains at runtime about no default constructor (of course).
问题是 Spring 在运行时抱怨没有默认构造函数（当然）。
Failed to instantiate [UserDetails]: No default constructor found
Failed to instantiate [UserDetails]: No default constructor found
But this is intended and I want to call my own factory to let it handle the Instantiation.
但这是有意的，我想调用我自己的工厂让它处理实例化。
How can I achieve this? Why is UserFactorynever called?
我怎样才能做到这一点？为什么UserFactory从不调用？
回答by M. Deinum
Basically you aren't using your scoped proxy. You cannot inject a scoped proxy into a method, you have to inject it into your controller.
基本上你没有使用你的范围代理。您不能将作用域代理注入到方法中，而必须将其注入到控制器中。
public List<String> getSomething(UserDetails userDetails) { ... }
This will lead to spring trying to create a new instance of UserDetailsthrough reflection, it will not inject your scoped bean. Hence it complains about the fact you need a default no-args constructor.
这将导致 spring 试图UserDetails通过反射创建一个新实例，它不会注入您的作用域 bean。因此它抱怨你需要一个默认的无参数构造函数。
Instead what you should do is wire the dependency into your controller instead of the controller method.
相反，您应该做的是将依赖项连接到您的控制器而不是控制器方法中。
@RestController
@RequestMapping(value = "/api/something")
public class MyResource {
@Autowired
private UserDetails userDetails;
@RequestMapping(method = RequestMethod.GET)
@ResponseBody
public List<String> getSomething() {
// the userdetails should be injected here per request, some annotations missing?
// do something
}
}
The idea is that the UserDetailsis a scoped proxy and when used will either use the already present object or create a new one based on the @Beanmethod.
这个想法是UserDetails一个作用域代理，使用时将使用已经存在的对象或基于该@Bean方法创建一个新对象。
Additonally, the @Scopeannotation in the UserFactoryhas to be modified as follows in order to work:
此外，必须按如下方式修改 中的@Scope注释UserFactory才能工作：
@Scope(value = "request", proxyMode = ScopedProxyMode.TARGET_CLASS)
回答by isah
You're trying to inject a request scoped bean on a singleton bean.
You need to use a proxy for the UserDetails
您正在尝试在单例 bean 上注入一个请求范围的 bean。您需要使用代理UserDetails
@Scope(value = "request", proxyMode = ScopedProxyMode.INTERFACES)
回答by Jens
You need a no arguments constructor in class UserDetails.
您需要在 class 中使用无参数构造函数UserDetails。
public class UserDetails {
private String name;
// getter / setter ...
public UserDetails() {
}
public UserDetails(String name) {
this.name = name;
}
}
