使用@RequestScope 创建 Final Class Bean 时出错

Question

使用@RequestScope创建String Bean会报错。但是使用 @Scope("request") 不会。 @RequestScope 不是@Scope("request") 的快捷方式吗？

下面是代码片段。

@SpringBootApplication
public class Application {

    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }

    @RequestScope
    @Bean(name = "requestBean")
    public String hiRequest() {

        return new String("Hi Request");

    }

}

下面是错误信息。

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'requestBean' defined in BeanDefinition defined in com.test.SpringTest.Application: Initialization of bean failed; nested exception is org.springframework.aop.framework.AopConfigException: Could not generate CGLIB subclass of class java.lang.String: Common causes of this problem include using a final class or a non-visible class; nested exception is java.lang.IllegalArgumentException: Cannot subclass final class java.lang.String
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:584) ~[spring-beans-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:498) ~[spring-beans-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean[=12=](AbstractBeanFactory.java:320) ~[spring-beans-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:827) ~[spring-beans-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:863) ~[spring-context-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:546) ~[spring-context-5.1.4.RELEASE.jar:5.1.4.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) [spring-boot-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) [spring-boot-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) [spring-boot-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) [spring-boot-2.1.2.RELEASE.jar:2.1.2.RELEASE]
    at com.test.SpringTest.Application.main(Application.java:12) [classes/:na]

感谢您的回复！

Answer 1

正如您在 documentation 中看到的 @RequestScope 代理模式是：

ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;

这创造了

a class-based proxy (uses CGLIB).

使用 CGLIB Spring 将能够创建一个代理，其 class 是目标 class.

的子class

对于 @Scope("request")，根据 documentation，代理模式为：

ScopedProxyMode proxyMode() default ScopedProxyMode.DEFAULT;

这意味着

    /**
     * Default typically equals {@link #NO}, unless a different default
     * has been configured at the component-scan instruction level.
     */
    DEFAULT,

    /**
     * Do not create a scoped proxy.
     * <p>This proxy-mode is not typically useful when used with a
     * non-singleton scoped instance, which should favor the use of the
     * {@link #INTERFACES} or {@link #TARGET_CLASS} proxy-modes instead if it
     * is to be used as a dependency.
     */
    NO,

这就是为什么它适用于 @Scope("request") 而不是 @RequestScope

的原因

使用@RequestScope 创建 Final Class Bean 时出错

Error when using @RequestScope to create Final Class Bean

spring

cglib

spring-ioc