@NotNull注释不起作用 - 传递 null 时不会引发异常

Question

下面的代码输出"内部方法"；即使我将null传递给函数。它应该抛出一个异常。下面的代码出了什么问题？当传递null参数时，它为什么不抛出异常。

import org.springframework.validation.annotation.Validated;
import javax.validation.constraints.NotNull;
@Validated
class MyClass {
public static void main(String[] args) {
MyClass m = new MyClass();
m.wontTakeNull(null);
}

public void wontTakeNull(@NotNull String param) {
System.out.println("Inside Method");
}

}

Answer 1

如果要验证MyClass，它需要是一个Spring管理的bean。现在你正在自己创建它，然后调用一个方法：

MyClass m = new MyClass();
m.wontTakeNull(null);

这意味着Spring对m一无所知，而且它不是Spring管理的bean。因此，当您使用null调用wontTakeNull时，Spring无法执行验证。

要使m成为Spring托管bean，需要使用@Component对其进行注释，并使用组件扫描或从配置类中的@Bean方法返回其实例。然后，您需要让Spring注入MyClass的实例，而不是自己创建它。下面是一个完整的例子，展示了基于@Component的方法：

package com.example.demo;
import javax.validation.constraints.NotNull;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.stereotype.Component;
import org.springframework.validation.annotation.Validated;
@SpringBootApplication
public class ValidationExampleApplication {

public ValidationExampleApplication(MyClass myClass) {
myClass.wontTakeNull(null);
}
public static void main(String[] args) {
SpringApplication.run(ValidationExampleApplication.class, args);
}

@Component
@Validated
static class MyClass {

public void wontTakeNull(@NotNull String param) {
System.out.println("Inside Method");
}

}
}

此应用程序将无法启动，根本原因如下：

Caused by: javax.validation.ConstraintViolationException: wontTakeNull.param: must not be null
at org.springframework.validation.beanvalidation.MethodValidationInterceptor.invoke(MethodValidationInterceptor.java:120) ~[spring-context-5.3.9.jar:5.3.9]
at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.3.9.jar:5.3.9]
at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.proceed(CglibAopProxy.java:750) ~[spring-aop-5.3.9.jar:5.3.9]
at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:692) ~[spring-aop-5.3.9.jar:5.3.9]
at com.example.demo.ValidationExampleApplication$MyClass$$EnhancerBySpringCGLIB$$82020c75.wontTakeNull(<generated>) ~[main/:na]
at com.example.demo.ValidationExampleApplication.<init>(ValidationExampleApplication.java:14) ~[main/:na]
at com.example.demo.ValidationExampleApplication$$EnhancerBySpringCGLIB$$4c0df4b8.<init>(<generated>) ~[main/:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490) ~[na:na]
at org.springframework.beans.BeanUtils.instantiateClass(BeanUtils.java:208) ~[spring-beans-5.3.9.jar:5.3.9]
... 20 common frames omitted