Question

我正在为方法参数创建自定义批注NullCheck，以检查值是否为空。你好（@NullCheck字符串文本），但是我无法在批注周围调用Aspect。

主类

package com.example.demo;
import org.springframework.boot.SpringApplication;
    import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
    import org.springframework.boot.autoconfigure.SpringBootApplication;
    import org.springframework.context.annotation.EnableAspectJAutoProxy;
    @SpringBootApplication
    @EnableAutoConfiguration
    @EnableAspectJAutoProxy
    public class DemoApplication {
        public static void main(String[] args) {
            SpringApplication.run(DemoApplication.class, args);
        }
    }

控制器类，仅调用POC的一个方面，不返回任何内容

package com.example.demo;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController; 
@RestController
@RequestMapping("/")
class HelloController {
    @GetMapping
    public void hello() {
        hello("hi");
    }
    private void hello(@NullCheck String text) {
        System.out.println(text);
    }
}

注释

package com.example.demo;
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;
import static java.lang.annotation.RetentionPolicy.RUNTIME;
@Documented
@Retention(RUNTIME)
@Target(ElementType.PARAMETER)
public @interface NullCheck { }

方面

package com.example.demo;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.springframework.stereotype.Component;
@Aspect
@Component
public class NullCheckAspect {

此功能正常

@Before("@annotation(org.springframework.web.bind.annotation.GetMapping)")

但这不是

@Before("@annotation(com.example.demo.NullCheck)")
    public void beforeAdvice(JoinPoint joinPoint) {
        System.out.println("Before method:" + joinPoint.getSignature());
    }
}

build.gradle

buildscript {
    ext {
        springBootVersion = '2.1.2.RELEASE'
    }
    repositories {
        mavenCentral()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:${springBootVersion}")
    }
}
apply plugin: 'java'
apply plugin: 'idea'
apply plugin: 'eclipse'
apply plugin: 'org.springframework.boot'
apply plugin: 'io.spring.dependency-management'
group = 'com.example'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = '1.8'
idea {
    module {
        // if you hate browsing Javadoc
        downloadJavadoc = true
        // and love reading sources :)
        downloadSources = true
    }
}
bootJar {
    launchScript()
}
repositories {
    mavenCentral()
    jcenter()
}
bootJar {
    launchScript()
}
dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-actuator'
    implementation 'org.springframework.boot:spring-boot-starter-aop'
    implementation 'org.springframework.boot:spring-boot-starter-web'
    runtimeOnly 'org.springframework.boot:spring-boot-devtools'
}

我想念什么？

Answer 1

据我了解，在Google上进行了一些搜索后，您可以通过以下代码获取方法参数及其带有特殊注释的值：

package com.example.demo;

import java.lang.annotation.Annotation;
import java.lang.reflect.Method;
import java.util.HashMap;
import java.util.Map;

import org.aspectj.lang.ProceedingJoinPoint;
import org.aspectj.lang.annotation.Around;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.reflect.MethodSignature;
import org.springframework.stereotype.Component;

@Component
@Aspect
public class NullCheckAspect {

    @Around("execution(* com.example.demo.HelloController.nullChecker(String))")
    public Object around(ProceedingJoinPoint pJoinPoint) throws Throwable {

        Object[] args = pJoinPoint.getArgs();

        Method method = MethodSignature.class.cast(pJoinPoint.getSignature()).getMethod();

        Annotation[][] parametersAnnotations = method.getParameterAnnotations();

        Map<String, Object> annotatedParameters = new HashMap<>();

        int i = 0;
        for(Annotation[] parameters : parametersAnnotations) {
                Object arg = args[i];
                String name = method.getParameters()[i++].getDeclaringExecutable().getName();
                for(Annotation parameter: parameters) {
                    if ((parameter instanceof NullCheck)) {
                        System.out.println("Found the null checker annotation with name: " + name);
                        System.out.println("Found the null checker annotation with arg:  " + arg);
                        annotatedParameters.put(name, arg);
                }
                }
        }
        System.out.println(annotatedParameters);

        return pJoinPoint.proceed(args);
    }
}

并带有界面注释：

package com.example.demo;

import static java.lang.annotation.RetentionPolicy.RUNTIME;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.Target;

import org.springframework.stereotype.Component;

@Component
@Retention(RUNTIME)
@Target(ElementType.PARAMETER)
public @interface NullCheck {
}

有关我的代码的更多详细信息，您可以在我的github存储库中检查它，我已经创建了spring boot演示版本，并将其推送到https://github.com/krishnaiitd/learningJava/blob/master/springBoot/gs-spring-boot/src/main/java/com/example/demo/HelloController.java

这还包括其他类型的方面，例如跟踪特定方法的时间。

希望这将帮助您在Spring Boot中对@Aspect有了基本的了解。

Answer 2

我不知道为什么会这样，但是我遇到了同样的问题。使用Pointcuts可以轻松解决此问题，例如：

@Before("nulllCheckAnnotation()")
    public void beforeAdvice(JoinPoint joinPoint) {
        System.out.println("Before method:" + joinPoint.getSignature());
    }
}

@Pointcut("@annotation(com.example.demo.NullCheck)")
private void nulllCheckAnnotation() { }

如果您有兴趣，请在这里阅读有关切入点的更多信息：https://www.baeldung.com/spring-aop-pointcut-tutorial

Spring Boot自定义注释中的方面

2 个答案: