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         AOP不用多说，是spring框架的两大基石之一。SpEL是Spring Expression Language的缩写，意为Spring表达式语言，，其支持在运行时查询和操作对象图提供了更加丰富的功能，最特别的是方法调用与字符串模板功能。熟悉js的es6语法的小伙伴都知道，模板字符串，这个spel就类似js的模板字符串。

         本次代码主要是熟悉使用语法，并布对应实际的应场景。

一、自定义注解

@Target({ElementType.PARAMETER,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface TestAopAnn {/*** spEL* @return*/String  spEL() default "";
}

二、自定义切面

@Aspect
@Component
public class TestAopAspect {private final static Logger LOGGER = LoggerFactory.getLogger(TestAopAspect.class);@Pointcut("@annotation(org.example.boot3.aop.TestAopAnn)")public void pointCut(){}@AfterReturning(value = "pointCut()",returning = "result")public   void  doAfter(JoinPoint joinPoint,Object result){Method method = getMethod(joinPoint);TestAopAnn annotation = method.getAnnotation(TestAopAnn.class);if(annotation!=null){LOGGER.info("TestAopAspect-->doAfter-------后置织入");/// 通过spel表达式获取到形参的中name的值String value =getValue(joinPoint, method, annotation.spEL());LOGGER.info("TestAopAspect-->doBefore-------value={}",value);/// 将name追加到返回的listtry {if(result!=null && result instanceof List){List  list = (List) result;list.add(value);}} catch (Exception e) {e.fillInStackTrace();}}}private   Method  getMethod(JoinPoint  joinPoint) {Signature signature = joinPoint.getSignature();MethodSignature methodSignature = (MethodSignature) signature;return methodSignature.getMethod();}/**解析spel*/private String  getValue(JoinPoint  joinPoint,  Method method,String elStr){StandardEvaluationContext context = new StandardEvaluationContext();DefaultParameterNameDiscoverer parameterNameDiscoverer = new DefaultParameterNameDiscoverer();/// 方法参数名称String[] parameterNames = parameterNameDiscoverer.getParameterNames(method);Assert.isTrue(parameterNames!=null,"参数列表不能为空");///方法参数值Object[] args = joinPoint.getArgs();for (int i = 0; i < parameterNames.length; i++) {context.setVariable(parameterNames[i],args[i]);}ExpressionParser parser = new SpelExpressionParser();Expression expression = parser.parseExpression(elStr);return (String) expression.getValue(context);}
}

三、测试接口

public class TestReqVO {private String  name;private String  remark;
}

@RestController
@RequestMapping("/api")
public class RestApi {/*** SpEL 调用对象方法* @param vo* @return*/@GetMapping("/testSpEL1")@TestAopAnn(spEL = "#vo.getName()")public List<String> getSpELList1(TestReqVO vo){String[] arr = { "C" ,"C++","JAVA","GoLang","Rust","Python"};return new ArrayList<>(Arrays.stream(arr).toList());}/*** SpEL 调用对象属性* @param vo* @return*/@GetMapping("/testSpEL2")@TestAopAnn(spEL = "#vo.name")public List<String> getSpELList2(TestReqVO vo){String[] arr = { "C" ,"C++","JAVA","GoLang","Rust","Python"};return  new ArrayList<>(Arrays.stream(arr).toList());}@GetMapping("/fluxList")public Flux<List<String>> getSpEL2(){String[] arr = { "C" ,"C++","JAVA","GoLang","Rust","Python"};ArrayList<String> list = new ArrayList<>(Arrays.asList(arr));return Flux.just(list);}}

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