AOP支持spEL表达式

在使用spring-data-cache时，我们使用aop注解是支持spEL(Spring Expression Language)的，
demo

 @Override@Cacheable(value = "#id",cacheNames = "CACHE1")public UserInfo getById(String id) {return userMappger.getById(id);}

自定义的AOP如何支持支持spEL表达式呢?

背景

AclCheckPoint

假设有切入点

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.METHOD})
public @interface AclCheckPoint {/*** id-expression* if "#paramX.name " means  paramX.getName().* if null, means args[0]* if "#paramX" has no "." ,means paramX .** @return*/String expression() default "";
}

业务代码

@Acl //自定义注解，后面会有说明
public class UserServiceImpl implements IUserService {@Override@AclCheckPoint(expression = "#dto.id")public int update(UserDto dto) {//do nothing}
}

Aspect切面

@Aspect
public class AclCheckAspect {@Before("@annotation(aclAnno)")public void before(JoinPoint joinPoint, AclCheckPoint aclAnno) throws Exception {MethodSignature signature = (MethodSignature) joinPoint.getSignature();Method method = signature.getMethod();Object args[] = joinPoint.getArgs(); //String expression = aclAnno.getExpression(); // "#dto.id"}
}

如何才能通过#dto.id解析出来请求我们真正需要的参数呢？

基本解决

回顾一下被拦截的方法

@Override@AclCheckPoint(expression = "#dto.id")public int update(UserDto dto) {//do nothing}

我们已知请求参数args[]和表达式#dto.id,接下来的几个问题

首先我们要将表达式split为参数名称和属性名称两个部分
获取被拦截的方法的参数名称列表,匹配找到目标参数
最后反射执行对应属性的getter

解析表达式

 void findParamPair(Method method, String expression) {String[] arr = expression.split("\\.");String paramName = arr[0].replace("#", "");String field = arr[1];//todo xxxx}

解析参数名称

JDK8 —不建议

 public int getParam(String paramName,MethodSignature signature){String[] parameterNames = signature.getParameterNames(); //依赖jdk8int index  = -1;for(int i = 0  ; i < parameterNames.length ; i++){if(parameterNames[i].equals(paramName)){index = i;break;}}if(index == -1){throw new RuntimeException("method [" + signature.getMethod().getName() + "] does not have parameter name:" + paramName);}return index; // param = args[index]}

spring:LocalVariableTableParameterNameDiscoverer

 public int getParam(String paramName,MethodSignature signature){LocalVariableTableParameterNameDiscoverer discoverer = new LocalVariableTableParameterNameDiscoverer();String[] definedParamNames = discoverer.getParameterNames(signature.getMethod());int index = definedParamNames.length;while (index >= 0) {index--;if (paramName.equals(definedParamNames[index])) {break;}}if (index < 0) {throw new RuntimeException("method [" + signature.getMethod().getName() + "] does not have parameter name:" + paramName);}return index; // param = args[index]}

获取getter

 public Method getter(int index ,MethodSignature signature,String field) throws NoSuchMethodException {Class parameterType = signature.getMethod().getParameterTypes()[index];String getterName = "getter" + field.substring(0, 1).toUpperCase() + field.substring(1);Method getter = parameterType.getMethod(getterName,null);return getter;}

AOP拦截获取expression-value

 @Before("@annotation(aclAnno)")public void before(JoinPoint joinPoint, AclCheckPoint aclAnno) throws Exception {MethodSignature signature = (MethodSignature) joinPoint.getSignature();Object[] args = joinPoint.getArgs();int index = getParam(paramName, signature, args);Object param = args[index];Method getter = getter(index, signature, field);Object expressionValue = getter.invoke(param); //获取value}

到此为止，似乎问题全部解决了，也能达到预期的目标，那么这个解决方案还有优化的点吗？

优化解决

在使用spring-data-cache时，在启动时会检测@Cacheable的注解是否合法有效,那么在上面的解决方案中(饿汉)，只有在方法被AOP切面拦截的时候候才能发现问题(懒汉)，这就给发现问题带来了一定难度以及带来一定的性能损耗(上述的解析过程,反射等),如何实现饿汉模式呢？

如果在Spring容器初始化的时候，就进行扫描出目标方法
对带有AclCheckPoint的方法，预先解析，并将解析方法存放于缓存之中
AOP切面直接从缓存中寻找对应的解析方法，并执行

扫描目标方法

Acl

为了增加扫描的效率我们新增一个注解，只对带有该注解的方法进行拦截

@Retention(RetentionPolicy.RUNTIME)
@Target({ElementType.TYPE})
public @interface Acl {}

basepackage

为了更进一步加快扫描效率，可以只对目标路径进行扫描。

扫描: ClassPathScanningCandidateComponentProvider

private Set<BeanDefinition> scan() {ClassPathScanningCandidateComponentProvider scanner = new ClassPathScanningCandidateComponentProvider(false);scanner.addIncludeFilter(new AnnotationTypeFilter(Acl.class));String[] packages = StringUtils.tokenizeToStringArray(this.basePackage, ",; \t\n");Set<BeanDefinition> definitions = new HashSet<>();for (String pkg : packages) {definitions.addAll(scanner.findCandidateComponents(pkg));}return definitions;
}

初始化并缓存

扫描并初始化

public class CacheableIdDetectorFactory<T> implements I InitializingBean {private static final Map<Method, IdDetector> cache = new HashedMap(); //自定义对象IdDetectorpublic IdDetector getIdDetector(Method method) {  //供外部调用，从cache获取IdDetector idDetector = cache.get(method);if (idDetector == null) {throw new RuntimeException("Did not find IdDetector for [" + method.getName() + "] ,maybe method's target-class does not have @Acl?");}return idDetector;}@Overridepublic void afterPropertiesSet() throws Exception {Set<BeanDefinition> definitions = scan();definitions.stream().map(bd -> {String className = bd.getBeanClassName();try {Class clazz = Class.forName(className);return clazz.getMethods();} catch (ClassNotFoundException e) {logger.error("[" + className + "] not found :", e);System.exit(-1);}return null;}).filter(Objects::nonNull).flatMap(Arrays::stream).forEach(this::initCache); }
}

切面获取cache的处理方法

 @Before("@annotation(aclAnno)")public void before(JoinPoint joinPoint, AclCheckPoint aclAnno) throws Exception {MethodSignature signature = (MethodSignature) joinPoint.getSignature();IdDetector<String> idDetector = idDetectorFactory.getIdDetector(signature.getMethod());Object[] args = joinPoint.getArgs();String expressValue = idDetector.detect(args);}

完整代码

自定义IdDetector

public class IdDetector<T> {private final Function<Object[], T> function;IdDetector(Function<Object[], T> f) {this.function = f;}public T detect(Object[] args) {return function.apply(args);}
}

IdDetectorFactory

public interface IdDetectorFactory<T> {IdDetector<T> getIdDetector(Method method) throws Exception;String EXPRESSION_PREFIX = "#";String EXPRESSION_SPLIT = "\\.";String GETTER_PREFIX = "get";default String getterMethodName(String field) {return GETTER_PREFIX + field.substring(0, 1).toUpperCase() + field.substring(1);}default Method getterMethod(Class clazz, String field) throws NoSuchMethodException {String fieldGetterName = getterMethodName(field);Method getter = clazz.getDeclaredMethod(fieldGetterName);return getter;}LocalVariableTableParameterNameDiscoverer PARAMETER_NAME_DISCOVERER = new LocalVariableTableParameterNameDiscoverer();default Pair findParamPair(Method method, String expression) {String[] arr = expression.split(EXPRESSION_SPLIT);String paramName = arr[0].replace(EXPRESSION_PREFIX, "");String[] definedParamNames = PARAMETER_NAME_DISCOVERER.getParameterNames(method);int index = definedParamNames.length;while (index >= 0) {index--;if (paramName.equals(definedParamNames[index])) {break;}}if (index < 0) {throw new RuntimeException("method [" + method.getName() + "] does not have parameter name:" + paramName);} if(arr.length == 1){return new Pair(index, null);}return new Pair(index, arr[1]);}@Getter@AllArgsConstructorclass Pair {int index;String field;}
}

CacheableIdDetectorFactory

public class CacheableIdDetectorFactory<T> implements IdDetectorFactory, InitializingBean {private static final Logger logger = LoggerFactory.getLogger(CacheableIdDetectorFactory.class);private static final Map<Method, IdDetector> cache = new HashedMap();public IdDetector getIdDetector(Method method) {IdDetector idDetector = cache.get(method);if (idDetector == null) {throw new RuntimeException("Did not find IdDetector for [" + method.getName() + "] ,maybe method's target-class does not have @Acl?");}return idDetector;}private void initCache(Method method) throws RuntimeException {AclCheckPoint aclAnno = method.getAnnotation(AclCheckPoint.class);if (aclAnno == null) {return;}String expression = aclAnno.expression();Function<Object[], T> function;build_function_label:{if (Strings.isNullOrEmpty(expression)) {//args[0]function = (objs) -> (T) objs[0];break build_function_label;}Pair pair = findParamPair(method, expression);int index = pair.getIndex();String field = pair.getField();if (Strings.isNullOrEmpty(field)) {//args[x]function = (objs) -> (T) objs[index];break build_function_label;}Class clazz = method.getParameterTypes()[index];//gettertry {Method fieldGetter = getterMethod(clazz, field);function = (objs) -> {try {//args[x].getterField()return (T) fieldGetter.invoke(objs[index]);} catch (IllegalAccessException | InvocationTargetException e) {throw new RuntimeException(e);}};} catch (NoSuchMethodException e) {function = (objs) -> (T) new RuntimeException("throwable IdDetector --- pls check your code");}}cache.put(method, new IdDetector(function));logger.info("Generate a id-detector for : {}.{} ", method.getDeclaringClass().getSimpleName(), method.getName());}private final String basePackage;public CacheableIdDetectorFactory(String basePackage) {this.basePackage = basePackage;}private Set<BeanDefinition> scan() {ClassPathScanningCandidateComponentProvider scanner = new ClassPathScanningCandidateComponentProvider(false);scanner.addIncludeFilter(new AnnotationTypeFilter(Acl.class));String[] packages = StringUtils.tokenizeToStringArray(this.basePackage, ",; \t\n");Set<BeanDefinition> definitions = new HashSet<>();for (String pkg : packages) {definitions.addAll(scanner.findCandidateComponents(pkg));}return definitions;}@Overridepublic void afterPropertiesSet() throws Exception {Set<BeanDefinition> definitions = scan();definitions.stream().map(bd -> {String className = bd.getBeanClassName();try {Class clazz = Class.forName(className);return clazz.getMethods();} catch (ClassNotFoundException e) {logger.error("[" + className + "] not found :", e);System.exit(-1);}return null;}).filter(Objects::nonNull).flatMap(Arrays::stream).forEach(this::initCache);}}

Aspect

@Aspect
public class AclCheckAspect {private final IdDetectorFactory idDetectorFactory;public AclCheckAspect(IdDetectorFactory idDetectorFactory) {this.idDetectorFactory = idDetectorFactory;}@Before("@annotation(aclAnno)")public void before(JoinPoint joinPoint, AclCheckPoint aclAnno) throws Exception {MethodSignature signature = (MethodSignature) joinPoint.getSignature();IdDetector<String> idDetector = idDetectorFactory.getIdDetector(signature.getMethod());Object[] args = joinPoint.getArgs();String expressionValue = idDetector.detect(args);//todo }}

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