Spring使用Spel表达式获取参数值

一、依赖

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

<!-- aop -->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-aop</artifactId>
</dependency>

二、注解

@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Limiter {
    /**
     * 使用spel表达式获取限流的key
     * @return
     */
    String value();
}

三、AOP切面的应用

@Aspect
@Component
public class LimiterAspect {
    private ExpressionParser parser = new SpelExpressionParser();
    private LocalVariableTableParameterNameDiscoverer discoverer = new LocalVariableTableParameterNameDiscoverer();

    @Pointcut("@annotation(limiter)")
    public void pointcut(Limiter limiter) {
    }

    @Around("pointcut(limiter)")
    public Object around(ProceedingJoinPoint pjp, Limiter limiter) throws Throwable {
        Method method = this.getMethod(pjp);
        String methodName = method.toString();

        //获取方法的参数值
        Object[] args = pjp.getArgs();
        EvaluationContext context = this.bindParam(method, args);

        //根据spel表达式获取值
        Expression expression = parser.parseExpression(limiter.value());
        Object key = expression.getValue(context);
        //打印
        System.out.println(key);
        
        return pjp.proceed();
    }

    /**
     * 获取当前执行的方法
     *
     * @param pjp
     * @return
     * @throws NoSuchMethodException
     */
    private Method getMethod(ProceedingJoinPoint pjp) throws NoSuchMethodException {
        MethodSignature methodSignature = (MethodSignature) pjp.getSignature();
        Method method = methodSignature.getMethod();
        Method targetMethod = pjp.getTarget().getClass().getMethod(method.getName(), method.getParameterTypes());
        return targetMethod;
    }

    /**
     * 将方法的参数名和参数值绑定
     *
     * @param method 方法，根据方法获取参数名
     * @param args   方法的参数值
     * @return
     */
    private EvaluationContext bindParam(Method method, Object[] args) {
        //获取方法的参数名
        String[] params = discoverer.getParameterNames(method);

        //将参数名与参数值对应起来
        EvaluationContext context = new StandardEvaluationContext();
        for (int len = 0; len < params.length; len++) {
            context.setVariable(params[len], args[len]);
        }
        return context;
    }

四、Controller

@RestController
public class TestController {

    //获取名为id的参数
    @Limiter("#id")
    @GetMapping("test")
    public String test(Long id){
        return "hello";
    }
}

五、获取对象（补充）

1、注解

@Limter(value = "#testObj")
public JSONObject test01(TestObj  testObj){
      // ......      
}

多个切点同时获取

/**
 * 设置操作日志切入点 记录操作日志 在注解的位置切入代码
 */
//@Pointcut("@annotation(com.test.Limter)")
@Pointcut("@annotation(limter)")
public void operLogPointCut(Limter limter) {
}

@Pointcut("execution(public * com.test.aaa..*.*(..))")
public void operLogPointMethod() {
}

线程变量的使用，当前切面类中使用线程变量存储变量

@Aspect
@Component
public class LogAspect {

    @Autowired
    private LogsService logsService;
    // 线程变量
    private ThreadLocal<String> threadLocal = new ThreadLocal<>();

    /**
     * 设置操作日志切入点 记录操作日志 在注解的位置切入代码
     */

方法体中存入数据

public void savaData(){
    threadLocal.set("asdf");
}

在另一个方法体中获取当前线程数据

public void savaData(){
    String value = threadLocal.get();
}

切点多条件限制 &&

@AfterReturning(value = "operLogPointCut(limter) && operLogPointMethod()", returning = "returnValue")
    public void saveOperLog(JoinPoint joinPoint, Limter limter, Object returnValue) {
        Object[] args = joinPoint.getArgs();
        // 从切面织入点处通过反射机制获取织入点处的方法
        MethodSignature signature = (MethodSignature) joinPoint.getSignature();
        // 获取切入点所在的方法
        Method method = signature.getMethod();
        EvaluationContext context = this.bindParam(method, args);
        Expression expression = parser.parseExpression(limter.value());

        TestObj testObj= expression.getValue(context, TestObj.class);
        // ......
        new Thread(() -> logsService.saveLogs(Obj...)).start();

        // 存入数据库后移除当前线程变量
        threadLocal.remove();
    }

 参考：

https://blog.csdn.net/weixin_45052750/article/details/105742934

 其他参考：

https://www.codeleading.com/article/30952452765/