简单示例：
//自己实现一个拦截器
public class TestHelloBefore:AspectBefore
{
public override Task Before(AspectContext aspectContext)
{
Console.WriteLine("TestHelloBefore");
return Task.CompletedTask;
}
}
[Component]
public class TestHello
{
[TestHelloBefore]//打上拦截器
public virtual void Say()
{
Console.WriteLine("Say");
}
}
先执行 TestHelloBefor的Before方法再执行你的Say方法
更多使用示例请查看 Aspect拦截器
切面是什么？
定义一个切面(根据筛选器去实现满足条件的多个类的多个方法的“拦截器”
简单示例：
[Component]
public class ProductController
{
public virtual string GetProduct(string productId)
{
return "GetProduct:" + productId;
}
public virtual string UpdateProduct(string productId)
{
return "UpdateProduct:" + productId;
}
}
[Component]
public class UserController
{
public virtual string GetUser(string userId)
{
return "GetUser:" + userId;
}
public virtual string DeleteUser(string userId)
{
return "DeleteUser:" + userId;
}
}
// *Controller 代表匹配 只要是Controller结尾的类都能匹配
// Get* 代表上面匹配成功的类下 所以是Get打头的方法都能匹配
[Pointcut(Class = "*Controller",Method = "Get*")]
public class LoggerPointCut
{
[Around]
public async Task Around(AspectContext context,AspectDelegate next)
{
Console.WriteLine("PointcutTest1.Around-start");
await next(context);
Console.WriteLine("PointcutTest1.Around-end");
}
[Before]
public void Before()
{
Console.WriteLine("PointcutTest1.Before");
}
[After]
public void After()
{
Console.WriteLine("PointcutTest1.After");
}
[AfterReturn(Returing = "value1")]
public void AfterReturn(object value1)
{
Console.WriteLine("PointcutTest1.AfterReturn");
}
[AfterThrows(Throwing = "ex1")]
public void Throwing(Exception ex1)
{
Console.WriteLine("PointcutTest1.Throwing");
}
}
更多示例请查看 Pointcut切面编程
如何实现的
分为3步
1.搜集拦截算子
因为拦截器的使用是约定了要继承 AspectInvokeAttribute
/// <summary>
/// AOP拦截器 默认包含继承关系
/// </summary>
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Class)]
public class AspectInvokeAttribute : Attribute
{
/// <summary>
/// 排序 值越低，优先级越高
/// </summary>
public int OrderIndex { get; set; }
/// <summary>
/// 分组名称
/// </summary>
public string GroupName { get; set; }
}
这一组注解是暴露给外部使用，来搜集哪些类的哪些方法需要增强
接下来需要去针对性去实现每一种增强器要做的事情
定义一个增强器接口IAdvice
internal interface IAdvice
{
/// <summary>
/// 拦截器方法
/// </summary>
/// <param name="aspectContext">执行上下文</param>
/// <param name="next">下一个增强器</param>
/// <returns></returns>
Task OnInvocation(AspectContext aspectContext, AspectDelegate next);
}
Before增强器
/// <summary>
/// 前置增强器
/// </summary>
internal class AspectBeforeInterceptor : IAdvice
{
private readonly AspectBefore _beforeAttribute;
public AspectBeforeInterceptor(AspectBefore beforeAttribute)
{
_beforeAttribute = beforeAttribute;
}
public async Task OnInvocation(AspectContext aspectContext, AspectDelegate next)
{
//先执行Before逻辑
await this._beforeAttribute.Before(aspectContext);
//在走下一个增强器
await next.Invoke(aspectContext);
}
}
After增强器
/// <summary>
/// 后置增强器
/// </summary>
internal class AspectAfterInterceptor : IAdvice
{
private readonly AspectAfter _afterAttribute;
private readonly bool _isAfterAround;
public AspectAfterInterceptor(AspectAfter afterAttribute, bool isAfterAround = false)
{
_afterAttribute = afterAttribute;
_isAfterAround = isAfterAround;
}
public async Task OnInvocation(AspectContext aspectContext, AspectDelegate next)
{
try
{
if (!_isAfterAround) await next.Invoke(aspectContext);
}
finally
{
//不管成功还是失败都会执行的
await this._afterAttribute.After(aspectContext, aspectContext.Exception ?? aspectContext.ReturnValue);
}
}
}
环绕增强器
/// <summary>
/// 环绕返回拦截处理器
/// </summary>
internal class AspectAroundInterceptor : IAdvice
{
private readonly AspectArround _aroundAttribute;
private readonly AspectAfterInterceptor _aspectAfter;
private readonly AspectAfterThrowsInterceptor _aspectThrows;
public AspectAroundInterceptor(AspectArround aroundAttribute, AspectAfter aspectAfter, AspectAfterThrows chainAspectAfterThrows)
{
_aroundAttribute = aroundAttribute;
if (aspectAfter != null)
{
_aspectAfter = new AspectAfterInterceptor(aspectAfter, true);
}
if (chainAspectAfterThrows != null)
{
_aspectThrows = new AspectAfterThrowsInterceptor(chainAspectAfterThrows, true);
}
}
public async Task OnInvocation(AspectContext aspectContext, AspectDelegate next)
{
Exception exception = null;
try
{
if (_aroundAttribute != null)
{
await _aroundAttribute.OnInvocation(aspectContext, next);
return;
}
}
catch (Exception ex)
{
exception = ex;
}
finally
{
if (exception == null && _aspectAfter != null) await _aspectAfter.OnInvocation(aspectContext, next);
}
try
{
if (exception != null && _aspectAfter != null)
{
await _aspectAfter.OnInvocation(aspectContext, next);
}
if (exception != null && _aspectThrows != null)
{
await _aspectThrows.OnInvocation(aspectContext, next);
}
}
finally
{
if (exception != null) throw exception;
}
}
}
返回值增强器
/// <summary>
/// 后置返值增强器
/// </summary>
internal class AspectAfterReturnInterceptor : IAdvice
{
private readonly AspectAfterReturn _afterAttribute;
public AspectAfterReturnInterceptor(AspectAfterReturn afterAttribute)
{
_afterAttribute = afterAttribute;
}
public async Task OnInvocation(AspectContext aspectContext, AspectDelegate next)
{
await next.Invoke(aspectContext);
//执行异常了不执行after 去执行Throw
if (aspectContext.Exception != null)
{
return;
}
if (_afterAttribute != null)
{
await this._afterAttribute.AfterReturn(aspectContext, aspectContext.ReturnValue);
}
}
}
异常返回增强器
/// <summary>
/// 异常返回增强器
/// </summary>
internal class AspectAfterThrowsInterceptor : IAdvice
{
private readonly AspectAfterThrows _aspectThrowing;
private readonly bool _isFromAround;
public AspectAfterThrowsInterceptor(AspectAfterThrows throwAttribute, bool isFromAround = false)
{
_aspectThrowing = throwAttribute;
_isFromAround = isFromAround;
}
public async Task OnInvocation(AspectContext aspectContext, AspectDelegate next)
{
try
{
if (!_isFromAround) await next.Invoke(aspectContext);
}
finally
{
//只有目标方法出现异常才会走 增强的方法出异常不要走
if (aspectContext.Exception != null)
{
Exception ex = aspectContext.Exception;
if (aspectContext.Exception is TargetInvocationException targetInvocationException)
{
ex = targetInvocationException.InnerException;
}
if (ex == null)
{
ex = aspectContext.Exception;
}
var currentExType = ex.GetType();
if (_aspectThrowing.ExceptionType == null || _aspectThrowing.ExceptionType == currentExType)
{
await _aspectThrowing.AfterThrows(aspectContext, aspectContext.Exception);
}
}
}
}
}
2. 组装增强器们成为一个调用链
每一个node的有三个信息，如下
/// <summary>
/// 拦截node组装
/// </summary>
internal class AspectMiddlewareComponentNode
{
/// <summary>
/// 下一个
/// </summary>
public AspectDelegate Next;
/// <summary>
/// 执行器
/// </summary>
public AspectDelegate Process;
/// <summary>
/// 组件
/// </summary>
public Func<AspectDelegate, AspectDelegate> Component;
}
采用LinkedList来构建我们的拉链式调用， 我们把上面的每个增强器作为一个个middeware，添加进来。
internal class AspectMiddlewareBuilder
{
private readonly LinkedList<AspectMiddlewareComponentNode> Components = new LinkedList<AspectMiddlewareComponentNode>();
/// <summary>
/// 新增拦截器链
/// </summary>
/// <param name="component"></param>
public void Use(Func<AspectDelegate, AspectDelegate> component)
{
var node = new AspectMiddlewareComponentNode
{
Component = component
};
Components.AddLast(node);
}
/// <summary>
/// 构建拦截器链
/// </summary>
/// <returns></returns>
public AspectDelegate Build()
{
var node = Components.Last;
while (node != null)
{
node.Value.Next = GetNextFunc(node);
node.Value.Process = node.Value.Component(node.Value.Next);
node = node.Previous;
}
return Components.First.Value.Process;
}
/// <summary>
/// 获取下一个
/// </summary>
/// <param name="node"></param>
/// <returns></returns>
private AspectDelegate GetNextFunc(LinkedListNode<AspectMiddlewareComponentNode> node)
{
return node.Next == null ? ctx => Task.CompletedTask : node.Next.Value.Process;
}
}
然后build方法会构建成一个一层嵌套一层的pipeline管道（一个委托）
更多关于这种设计模式更多信息请参考我另外一篇文章: 中间件(middlewware)模式
按照我们的需求构建的完整执行示意图如下：
单个拦截器或者切面
多个拦截器或者切面
生成代理类代理目标方法去执行上面构造的拦截器链
这一步就简单了，如果检测到目标有打拦截器注解，则会给这个类动态创建一个proxy类，
生成代理类用的是castle.core的dynamic组件
默认的是Class+virtual的方式对目标方法进行拦截
注意:考虑到性能，在项目启动的时候把构建好进行缓存，然后再拦截器里面使用
好了，拦截器和切面介绍到此，更多教程请参考项目wiki(教程很详细哦，别忘记给个star)
https://github.com/yuzd/Autofac.Annotation/wiki
关注公众号一起学习