Spring系列(1)--创建动态代理类

象DotNet,Java之类的语言能够进行动态代理类的创建，得益于其本身并不是直接编译成机器代码，而是编译成中间语言，在运行时才解释或动态编译成目标机器语言。这也是为什么这些概念先在Java兴起的根本原因。产生动态代理类，一般都是利用Emit命名空间的指令，但这个对IL的要求比较高，我这里利用C#提供的动态编译功能实现，

优点是直观，容易理解，不用熟悉IL指令，缺点当然是显得不怎么专业。

（网上很多利用Emit,IL指令构建动态代理类的代码）

能够动态代理(我更倾向于用装饰),一个很关键的地方就是要求你的类中需要被监视(hook)的成员至少是保

护的虚方法.

下面就是动态代理类的工厂类，这里先介绍这个类，后面的博文会解释为什么要这么做:

//代理类工厂，简单的工厂方法.

public class MyProxyFactory
    {

        object _target;
        private List<IMethodInterceptor> _adviceList = new List<IMethodInterceptor>();

       //所谓的前置，后置等通知性类，其实就是要注入的间谍。
        public void Add(IMethodInterceptor advice)
        {
            _adviceList.Add(advice);
        }

       //构造函数，传入目标对象.
        public MyProxyFactory(object target)
        {
            _target = target;
        }

       // 创建并放回代理类。注意，这里是每次都创建，实际上是可以缓存的.

        public object GetProxyClass()
        {
            StringBuilder theClassBuilder = new StringBuilder();
            Type theTargetType = _target.GetType();
            string theProxyClassName = "__" + theTargetType.Name + "_Proxy";
            
            theClassBuilder.AppendLine("using System;");
            theClassBuilder.AppendLine("using System.Collections.Generic;");
            theClassBuilder.AppendLine("using System.Text;");
            theClassBuilder.AppendLine("using System.Reflection;");
            theClassBuilder.AppendLine("using System.Reflection.Emit;");

            theClassBuilder.AppendLine("namespace " + theTargetType.Namespace);
            theClassBuilder.AppendLine("{");
            theClassBuilder.AppendLine("public class "+theProxyClassName+" : " + theTargetType.FullName + "{");
            theClassBuilder.AppendLine("   private " + theTargetType.FullName + " _target;");
            theClassBuilder.AppendLine("   private List<IMethodInterceptor> _adviceList = null;");
            theClassBuilder.AppendLine("   public __" + theTargetType.Name + "_Proxy(" + theTargetType.FullName + " target, List<IMethodInterceptor> AdviceList)");
            theClassBuilder.AppendLine("   {");
            theClassBuilder.AppendLine("   _target = target;");
            theClassBuilder.AppendLine("   this._adviceList = AdviceList;");
            theClassBuilder.AppendLine("   }");
            //获取目标类的方法,准备给代理类继承
            MethodInfo[] methodinfos = theTargetType.GetMethods(BindingFlags.Public | BindingFlags.InvokeMethod | BindingFlags.Instance);
            foreach (MethodInfo mi in methodinfos)
            {
                if (mi.IsVirtual)
                {

                    string theRetType = mi.ReturnType.FullName;
                    if (mi.ReturnType == typeof(void))
                    {
                        theRetType = "void";
                    }
                    string theParams = "";
                    string theTypes = "";
                    string thePMInsts = "";
                    ParameterInfo[] thePs = mi.GetParameters();
                    for (int i = 0; i < thePs.Length; i++)
                    {

                        if (i == 0)
                        {
                            theTypes = "typeof(" + thePs[i].ParameterType.FullName + ")";
                            if (thePs[i].IsOut)
                            {
                                theParams = "out " + thePs[i].ParameterType.FullName + " " + thePs[i].Name;
                                thePMInsts = "out " + thePs[i].Name;
                            }
                            else
                            {
                                theParams = "" + thePs[i].ParameterType.FullName + " " + thePs[i].Name;
                                thePMInsts = "" + thePs[i].Name;
                            }
                        }
                        else
                        {
                            theTypes = ",typeof(" + thePs[i].ParameterType.FullName + ")";
                            if (thePs[i].IsOut)
                            {
                                thePMInsts = ",out " + thePs[i].Name;
                                theParams = ",out " + thePs[i].ParameterType.FullName + " " + thePs[i].Name;
                            }
                            else
                            {
                                thePMInsts = "," + thePs[i].Name;
                                theParams = "," + thePs[i].ParameterType.FullName + " " + thePs[i].Name;
                            }
                        }
                    }

                    theClassBuilder.AppendLine("   public override " + theRetType + " " + mi.Name + "(" + theParams + ")");
                    theClassBuilder.AppendLine("   {");
                    theClassBuilder.AppendLine("   if (_adviceList != null)");
                    theClassBuilder.AppendLine("   {");
                    theClassBuilder.AppendLine("       foreach (IMethodInterceptor item in _adviceList)");
                    theClassBuilder.AppendLine("       {");
                    theClassBuilder.AppendLine("           MethodInfo theMI = _target.GetType().GetMethod(\"" + mi.Name + "\", new Type[] { " + theTypes + "});");
                    theClassBuilder.AppendLine("           AdviseInvocation theInvocation = new AdviseInvocation(_target, theMI, new object[]{" + thePMInsts + "});");
                    if (mi.ReturnType == typeof(void))
                    {
                        theClassBuilder.AppendLine("           item.Invoke(theInvocation);");
                    }
                    else
                    {
                        theClassBuilder.AppendLine("           return (" + theRetType + ")(item.Invoke(theInvocation));");
                    }
                    theClassBuilder.AppendLine("      }");

                    theClassBuilder.AppendLine("   }");
                    if (mi.ReturnType == typeof(void))
                    {
                        theClassBuilder.AppendLine("     _target." + mi.Name + "(" + thePMInsts + ");");
                    }
                    else
                    {
                        theClassBuilder.AppendLine("  return (" + theRetType + ")(_target." + mi.Name + "(" + thePMInsts + "));");
                    }
                    theClassBuilder.AppendLine("}");
                }
            }
            theClassBuilder.AppendLine("}");
            theClassBuilder.AppendLine("}");

           //测试观察用
            Console.WriteLine(theClassBuilder.ToString());

            //===============================动态编译代理类代码====================================
            //创建编译器实例。   
            CSharpCodeProvider provider = new CSharpCodeProvider();
            //设置编译参数。   
            CompilerParameters paras = new CompilerParameters();
            paras.GenerateExecutable = false;
            paras.GenerateInMemory = true;
            //paras.ReferencedAssemblies.Add("System.dll");
            paras.ReferencedAssemblies.Add("SpringNetStudy.exe");
            //paras.ReferencedAssemblies.Add("mscorlib.dll");
            //paras.ReferencedAssemblies.Add("");
            //编译代码。   
            CompilerResults result = provider.CompileAssemblyFromSource(paras, theClassBuilder.ToString());

            //获取编译后的程序集。   
            Assembly assembly = result.CompiledAssembly;
            Type theType = assembly.GetType(theTargetType.Namespace+"."+ theProxyClassName,false,true);
            var obj = Activator.CreateInstance(theType, new object[] {_target,_adviceList});
            return obj;
        }
    }

后记：有些东西看起来很神秘，但实际上也不过如此。国内没法做出好的框架，其实一个主要的原因就是编译技术不过关，没有自己的语言。如果Emit和动态编译命名空间的方法不公开，就很难做了.