try
{
}
catch (Exception ex)
{
    throw ex;

try
{
}
catch (Exception ex)
{
    throw;

try
{
}
catch 
{
    throw;
}

第四种：经过对异常重新包装，但是会保留原始异常点信息。推荐使用。

try
{
}
catch (Exception ex)
{
    throw new Exception("经过进一步包装的异常", ex);
}

下面举例测试:

 1 using System;
 2 using System.Collections.Generic;
 3 using System.Text;
 4 
 5 namespace Api.Service.Common
 6 {
 7     public class ExceptionClass
 8     {
 9         /// <summary>
10         /// 抛出异常方法
11         /// </summary>
12         public void ExceptionThrow1()
13         {
14             try
15             {
16                 // 调用原始异常抛出方法来抛出异常
17                 this.ExceptionMethod();
18             }
19             catch (Exception ex)
20             {
21                 throw ex;
22             }
23         }
24 
25         /// <summary>
26         /// 抛出异常方法1
27         /// </summary>
28         public void ExceptionThrow2()
29         {
30             try
31             {
32                 this.ExceptionMethod();
33             }
34             catch (Exception ex)
35             {
36                 throw;
37             }
38         }
39 
40         /// <summary>
41         /// 抛出异常方法2
42         /// </summary>
43         public void ExceptionThrow3()
44         {
45             try
46             {
47                 this.ExceptionMethod();
48             }
49             catch
50             {
51                 throw;
52             }
53         }
54 
55         /// <summary>
56         /// 抛出异常方法3
57         /// </summary>
58         public void ExceptionThrow4()
59         {
60             try
61             {
62                 this.ExceptionMethod();
63             }
64             catch (Exception ex)
65             {
66                 throw new Exception("经过进一步包装的异常", ex);
67             }
68         }
69 
70         /// <summary>
71         /// 原始异常抛出方法
72         /// </summary>
73         private void ExceptionMethod()
74         {
75             throw new DivideByZeroException();
76         }
77     }
78 }

　　　　　　　ExceptionClass exceptionClass = new ExceptionClass();
            try
            {
                exceptionClass.ExceptionThrow1();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
            Console.WriteLine("分割线--------------------------------------");
            try
            {
                exceptionClass.ExceptionThrow2();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
            Console.WriteLine("分割线--------------------------------------");
            try
            {
                exceptionClass.ExceptionThrow3();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }
            Console.WriteLine("分割线--------------------------------------");
            try
            {
                exceptionClass.ExceptionThrow4();
            }
            catch (Exception ex)
            {
                Console.WriteLine(ex.ToString());
            }

举例结果:

 我们可以明显看出new Exception()自己包装的异常比较详细，能找到异常的跟踪，其次是throw  都可以找到异常源。

throw ex;会把异常吞掉，抛出新的异常，这样会让开发人员找不到异常源。

推荐使用new Excetion()也就是第四种方式。