【转】throw 和 throw ex 的区别

源地址：http://blog.csdn.net/Joy_Zhao/archive/2006/10/27/1352777.aspx

很多时候，大家当用到向上抛出异常的时候，常常是throw;和throw ex;随便用，从来都没有留意它们之间的区别．今天我才知道，它们之间是有区别的．原文出自：http://mattgollob.blogspot.com/2006/08/throw-vs-throw-ex-heres-difference.html．

　　大家先看看这个例子．

class Program
{
static void Main(string[] args)
{

ThrowSample ts = new ThrowSample();

 try { ts.ThrowMethod(); }
  catch(Exception ex)

  {

  Trace.WriteLine(

  "Exception caught from ThrowMethod:");

  Trace.WriteLine(ex.ToString());
 }

    try { ts.ThrowExMethod2(); }

  catch (Exception ex)
  {

 Trace.WriteLine( "Exception caught from ThrowExMethod:");

 Trace.WriteLine(ex.ToString());

  }
  }

下面是ThrowSample类：

    class ThrowSample
    {
        public ThrowSample()
        {

        }

        private void ExceptionMethod()
        {
            throw;
        }

        public void ThrowExMethod()
        {

            try { this.ExceptionMethod(); }
            catch (Exception ex)
            {
                // Log the exception
                throw;
            }
        }

        public void ThrowExMethod2()
        {

            try { this.ExceptionMethod(); }
            catch (Exception ex)
            {
                // Log the exception
                throw ex;
            }
        }
    }大家可以看到它的两个方法ThrowMethod()与ThrowMethod２()之间的区别，一个是用了throw，另外一个则是用throw ex，好，执行第一段代码，输出结果如下：

Exception caught from ThrowMethod:
System.Exception: DOH!
   at ThrowSample.ThrowSample.ExceptionMethod() in
      C:ThrowSampleProgram.cs:line 55
   at ThrowSample.ThrowSample.ThrowMethod() in
      C:ThrowSampleProgram.cs:line 38
   at ThrowSample.Program.Main(String[] args) in
      C:ThrowSampleProgram.cs:line 14

Exception caught from ThrowExMethod２:
System.Exception: DOH!
   at ThrowSample.ThrowSample.ThrowExMethod２() in
      C:ThrowSampleProgram.cs:line 48
   at ThrowSample.Program.Main(String[] args) in
      C:ThrowSampleProgram.cs:line 21
从结果我们不难发现，前者比后者多了一条信息，而这条信息正是发生异常的根本来源的说明，而后者显然漏掉了这一关键信息．如果我们采用后者，那么我们势必会很难发现问题的来源，特别是当ThrowExMethod方法非常复杂的时候．现在让我们做个假设，如果从ThrowExMethod到ExceptionMethod之间还夹杂了一系列的方法调用，每一个方法都往上抛出一个新的异常（throw ex;）那我们将更加困难的知道异常真正发生的地方，所以明白它们之间的区别非常重要．

　　尽管如此，也不是说throw ex;就是一无是处，就是完全不好的，你可以在当你需要向你捕获的异常中添加一些信息的时候，可以新建一个异常，然后初始化原始异常为其内部异常，比如：

public void ThrowExMethod2()
...{

    try ...{ this.ExceptionMethod(); }
    catch (Exception ex)
    ...{
        // Log the exception
         throw new ApplicationException("Uh-oh!", ex);
    }
}那么异常的堆栈信息将会被正确保存：

Exception caught from ThrowExMethod:
System.ApplicationException: Uh-oh! ---> System.Exception: DOH!
   at ThrowSample.ThrowSample.ExceptionMethod() in
      C:ThrowSampleProgram.cs:line 65
   at ThrowSample.ThrowSample.ThrowExMethod2() in
      C:ThrowSampleProgram.cs:line 54
--- End of inner exception stack trace ---
   at ThrowSample.ThrowSample.ThrowExMethod2() in
      C:ThrowSampleProgram.cs:line 58
   at ThrowSample.Program.Main(String[] args) in
      C:ThrowSampleProgram.cs:line 21
头一次翻译别人的文章，力求把文章意思弄清楚，没有可以去字字句句去对照．

 

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