我一直以來就是這樣寫代碼:
01: public void ThrowFunction()
02: {
03: //Initialize
04: String errMessage = "Just sample throwing.";
05: Boolean isSomeWrong = true;
06: //do something
07: if(isSomeWrong)
08: throw new Exception(errMessage);
09: }
10:
11: public Object GetSomeReturn()
12: {
13: Object ret = null; // return value.
14: Object someObj = null; // local value.
15:
16: try
17: {
18: //Initialize
19: ret = new Object();
20: somObj = new Object();
21: // do some thing
22: ThrowFunction();
23: }
24: catch(Exception e)
25: {
26: // Clean up return value.
27: if(ret != null) { ret.Dispose(); ret = null; }
28: throw e;
29: }
30: finally
31: {
32: if(somObj != null) { somObj.Dispose(); somObj = null; }
33: }
34: return ret;
35: }
怎麼看都好像沒問題,msdn也是這樣寫的,連Java都是這樣寫的。但在總是在上一層的
catch中發現少了些信息。最近搜索到一篇文章才發現我正正寫錯了2年。而且,文章提
到的書也頗有名氣。問題在哪?就在於"throw e"。這些寫打斷了錯誤棧(stack)鏈
(break the exception chain or exception stack trace)。如果你查看這個
Exception變量的StackTrace屬性:
Exception: System.Exception: "Just sample throwing."
at XXX.GetSomeReturn() in YourProgramPath/SourceCodeName.cs:line 18
是line:28。但是就丟失了關於ThrowFunction發生的事。實際上如果這不是你要的結
果,你只要把28行改爲'throw;'即可。如果你catch exception僅僅爲了clean-up。
還可以把24行改爲'catch(Exception)' 甚至'catch'。最懶惰的寫法就是:
01: public void ThrowFunction()
02: {
03: //Initialize
04: String errMessage = "Just sample throwing.";
05: Boolean isSomeWrong = true;
06: //do something
07: if(isSomeWrong)
08: throw new Exception(errMessage);
09: }
10:
11: public Object GetSomeReturn()
12: {
13: Object ret = null; // return value.
14: Object someObj = null; // local value.
15:
16: try
17: {
18: //Initialize
19: ret = new Object();
20: somObj = new Object();
21: // do some thing
22: ThrowFunction();
23: }
24: catch
25: {
26: // Clean up return value.
27: if(ret != null) { ret.Dispose(); ret = null; }
28: throw;
29: }
30: finally
31: {
32: if(somObj != null) { somObj.Dispose(); somObj = null; }
33: }
34: return ret;
35: }
當然如果你想重新包裝你的異常,則:
01: public void ThrowFunction()
02: {
03: //Initialize
04: String errMessage = "Just sample throwing.";
05: Boolean isSomeWrong = true;
06: //do something
07: if(isSomeWrong)
08: throw new Exception(errMessage);
09: }
10:
11: public Object GetSomeReturn()
12: {
13: Object ret = null; // return value.
14: Object someObj = null; // local value.
15:
16: try
17: {
18: //Initialize
19: ret = new Object();
20: somObj = new Object();
21: // do some thing
22: ThrowFunction();
23: }
24: catch(Exception e)
25: {
26: // Clean up return value.
27: if(ret != null) { ret.Dispose(); ret = null; }
28: throw new YourException("Your costum error message",e);
29: }
30: finally
31: {
32: if(somObj != null) { somObj.Dispose(); somObj = null; }
33: }
34: return ret;
35: }
上面的寫法:
throw new YourException("Your costum error message",e);
同樣不會打斷stack trace。比如需要Log下異常然後重拋該異常而不打斷stack trace。
可以這樣寫:
01: public void ThrowFunction()
02: {
03: //Initialize
04: String errMessage = "Just sample throwing.";
05: Boolean isSomeWrong = true;
06: //do something
07: if(isSomeWrong)
08: throw new Exception(errMessage);
09: }
10:
11: public Object GetSomeReturn()
12: {
13: Object ret = null; // return value.
14: Object someObj = null; // local value.
15:
16: try
17: {
18: //Initialize
19: ret = new Object();
20: somObj = new Object();
21: // do some thing
22: ThrowFunction();
23: }
24: catch(Exception e)
25: {
26: // Clean up return value.
27: if(ret != null) { ret.Dispose(); ret = null; }
28: YourLogClass.LogException(e);
29: throw;
30: }
31: finally
32: {
33: if(somObj != null) { somObj.Dispose(); somObj = null; }
34: }
35: return ret;
25: }
Link
Read the original article about re-throw exception.
你會重拋異常(re-throw Exception)不?
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