[2]rubyruby on rails入门笔记---Ruby中的异常

Ruby中异常处理非常的重要，Ruby中异常处理，包括Exception 捕获，Retry，Raise，ensure ，Else格式，Throw...Catch已经类级别的异常。其具体格式和用法如下。

1. Exception 捕获，其格式如下，和Java中的try...catch...finally有的一拼

begin

# -

rescue OneTypeOfException

# -

rescue AnotherTypeOfException

# -

else

# Other exceptions

ensure

# Always will be executed

end

--------Sample------

begin

file= open("/unexistant_file")

puts"-----1111111----"

iffile

puts"-----222222----"

puts"File opened successfully"

end

rescue

puts"-----exceptions----"

file=STDIN

end

printfile,"==",STDIN,"\n"

-----------输出结果-------------

-----exceptions----

#<IO:0x22703d0>==#<IO:0x22703d0>

2. Retry

begin

# Exceptions raised by this code will

# be caught by the following rescue clause

rescue

# This block will capture all types of exceptions

retry # This will move control to the beginning of begin

end

--------Sample------

begin

puts"Try to open file"

file= open("/unexistant_file")

iffile

puts"File opened successfully"

end

rescue

fname="existant_file"

puts"Begin to retry"

retry

end

-----------输出结果会有无限的循环-------------

Try to open file

Begin to retry

Try to open file

Begin to retry

Try to open file

Begin to retry

。。。。。

3.Raise 相当于java中的throw 关键字，自己显式抛出异常

raise

raise "Error Message"

raise ExceptionType, "Error Message"

raise ExceptionType, "Error Message" condition

begin

puts 'I am before the raise.'

raise 'An error has occurred.'

puts 'I am after the raise.'

rescue

puts 'I am rescued.'

end

puts 'I am after the begin block.'

------------------------------------------

I am before the raise.

I am rescued.

I am after the begin block.

4.ensure 相当于java中的finally语句

begin

#.. process

#..raise exception

rescue

#.. handle error

ensure

#.. finally ensure execution

#.. This will always execute.

end

begin

raise'A test exception.'

rescueException=>e

putse.message

putse.backtrace.inspect

ensure

puts"Ensuring execution"

end

-----------输出结果如下-------------

A test exception.

["D:/ruby/learnruby/exception_test.rb:28:in `<top (required)>'", "-e:1:in `load'", "-e:1:in `<main>'"] Ensuring execution

5. Else格式 Else用在异常语句中的情形是，当没有exception抛出来的时候

begin

#.. process

#..raise exception

rescue

# .. handle error

else

#.. executes if there is no exception

ensure

#.. finally ensure execution

#.. This will always execute.

end

--------Sample Code-----------

begin

# raise'A test exception.'

puts"I'm not raising exception"

rescueException=>e

putse.message

putse.backtrace.inspect

else

puts"Congratulations-- no errors!"

ensure

puts"Ensuring execution"

end

-----------输出结果如下-------------

I'm not raising exception

Congratulations-- no errors!

Ensuring execution

6. Throw...Catch 用来跳出循环,这个和Java的try catch有点区别

throw :lablename

#.. this will not be executed

catch :lablename do

#.. matching catch will be executed after a throw is encountered.

end

throw :lablename condition

#.. this will not be executed

catch :lablename do

#.. matching catch will be executed after a throw is encountered.

end

--------------Sample----------------

puts"catchcatchcatchcatchcatchcatchcatchcatchcatchcatchcatchcatchcatch"

defpromptAndGet(prompt)

printprompt

res= readline.chomp

throw:quitRequestedifres=="!"

returnres

end

puts"111111111111111111111111111111111111"

catch:quitRequesteddo

puts"2222222222222222222222222222222"

name= promptAndGet("Name: ")

puts"333333333333333333333333333333"

age= promptAndGet("Age: ")

puts"444444444444444444444444444"

sex= promptAndGet("Sex: ")

puts"5555555555555555555555555555"

# ..

# process information

end

promptAndGet("Name1:")

-----------输出结果如下-------------

catchcatchcatchcatchcatchcatchcatchcatchcatchcatchcatchcatchcatch

111111111111111111111111111111111111

2222222222222222222222222222222

Name: Rodney

333333333333333333333333333333

Age: 33

444444444444444444444444444

Sex: Male

5555555555555555555555555555

Name1:Henry

Process finished with exit code 0

7. Class级别的异常

Ruby's standard classes and modules raise exceptions. All the exception classes

form a hierarchy, with the class Exception at the top. The next level contains

seven different types:

 Interrupt

 NoMemoryError

 SignalException

 ScriptError

 StandardError

 SystemExit

classFileSaveError<NoMemoryError

attr_reader:reason

definitialize(reason)

@reason=reason

end

File.open("input223g.txt","r")do|file|

begin

# Write out the data ...

puts"File can be opened!!!!"

raise'A test exception.'

rescue

# Something went wrong!

puts"Error happend!!!!"

puts$!

puts"-----Test----"

raiseFileSaveError.new($!)

puts"-----end----"

end

-----------输出结果如下-------------

C:\RailsInstaller\Ruby2.2.0\bin\ruby.exe -e $stdout.sync=true;$stderr.sync=true;load($0=ARGV.shift) D:/ruby/learnruby/class_exception.rb

D:/ruby/learnruby/class_exception.rb:18:in `rescue in block in <top (required)>': FileSaveError (FileSaveError)

from D:/ruby/learnruby/class_exception.rb:9:in `block in <top (required)>'

from D:/ruby/learnruby/class_exception.rb:8:in `open'

from D:/ruby/learnruby/class_exception.rb:8:in `<top (required)>'

from -e:1:in `load'

from -e:1:in `<main>'

File can be opened!!!!

Error happend!!!!

A test exception.

-----Test----

Process finished with exit code 1

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[2]rubyruby on rails入门笔记---Ruby中的异常

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