PHP异常详解
PHP的异常是什么?
PHP 5 提供了一种新的面向对象的错误处理方法。异常处理用于在指定的错误(异常)情况发生时改变脚本的正常流程。这种情况称为异常。
一般使用方法:
<?php function test() { throw new Exception("异常啦"); } try { test(); } catch (Exception $e) { echo $e->getMessage(); }
- throw new Exception('XXX') : 抛出一个异常
- try : 使用异常的函数应该位于 "try" 代码块内。如果没有触发异常,则代码将照常继续执行。但是如果异常被触发,会抛出一个异常。
-
Catch:代码块会捕获异常,并创建一个包含异常信息的对象
自定义异常类:
class myException extends Exception { public function errorMessage() { $errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile() .': <b>'.$this->getMessage().'</b> is not a valid E-Mail address'; return $errorMsg; } } try { throw new myException($email); }catch (myException $e){ echo $e->errorMessage(); }
- myException类是一个自定义的异常类,必须继承Exception
- Exception是一个PHP自带的内置的异常类,默认情况下会使用PHP默认的内置异常类,但是我们可以通过自定义的方式,自定义成满足自己需求的异常类。
- 使用自定义异常类的时候,throw new myException 抛出异常也需要抛出自定义的异常类类名
- catch的时候也需要捕获自定义的异常类
- 如果抛出了异常而不捕获处理的话,就会发生PHP代码报错,如下:
Fatal error: Uncaught exception 'myException' in D:\AppServ\www\cctv\trunk\index.php:12 Stack trace: #0 {main} thrown in D:\AppServ\www\cctv\trunk\index.php on line 12
PHP默认异常类详细:
class exception { protected $message = 'Unknow exception'; //自定义的异常信息 protected $code = 0; //定义的异常代码 protected $file; //发生异常的PHP程序名 protected $line; //发生异常的PHP行号 //用于传递用户自定义异常信息和用户自定义异常代码的构造函数 function __construct($message=null,$code=0); final function getMessage(); final function getCode(); final function getFile(); final function getLine(); final function getTrace(); //以数组形式返回异常传递的路线 final function getTraceAsString(); //返回格式化成字符串的getTrace函数信息 function __toString(); //可重载,用于返回可输出的字符串 }
- 可以看到PHP默认异常类中有很多自定义变量和方法
- $e->getMessage 一般是获取错误信息
- $e->getCode() 一般是获取错误码
- $e->getFile() 获取错误的文件信息
- $e->getLine() 获取错误行数
- $e->getTrace() 异常经过的文件路径
- __toString() 一般可以重载,用于返回可输出的字符串
PHP异常类的作用:
- 捕获异常,一般可以在MYSQL链接不上,或者业务逻辑错误的时候,抛出异常,在代码最顶端接收。
- 异常分析处理。可以在出异常的时候,捕获到异常的错误信息,写入日志。
- 可以返回友好化的提示信息,例如WEB端可以返回页面形式,也可以在AJAX端返回JSON数据格式。
- 原则:如果异常抛出了,就必须捕获它,否则会PHP报错。

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