Detailed explanation of catching specific types of exceptions in php

Exception capture can be easily added in many current IDE tools using shortcut keys to prevent users from seeing errors they cannot understand or even crashing inexplicably, resulting in a poor user experience. Even displaying a friendly crash prompt is much better than directly displaying error:xxxx xxxxxxxxx. This article will introduce in detail how PHP throws exceptions and catches specific types of exceptions. I hope it will be helpful to everyone.

What is an exception?

PHP 5 provides a new object-oriented error handling method.

Exception handling is used to change the normal flow of the script when a specified error (exception) situation occurs. This situation is called an exception.

When an exception is triggered, what usually happens is:

The current code state is saved

Code execution Switched to a predefined exception handler function

Depending on the situation, the handler may restart code execution from the saved code state, terminate script execution, or continue script execution from another location in the code

We will show different error handling methods:

Basic use of exceptions

Creating custom Exception handler

Multiple exceptions

Re-throw exception

Set top-level exception handler

php throw The ultimate goal of throwing exceptions and catching specific types of exceptions is to provide corresponding solutions so that the code can continue to run.

The test environment of this article: PHP5.5.36 Safari 9.1.2

 1 <?php
 2 header("content-type:text/html; charset=utf-8");
 3 /**
 4 * 包裹重量异常
 5 */
 6 class HeavyParcelException extends Exception {}
 7 
 8 /**
 9 * 包裹类
10 */
11 class Parcel {
12 
13   /**
14   * 包裹寄送目的地地址
15   */
16   public $address;
17 
18   /**
19   * 包裹重量
20   */
21   public $weight;
22 }
23 
24 /**
25 * 派送员
26 */
27 class Courier {
28  
29   /** 
30   * 运送
31   */
32   public function ship(Parcel $parcel) {
33     //check we have an address
34     //如果包裹的目的地为空
35     if(empty($parcel->address)) {
36       throw new Exception(&#39;address not Specified(未填写地址)!&#39;);
37     } 
38 
39     //check the weight
40     //如果重量超过5
41     if($parcel->weight > 5) {
42       throw new HeavyParcelException(&#39;Parcel exceeds courier limit(包裹超过运送上限)!&#39;);
43     } 
44 
45     //otherwise we&#39;re coll
46     return true;
47   }
48 }
49 
50 $myCourier = new Courier();
51 $parcel = new Parcel();
52 //add the address if we have it 为了测试这里不填写地址
53 $parcel->weight = 7;
54 try {
55   $myCourier->ship($parcel);
56   echo "parcel shipped";
57 } catch (HeavyParcelException $e) {//捕获HeavyParcelException 不写这个异常的类型名字，就跑到普通Exception抛出去了
58   echo "Parcel weight error(重量错误): " . $e->getMessage();
59   //redirect them to choose another courier
60 } catch (Exception $e) {
61   echo "Someting went wrong(地址错误): " . $e->getMessage();
62   //exit so we don&#39;t try to proceed any further
63   exit;
64 }
65 echo &#39;<br/>&#39;;
66 $a = 123;
67 echo $a;

The code execution sequence starting from line 54:

55 >

32 >

35(The ship method first checks that the address is empty, and Exception will be thrown here instead of HeavyParcelException) on line 57 >

60(caughtException) >

616263 Output address errorexit ; Lines 65 to 67 will not be output.

Tips:

I feel that the most important thing in this area is to figure out the order of code execution. Write a few paragraphs, then revise them and run them.

1. The order of capture depends on which type of Exception is throw in the code in try, and then ## The order in #catch.

Line 2.57 captures a specific type

HeavyParcelException cannot be written incorrectly, or there will be problems if you write Exception. You can try it yourself.

　1) For example, if the address is not empty and line 57 is written as

HeavyParcelException111, then the weight error will be captured in its parent class object on line 60. This is not what we want.

2) For example, if the address is empty and line 57 is written as

Exception, an address error will be thrown, but the catch originally responsible for the weight will be captured. This is not what we want either.

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Customization of PHP exception handler

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