PHP出现异常该怎么办

<?php
/****************************************************
 * php处理异常
 * try中不主动throw，会先出现PHP的系统错误
 ****************************************************/
header("content-type:test/html:charset=utf-8");
error_reporting(-1);
try {
    $num1 = 3;
    $num2 = 0;
    if ($num2 == 0) {
        throw new Exception("自定义错误");
    } else {
        $res = $num1 / $num2;
    }

} catch (Exception $e) {
    echo $e->getMessage();
    // die(); // 终止异常
}
/******************************************************
 * php+mysql+pdo
 *****************************************************/
try {
    $pdo = new PDO("mysql:host=localhost;dbname=mysql", "root", "");
} catch (PDOException $e) {
    echo $e->getMessage();
    // die(); // 终止异常
}
/******************************************************
 * php+文件异常
 *****************************************************/

/**
 * PHP 读取大文件 SplFileObject :
 * https://blog.csdn.net/ekliu/article/details/8855907
 */
// SqlFileObject相对于传统的open($filename, 'r')产生的对象的优点在于不需要打开文件句柄  不需要关闭句柄更加的方便
$handle = new SplFileObject("sid_list.txt");
while (!$handle->eof()) {
    $item = $handle->fgets();
}

try {
    $pdo = new SplFileObject("text.txt", "r");
    echo "read File";
} catch (Exception $e) {
    echo $e->getMessage();
    // die(); // 终止异常
}
/******************************************************
 * php异常 嵌套
 *****************************************************/
try {
    throw new Exception("测试异常1");
} catch (Exception $e) {
    echo $e->getMessage();
    // die(); // 终止异常
    try {
        throw new Exception("测试异常2");
    } catch (Exception $e) {
        echo $e->getMessage();
    }
}

/******************************************************
 * php异常 自定义异常封装
 *****************************************************/
class MyException extends Exception
{
    public function __construct($message = "", $code = 0, $previous = null)
    {
        parent::__construct($message, $code, $previous);
    }

    public function __toString()
    {
        $message = "<h2>出现异常，如下：</h2>";
        $message .= "<p>" . __CLASS__ . "[{$this->code}:{$this->message}]</p>";
        return $message;
    }

    /****************自定义异常方法***************/
    public function test()
    {
        echo "这是自定义错误";
    }

    public function stop()
    {
        exit("异常 end...");
    }
}

// 开始调用 MyException
try {
    echo "出现异常啦";
    throw new MyException("测试自定义异常", 3);
} catch (MyException $e) {
    echo $e->getMessage();
}

// 嵌套使用 MyException 与 Exception (没有顺序)
try {
    throw new MyException("测试自定义异常");
} catch (Exception $e) {
    echo $e->getMessage();
} catch (MyException $e) {
    echo $e->getMessage();
}

/******************************************************
 * php异常 自定义异常封装    文件
 *****************************************************/
class FileException extends Exception
{
    public function getDetails()
    {
        switch ($this->code) {
            case 0:
                return "没有提供文件";
                break;
            case 1:
                return "文件不存在";
                break;
            case 2:
                return "不是一个文件";
                break;
            case 3:
                return "文件不可写";
                break;
            case 4:
                return "非法文件的操作模式";
                break;
        }
    }
}

class WriteData
{
    private $_message = "";
    private $_fp = null;

    public function __construct($filename = null, $mode = "w")
    {
        $this->_message = "文件:{$filename} ; 模式:{$mode}";
        if (empty($filename)) throw new FileException($this->_message, 0);
        if (!file_exists($filename)) throw new FileException($this->_message, 1);
        if (!is_file($filename)) throw new FileException($this->_message, 2);
        // is_writable — 判断给定的文件名是否可写
        if (!is_writable($filename)) throw new FileException($this->_message, 3);
        if (!in_array($mode, array("w", "w+", "a", "a
        +"))) throw new FileException($this->_message, 4);

        $this->_fp = fopen($filename, $mode);
    }

    public function write($data)
    {
        if (@!fwrite($this->_fp, $data . PHP_EOL)) throw new FileException($this->_message, 5);
    }

    public function close()
    {
        if ($this->_fp) {
            if (!fclose($this->_fp)) throw new FileException($this->_message, 6);
            $this->_fp = null;

        }
    }

    public function __destruct()
    {
        $this->close();
    }
}