【PHP系列】PHP推薦標准之PSR-3，日志記錄器接口

上節聊完了PHP官方的相關代碼規范，下面給大家帶來了PHP系列的PHP推薦標准的另外兩個，PSR-3，PSR-4。

首先，我們先來了解下PSR-3是怎么回事。

PHP-FIG發布的第三個推薦規范與前兩個不同，不是一系列的指導方針，而是一個接口，規定PHP日志記錄器組件可以實現的方法。

基礎

The LoggerInterface exposes eight methods to write logs to the eight RFC 5424levels (debug, info, notice, warning, error, critical, alert, emergency).

<?php

namespace Psr\Log;

/**
 * Describes a logger instance
 *
 * The message MUST be a string or object implementing __toString().
 *
 * The message MAY contain placeholders in the form: {foo} where foo
 * will be replaced by the context data in key "foo".
 *
 * The context array can contain arbitrary data, the only assumption that
 * can be made by implementors is that if an Exception instance is given
 * to produce a stack trace, it MUST be in a key named "exception".
 *
 * See https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-3-logger-interface.md
 * for the full interface specification.
 */
interface LoggerInterface
{
    /**
     * System is unusable.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function emergency($message, array $context = array());

    /**
     * Action must be taken immediately.
     *
     * Example: Entire website down, database unavailable, etc. This should
     * trigger the SMS alerts and wake you up.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function alert($message, array $context = array());

    /**
     * Critical conditions.
     *
     * Example: Application component unavailable, unexpected exception.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function critical($message, array $context = array());

    /**
     * Runtime errors that do not require immediate action but should typically
     * be logged and monitored.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function error($message, array $context = array());

    /**
     * Exceptional occurrences that are not errors.
     *
     * Example: Use of deprecated APIs, poor use of an API, undesirable things
     * that are not necessarily wrong.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function warning($message, array $context = array());

    /**
     * Normal but significant events.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function notice($message, array $context = array());

    /**
     * Interesting events.
     *
     * Example: User logs in, SQL logs.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function info($message, array $context = array());

    /**
     * Detailed debug information.
     *
     * @param string $message
     * @param array $context
     * @return null
     */
    public function debug($message, array $context = array());

    /**
     * Logs with an arbitrary level.
     *
     * @param mixed $level
     * @param string $message
     * @param array $context
     * @return null
     */
    public function log($level, $message, array $context = array());
}

A ninth method, log, accepts a log level as the first argument. Calling this method with one of the log level constants MUST have the same result as calling the level-specific method.

Message參數

1、Every method accepts a string as the message, or an object with a__toString() method. Implementors MAY have special handling for the passed objects. If that is not the case, implementors MUST cast it to a string.

2、The message MAY contain placeholders which implementors MAY replace with values from the context array.

Placeholder names MUST correspond to keys in the context array.

Implementors MAY use placeholders to implement various escaping strategies and translate logs for display. Users SHOULD NOT pre-escape placeholder values since they can not know in which context the data will be displayed.

總的來講，占位符是為后面的Context參數提供占位服務，$context參數用於構造復雜的日志消息，$context參數的值是一個關聯數組，鍵是占位符的名稱（不能有花括號），對應的值用於替換Message參數中的占位符。

The following is an example implementation of placeholder interpolation provided for reference purposes only:

/**
 * Interpolates context values into the message placeholders.
 */
function interpolate($message, array $context = array())
{
    // build a replacement array with braces around the context keys
    $replace = array();
    foreach ($context as $key => $val) {
        // check that the value can be casted to string
        if (!is_array($val) && (!is_object($val) || method_exists($val, '__toString'))) {
            $replace['{' . $key . '}'] = $val;
        }
    }

    // interpolate replacement values into the message and return
    return strtr($message, $replace);
}

// a message with brace-delimited placeholder names
$message = "User {username} created";

// a context array of placeholder names => replacement values
$context = array('username' => 'bolivar');

// echoes "User bolivar created"
echo interpolate($message, $context);

Context參數

1、Every method accepts an array as context data. This is meant to hold any extraneous information that does not fit well in a string.

2、If an Exception object is passed in the context data, it MUST be in the'exception' key.

這個參數是可選的，提供用於替換message參數中的占位標記的值。

輔助類和接口

1、The Psr\Log\AbstractLogger class lets you implement the LoggerInterface very easily by extending it and implementing the generic log method. The other eight methods are forwarding the message and context to it.

2、Similarly, using the Psr\Log\LoggerTrait only requires you to implement the generic log method. Note that since traits can not implement interfaces, in this case you still have to implement LoggerInterface.

3、The Psr\Log\NullLogger is provided together with the interface. It MAY be used by users of the interface to provide a fall-back “black hole” implementation if no logger is given to them. However, conditional logging may be a better approach if context data creation is expensive.

4、The Psr\Log\LoggerAwareInterface only contains a setLogger(LoggerInterface $logger) method and can be used by frameworks to auto-wire arbitrary instances with a logger.

<?php

namespace Psr\Log;

/**
 * Describes a logger-aware instance
 */
interface LoggerAwareInterface
{
    /**
     * Sets a logger instance on the object
     *
     * @param LoggerInterface $logger
     * @return null
     */
    public function setLogger(LoggerInterface $logger);
}

5、The Psr\Log\LoggerAwareTrait trait can be used to implement the equivalent interface easily in any class. It gives you access to $this->logger.

6、The Psr\Log\LogLevel class holds constants for the eight log levels.

<?php

namespace Psr\Log;

/**
 * Describes log levels
 */
class LogLevel
{
    const EMERGENCY = 'emergency';
    const ALERT     = 'alert';
    const CRITICAL  = 'critical';
    const ERROR     = 'error';
    const WARNING   = 'warning';
    const NOTICE    = 'notice';
    const INFO      = 'info';
    const DEBUG     = 'debug';
}

總結

如果你想自己寫個PSR-3日志記錄器，那可沒什么必要了，因為已經有很多人干過這件事了。

如果你正在使用Yii2.0框架寫代碼，你可以搜索下Logger.php這個文件，已經實現的非常好了。你需要做的只是一句簡單的：

Yii::info($message, $category);

即可，后面我會帶大家討論更多框架的事。

如果你不適用框架，楓爺這里給大家推薦一個很好的組件：monolog/monolog。

Monolog已經完全實現了PSR-3的接口，而且便於使用自定義的消息格式化程序和處理程序擴展功能。

如果大家對monolog感興趣，可以去到他的官網進行查看，http://monolog.ow2.org/doc/index.html。

有了日志收集功能，如何進行日志的篩選，日志的盤查啥的，楓爺再推薦大家一款非常好用的軟件，splunk，免費500M，超過部分要收錢，當然了，國人不會放過任何領域的，如果要免費，那就用用日志易吧，我就用的他，感覺不錯的。

splunk：http://10data.com/splunk/

日志易：https://www.rizhiyi.com/

至於怎么用，大家可以先行去他們的官網先行了解，以后有機會，楓爺再教大家搭建日志平台的相關知識。