【PHP系列】PHP推荐标准之PSR-3，日志记录器接口

上节聊完了PHP官方的相关代码规范，下面给大家带来了PHP系列的PHP推荐标准的另外两个，PSR-3，PSR-4。

首先，我们先来了解下PSR-3是怎么回事。

PHP-FIG发布的第三个推荐规范与前两个不同，不是一系列的指导方针，而是一个接口，规定PHP日志记录器组件可以实现的方法。

基础

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参数

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.

总的来讲，占位符是为后面的Context参数提供占位服务，$context参数用于构造复杂的日志消息，$context参数的值是一个关联数组，键是占位符的名称（不能有花括号），对应的值用于替换Message参数中的占位符。

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参数

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.

这个参数是可选的，提供用于替换message参数中的占位标记的值。

辅助类和接口

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';
}

总结

如果你想自己写个PSR-3日志记录器，那可没什么必要了，因为已经有很多人干过这件事了。

如果你正在使用Yii2.0框架写代码，你可以搜索下Logger.php这个文件，已经实现的非常好了。你需要做的只是一句简单的：

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

即可，后面我会带大家讨论更多框架的事。

如果你不适用框架，枫爷这里给大家推荐一个很好的组件：monolog/monolog。

Monolog已经完全实现了PSR-3的接口，而且便于使用自定义的消息格式化程序和处理程序扩展功能。

如果大家对monolog感兴趣，可以去到他的官网进行查看，http://monolog.ow2.org/doc/index.html。

有了日志收集功能，如何进行日志的筛选，日志的盘查啥的，枫爷再推荐大家一款非常好用的软件，splunk，免费500M，超过部分要收钱，当然了，国人不会放过任何领域的，如果要免费，那就用用日志易吧，我就用的他，感觉不错的。

splunk：http://10data.com/splunk/

日志易：https://www.rizhiyi.com/

至于怎么用，大家可以先行去他们的官网先行了解，以后有机会，枫爷再教大家搭建日志平台的相关知识。