关于Composer
Composer 是 PHP 的一个依赖管理工具。它允许你申明项目所依赖的代码库，它会在你的项目中为你安装他们。
关于Composer的更多介绍可以查看下面的中文文档，里面介绍的很详细。我的理解是Composer提供了我们如下的好处和功能：
-
“帮助”
PHP项目模块化，我们可以编写或使用功能模块来组成我们的项目。 -
将那些提供功能的第三方库集中管理，减小了
PHP项目迁移中的体积，同时增加了项目的可迁移性。 -
解决项目的依赖关系及依赖库的依赖关系。方便开发的同时也方便了测试、运维等工作。
安装配置
curl -sS https://getcomposer.org/installer | php
注意：如果出现如下的错误，请编译安装php拓展openssl。(可见PHP编译安装openssl拓展 )
Some settings on your machine make Composer unable to work properly.
Make sure that you fix the issues listed below and run this script again:
The openssl extension is missing, which means that secure HTTPS transfers are impossible.
If possible you should enable it or recompile php with --with-openssl
如果成功下载并安装，会在目录生成composer.phar文件：
[shebnowei@localhost composer]$ curl -sS https://getcomposer.org/installer | php
Downloading 1.2.2...
Composer successfully installed to: /home/shebnowei/composer/composer.phar
Use it: php composer.phar
Some settings on your machine may cause stability issues with Composer.
If you encounter issues, try to change the following:
The zlib extension is not loaded, this can slow down Composer a lot.
If possible, install it or recompile php with --with-zlib
The php.ini used by your command-line PHP is: /usr/local/php/etc/php.ini
If you can not modify the ini file, you can also run `php -d option=value` to modify ini values on the fly. You can use -d multiple times.
[shebnowei@localhost composer]$ ls -l
总用量 1668
-rwxr-xr-x 1 shebnowei shebnowei 1706886 11月 30 23:46 composer.phar
[shebnowei@localhost composer]$ php composer.phar -V
Composer version 1.2.2 2016-11-03 17:43:15
从上述的显示可以看到虽然成功安装了Composer，但是还是建议我们安装PHP的zlib拓展，所以继续动态编译安装zlib拓展即可（过程和上述openssl拓展类似，略过）。
安装配置完PHP的zlib的拓展后重新下载安装composer：
[shebnowei@localhost composer]$ curl -sS https://getcomposer.org/installer | php
All settings correct for using Composer
Downloading 1.2.2...
Composer successfully installed to: /home/shebnowei/composer/composer.phar
Use it: php composer.phar
为了每次使用composer不再指定composer.phar文件路径，我们将composer.phar移动到系统环境变量PATH所包含的路径下面，然后就能够直接执行composer命令:
[shebnowei@localhost composer]$ sudo mv composer.phar /usr/local/bin/composer
[sudo] password for shebnowei:
[shebnowei@localhost composer]$ composer -V
Composer version 1.2.2 2016-11-03 17:43:15
使用
安装配置好composer后我们简单地进行测试，来学习使用composer的一些实用功能。
首先我们建立一个TestProject目录，在里面新建composer.json文件，这个composer.json文件就是用来管理该项目所用到的第三方库依赖关系的。
[shebnowei@localhost composer]$ mkdir TestProject
[shebnowei@localhost composer]$ cd TestProject/
[shebnowei@localhost TestProject]$ vim composer.json
我们使用官网文档的例子，在composer.json中添加monolog依赖：
{
"require": {
"monolog/monolog": "1.*"
}
}
那么我们去哪搜索需要的资源信息，或者当我们想发布自己造的轮子、定制的库资源需要上传发布到哪里？
composer主要资源库packagist是官方提供的资源列表仓库，里面可以搜索项目需要的库或者发布自己的软件包。 同时，国内也提供了资源库镜像，可以解决下载速度慢的问题：Packagist / Composer 中国全量镜像。
保存后，执行composer install将会处理composer.json中的依赖关系，并把其安装到vendor目录下:
[shebnowei@localhost TestProject]$ composer install
Loading composer repositories with package information
Updating dependencies (including require-dev)
[Composer\Downloader\TransportException]
Content-Length mismatch
install [--prefer-source] [--prefer-dist] [--dry-run] [--dev] [--no-dev] [--no-custom-installers] [--no-autoloader] [--no-scripts] [--no-progress] [--no-suggest] [-v|vv|vvv|--verbose] [-o|--optimize-autoloader] [-a|--classmap-authoritative] [--ignore-platform-reqs] [--] [<packages>]...
上述问题应该是网络传输过程出错，我们需要配置使用Packagist / Composer 中国全量镜像。首先我们查看目前composer的全局配置并记录，以保证以后可以恢复：
[shebnowei@localhost TestProject]$ composer config --global --list
[repositories.packagist.type] composer
[repositories.packagist.url] https?://packagist.org
[repositories.packagist.allow_ssl_downgrade] true
[process-timeout] 300
[use-include-path] false
[preferred-install] auto
[notify-on-install] true
[github-protocols] [https, ssh]
[vendor-dir] vendor (/home/shebnowei/composer/TestProject/vendor)
[bin-dir] {$vendor-dir}/bin (/home/shebnowei/composer/TestProject/vendor/bin)
[cache-dir] /home/shebnowei/.cache/composer
[data-dir] /home/shebnowei/.local/share/composer
[cache-files-dir] {$cache-dir}/files (/home/shebnowei/.cache/composer/files)
[cache-repo-dir] {$cache-dir}/repo (/home/shebnowei/.cache/composer/repo)
[cache-vcs-dir] {$cache-dir}/vcs (/home/shebnowei/.cache/composer/vcs)
[cache-ttl] 15552000
[cache-files-ttl] 15552000
[cache-files-maxsize] 300MiB (314572800)
[bin-compat] auto
[discard-changes] false
[autoloader-suffix]
[sort-packages] false
[optimize-autoloader] false
[classmap-authoritative] false
[prepend-autoloader] true
[github-domains] [github.com]
[bitbucket-expose-hostname] true
[disable-tls] false
[secure-http] true
[cafile]
[capath]
[github-expose-hostname] true
[gitlab-domains] [gitlab.com]
[store-auths] prompt
[archive-format] tar
[archive-dir] .
[home] /home/shebnowei/.config/composer
之后执行命令：composer config -g repo.packagist composer https://packagist.phpcomposer.com，更改composer仓库目录为中国镜像地址：
[shebnowei@localhost TestProject]$ composer config -g repo.packagist composer https://packagist.phpcomposer.com
[shebnowei@localhost TestProject]$ composer config --global --list[repositories.packagist.type] composer
[repositories.packagist.url] https://packagist.phpcomposer.com
...省略
可以看到全局配置中的[repositories.packagist.url]已经改为中国镜像地址。之后我们重新执行composer install命令：
[shebnowei@localhost TestProject]$ composer install
Loading composer repositories with package information
Updating dependencies (including require-dev)
- Installing psr/log (1.0.2)
Downloading: 100%
- Installing monolog/monolog (1.22.0)
Downloading: 100%
monolog/monolog suggests installing aws/aws-sdk-php (Allow sending log messages to AWS services like DynamoDB)
monolog/monolog suggests installing doctrine/couchdb (Allow sending log messages to a CouchDB server)
monolog/monolog suggests installing ext-amqp (Allow sending log messages to an AMQP server (1.0+ required))
monolog/monolog suggests installing ext-mongo (Allow sending log messages to a MongoDB server)
monolog/monolog suggests installing graylog2/gelf-php (Allow sending log messages to a GrayLog2 server)
monolog/monolog suggests installing mongodb/mongodb (Allow sending log messages to a MongoDB server via PHP Driver)
monolog/monolog suggests installing php-amqplib/php-amqplib (Allow sending log messages to an AMQP server using php-amqplib)
monolog/monolog suggests installing php-console/php-console (Allow sending log messages to Google Chrome)
monolog/monolog suggests installing rollbar/rollbar (Allow sending log messages to Rollbar)
monolog/monolog suggests installing ruflin/elastica (Allow sending log messages to an Elastic Search server)
monolog/monolog suggests installing sentry/sentry (Allow sending log messages to a Sentry server)
Writing lock file
Generating autoload files
上述安装过程非常快，所以还是非常推荐使用中国镜像地址。我们会发现项目目录中出现了以下文件：
[shebnowei@localhost TestProject]$ ls -l
总用量 12
-rw-rw-r-- 1 shebnowei shebnowei 60 12月 1 19:04 composer.json
-rw-rw-r-- 1 shebnowei shebnowei 5523 12月 1 19:31 composer.lock
drwxrwxr-x 5 shebnowei shebnowei 64 12月 1 19:31 vendor
[shebnowei@localhost TestProject]$ ls -l vendor/
总用量 8
-rw-rw-r-- 1 shebnowei shebnowei 178 12月 1 19:31 autoload.php
drwxrwxr-x 2 shebnowei shebnowei 4096 12月 1 19:31 composer
drwxrwxr-x 3 shebnowei shebnowei 20 12月 1 19:30 monolog
drwxrwxr-x 3 shebnowei shebnowei 16 12月 1 19:30 psr
composer.lock
其中composer.lock记录了依赖包的确切的版本号和依赖包的详细信息，可以称作“锁文件”。
[shebnowei@localhost TestProject]$ cat composer.lock
{
"_readme": [
"This file locks the dependencies of your project to a known state",
"Read more about it at https://getcomposer.org/doc/01-basic-usage.md#composer-lock-the-lock-file",
"This file is @generated automatically"
],
"hash": "861a979d5c0fcd916dbdb669c5f9e89d",
"content-hash": "585e47049b6c4143c5a31fb29d48a3a5",
"packages": [
{
"name": "monolog/monolog",
"version": "1.22.0",
"source": {
"type": "git",
"url": "https://github.com/Seldaek/monolog.git",
"reference": "bad29cb8d18ab0315e6c477751418a82c850d558"
},
"dist": {
"type": "zip",
"url": "https://packagist.phpcomposer.com/files/Seldaek/monolog/bad29cb8d18ab0315e6c477751418a82c850d558.zip",
"reference": "bad29cb8d18ab0315e6c477751418a82c850d558",
"shasum": ""
},
"require": {
"php": ">=5.3.0",
"psr/log": "~1.0"
},
"provide": {
"psr/log-implementation": "1.0.0"
},
"require-dev": {
"aws/aws-sdk-php": "^2.4.9 || ^3.0",
"doctrine/couchdb": "~1.0@dev",
"graylog2/gelf-php": "~1.0",
"jakub-onderka/php-parallel-lint": "0.9",
"php-amqplib/php-amqplib": "~2.4",
"php-console/php-console": "^3.1.3",
"phpunit/phpunit": "~4.5",
"phpunit/phpunit-mock-objects": "2.3.0",
"ruflin/elastica": ">=0.90 <3.0",
"sentry/sentry": "^0.13",
"swiftmailer/swiftmailer": "~5.3"
},
"suggest": {
"aws/aws-sdk-php": "Allow sending log messages to AWS services like DynamoDB",
"doctrine/couchdb": "Allow sending log messages to a CouchDB server",
"ext-amqp": "Allow sending log messages to an AMQP server (1.0+ required)",
"ext-mongo": "Allow sending log messages to a MongoDB server",
"graylog2/gelf-php": "Allow sending log messages to a GrayLog2 server",
"mongodb/mongodb": "Allow sending log messages to a MongoDB server via PHP Driver",
"php-amqplib/php-amqplib": "Allow sending log messages to an AMQP server using php-amqplib",
"php-console/php-console": "Allow sending log messages to Google Chrome",
"rollbar/rollbar": "Allow sending log messages to Rollbar",
"ruflin/elastica": "Allow sending log messages to an Elastic Search server",
"sentry/sentry": "Allow sending log messages to a Sentry server"
},
"type": "library",
"extra": {
"branch-alias": {
"dev-master": "2.0.x-dev"
}
},
"autoload": {
"psr-4": {
"Monolog\\": "src/Monolog"
}
},
"notification-url": "https://packagist.org/downloads/",
"license": [
"MIT"
],
"authors": [
{
"name": "Jordi Boggiano",
"email": "j.boggiano@seld.be",
"homepage": "http://seld.be"
}
],
"description": "Sends your logs to files, sockets, inboxes, databases and various web services",
"homepage": "http://github.com/Seldaek/monolog",
"keywords": [
"log",
"logging",
"psr-3"
],
"time": "2016-11-26 00:15:39"
},
{
"name": "psr/log",
"version": "1.0.2",
"source": {
"type": "git",
"url": "https://github.com/php-fig/log.git",
"reference": "4ebe3a8bf773a19edfe0a84b6585ba3d401b724d"
},
"dist": {
"type": "zip",
"url": "https://packagist.phpcomposer.com/files/php-fig/log/4ebe3a8bf773a19edfe0a84b6585ba3d401b724d.zip",
"reference": "4ebe3a8bf773a19edfe0a84b6585ba3d401b724d",
"shasum": ""
},
"require": {
"php": ">=5.3.0"
},
"type": "library",
"extra": {
"branch-alias": {
"dev-master": "1.0.x-dev"
}
},
"autoload": {
"psr-4": {
"Psr\\Log\\": "Psr/Log/"
}
},
"notification-url": "https://packagist.org/downloads/",
"license": [
"MIT"
],
"authors": [
{
"name": "PHP-FIG",
"homepage": "http://www.php-fig.org/"
}
],
"description": "Common interface for logging libraries",
"homepage": "https://github.com/php-fig/log",
"keywords": [
"log",
"psr",
"psr-3"
],
"time": "2016-10-10 12:19:37"
}
],
"packages-dev": [],
"aliases": [],
"minimum-stability": "stable",
"stability-flags": [],
"prefer-stable": false,
"prefer-lowest": false,
"platform": [],
"platform-dev": []
}
当这个锁文件存在时，composer install会优先下载锁文件里指定版本的依赖包，而忽略composer.json文件中的定义。
而如果我们想更新锁文件里的内容，应该执行composer update命令，改命令会根据composer.json文件里的信息更新依赖，并将新版本更新进锁文件。
注意我们应该提交项目的composer.lock（包括 composer.json）到git之类的版本库中，以保证团队开发使用相同的依赖。
vendor
这个目录存放了该项目所依赖的所有依赖包及依赖包所依赖的软件包，除此之外还包含了自动加载的相关php脚本，只要在我们项目中包含autoload.php,便可以直接使用所有的依赖项目的代码。
[shebnowei@localhost vendor]$ ls
autoload.php composer monolog psr
[shebnowei@localhost vendor]$ cat autoload.php
<?php
// autoload.php @generated by Composer
require_once __DIR__ . '/composer/autoload_real.php';
return ComposerAutoloaderInit676f5dca7eaa86827f92e24f967c5dbc::getLoader();
上边为autoload.php的内容，该脚本主要引用了另一个脚本autoload_real.php,从名字上我们可以猜出这个才是真正实现自动加载的文件（核心）：
[shebnowei@localhost vendor]$ cat ./composer/autoload_real.php
<?php
// autoload_real.php @generated by Composer
class ComposerAutoloaderInit676f5dca7eaa86827f92e24f967c5dbc
{
private static $loader;
public static function loadClassLoader($class)
{
if ('Composer\Autoload\ClassLoader' === $class) {
require __DIR__ . '/ClassLoader.php';
}
}
public static function getLoader()
{
if (null !== self::$loader) {
return self::$loader;
}
spl_autoload_register(array('ComposerAutoloaderInit676f5dca7eaa86827f92e24f967c5dbc', 'loadClassLoader'), true, true);
self::$loader = $loader = new \Composer\Autoload\ClassLoader();
spl_autoload_unregister(array('ComposerAutoloaderInit676f5dca7eaa86827f92e24f967c5dbc', 'loadClassLoader'));
$useStaticLoader = PHP_VERSION_ID >= 50600 && !defined('HHVM_VERSION');
if ($useStaticLoader) {
require_once __DIR__ . '/autoload_static.php';
call_user_func(\Composer\Autoload\ComposerStaticInit676f5dca7eaa86827f92e24f967c5dbc::getInitializer($loader));
} else {
$map = require __DIR__ . '/autoload_namespaces.php';
foreach ($map as $namespace => $path) {
$loader->set($namespace, $path);
}
$map = require __DIR__ . '/autoload_psr4.php';
foreach ($map as $namespace => $path) {
$loader->setPsr4($namespace, $path);
}
$classMap = require __DIR__ . '/autoload_classmap.php';
if ($classMap) {
$loader->addClassMap($classMap);
}
}
$loader->register(true);
return $loader;
}
}
强烈推荐如何使用composer的autoload来自动加载自己编写的函数库与类库？，
对照着自己的项目读完后会对composer的autoload机制原理有一个较为深入的理解。同时可以查看这篇blog：深入 Composer autoload。
composer command
更多composer命令行指令请查阅：composer命令行。
技巧
附上官方推荐的链接（随着自己的积累之后会更新自己的小心得）：
参考文献
