用composer安装php代码（以安装phpmailer为例）

1.安装composer.exe软件

2.下载composer.phar

3.创建composer.json文件

{
    "require": {
        "php": ">=5.5.9",
        "phpmailer/phpmailer": "~5.2"
    },
    "config": {
        "preferred-install": "dist"
    },
    "repositories": {
        "packagist": {
            "type": "composer",
            "url": "https://packagist.phpcomposer.com"
        }
    }
}

4.composer.phar和composer.json都放在项目根目录下

5.安装命令：php composer.char install