参考： https://segmentfault.com/a/11...
参考： https://segmentfault.com/a/11...

使用加载器的目的

现在基本上所有的框架都使用composer来安装第三方包，并使用它的loader来加载类文件

要想使用某个类，或某个函数，必须要先导入定义该类或该函数的文件，使用自动加载器就不用手动加载，会自动加载相应的文件

如何配置composer.json看的自动加载

"autoload": {
 "psr-4": {
 "Barryvdh\\Debugbar\\": "src/", //值中最后的/可以省略，但键中最后的\不能省略
 "HieuLe\\Active\\": "src/",
 "HieuLe\\ActiveTest\\": "tests/",
 "Wang\\": "./src/"
 },
 "psr-0": {
 "DoctrineTest\\InstantiatorPerformance\\": "tests",
 "DoctrineTest\\InstantiatorTest\\": "tests",
 "DoctrineTest\\InstantiatorTestAsset\\": "tests",
 "JakubOnderka\\PhpConsoleHighlighter": "src/",
 "Mockery": "library/",
 "Zhang\\": "./src/"
 },
 "files": [
 "src/helpers.php","src/carbon_compat.php",
 "src/Illuminate/Foundation/helpers.php",
 "src/Illuminate/Support/helpers.php"
 ],
 "classmap": ["hamcrest"],
},
// psr-0和psr-4对应的文件名不一样，psr-0的路径更深
// 官方推荐使用psr-4，慢慢淘汰psr-0
// psr-4必须以\结尾，psr-0没关系
// psr-0将类名中的_转为\，psr-4不转
use Wang\testClass, 那就对应src/testClass.php
use Wang\test\testClass, 那就对应src/test/testClass.php
use Zhang\testClass, 那就对应src/Zhang/testClass.php
use Zhang\test\testClass, 那就对应src/Zhang/test/testClass.php
// 对于不符合PSR规范的类，使用classmap来

了解加载器的几个属性

Composer\Autoload\ClassLoader Object(
 // 与psr-4相关的3个属性
 prefixLengthsPsr4 => [
 //先小写字母倒序,后大写字母倒序，键名以\结尾，值为键名的长度
 p => [
 phpDocumentor\Reflection\ => 25
 ] 
 S =>[
 Symfony\Polyfill\Mbstring\ => 26
 Symfony\Component\VarDumper\ => 28
 ] 
 A => [
 App\ => 4
 ]
 ]
 prefixDirsPsr4 => [
 phpDocumentor\Reflection\ => [
 0 => 项目根目录/vendor/composer/../phpdocumentor/reflection-common/src
 1 => 项目根目录/vendor/composer/../phpdocumentor/reflection-docblock/src
 2 => 项目根目录/vendor/composer/../phpdocumentor/type-resolver/src
 ]
 Symfony\Polyfill\Mbstring\ => [
 [0] => 项目根目录/vendor/composer/../symfony/polyfill-mbstring
 ]
 Symfony\Component\VarDumper\ => [
 0 => 项目根目录/vendor/composer/../symfony/var-dumper
 ]
 Symfony\Component\Translation\ => [
 0 => 项目根目录/vendor/composer/../symfony/translation
 ] 
 App\ =>[
 0 => 项目根目录/vendor/composer/../../app
 ]
 ]
 fallbackDirsPsr4 => [] 
 prefixesPsr0 => [
 P => [
 Prophecy\ => [
 0 => 项目根目录/vendor/composer/../phpspec/prophecy/src
 ]
 Parsedown => [
 0 => 项目根目录/vendor/composer/../erusev/parsedown
 ]
 ]
 D => [
 Doctrine\Common\Lexer\ => [
 0 => 项目根目录/vendor/composer/../doctrine/lexer/lib
 ]
 ]
 ]
 fallbackDirsPsr0 => []
 classMap => [
 App\Console\Commands\CalculateActiveUser => 项目根目录/vendor/composer/../../app/Console/Commands/CalculateActiveUser.php
 // 根据类名映射，导入相应文件
 // 省略4300个，这里比较多
 // "autoload": {
 // "classmap": ["src/", "lib/", "Something.php"]
 // }
 phpDocumentor\Reflection\Types\Void_ => 项目根目录/vendor/composer/../phpdocumentor/type-resolver/src/Types/Void_.php
 ]
 classMapAuthoritative => 
 useIncludePath => 
 missingClasses => [],
 apcuPrefix => 
)

使用静态加载器

针对php版本大于5.06，没有安装HHVM虚拟机，并且没有将代码加密的情况，使用静态加载器

除了ClassLoader.php,其余文件是自动生成的，它是根据package.json文件，当执行命令compser dumpautoload，就会生成这些文件，当使用静态加载器时，会读取autoload_static.php中相应的值