本篇主要介紹了淺談express 中間件機制及實現原理，小編覺得挺不錯的，現在分享給大家，也給大家做個參考。一起跟隨小編過來看看吧
簡介
中間件機制可以讓我們在一個給定的流程中添加一個處理步驟，從而對這個流程的輸入或輸出會產生影響，或是產生一些中作用、狀態，或是攔截這個流程。中間件機制和tomcat的過濾器類似，這兩者都屬於責任鏈模式的具體實現。
express 中間件使用案例
let express = require('express')
let app = express()
//解析request 的body
app.use(bodyParser.json())
//解析 cookie
app.use(cookieParser())
//拦截
app.get('/hello', function (req, res) {
res.send('Hello World!');
});模擬中間件機制並且模擬實作解析request的中間件
先模擬一個request
request = { //模拟的request
requestLine: 'POST /iven_ HTTP/1.1',
headers: 'Host:www.php.cn\r\nCookie:BAIDUID=E063E9B2690116090FE24E01ACDDF4AD:FG=1;BD_HOME=0',
requestBody: 'key1=value1&key2=value2&key3=value3',
}一個http請求分為請求行、請求頭、和請求體，這三者之間透過\r\n\r\n即一個空白行來分割，這裡假設已經將這三者分開，requestLine （請求行）中有方法類型，請求url，http版本號，這三者透過空格來區分，headers（請求頭）中的各部分透過\r\n 來分割，requestBody（請求體）中透過& 來區分參數
模擬中間件機制
約定中間件一定是一個函數並且接受request, response, next三個參數
function App() {
if (!(this instanceof App))
return new App();
this.init();
}
App.prototype = {
constructor: App,
init: function() {
this.request = { //模拟的request
requestLine: 'POST /iven_ HTTP/1.1',
headers: 'Host:www.php.cn\r\nCookie:BAIDUID=E063E9B2690116090FE24E01ACDDF4AD:FG=1;BD_HOME=0',
requestBody: 'key1=value1&key2=value2&key3=value3',
};
this.response = {}; //模拟的response
this.chain = []; //存放中间件的一个数组
this.index = 0; //当前执行的中间件在chain中的位置
},
use: function(handle) { //这里默认 handle 是函数，并且这里不做判断
this.chain.push(handle);
},
next: function() { //当调用next时执行index所指向的中间件
if (this.index >= this.chain.length)
return;
let middleware = this.chain[this.index];
this.index++;
middleware(this.request, this.response, this.next.bind(this));
},
}對request 處理的中間件
function lineParser(req, res, next) {
let items = req.requestLine.split(' ');
req.methond = items[0];
req.url = items[1];
req.version = items[2];
next(); //执行下一个中间件
}
function headersParser(req, res, next) {
let items = req.headers.split('\r\n');
let header = {}
for(let i in items) {
let item = items[i].split(':');
let key = item[0];
let value = item[1];
header[key] = value;
}
req.header = header;
next(); //执行下一个中间件
}
function bodyParser(req, res, next) {
let bodyStr = req.requestBody;
let body = {};
let items = bodyStr.split('&');
for(let i in items) {
let item = items[i].split('=');
let key = item[0];
let value = item[1];
body[key] = value;
}
req.body = body;
next(); //执行下一个中间件
}
function middleware3(req, res, next) {
console.log('url: '+req.url);
console.log('methond: '+req.methond);
console.log('version: '+req.version);
console.log(req.body);
console.log(req.header);
next(); //执行下一个中间件
}測試程式碼
let app = App(); app.use(lineParser); app.use(headersParser); app.use(bodyParser); app.use(middleware3); app.next();
#整體程式碼
function App() {
if (!(this instanceof App))
return new App();
this.init();
}
App.prototype = {
constructor: App,
init: function() {
this.request = { //模拟的request
requestLine: 'POST /iven_ HTTP/1.1',
headers: 'Host:www.php.cn\r\nCookie:BAIDUID=E063E9B2690116090FE24E01ACDDF4AD:FG=1;BD_HOME=0',
requestBody: 'key1=value1&key2=value2&key3=value3',
};
this.response = {}; //模拟的response
this.chain = []; //存放中间件的一个数组
this.index = 0; //当前执行的中间件在chain中的位置
},
use: function(handle) { //这里默认 handle 是函数，并且这里不做判断
this.chain.push(handle);
},
next: function() { //当调用next时执行index所指向的中间件
if (this.index >= this.chain.length)
return;
let middleware = this.chain[this.index];
this.index++;
middleware(this.request, this.response, this.next.bind(this));
},
}
function lineParser(req, res, next) {
let items = req.requestLine.split(' ');
req.methond = items[0];
req.url = items[1];
req.version = items[2];
next(); //执行下一个中间件
}
function headersParser(req, res, next) {
let items = req.headers.split('\r\n');
let header = {}
for(let i in items) {
let item = items[i].split(':');
let key = item[0];
let value = item[1];
header[key] = value;
}
req.header = header;
next(); //执行下一个中间件
}
function bodyParser(req, res, next) {
let bodyStr = req.requestBody;
let body = {};
let items = bodyStr.split('&');
for(let i in items) {
let item = items[i].split('=');
let key = item[0];
let value = item[1];
body[key] = value;
}
req.body = body;
next(); //执行下一个中间件
}
function middleware3(req, res, next) {
console.log('url: '+req.url);
console.log('methond: '+req.methond);
console.log('version: '+req.version);
console.log(req.body);
console.log(req.header);
next(); //执行下一个中间件
}
let app = App();
app.use(lineParser);
app.use(headersParser);
app.use(bodyParser);
app.use(middleware3);
app.next();url: /iven_
methond: POST
version: HTTP/1.1
{key1: "value1", key2: "value2", key3: "value3"}
{Host: "www.php.cn", Cookie: "BAIDUID=E063E9B2690116090FE24E01ACDDF4AD"}以上是解析express中介軟體機制及其實作原理的詳細內容。更多資訊請關注PHP中文網其他相關文章！
