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者輸出產生影響，或者產生一些中作用、狀態，或者攔截這個流程。中間件機制和tomcat的過濾器類似，這兩者都屬于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bodyapp.use(bodyParser.json())//解析 cookieapp.use(cookieParser())//攔截app.get('/hello', function (req, res) { res.send('Hello World!');});模擬中間件機制并且模擬實現解析request的中間件
首先模擬一個request
request = { //模擬的request requestLine: 'POST /iven_ HTTP/1.1', headers: 'Host:www.baidu.com/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，這三者之間通過/r/n/r/n即一個空行來分割，這里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，這三者通過空格來區分，headers（請求頭）中的各部分通過/r/n來分割，requestBody（請求體）中通過 & 來區分參數
模擬中間件機制
約定 中間件一定是一個函數并且接受 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 = { //模擬的request requestLine: 'POST /iven_ HTTP/1.1', headers: 'Host:www.baidu.com/r/nCookie:BAIDUID=E063E9B2690116090FE24E01ACDDF4AD:FG=1;BD_HOME=0', requestBody: 'key1=value1&key2=value2&key3=value3', }; this.response = {}; //模擬的response this.chain = []; //存放中間件的一個數組 this.index = 0; //當前執行的中間件在chain中的位置 }, use: function(handle) { //這里默認 handle 是函數，并且這里不做判斷 this.chain.push(handle); }, next: function() { //當調用next時執行index所指向的中間件 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(); //執行下一個中間件 }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(); //執行下一個中間件}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(); //執行下一個中間件}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(); //執行下一個中間件}測試代碼
let app = App();app.use(lineParser);app.use(headersParser);app.use(bodyParser);app.use(middleware3);app.next();
整體代碼
function App() { if (!(this instanceof App)) return new App(); this.init();}App.prototype = { constructor: App, init: function() { this.request = { //模擬的request requestLine: 'POST /iven_ HTTP/1.1', headers: 'Host:www.baidu.com/r/nCookie:BAIDUID=E063E9B2690116090FE24E01ACDDF4AD:FG=1;BD_HOME=0', requestBody: 'key1=value1&key2=value2&key3=value3', }; this.response = {}; //模擬的response this.chain = []; //存放中間件的一個數組 this.index = 0; //當前執行的中間件在chain中的位置 }, use: function(handle) { //這里默認 handle 是函數，并且這里不做判斷 this.chain.push(handle); }, next: function() { //當調用next時執行index所指向的中間件 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(); //執行下一個中間件 }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(); //執行下一個中間件}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(); //執行下一個中間件}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(); //執行下一個中間件}let app = App();app.use(lineParser);app.use(headersParser);app.use(bodyParser);app.use(middleware3);app.next();運行結果
將以上整體代碼運行后將打印以下信息
url: /iven_methond: POSTversion: HTTP/1.1{key1: "value1", key2: "value2", key3: "value3"}{Host: "www.baidu.com", Cookie: "BAIDUID=E063E9B2690116090FE24E01ACDDF4AD"}以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持武林網。
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