随着Node.js的日益火热，各种框架开始层出不穷的涌现出来，Node.js也开始逐渐的被应用到处理服务端请求的场景中。搭建Web项目的框架也随之开始出现——express、koa、koa2、egg等，当然要了解其好坏还是要自己去啃源码的。本文将不会涉及到源码，只是带领初学者简单了解下Koa2的基本使用，欢迎大家在评论中互相交流学习。
???注意：koa2使用了ES7的语法，所以使用时请升级Node版本到最新。
了解更详细的源码信息可以到git上的koajs/koa去了解。
1.项目目录结构
2. 代码逻辑解析
2.1. 包结构文件
{ ?"name": "weixin-node-koa", ?"version": "1.0.0", ?"description": "node.js with koa2", ?"private": true, ?"dependencies": { ???"koa": "^2.0.0", ???"koa-router": "^7.0.0", ???"mysql":"2.13.0" ?}, ?"scripts": { ???"start": "node app.js" ?}, ?"engines": { ???"node": ">=6.0.0" ?}, ?"author": "Fly", ?"license": "CENTERM"}2.2. 启动入口文件
app.js
const Koa = require(‘koa‘);const app = new Koa();const router2controller = require(‘./app/router2controller.js‘);const config = require(‘./config/config.local.js‘);app.use(router2controller());app.listen(config.port);console.log("Server started and listen on port " + config.port);如果请求的报文体是XML格式，可以添加下面的代码自动解析报文（注意引用koa-xxx的版本要与koa2对应）
const Koa = require(‘koa‘);const app = new Koa();const router2controller = require(‘./app/router2controller.js‘);const config = require(‘./config/config.local.js‘);//start接收到的xml数据请求单独解析存储const xmlParser = require(‘koa-xml-body‘);app.use(xmlParser()).use((ctx,next) => { ???ctx.data = ctx.request.body; ???return next();});//endapp.use(router2controller());app.listen(config.port);console.log("Server started and listen on port " + config.port);从代码看到引入了一个router2controller.js的文件，这个文件是完成前端请求到具体处理方法的路由过程
2.3. 路由器文件
router2controller.js，该类将会自动扫描controller文件夹中的文件来加载请求映射，不需要挨个请求单独配置
koa-router原生提供方法如下：
router.get(‘/‘, async (ctx,next) => {this.body = ‘Hello World!‘;}).post(‘/users‘, async (ctx,next) => {//TODO}).put(‘/users/:id‘, async (ctx,next) => {//TODO}).del(‘/users/:id‘, async (ctx,next) => {//TODO});自动扫描controller包实现方法如下
const fs = require(‘fs‘);const router = require(‘koa-router‘)();function addMapping(router, mapping) { ???for (var url in mapping) { ???????if (url.startsWith(‘GET ‘)) { ???????????var path = url.substring(4); ???????????router.get(path, mapping[url]); ???????????console.log(`register URL mapping: GET ${path}`); ???????} else if (url.startsWith(‘POST ‘)) { ???????????var path = url.substring(5); ???????????router.post(path, mapping[url]); ???????????console.log(`register URL mapping: POST ${path}`); ???????} else if (url.startsWith(‘PUT ‘)) { ???????????var path = url.substring(4); ???????????router.put(path, mapping[url]); ???????????console.log(`register URL mapping: PUT ${path}`); ???????} else if (url.startsWith(‘DELETE ‘)) { ???????????var path = url.substring(7); ???????????router.del(path, mapping[url]); ???????????console.log(`register URL mapping: DELETE ${path}`); ???????} else { ???????????console.log(`invalid URL: ${url}`); ???????} ???}}function addControllers(router, dir) { ???fs.readdirSync(__dirname + ‘/‘ + dir).filter((f) => { ???????return f.endsWith(‘.js‘); ???}).forEach((f) => { ???????console.log(`process controller: ${f}...`); ???????let mapping = require(__dirname + ‘/‘ + dir + ‘/‘ + f); ???????addMapping(router, mapping); ???});}module.exports = function (dir) { ???var controllersDir = dir || ‘controller‘; ???addControllers(router, controllersDir); ???return router.routes();};2.4. 控制器
userController.js，***Controller.js是用来处理具体请求信息以及返回数据的，userController.js中处理了GET请求获取用户信息，POST请求保存用户信息
const userService = require(‘./../service/userService.js‘);var getUserinfo = (ctx, next) => { ???let query = ctx.query; ???let userId = query.id; ???let userInfo = userService.getUserById(userId); ???let html = ‘<html><body>‘ ???????+ ‘<div> userinfo: ‘ + userInfo + ‘</div>‘ ???????+ ‘</body></html>‘; ???ctx.response.type =‘text/html‘; ???ctx.response.body = html;};var saveUserinfo = (ctx, next) => { ???const requestString = ctx.data; ???//TODO数据处理 ???Console.log(requestString);};module.exports = { ???‘GET /getUserinfo‘: getUserinfo, ???‘POST /saveUserinfo‘: saveUserinfo};2.5. 数据处理
userService.js，处理封装从***Dao.js获取到的数据返回给Controller
const userDao = require(‘./../dao/userDao.js‘);var getUserById = async (userId) => { ???var users = userDao.getUserById(userId); ???var responseContent = ‘‘; ???for(let user of users) { ???????reaponseContent += ‘姓名：‘ + user.name + ‘ |‘; ???????reaponseContent += ‘年龄：‘ + user.age + ‘ |‘; ???????reaponseContent += ‘身高：‘ + user.height + ‘<br />‘; ???} ???return responseContent;}module.exports = { ???getUserById : getUserById};2.6. 数据获取
userDao.js，通过请求传入参数来获取user数据
const mysql = require(‘./../utils/mysqlUtil.js‘);var getUserById = async (userId) => { ???let mysqlOptions = { ???????sql : ‘select * from table_user where user_id = ?‘, ???????args : [userId] ???}; ???var users = await mysql.execQuery(mysqlOptions); ???if(users.length == 0) { ???????return null; ???} else { ???????return users; ???}};module.exports = { ???getUserById : getUserById};2.7. 数据库操作
mysqlUtil.js，包含了数据库连接池控制，连接建立、释放管理，执行Dao发起的数据库操作请求
const mysql = require(‘mysql‘);const config = require(‘./../../config/config.local.js‘);var connectionPool = mysql.createPool({ ???‘host‘ : config.database.host, ???‘port‘:config.database.port, ???‘user‘ : config.database.user, ???‘password‘ : config.database.password, ???‘database‘ : config.database.database, ???‘charset‘: config.database.charset, ???‘connectionLimit‘: config.database.connectionLimit, ???‘supportBigNumbers‘: true, ???‘bigNumberStrings‘: true});var release = connection => { ???connection.end(function(error) { ???????if(error) { ???????????console.log(‘Connection closed failed.‘); ???????} else { ???????????console.log(‘Connection closed succeeded.‘); ???????} ???});};var execQuery = sqlOptions => { ???var results = new Promise((resolve, reject) => { ???????????connectionPool.getConnection((error,connection) => { ???????????if(error) { ???????????????console.log("Get connection from mysql pool failed !"); ???????????????throw error; ???????????} ???????????var sql = sqlOptions[‘sql‘]; ???????????var args = sqlOptions[‘args‘]; ???????????if(!args) { ???????????????var query = connection.query(sql, (error, results) => { ???????????????????if(error) { ???????????????????????console.log(‘Execute query error !‘); ???????????????????????throw error; ???????????????????} ???????????????????resolve(results); ???????????????}); ???????????} else { ???????????????var query = connection.query(sql, args, function(error, results) { ???????????????????if(error) { ???????????????????????console.log(‘Execute query error !‘); ???????????????????????throw error; ???????????????????} ???????????????????resolve(results); ???????????????}); ???????????} ???????????connection.release(function(error) { ???????????????if(error) { ???????????????????console.log(‘Mysql connection close failed !‘); ???????????????????throw error; ???????????????} ???????????}); ???????}); ???}).then(function (chunk) { ???????return chunk; ???}); ???return results;};module.exports = { ???release : release, ???execQuery : execQuery}此实例我并没有整理并在本机运行过，但这个包结构的思路还是值得学习的，整个实例的代码详见http://bijian1013.iteye.com/blog/2425085。
文章来源：https://blog.csdn.net/ererfei/article/details/68060551
使用Koa2搭建web项目
原文地址：https://www.cnblogs.com/flyingeagle/p/9192460.html