214 lines
3.8 KiB
Markdown
214 lines
3.8 KiB
Markdown
---
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title: learn express
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date: 2017-12-20 10:27:29
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tags: [express, 未完成]
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categories: nodeJS
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---
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## 深入了解express
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### 构建一个 express 实例
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> cnpm i express-generator -g
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### 目录结构
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```json
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.
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├── app.js
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├── bin
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│ └── www
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├── package.json
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├── public
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│ ├── images
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│ ├── javascripts
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│ └── stylesheets
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│ └── style.css
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├── routes
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│ ├── index.js
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│ └── users.js
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└── views
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├── error.jade
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├── index.jade
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└── layout.jade
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7 directories, 9 files
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```
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### 中间件
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#### 应用级中间件
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```js
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<!-- 没有挂载路径 -->
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app.use(function (req, res, next) {
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...
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next()
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}, function (req, res, next) {
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console.log('Request Type:', req.method);
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next();
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})
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<!-- 挂载路径的中间件 -->
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app.use('/user/', function(req, res, next){
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...
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next()
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})
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路由和句柄函数，处理get（post）请求
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app.get('/', function() {
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res.send('USER')
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})
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```
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#### 路由级中间件
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> var app = express()
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> var router = express.Router()
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```js
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和上面类似，只是写法不同
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router.use('/', function(req, res, next) {
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...
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next()
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})
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<!-- 此处理是在同一个文件夹下 -->
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app.use('/', router)
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```
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#### 错误处理中间件
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```js
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app.use(function (err, req, res, next) {
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console.error(err.stack);
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res.status(500).send('Something broke!');
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});
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```
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#### 内置中间件
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> 唯一内置中间件：express.static()
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* dotfiles
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是否对外输出文件名以点（.）开头的文件。
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可选值为 “allow”、“deny” 和 “ignore”
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默认：ignore
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* etag
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是否启用 etag 生成
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默认：true
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* extensions
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设置文件扩展名备份选项
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默认：[]
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* index
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发送目录索引文件，设置为 false 禁用目录索引。
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Mixed
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默认：“index.html”
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* lastModified
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设置 Last-Modified 头为文件在操作系统上的最后修改日期。可能值为 true 或 false。
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默认：true
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* maxAge
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以毫秒或者其字符串格式设置 Cache-Control 头的 max-age 属性。
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默认：0
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* redirect
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当路径为目录时，重定向至 “/”。
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默认：true
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* setHeaders
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设置 HTTP 头以提供文件的函数。
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Function
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```js
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app.use(express.static('public', options));
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```
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#### 第三方中间件
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##### cookie-parser
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用于解析 cookie 的中间件
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##### body-parser
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用于解析request body部分，并对上传内容大小作出限制
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```js
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app.use(bodyParser.json({ limit: '50mb' }));
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app.use(bodyParser.urlencoded({ limit: '50mb', extended: true }));
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```
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#### canvas
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```js
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var base64Data = req.body.imgData;
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var img = new Canvas.Image;
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img.onload = function(){
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var w = img.width;
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var h = img.height;
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var canvas = new Canvas(w, h);
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var ctx = canvas.getContext('2d');
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ctx.drawImage(img, 0, 0);
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var out = fs.createWriteStream(__dirname + '/crop.jpg');
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var stream = canvas.createJPEGStream({
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bufsize : 2048,
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quality : 80
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});
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stream.on('data', function(chunk){
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out.write(chunk);
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});
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stream.on('end', function(){
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out.end();
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res.send("上传成功！");
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});
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}
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img.onerror = function(err){
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res.send(err);
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}
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img.src = base64Data;
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```
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#### fs模块 (node自带模块)
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对文件执行读取和写入
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```js
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function(req, res, next) {
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if (req.body.formFile) {
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// 对象转换为字符串
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<!-- 先取出base64码 -->
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var base64Data = req.body.formFile.replace(/^data:image\/\w+;base64,/, "");
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<!-- 将base64码进行转码 -->
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var dataBuffer = new Buffer(base64Data, 'base64');
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<!-- 将文件导出为图片格式 -->
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fs.writeFile("out.png", dataBuffer, function (err) {
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if (err) {
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res.send(err);
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} else {
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res.send("保存成功！");
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}
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});
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}
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}
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```
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未完待续... |