本節我們將實現,用戶上傳圖片,並將該圖片在浏覽器中顯示出來。
這裡我們要用到的外部模塊是Felix Geisendörfer開發的node-formidable模塊。它對解析上傳的文件數據做了很好的抽象。
要安裝這個外部模塊,需在cmd下執行命令:
代碼如下:
npm install formidable
如果輸出類似的信息就代表安裝成功了:
代碼如下:
npm info build Success: formidable@1.0.14
安裝成功後我們用request將其引入即可:
代碼如下:
var formidable = require(“formidable”);
這裡該模塊做的就是將通過HTTP POST請求提交的表單,在Node.js中可以被解析。我們要做的就是創建一個新的IncomingForm,它是對提交表單的抽象表示,之後,就可以用它解析request對象,獲取表單中需要的數據字段。
本文案例的圖片文件存儲在 /tmp文件夾中。
我們先來解決一個問題:如何才能在浏覽器中顯示保存在本地硬盤中的文件?
我們使用fs模塊來將文件讀取到服務器中。
我們來添加/showURL的請求處理程序,該處理程序直接硬編碼將文件/tmp/test.png內容展示到浏覽器中。當然了,首先需要將該圖片保存到這個位置才行。
我們隊requestHandlers.js進行一些修改:
代碼如下:
var querystring = require("querystring"),
fs = require("fs");
function start(response, postData) {
console.log("Request handler 'start' was called.");
var body = '<html>'+
'<head>'+
'<meta http-equiv="Content-Type" '+
'content="text/html; charset=UTF-8" />'+
'</head>'+
'<body>'+
'<form action="/upload" method="post">'+
'<textarea name="text" rows="20" cols="60"></textarea>'+
'<input type="submit" value="Submit text" />'+
'</form>'+
'</body>'+
'</html>';
response.writeHead(200, {"Content-Type": "text/html"});
response.write(body);
response.end();
}
function upload(response, postData) {
console.log("Request handler 'upload' was called.");
response.writeHead(200, {"Content-Type": "text/plain"});
response.write("You've sent the text: "+ querystring.parse(postData).text);
response.end();
}
function show(response, postData) {
console.log("Request handler 'show' was called.");
fs.readFile("/tmp/test.png", "binary", function(error, file) {
if(error) {
response.writeHead(500, {"Content-Type": "text/plain"});
response.write(error + "\n");
response.end();
} else {
response.writeHead(200, {"Content-Type": "image/png"});
response.write(file, "binary");
response.end();
}
});
}
exports.start = start;
exports.upload = upload;
exports.show = show;
我們還需要將這新的請求處理程序,添加到index.js中的路由映射表中:
代碼如下:
var server = require("./server");
var router = require("./router");
var requestHandlers = require("./requestHandlers");
var handle = {}
handle["/"] = requestHandlers.start;
handle["/start"] = requestHandlers.start;
handle["/upload"] = requestHandlers.upload;
handle["/show"] = requestHandlers.show;
server.start(router.route, handle);
重啟服務器之後,通過訪問http://localhost:8888/show,就可以看到保存在/tmp/test.png的圖片了。
好,最後我們要的就是:
在/start表單中添加一個文件上傳元素
將node-formidable整合到我們的upload請求處理程序中,用於將上傳的圖片保存到/tmp/test.png
將上傳的圖片內嵌到/uploadURL輸出的HTML中
第一項很簡單。只需要在HTML表單中,添加一個multipart/form-data的編碼類型,移除此前的文本區,添加一個文件上傳組件,並將提交按鈕的文案改為“Upload file”即可。 如下requestHandler.js所示:
代碼如下:
var querystring = require("querystring"),
fs = require("fs");
function start(response, postData) {
console.log("Request handler 'start' was called.");
var body = '<html>'+
'<head>'+
'<meta http-equiv="Content-Type" '+
'content="text/html; charset=UTF-8" />'+
'</head>'+
'<body>'+
'<form action="/upload" enctype="multipart/form-data" '+
'method="post">'+
'<input type="file" name="upload">'+
'<input type="submit" value="Upload file" />'+
'</form>'+
'</body>'+
'</html>';
response.writeHead(200, {"Content-Type": "text/html"});
response.write(body);
response.end();
}
function upload(response, postData) {
console.log("Request handler 'upload' was called.");
response.writeHead(200, {"Content-Type": "text/plain"});
response.write("You've sent the text: "+ querystring.parse(postData).text);
response.end();
}
function show(response, postData) {
console.log("Request handler 'show' was called.");
fs.readFile("/tmp/test.png", "binary", function(error, file) {
if(error) {
response.writeHead(500, {"Content-Type": "text/plain"});
response.write(error + "\n");
response.end();
} else {
response.writeHead(200, {"Content-Type": "image/png"});
response.write(file, "binary");
response.end();
}
});
}
exports.start = start;
exports.upload = upload;
exports.show = show;
接下來,我們要完成第二步,我們從server.js開始 —— 移除對postData的處理以及request.setEncoding (這部分node-formidable自身會處理),轉而采用將request對象傳遞給請求路由的方式:
代碼如下:
var http = require("http");
var url = require("url");
function start(route, handle) {
function onRequest(request, response) {
var pathname = url.parse(request.url).pathname;
console.log("Request for " + pathname + " received.");
route(handle, pathname, response, request);
}
http.createServer(onRequest).listen(8888);
console.log("Server has started.");
}
exports.start = start;
接下來修改router.js,這次要傳遞request對象:
代碼如下:
function route(handle, pathname, response, request) {
console.log("About to route a request for " + pathname);
if (typeof handle[pathname] === 'function') {
handle[pathname](response, request);
} else {
console.log("No request handler found for " + pathname);
response.writeHead(404, {"Content-Type": "text/html"});
response.write("404 Not found");
response.end();
}
}
exports.route = route;
現在,request對象就可以在我們的upload請求處理程序中使用了。node-formidable會處理將上傳的文件保存到本地/tmp目錄中,而我們需
要做的是確保該文件保存成/tmp/test.png。
接下來,我們把處理文件上傳以及重命名的操作放到一起,如下requestHandlers.js所示:
代碼如下:
var querystring = require("querystring"),
fs = require("fs"),
formidable = require("formidable");
function start(response) {
console.log("Request handler 'start' was called.");
var body = '<html>'+
'<head>'+
'<meta http-equiv="Content-Type" content="text/html; '+
'charset=UTF-8" />'+
'</head>'+
'<body>'+
'<form action="/upload" enctype="multipart/form-data" '+
'method="post">'+
'<input type="file" name="upload" multiple="multiple">'+
'<input type="submit" value="Upload file" />'+
'</form>'+
'</body>'+
'</html>';
response.writeHead(200, {"Content-Type": "text/html"});
response.write(body);
response.end();
}
function upload(response, request) {
console.log("Request handler 'upload' was called.");
var form = new formidable.IncomingForm();
console.log("about to parse");
form.parse(request, function(error, fields, files) {
console.log("parsing done");
fs.renameSync(files.upload.path, "/tmp/test.png");
response.writeHead(200, {"Content-Type": "text/html"});
response.write("received image:<br/>");
response.write("<img src='/show' />");
response.end();
});
}
function show(response) {
console.log("Request handler 'show' was called.");
fs.readFile("/tmp/test.png", "binary", function(error, file) {
if(error) {
response.writeHead(500, {"Content-Type": "text/plain"});
response.write(error + "\n");
response.end();
} else {
response.writeHead(200, {"Content-Type": "image/png"});
response.write(file, "binary");
response.end();
}
});
}
exports.start = start;
exports.upload = upload;
exports.show = show;
做到這裡,我們的服務器就全部完成了。
在執行圖片上傳的過程中,有的人可能會遇到這樣的問題:
照成這個問題的原因我猜測是由於磁盤分區導致的,要解決這個問題就需要改變formidable的默認零時文件夾路徑,保證和目標目錄處於同一個磁盤分區。
我們找到requestHandlers.js的 upload函數,將它做一些修改:
代碼如下:
function upload(response, request) {
console.log("Request handler 'upload' was called.");
var form = new formidable.IncomingForm();
console.log("about to parse");
form.uploadDir = "tmp";
form.parse(request, function(error, fields, files) {
console.log("parsing done");
fs.renameSync(files.upload.path, "/tmp/test.png");
response.writeHead(200, {"Content-Type": "text/html"});
response.write("received image:<br/>");
response.write("<img src='/show' />");
response.end();
});
}
我們增加了一句 form.uploadDir = “tmp”,現在重啟服務器,再執行上傳操作,問題完美解決。