werkzeug實現簡單Python web框架（2）：添加jinjia2模板支持

完整代碼：
https://github.com/yangzhezjgs/Light/tree/master/webapp

jinjia2是什麼？
Jinja2是Python下一個被廣泛應用的模版引擎，他的設計思想來源於Django的模板引擎，並擴展了其語法和一系列強大的功能。其中最顯著的一個是增加了沙箱執行功能和可選的自動轉義功能，這對大多應用的安全性來說是非常重要的。
他基於unicode並能在python2.4之後的版本運行，包括python3。
添加了render_template函數，提供了模板支持，並進行了重構將處理函數和wsgi接口分開。

爲什麼需要模板引擎？
通過向模板中填充數據來生成動態頁面，就可以通過不同組合生成不同的頁面，使得代碼重用性和靈活性大大提高。

代碼：

import os
from werkzeug.wrappers import BaseRequest, BaseResponse
from werkzeug.exceptions import HTTPException, MethodNotAllowed, \
     NotImplemented, NotFound
from werkzeug.serving import run_simple
from jinja2 import Environment, FileSystemLoader

def render_template(template_name, **context):
    template_path = os.path.join(os.getcwd(), 'templates')
    jinja_env = Environment(loader=FileSystemLoader(template_path),autoescape=True)
    text = jinja_env.get_template(template_name).render(context)
    return text


class Request(BaseRequest):
    """Encapsulates a request."""


class Response(BaseResponse):
    """Encapsulates a response."""


class View(object):
    """Baseclass for our views."""
    def __init__(self):
        self.methods_meta = {
            'GET': self.GET,
            'POST': self.POST,
            'PUT': self.PUT,
            'DELETE': self.DELETE,
        }
    def GET(self):
        raise MethodNotAllowed()
    POST = DELETE = PUT = GET

    def HEAD(self):
        return self.GET()
    def dispatch_request(self, request, *args, **options):
        if request.method in self.methods_meta:
            return self.methods_meta[request.method](request, *args, **options)
        else:
            return '<h1>Unknown or unsupported require method</h1>'

    @classmethod
    def get_func(cls):
        def func(*args, **kwargs):
            obj = func.view_class()
            return obj.dispatch_request(*args, **kwargs)
        func.view_class = cls
        return func

class WebApp(object):
    """
    An interface to a web.py like application.  It works like the web.run
    function in web.py
    """
    def __init__(self):
        self.url_map = {}
    def wsgi_app(self,environ,start_response):
        req = Request(environ)
        response = self.dispatch_request(req)
        if response:
            response = Response(response,content_type='text/html; charset=UTF-8')
        else:
            response = Response('<h1>404 Source Not Found<h1>', content_type='text/html; charset=UTF-8', status=404)
        return response(environ, start_response)


    def __call__(self,environ,start_response):
        return self.wsgi_app(environ,start_response)

    def dispatch_request(self,req):
        try:
            url = req.path
            view = self.url_map.get(url, None)
            if view:
                response = view(req)
            else:
                response = None
        except HTTPException as e:
            response = e
        return response

    def add_url_rule(self,urls):
         for url in urls:
             self.url_map[url['url']] = url['view'].get_func() 

    def run(self, port=5000, ip='', debug=False):
        run_simple(ip, port, self, use_debugger=debug, use_reloader=True)

測試代碼：

from webapp import WebApp,View,render_template

class Index(View):
    def GET(self,request):
        return render_template("index.html",name="world")

class Test(View):
    def GET(self,request):
        return "test"

urls = [
{
    'url':'/',
    'view':Index
},
{
   'url':'/test',
   'view':Test
}
] 


app = WebApp()

app.add_url_rule(urls)

app.run()

templates/index.html

<h1>hello {{ name }}</h1>

效果：