servlet init parameters和context init parameters的區別

Context init parameters   在web.xml中以下

<web-app ...>
<context-param>
<param-name>foo</param-name>
<param-value>bar</param-value>
</context-param>
<!-- other stuff including
servlet declarations -->
</web-app>
Within the <web-app> element but NOT

within a specific <servlet> element

Servlet init parameters在web.xml中以下

<servlet>

<servlet-name>

BeerParamTests
</servlet-name>
<servlet-class>
TestInitParams
</servlet-class>
<init-param>
<param-name>foo</param-name>
<param-value>bar</param-value>
</init-param>
<!-- other stuff -->
</servlet>
Within the <servlet> element for each

specific servlet

經過這樣的代碼獲取ServletContext

getServletContext().getInitParameter(「foo」);

經過這樣的代碼獲取ServletConfig

getServletConfig().getInitParameter(「foo」);

Availability

To any servlets and JSPs that are part

of this web app.(ServletContext是對於任何的jsp或者servlet都是有效的，能夠訪問的)

To only the servlet for which the <init-param> was
configured.
(Although the servlet can choose to make it more

widely available by storing it in an attribute.)

（ServletConfig對於特定配置好<inti-param>的servlet有效）

對於每個servlet都有一個servletConfig

對於整個webapp有一個ServletContext

當web app初始化的時候，容器（好比tomcat）讀取web.xml，而且爲<context-param>建立一個鍵值對，

容器建立一個新的ServletContext實例,

容器將鍵值對傳遞給建立好的實例ServletContext

web app中的任何一部分都有訪問這個ServletContext的權限