jsp application内置对象深入理解与应用

// javax.servlet.jsp.PageContext:

public abstract ServletContext getServletContext();// application = pageContext.getServletContext();

// web容器实现了此抽象方法！ 凡是接口或类中的抽象方法直接使用，都是因为容器或JVM内部实现了抽象！
// 此方法表示获取当前页面会话的服务器应用程序对象，也就是application，通过他可以设置和获取服务器的属性！
    The ServletContext instance.
// javax.servlet.ServeletContext:

public interface ServletContext；// 每个servletContext对象代表一个服务器应用程序，application是一个对象！

Defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file.
There is one context per “web application” per Java Virtual Machine. (A “web application” is a collection of servlets and content installed under a specific subset of the server's URL namespace such as /catalog and possibly installed via a .war file.)
// 方法：

ServletContext getContext(String uripath)；// 获取指定定位目录的服务器上下文对象，

Returns a ServletContext object that corresponds to a specifi

String getRealPath(String path)；// 获取虚拟目录的真实路径

Returns a String containing the real path for a given virtual path. For example, the path “/index.html” returns the absolute file path on the server's filesystem would be served by a request for “https://host/contextPath/index.html”, where contextPath is the context path of this ServletContext..
—获取虚拟目录的在服务器上的真实目录

// 以上代码等价于以下代码：

————application内置对象：
// javax.servlet.jsp.PageContext:

public abstract ServletContext getServletContext();// application = pageContext.getServletContext();

// web容器实现了此抽象方法！ 凡是接口或类中的抽象方法直接使用，都是因为容器或JVM内部实现了抽象！
// 此方法表示获取当前页面会话的服务器应用程序对象，也就是application，通过他可以设置和获取服务器的属性！
    The ServletContext instance.
// javax.servlet.ServeletContext:

public interface ServletContext；// 每个servletContext对象代表一个服务器应用程序，application是一个对象！

Defines a set of methods that a servlet uses to communicate with its servlet container, for example, to get the MIME type of a file, dispatch requests, or write to a log file.
There is one context per “web application” per Java Virtual Machine. (A “web application” is a collection of servlets and content installed under a specific subset of the server's URL namespace such as /catalog and possibly installed via a .war file.)
// 方法：

ServletContext getContext(String uripath)；// 获取指定定位目录的服务器上下文对象，

Returns a ServletContext object that corresponds to a specifi

String getRealPath(String path)；// 获取虚拟目录的真实路径

Returns a String containing the real path for a given virtual path. For example, the path “/index.html” returns the absolute file path on the server's filesystem would be served by a request for “https://host/contextPath/index.html”, where contextPath is the context path of this ServletContext..
—获取虚拟目录的在服务器上的真实目录

// 以上代码等价于以下代码：

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