ServletContext

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本文详细介绍了Servlet Context接口的功能和使用方法，包括如何通过Servlet Config获取ServletContext对象、如何利用它获取初始化参数、文件路径等信息，以及提供了多种管理和操作Web应用程序资源的方法。

http://tomcat.apache.org/tomcat-8.5-doc/servletapi/javax/servlet/ServletContext.html

1.可以由ServletConfig获取
2.该对象代表当前WEB 应用：可以认为SevletContext是当前web应用的大管家，可以获取各个方面的信息
1）获取当前WEB应用的参数

设置初始化参数

<!-- 配置当前web应用的初始化参数>
<context-param>
	<param-name>driver</parma-name>
	<param-value>com.mysql.jdbc.Driver</param-value>
</context-param>

ServletContext servletContext == servletConfig.getServletContext();
String driver = servletContext.getInitParameter("driver");

Enumeration<String> names = servletContext.getInitParameterNames()
while(names.hasMoreElements()){
	String name = names.nextElement();
	System.out.println("name: " + name);
}

2)获取当前WEB应用的某一个文件的绝对路径
getRealPath(String path);

Method Summary

Methods
Modifier and Type	Method and Description
`FilterRegistration.Dynamic`	`addFilter(java.lang.String filterName, java.lang.Class<? extends Filter> filterClass)` Add filter to context.
`FilterRegistration.Dynamic`	`addFilter(java.lang.String filterName, Filter filter)` Add filter to context.
`FilterRegistration.Dynamic`	`addFilter(java.lang.String filterName, java.lang.String className)` Add filter to context.
`void`	`addListener(java.lang.Class<? extends java.util.EventListener> listenerClass)` TODO SERVLET3 - Add comments
`void`	`addListener(java.lang.String className)` TODO SERVLET3 - Add comments
`<T extends java.util.EventListener> void`	`addListener(T t)` TODO SERVLET3 - Add comments
`ServletRegistration.Dynamic`	`addServlet(java.lang.String servletName, java.lang.Class<? extends Servlet> servletClass)` Add servlet to context.
`ServletRegistration.Dynamic`	`addServlet(java.lang.String servletName, Servlet servlet)` Register a servlet instance for use in this ServletContext.
`ServletRegistration.Dynamic`	`addServlet(java.lang.String servletName, java.lang.String className)` Register a servlet implementation for use in this ServletContext.
`<T extends Filter> T`	`createFilter(java.lang.Class<T> c)` TODO SERVLET3 - Add comments
`<T extends java.util.EventListener> T`	`createListener(java.lang.Class<T> c)` TODO SERVLET3 - Add comments
`<T extends Servlet> T`	`createServlet(java.lang.Class<T> c)` TODO SERVLET3 - Add comments
`void`	`declareRoles(java.lang.String... roleNames)` Add to the declared roles for this ServletContext.
`java.lang.Object`	`getAttribute(java.lang.String name)` Returns the servlet container attribute with the given name, or `null` if there is no attribute by that name.
`java.util.Enumeration<java.lang.String>`	`getAttributeNames()` Returns an `Enumeration` containing the attribute names available within this servlet context.
`java.lang.ClassLoader`	`getClassLoader()` Get the web application class loader associated with this ServletContext.
`ServletContext`	`getContext(java.lang.String uripath)` Returns a `ServletContext` object that corresponds to a specified URL on the server.
`java.lang.String`	`getContextPath()` Return the main path associated with this context.
`java.util.Set<SessionTrackingMode>`	`getDefaultSessionTrackingModes()` Obtains the default session tracking modes for this web application.
`int`	`getEffectiveMajorVersion()`
`int`	`getEffectiveMinorVersion()`
`java.util.Set<SessionTrackingMode>`	`getEffectiveSessionTrackingModes()` Obtains the currently enabled session tracking modes for this web application.
`FilterRegistration`	`getFilterRegistration(java.lang.String filterName)` TODO SERVLET3 - Add comments
`java.util.Map<java.lang.String,? extends FilterRegistration>`	`getFilterRegistrations()`
`java.lang.String`	`getInitParameter(java.lang.String name)` Returns a `String` containing the value of the named context-wide initialization parameter, or `null` if the parameter does not exist.
`java.util.Enumeration<java.lang.String>`	`getInitParameterNames()` Returns the names of the context's initialization parameters as an `Enumeration` of `String` objects, or an empty `Enumeration` if the context has no initialization parameters.
`JspConfigDescriptor`	`getJspConfigDescriptor()`
`int`	`getMajorVersion()` Returns the major version of the Java Servlet API that this servlet container supports.
`java.lang.String`	`getMimeType(java.lang.String file)` Returns the MIME type of the specified file, or `null` if the MIME type is not known.
`int`	`getMinorVersion()` Returns the minor version of the Servlet API that this servlet container supports.
`RequestDispatcher`	`getNamedDispatcher(java.lang.String name)` Returns a `RequestDispatcher` object that acts as a wrapper for the named servlet.
`java.lang.String`	`getRealPath(java.lang.String path)` Returns a `String` containing the real path for a given virtual path.
`RequestDispatcher`	`getRequestDispatcher(java.lang.String path)` Returns a `RequestDispatcher` object that acts as a wrapper for the resource located at the given path.
`java.net.URL`	`getResource(java.lang.String path)` Returns a URL to the resource that is mapped to a specified path.
`java.io.InputStream`	`getResourceAsStream(java.lang.String path)` Returns the resource located at the named path as an `InputStream` object.
`java.util.Set<java.lang.String>`	`getResourcePaths(java.lang.String path)` Returns a directory-like listing of all the paths to resources within the web application whose longest sub-path matches the supplied path argument.
`java.lang.String`	`getServerInfo()` Returns the name and version of the servlet container on which the servlet is running.
`Servlet`	`getServlet(java.lang.String name)` Deprecated. As of Java Servlet API 2.1, with no direct replacement.
`java.lang.String`	`getServletContextName()` Returns the name of this web application corresponding to this ServletContext as specified in the deployment descriptor for this web application by the display-name element.
`java.util.Enumeration<java.lang.String>`	`getServletNames()` Deprecated. As of Java Servlet API 2.1, with no replacement.
`ServletRegistration`	`getServletRegistration(java.lang.String servletName)` Obtain the details of the named servlet.
`java.util.Map<java.lang.String,? extends ServletRegistration>`	`getServletRegistrations()` TODO SERVLET3 - Add comments
`java.util.Enumeration<Servlet>`	`getServlets()` Deprecated. As of Java Servlet API 2.0, with no replacement.
`SessionCookieConfig`	`getSessionCookieConfig()`
`java.lang.String`	`getVirtualServerName()` Get the primary name of the virtual host on which this context is deployed.
`void`	`log(java.lang.Exception exception, java.lang.String msg)` Deprecated. As of Java Servlet API 2.1, use `log(String message, Throwable throwable)` instead. This method was originally defined to write an exception's stack trace and an explanatory error message to the servlet log file.
`void`	`log(java.lang.String msg)` Writes the specified message to a servlet log file, usually an event log.
`void`	`log(java.lang.String message, java.lang.Throwable throwable)` Writes an explanatory message and a stack trace for a given `Throwable` exception to the servlet log file.
`void`	`removeAttribute(java.lang.String name)` Removes the attribute with the given name from the servlet context.
`void`	`setAttribute(java.lang.String name, java.lang.Object object)` Binds an object to a given attribute name in this servlet context.
`boolean`	`setInitParameter(java.lang.String name, java.lang.String value)` Set the given initialisation parameter to the given value.
`void`	`setSessionTrackingModes(java.util.Set<SessionTrackingMode> sessionTrackingModes)` Configures the available session tracking modes for this web application.