关于今天学习Filter的资料及总结：
why
getRequestDispatcher(String path) of the ServletRequest interface cannot extend outside the current servlet context
where as
getRequestDispatcher(String path) of the ServletContext can use the getContext(String uripath) method to obtain RequestDispatcher for resources in foreign contexts.
and how??
Please help
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If you use absolute path ("/index.jsp"), there is no difference.
If you use relative path, you must use
HttpServletRequest.getRequestDispatcher().ServletContext.getRequestDispatcher()doesn't allow it.For example, if you receive your request on
http://example.com/myapp/subdir,RequestDispatcher dispatcher = request . getRequestDispatcher ( "index.jsp); dispatcher.forward( request, response );Will forward the request to the page
http://example.com/myapp/subdir/index.jsp.In any case, you can't forward request to a resource outside of the context.
I would think that your first question is simply a matter of scope. The ServletContext is a much more broad scoped object (the whole servlet context) than a ServletRequest, which is simply a single request. You might look to the Servlet specification itself for more detailed information.
As to how, I am sorry but I will have to leave that for others to answer at this time.
Context is stored at the application level scope where as request is stored at page level i.e to say
Web Container brings up the applications one by one and run them inside its JVM. It stores a singleton object in its jvm where it registers anyobject that is put inside it.This singleton is shared across all applications running inside it as it is stored inside the JVM of the container itself.
However for requests, the container creates a request object that is filled with data from request and is passed along from one thread to the other (each thread is a new request that is coming to the server), also request is passed to the threads of same application.
ServletContext的作用是什么：
ServletContext.getContect(java.lang.String uripath)的作用是什么？
返回同一Server中指定的path对应的ServletContext对象,通过该对象可以实现与Server中的其他Context打交道。
uripath必须是以"/"开始（该路径的含义是相对于整个Servlet文档的根路径，而不是当前ServletContext的根路径）。
ServletContext.getRequestDispatcher(String url)和ServletRequest.getRequestDispatcher(String url)的区别是什么？为什么？
ServletContext.getRequestDispatcher(String url)中的url只能使用绝对路径；而ServletRequest.getRequestDispatcher(String url)中的url可以使用相对路径。
因为ServletRequest具有相对路径的概念；而ServletContext对象无次概念。
如何把请求转移到另外一个Web App中的某个地址？
ServletContext.getRequestDispatcher(String url)和ServletRequest.getRequestDispatcher(String url)只能把请求转移到同一个Web App中的地址。
如果需要把请求转移到另外一个Web App中的某个地址，可以按下面的做法：
1. 获得另外一个Web App的ServletConext对象(currentServletContext.getContext(uripath)).
2. 调用ServletContext.getRequestDispatcher(String url)方法。
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javax.servlet.FilterConfig翻译
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<!-- ======== START OF CLASS DATA ======== -->javax.servlet
Interface FilterConfig
public interface FilterConfig A filter configuration object used by a servlet container to pass information to a filter during initialization. 一个过滤器配置对象，在初始化过程中由servlet容器传递信息给过滤器。
Since: Servlet 2.3 See Also: Filter
<!-- ======== NESTED CLASS SUMMARY ======== --><!-- =========== FIELD SUMMARY =========== --><!-- ======== CONSTRUCTOR SUMMARY ======== --><!-- ========== METHOD SUMMARY =========== --><!-- -->
Method Summary StringgetFilterName ()
Returns the filter-name of this filter as defined in the deployment descriptor. 返回过滤器在部署描述符中定义的名称。StringgetInitParameter ( String name)
Returns aStringcontaining the value of the named initialization parameter, ornullif the parameter does not exist. 返回命名的初始化参数的对应值，如果参数不存在返回null。EnumerationgetInitParameterNames ()
Returns the names of the filter's initialization parameters as anEnumerationofStringobjects, or an emptyEnumerationif the filter has no initialization parameters. 返回以String对象的Enumeration形式的过滤器初始化参数名称，如果过滤器不含初始化参数，返回一个空Enumeration。ServletContextgetServletContext ()
Returns a reference to theServletContextin which the caller is executing. 返回调用者正在执行的ServletContext的引用。<!-- ============ FIELD DETAIL =========== --><!-- ========= CONSTRUCTOR DETAIL ======== --><!-- ============ METHOD DETAIL ========== --><!-- -->
<!-- -->
Method Detail getFilterName
public String getFilterName ()Returns the filter-name of this filter as defined in the deployment descriptor. 返回过滤器在部署描述符中定义的名称。
<!-- -->getServletContext
public ServletContext getServletContext ()Returns a reference to the ServletContextin which the caller is executing. 返回调用者正在执行的ServletContext的引用。Returns: a ServletContextobject, used by the caller to interact with its servlet container 由调用者和servlet容器交互的对象See Also: ServletContext
<!-- -->getInitParameter
public String getInitParameter ( String name)Returns a Stringcontaining the value of the named initialization parameter, ornullif the parameter does not exist. 返回命名的初始化参数的对应值，如果参数不存在返回null。Parameters: name- aStringspecifying the name of the initialization parameter 指定初始化参数名称的StringReturns: a Stringcontaining the value of the initialization parameter 初始化参数的对应String值
<!-- -->getInitParameterNames
public Enumeration getInitParameterNames ()Returns the names of the filter's initialization parameters as an EnumerationofStringobjects, or an emptyEnumerationif the filter has no initialization parameters. 返回以String对象的Enumeration形式的过滤器初始化参数名称，如果过滤器不含初始化参数，返回一个空Enumeration。Returns: an <!-- ========= END OF CLASS DATA ========= -->EnumerationofStringobjects containing the names of the filter's initialization parameters 包含过滤器初始化参数的String对象的枚举
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