simple.http.serve
Interface Context

All Known Implementing Classes:
CacheContext, ExtendedContext, FactoryContext, FileContext

public interface Context

The Context interface is used to give a view of the file system to the ResourceEngine. This provides the information to the ResourceEngine that it needs in order to serve content to the client browser. This provides the path translations for the HTTP request URI. This also provides the Format object that is used to create directory listings and error messages.

This object essentially provides a mechanism that allows the file engine to convert the HTTP request URI into OS system paths and system objects such as the File object. A context is rooted a a certain directory in the system. This directory is where the resources are gathered from. For example suppose that a Context implementation is rooted at the directory "c:\web\html\" on a DOS system. Now if the target of the browser was "http://some.host/web/pub/README". The context needs to be consulted to convert "/web/pub/README" into the real path within the system. So Context.getRealPath is invoked with the path "/web/pub/README", which responds with the system path "c:\web\html\web\pub\README". Also if this was a UNIX system with the same context rooted at "/home/user/html" then the same URL would result in "/home/user/html/web/pub/README".

The meaning of HTTP URI in this instance is the request URI from a HTTP/x.x request, as RFC 2616 and RFC 2396 defines it

 
 Request-Line = Method SP Request-URI SP HTTP-Version CRLF

 Request-URI = "*" | absoluteURI | abs_path | authority
 absoluteURI = "http:" "//" host [":" port] [abs_path ["?" query]] 
 abs_path = "/" path_segments         
 path_segments = segment *( "/" segment )
 
So the Context object must be prepared to accept the request URI that come in the form outlined above. These can include formats like
 
 http://some.host/pub;param=value/bin/index.html?name=value
 http://some.host:8080/index.en_US.html
 some.host:8080/index.html
 /usr/bin;param=value/README.txt
 /usr/bin/compress.tar.gz
 
The Context implementation should be able to directly take a Request-URI as defined in RFC 2616 and translate this into a path compatible with the OS specific file system. This keeps the objects semantics simple and explicit, although at the expense of performance.

Author:
Niall Gallagher
See Also:
URIParser, PathParser

Method Summary
 java.lang.String getBasePath()
          This is used to retrieve the base path of the context.
 Content getContent(java.lang.String target)
          This enables the contents of some resource to be acquired using a request URI.
 java.lang.String getContentType(java.lang.String target)
          This method will extract the type attribute of this URI.
 java.io.File getDirectory(java.lang.String target)
          This is used to translate the HTTP request URI into the File object that it represent the parent directory of the URI.
 java.io.File getFile(java.lang.String target)
          This is used to translate the HTTP request URI into the File object that it represents.
 Format getFormat()
          Each Context object must be coupled with an instance of the Format object.
 Index getIndex(java.lang.String target)
          This is an all in one method that allows all the information on the target URI to be gathered at once.
 java.util.Locale getLocale(java.lang.String target)
          This will parse the HTTP request URI specified and return the Locale for that resource.
 Locator getLocator()
          Each Context must supply a Locator to enable the system to locate configuration information and other resources that reside outside the context path.
 java.lang.String getName(java.lang.String target)
          This will parse and return the file name that this request URI references.
 Path getPath(java.lang.String target)
          This is used to translate the HTTP request URI into the Path object that it represents.
 java.util.Properties getProperties(java.lang.String target)
          This provides a convenient way for a Java properties file to be loaded.
 java.lang.String getRealPath(java.lang.String target)
          This is used to translate the HTTP request URI into the OS specific path that it represents.
 java.lang.String getRequestPath(java.lang.String target)
          This is used to translate the HTTP request URI into the URI path normalized and without query or parameter parts.
 

Method Detail

getBasePath

java.lang.String getBasePath()
This is used to retrieve the base path of the context. The base path of the context is that path that that this will retrieve system information from. This represents a base that the request URI paths are served from on the system. For instance a base of "c:\path" would translate a URI path of "/index.html" into "c:\path\index.html". Every resource request must be relative to the context path this allows the ResourceEngine to map the URIs onto the specific OS. The base path is the OS file system specific path. So on UNIX it could be "/home/user/" and on a DOS system it could be "c:\web\html" for example.

Returns:
this returns the base path of the context

getRealPath

java.lang.String getRealPath(java.lang.String target)
This is used to translate the HTTP request URI into the OS specific path that it represents. This will convert the URI to a format that the system can use and also represents the resource path on that system. So if for example the context path was "c:\path" on a DOS system and the HTTP URI given was "/index.html" this returns "c:\path\index.html". If a UNIX system was running the VM and the context base was for example "/home/" then this would return the UNIX path "/home/index.html" for the same request URI.

Parameters:
target - this is the HTTP request URI path that is to be translated into the OS specific path
Returns:
this returns the OS specific path name for the translate request URI

getRequestPath

java.lang.String getRequestPath(java.lang.String target)
This is used to translate the HTTP request URI into the URI path normalized and without query or parameter parts. This is used so that the resource requested by the client can be discovered. For example this will convert the HTTP request URI "http://hostname/bin;param=value/../index.html?query" into the relative URI path /index.html. This is useful if a logging mechanism requires the name of the resource that was requested, it can also be used help find the resource.

Parameters:
target - this is the HTTP request URI that is to be converted into a normalized relative URI path
Returns:
the HTTP request URI as a normalized relative path

getPath

Path getPath(java.lang.String target)
This is used to translate the HTTP request URI into the Path object that it represents. This enables the HTTP request URI to be examined thoroughly an allows various other files to be examined relative to it. For example if the URI referenced a path "/usr/bin/file" and some resource in the same directory is required then the Path can be used to acquire the relative path. This is useful if links within a HTML page are to be dynamically generated. The Path.getRelative provides this functionality.

Parameters:
target - this is the HTTP request URI path that is used to retrieve the Path object
Returns:
returns the Path for the given path

getFile

java.io.File getFile(java.lang.String target)
This is used to translate the HTTP request URI into the File object that it represents. This will convert the URI to a format that the system can use and then create the File object for that path. So if for example the context path was "c:\path" on a DOS system and the HTTP URI given was "/index.html" this returns the File "c:\path\index.html". This is basically for convenience as the same could be achieved using the getRealPath and then creating the File from that OS specific path.

Parameters:
target - this is the HTTP request URI path that is used to retrieve the File object
Returns:
returns the File for the given path

getDirectory

java.io.File getDirectory(java.lang.String target)
This is used to translate the HTTP request URI into the File object that it represent the parent directory of the URI. This will convert the URI to a format that the host system can use and then create the File object for that path. So if for example the context path was "c:\path" on a DOS system and the HTTP URI given was "/index.html" this returns the File "c:\path\". This is basically for convenience as the same could be achieved using the file retrieved from getFile and acquiring the parent.

Parameters:
target - this is the HTTP request URI path that is used to retrieve the File object
Returns:
returns the File for the directory

getLocale

java.util.Locale getLocale(java.lang.String target)
This will parse the HTTP request URI specified and return the Locale for that resource. The Locale is extracted from the target by examining the path segment of the HTTP request URI. The path segment is the abs_path token defined in RFC 2396. It is extracted from a second extension in the file name. So for example if the HTTP request URI was "http://some.host/usr;param=value/index.en_US.html" then the file name "index.en_US.html" would have the second file extension en_US converted into a Locale. This will not interfere if the file name was "compressed.tar.gz", it will simply ignore the "tar" second file extension and return Locale.getDefault.

Parameters:
target - the request URI to be parsed for its locale
Returns:
this will return the locale for the specified URI

getContentType

java.lang.String getContentType(java.lang.String target)
This method will extract the type attribute of this URI. The MIME type of the request URI is extracted from the name of the target. The name for the Context is the last path segment is the token defined by RFC 2396 as path_segments. So for example if the target was "some.host:8080/bin/index.html" then the name for that resource would be "index.html". Once the name has been extracted the MIME is defined by the file extension which, for the example is text/html.

Implementations of the Context may also choose to implement a method that consults the underlying resource and inspect its contents to determine its MIME type. Or for a MAC it may contain its MIME type. If the MIME type cannot be found by any of the above methods RFC 2616 suggests that the resource be given the MIME type application/octetstream. This should also make not predictions as to how the file will be served. So if the target references a directory this does not mean that the Format.getContentType can be used.

Parameters:
target - the request URI to be parsed for its type
Returns:
the type of the file this path refers to

getName

java.lang.String getName(java.lang.String target)
This will parse and return the file name that this request URI references. The name for the Context is the last path segment is the token defined by RFC 2396 as path_segments. So for example if the target was "some.host:8080/home/user/" then the name for that resource would be "user". If the path references the root path "/" then null should be returned.

Parameters:
target - the request URI to be parsed for its name
Returns:
this will return the name that this references

getIndex

Index getIndex(java.lang.String target)
This is an all in one method that allows all the information on the target URI to be gathered at once. The motivation for this method is primarily convenience. However it is also used to increase the performance of the ResourceEngine when the Context implementation is synchronized. This will enable the ResourceEngine to gather the information on the target by acquiring the lock for the object instance only once.

Parameters:
target - this is the request URI that is to be parsed

getContent

Content getContent(java.lang.String target)
                   throws java.io.IOException
This enables the contents of some resource to be acquired using a request URI. The Content is a resource that can be transmitted using an OutputStream which avoids having to deal with FileInputStream objects for files and also facilitates dynamic content. The purpose of this is to discourage the use of chaining which does not result in transferring control, that is, avoid the Java Servlet include technique used by javax.servlet.RequestDispatcher.

Parameters:
target - the request URI that refers to a resource
Returns:
this returns the specified resource wrapped in the Content interface
Throws:
java.io.IOException - this is thrown if the resource does not exist or cannot be accessed

getProperties

java.util.Properties getProperties(java.lang.String target)
                                   throws java.io.IOException
This provides a convenient way for a Java properties file to be loaded. This resolves the target URI to a relative file within the context to be the same as the getFile method would return. Once the file has been acquired the Java properties file is loaded, each time, there is no caching of the loaded properties. This ensures that changes to a loaded object does not affect other users of the properties file.

Parameters:
target - the request URI that refers to the properties
Returns:
returns a populated Properties object using the specified Java properties file
Throws:
java.io.IOException - this is thrown if the resource does not exist or cannot be accessed

getLocator

Locator getLocator()
Each Context must supply a Locator to enable the system to locate configuration information and other resources that reside outside the context path. This is useful when there are Java properties and XML configuration files required by objects interacting with a Context. The Locator employs a search to locate resources, which are identified either by name or using aliases.

Returns:
this returns the locator used by this context object

getFormat

Format getFormat()
Each Context object must be coupled with an instance of the Format object. This is required because each ResourceEngine needs to serve the directory listing and the error messages in a consistent format. The resources of the instances can thus be pooled by comparing the equality of the various Context objects. When there is an object that requires a ResourceEngine it can create an instance of the Context and using a static factory method ResourceEngine with the context object there is a search for an active instance of the ResourceEngine. If one is found that uses a similar context object then it is returned to the caller. This enables instances and thus resources to be shared transparently.

Returns:
this returns the format used with this context object