javawebparts.servlet
Class ResourceServerServlet

java.lang.Object
  |
  +--javax.servlet.GenericServlet
        |
        +--javax.servlet.http.HttpServlet
              |
              +--javawebparts.servlet.ResourceServerServlet

All Implemented Interfaces:

java.io.Serializable, javax.servlet.Servlet, javax.servlet.ServletConfig

public class ResourceServerServlet

extends javax.servlet.http.HttpServlet

The ResourceServerServlet can be used to serve resources from various sources. It uses an implementation of the ResourceStream interface, each of which is specific to a given source. There is an implementation for serving resources from a JAR file in the classpath, from the file system, from a URL and from a database. Multiple instance of this servlet can be used, under different names of course, each with its own set of init parameters.

This servlet recognizes the following init parameters:

• requestParameter - This is the request parameter that will have the value used to determine the resource to serve. For instance, if you set this to "res", and use the ResourceStreamFromURL ResourceStream implementation, then the servlet expects to receive a request parameter named "res" that is a URL, the contents from which will be returned. Default: res. Required: No.
• resourceStreamClass - This is the fully-qualified name of the class which implements the ResourceStream interface. This class is responsible for returning to this servlet an InputStream to the resource to be served. Default: None. Required: Yes.
• serveUnbounded - The value of this is either "true" or "false". When set to true, it means that ANY requested resource that can be resolved by the servlet (and the associated ResourceStream class) will be served. In other words, if this servlet receives a request for a resource in a JAR that it can find, it will be served, whether you intend for it to be servable or not. When set to false, only resources listed in the named mapping file will be served. Setting this to true can be a security issue obviously, so you need to be very careful when doing so, and you will probably want to use some sort of security mechanism in front of this servlet in that case. Required: No. Default: false (not that in this case the servlet may not initialize because a mapping file would be required, which may not be present).
• resourceMappingFile - This is a context-relative full path to a configuration file that does two things. First, it lists all the resources that can be served, and no resource that is not listed can be served. Second, it defines the content type for each resource. Required: no (unless serveUnbound is false, in which case it IS required). Default: none.
• defaultContentType - This is simply the content type that will be used if the content type is not specified otherwise. The ResourceStream implementation class is first asked for the contentType. If it does not supply it, the mapping file, if present, is checked, If it is still not determined, then the default value here is used. Required: yes. Default: none.
• streamParam1 - This is an arbitrary piece of data that will be passed to the ResourceStream implementation class for every requested resource. This can be whatever you want. Required: no. Default: none.
• streamParam2 - This is another arbitrary piece of data that will be passed to the ResourceStream implementation class for every requested resource. This can be whatever you want. Required: no. Default: none.

Here is an example configuration:

<servlet>
<servlet-name>ServeResourceFromFileSystem </servlet-name>
<servlet-class>javawebparts.servlet.ResourceServerServlet </servlet-class>
<init-param>
<param-name>requestParameter </param-name>
<param-value>fsres</param-value>
</init-param>
<init-param>
<param-name>resourceStreamClass </param-name>
<param-value>javawebparts.servlet. ResourceStreamFromFileSystem</param-value>
</init-param>
<init-param>
<param-name>serveUnbounded</param-name >
<param-value>false</param-value>
</init-param>
<init-param>
<param-name>resourceMappingFile </param-name>
<param-value>/WEB-INF/resource-mappings.xml </param-value>
</init-param>
<init-param>
<param-name>defaultContentType </param-name>
<param-value>dummy</param-value>
</init-param>
</servlet>

You can write your own implementation of ResourceStream to serve resources from other sources. One logical implementation would be to serve from a database. In this case, you may decide that the request parameter will be giving a key in a table. You may also use the streamParams to name the connection string and userID/password. The getStream() method simply needs to return an InputStream on the BLOB from the database. It should return null if the resource cannot be found (in which case nothing will be returned by the servlet). Also, if applicable, implement the getContentType() method. In the case of serving from a database, one can envision having a field in the table that stores the content type. You can of course just use the defaultContentType, or a mapping file, whichever is most appropriate (it is likely such a database implementation will be supplied with JWP in the future).

Author:

Frank W. Zammetti.

See Also:

Serialized Form

Nested Class Summary

static class

ResourceServerServlet.ResourceMapping ResourceMapping is an inner class which holds the information for each element in the mapping file, if present.

Field Summary

private java.lang.String	defaultContentType If the ResourceStream implementation class doesn't provide the contentType, and if no mapping file is used, then this default contentType will be set for each resource served.
private static org.apache.commons.logging.Log	log Log instance.
private java.util.HashMap	mappings mappings is a collection of ResourceMapping objects (which correspond to elements in a mapping file) for each resource.
private java.lang.String	requestParameter requestParameter is the name of the request parameter that will be examined to determine what the requested resource is.
private java.lang.String	resourceMappingFile resourceMappingFile is the context-relative path to a file which maps requested resources to contentTypes.
private java.lang.String	resourceStreamClass resourceStreamClass is the class that implements the ResourceStream interface and knows how to provide a stream to a requested resource, and optionally the contentType for the resource.
private boolean	serveUnbounded serveUnbounded, when set to true, means that any resource that the servlet, and by extension the applicable ResourceStream class, can find.
private java.lang.String	streamParam1 streamParam1 is an arbitrary piece of information passed to the ResourceStream implementation class.
private java.lang.String	streamParam2 streamParam2 is an arbitrary piece of information passed to the ResourceStream implementation class.

Fields inherited from class javax.servlet.http.HttpServlet

Fields inherited from class javax.servlet.GenericServlet

Constructor Summary

ResourceServerServlet()

Method Summary

void	addMapping(ResourceServerServlet.ResourceMapping rm) Add a ResourceMapping to the mappings collection.
void	doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response) doGet.
void	doPost(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response) doPost.
void	init(javax.servlet.ServletConfig config) init.
java.lang.String	toString() Overriden toString method.

Methods inherited from class javax.servlet.http.HttpServlet

doDelete, doHead, doOptions, doPut, doTrace, getLastModified, service, service

Methods inherited from class javax.servlet.GenericServlet

destroy, getInitParameter, getInitParameterNames, getServletConfig, getServletContext, getServletInfo, getServletName, init, log, log

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

log

private static org.apache.commons.logging.Log log

Log instance.

requestParameter

private java.lang.String requestParameter

requestParameter is the name of the request parameter that will be examined to determine what the requested resource is.

resourceStreamClass

private java.lang.String resourceStreamClass

resourceStreamClass is the class that implements the ResourceStream interface and knows how to provide a stream to a requested resource, and optionally the contentType for the resource.

resourceMappingFile

private java.lang.String resourceMappingFile

resourceMappingFile is the context-relative path to a file which maps requested resources to contentTypes. This file is optional in many cases, but not always, depending on how other init parameters are set.

serveUnbounded

private boolean serveUnbounded

serveUnbounded, when set to true, means that any resource that the servlet, and by extension the applicable ResourceStream class, can find. You need to be careful when setting this to true because it potentially opens up security holes (i.e., resources you don't intend might be reachable).

defaultContentType

private java.lang.String defaultContentType

If the ResourceStream implementation class doesn't provide the contentType, and if no mapping file is used, then this default contentType will be set for each resource served.

mappings

private java.util.HashMap mappings

mappings is a collection of ResourceMapping objects (which correspond to elements in a mapping file) for each resource.

streamParam1

private java.lang.String streamParam1

streamParam1 is an arbitrary piece of information passed to the ResourceStream implementation class.

streamParam2

private java.lang.String streamParam2

streamParam2 is an arbitrary piece of information passed to the ResourceStream implementation class.

Constructor Detail

ResourceServerServlet

public ResourceServerServlet()

Method Detail

init

public void init(javax.servlet.ServletConfig config)
          throws javax.servlet.ServletException

init.

Specified by:

init in interface javax.servlet.Servlet

Overrides:

init in class javax.servlet.GenericServlet

Parameters:

config - ServletConfig.

Throws:

javax.servlet.ServletException - ServletException.

addMapping

public void addMapping(ResourceServerServlet.ResourceMapping rm)

Add a ResourceMapping to the mappings collection.

Parameters:

rm - The ResourceMapping object to add to the collection.

doGet

public void doGet(javax.servlet.http.HttpServletRequest request,
                  javax.servlet.http.HttpServletResponse response)
           throws javax.servlet.ServletException,
                  java.io.IOException

doGet. Calls doPost() to do real work.

Overrides:

doGet in class javax.servlet.http.HttpServlet

Parameters:

request - HTTPServletRequest.

response - HTTPServletResponse.

Throws:

javax.servlet.ServletException - ServletException.

java.io.IOException - IOException.

doPost

public void doPost(javax.servlet.http.HttpServletRequest request,
                   javax.servlet.http.HttpServletResponse response)
            throws javax.servlet.ServletException,
                   java.io.IOException

doPost.

Overrides:

doPost in class javax.servlet.http.HttpServlet

Parameters:

request - HTTPServletRequest

response - HTTPServletResponse

Throws:

javax.servlet.ServletException - ServletException

java.io.IOException - IOException

toString

public java.lang.String toString()

Overriden toString method.

Overrides:

toString in class java.lang.Object

Returns:

A reflexively-built string representation of this bean.