1 / 29

OLFS Extensions

OLFS Extensions. Writing a Custom DispatchHandler. Extending the OLFS. Extension ‘modules’ written in Java Jar files added to a directory within Tomcat and called out in the olfs.xml file. The new modules have complete access to the request information Both HTTP GET and POST requests

aolivares
Download Presentation

OLFS Extensions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. OLFS Extensions Writing a Custom DispatchHandler

  2. Extending the OLFS • Extension ‘modules’ written in Java • Jar files added to a directory within Tomcat and called out in the olfs.xml file. • The new modules have complete access to the request information • Both HTTP GET and POST requests • There is some significant processing done before the handler is called: • Conditional GET Requests (Handler is called on to provide last modified dates) • Authorization & Authentication

  3. The OLFS uses an ordered list of Dispatch Handlers to handle requests. • Each handler on the list is asked if it can handle the incoming request. • The first handler on the list that claims the request gets to handle it. • List order is important, as some handlers (for example THREDDS) may claim to handle requests that could (should) be handled by a different handler. • Handlers are free to do anything they need to handle a request: Contact a remote system/process, read files, spawn threads, et cetera. OLFS Dispatch Handlers

  4. DispatchHandler Interface Dispatch Handlers must implement the DispatchHandler interface: public interface DispatchHandler { public void init(DispatchServlet servlet, Element config) throws Exception; public boolean requestCanBeHandled(HttpServletRequest request) throws Exception; public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception; public long getLastModified(HttpServletRequest req); public void destroy(); }

  5. Dispatch Handler Interface:init() method Declaration: public void init(DispatchServlet servlet, Element config) throws Exception; Parameters: servlet: This will be the DispatchServlet that creates the instance of DispatchHandler that is being initialized. DispatchServlet is a child of HttpServlet. config: A JDOM Element object containing the XML Element that announced which implementation of DispatchHandler to use. It may (or may not) contain additional confguration information. Exceptions: Throws an Exception when the bad things happen.

  6. Dispatch Handler Interface:requestCanBeHandled() method Declaration: public boolean requestCanBeHandled(HttpServletRequest request) throws Exception; Parameters: request: The request to be handled. Return: True if the DispatchHandler can service the request, false otherwise. Exceptions: Throws an Exception when the bad things happen.

  7. Dispatch Handler Interface:handleRequest() method public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception; Parameters: request: The request to be handled. response: The response object thru which the response information will placed/written. Exceptions: Throws an Exception when the bad things happen.

  8. Dispatch Handler Interface:getLastModified() method Declaration: public long getLastModified(HttpServletRequest request); Parameters: request: The request for which we need to get a last modified date. Return: The last modified date of the URI referenced in the request. If the date cannot be determined then return -1. Exceptions: May not throw an Exception.

  9. Dispatch Handler Interface:destroy() method Declaration: public void destroy(); Parameters: None Return: None. Exceptions: May not throw an Exception.

  10. DispatchHandler:A Simple Example

  11. requestCanBeHandled() method: public boolean requestCanBeHandled(HttpServletRequest request) throws Exception{ String sName = ReqInfo.getFullSourceName(request); return sName.startsWith("/helloWorld"); } This simple test will cause our example DispatchHandler to claim all requests that begin with “/helloWorld”

  12. handleRequest() method: public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception{ response.setContentType("text/html"); response.setStatus(HttpServletResponse.SC_OK); String msg = "<html><body><br><br><br><br>"; msg += "<center><h1>HELLO WORLD!</h1></center>"; msg += "</body></html>"; response.getWriter().print(msg); } Provides a simple “Hello World” response.

  13. getLastModified() method: public long getLastModified(HttpServletRequest request) { return -1; } Returning a negative one will cause the page to always reload.

  14. Installing your Handler • Edit the olfs.xml file in $CATALINA_HOME/content/opendap • Add your new DispatchHandler implementation to the list of handlers by inserting XML element: <Handler className="bom.tutorial.ExampleDispatchHandler" />Immediately after the BESManager handler. • Restart Tomcat.

  15. Testing your Handler • Point your browser at: http://localhost:8080/opendap/helloWorld

  16. Experiment • Edit the olfs.xml file in $CATALINA_HOME/content/opendap • Move the element that defines your handler to the end of the handler list and restart Tomcat. • Try other permutations of the Handler list (be sure to restart Tomcat after each change). This will probably break Hyrax :)

  17. DispatchHandler:A File Service

  18. FileService:init() method public void init(DispatchServlet s, Element config) throws Exception { if(initialized) return; String dir; Element dv = config.getChild("TopDir"); if(dv!=null){ dir = dv.getTextTrim(); if(dir!=null) { File f = new File(dir); if (f.exists() && f.isDirectory()) fileRoot = dir; else fileRoot = s.getServletContext().getRealPath("docs"); } } while(fileRoot.endsWith("/")) fileRoot = fileRoot.substring(0,fileRoot.length()-1); log.info("fileRoot: " + fileRoot); initialized = true; }

  19. FileService:init() method public void init(DispatchServlet s, Element config) throws Exception { if(initialized) return; String dir; Element dv = config.getChild("TopDir"); if(dv!=null){ dir = dv.getTextTrim(); if(dir!=null) { File f = new File(dir); if (f.exists() && f.isDirectory()) fileRoot = dir; else fileRoot = s.getServletContext().getRealPath("docs"); } } while(fileRoot.endsWith("/")) fileRoot = fileRoot.substring(0,fileRoot.length()-1); log.info("fileRoot: " + fileRoot); initialized = true; }

  20. FileService: requestCanBeHandled() and handleRequest() methods public boolean requestCanBeHandled(HttpServletRequest request) throws Exception{ return fileService(request,null,false); } public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception{ fileService(request,response,true); } Both of these methods call on the fileService() method to perform both the handling evaluation and the response evaluation.

  21. FileService: fileService() method private boolean fileService(HttpServletRequest request, HttpServletResponse response, boolean sendResponse) throws Exception{ String path = getPath(request); boolean isFileRequest = false; if(path!=null){ isFileRequest = true; if(sendResponse){ File file = new File(path); if(file.exists()){ if(file.isDirectory()) sendDirPage(file,request, response); else if(file.isFile()) sendFile(file,response); else sendFileNotFound(response); } else { sendFileNotFound(response); } } } return isFileRequest; }

  22. FileService: getPath() method private String getPath(HttpServletRequest req){ String sName = ReqInfo.getFullSourceName(req); String path = null; if(sName.startsWith(urlPrefix)){ path = sName.substring(urlPrefix.length(),sName.length()); if( ! path.startsWith("/")) path = "/" + path; path = fileRoot + path; } return path; }

  23. FileService: getLastModifed() method public long getLastModified(HttpServletRequest req){ String path = getPath(req); if(path!=null){ File file = new File(path); if(file.exists()) return file.lastModified(); } return -1; } • Utilizes the getPath() method. Ignores a bad return (that will be handled later with a 404 page). • Interacts directly with the file system to ascertain the last modified date of the file/directory.

  24. Installing your Handler • Edit the olfs.xml file in $CATALINA_HOME/content/opendap • Add your new DispatchHandler implementation to the list of handlers by inserting XML element: <Handler className="bom.tutorial.FileService> <TopDir>/path/of/dir/to/access</TopDir> </Handler>Immediately after the BESManager handler. • Restart Tomcat.

  25. FileDispatchHandler:A Hyrax DispatchHandler. • Hyrax will serve files that it does not recognize as data. • It is also possible to configure Hyrax to allow users to directly download the source data files.

  26. FileDispatchHandler:init() method public void init(DispatchServlet servlet,Element config) throwsException { if(initialized) return; Element dv = config.getChild("AllowDirectDataSourceAccess"); if(dv!=null){ allowDirectDataSourceAccess = true; } log.info("Intialized. Direct Data Source Access: ” + (allowDirectDataSourceAccess?"Enabled":"Disabled") ); initialized = true; }

  27. FileDispatchHandler:requestCanBeHandled() and handleRequest() methods public boolean requestCanBeHandled(HttpServletRequest request) throws Exception { return fileDispatch(request, null, false); } public void handleRequest(HttpServletRequest request, HttpServletResponse response) throws Exception { if(!fileDispatch(request, response, true)) log.debug("FileDispatch request failed inexplicably!"); } public boolean fileDispatch(HttpServletRequest request, HttpServletResponse response, boolean sendResponse) throws Exception;

  28. FileDispatchHandler:fileDispatch() method public boolean fileDispatch(HttpServletRequest request, HttpServletResponse response, boolean sendResponse) throws Exception { DataSourceInfo dsi = new BESDataSource(ReqInfo.getFullSourceName(request)); boolean isFileResponse = false; if (dsi.sourceExists()) { if (!dsi.isCollection()) { isFileResponse = true; if (sendResponse) { if (!dsi.isDataset() || allowDirectDataSourceAccess) { sendFile(request, response); } else { sendDirectAccessDenied(request, response); } } } } return isFileResponse; }

  29. Summary • DispatchHandler implementations are free to conduct business using any available tools • Sockets • JDBC • File Systems • Etc. • Care should be taken in ordering them in the olfs.xml configuration file. Improper ordering can create unintended results, including disabling of desired functionality.

More Related