basepageservlet.java

这个weblogging 设计得比较精巧

package org.roller.presentation.velocity;

import java.io.IOException;
import java.io.StringWriter;
import java.util.Map;

import javax.servlet.ServletConfig;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.jsp.JspFactory;
import javax.servlet.jsp.PageContext;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.velocity.Template;
import org.apache.velocity.VelocityContext;
import org.apache.velocity.context.Context;
import org.apache.velocity.exception.ParseErrorException;
import org.apache.velocity.exception.ResourceNotFoundException;
import org.apache.velocity.servlet.VelocityServlet;
import org.roller.RollerException;
import org.roller.model.UserManager;
import org.roller.pojos.PageData;
import org.roller.pojos.UserData;
import org.roller.pojos.WebsiteData;
import org.roller.presentation.RollerRequest;

/**
 * Base Servlet for Servlets that render user page templates. Loads the
 * Velocity context using the ContextLoader and runs the page template
 * selected by the request.
 *
 * @author llavandowska
 * @author David M Johnson
 */
public abstract class BasePageServlet extends VelocityServlet
{
    private static Log mLogger =
        LogFactory.getFactory().getInstance(BasePageServlet.class);
	/**
	 *  <p>Sets servletContext for WebappResourceLoader.</p>
	 *
	 * @param config servlet configuation
	 */
	public void init( ServletConfig config )
		throws ServletException
	{
		super.init( config );
		WebappResourceLoader.setServletContext( getServletContext() );
	}
    public Template handleRequest( HttpServletRequest request,
                                   HttpServletResponse response,
                                   Context ctx ) throws Exception
    {
        String pid = null;
        Template outty = null;
        Exception pageException = null;
        
        try
        {
            PageContext pageContext =
                JspFactory.getDefaultFactory().getPageContext(
                    this, request, response,"", true, 8192, true);
            // Needed to init request attributes, etc.
            RollerRequest rreq = RollerRequest.getRollerRequest(pageContext);
            UserManager userMgr = rreq.getRoller().getUserManager();
            
            WebsiteData wd = null;
            if (request.getAttribute(RollerRequest.OWNING_USER) != null) {
                UserData user = (UserData)
                    request.getAttribute(RollerRequest.OWNING_USER);
                wd = userMgr.getWebsite(user.getUserName());
            }
            else
            {
                wd = rreq.getWebsite();
            }
            
            // If request specified the page, then go with that
            PageData pd = null;
            if (rreq.getPage() != null // RollerRequest does too much guess work
                    && request.getAttribute(RollerRequest.OWNING_USER) == null)
            {
                pd = rreq.getPage();
                pid = pd.getId();
            }
            // If page not available from request, then use website's default
            else if (wd != null)
            {
                pd = userMgr.retrievePage(wd.getDefaultPageId());
                pid = pd.getId();
                rreq.setPage(pd); 
            }
            // Still no page ID, then we have a problem
            if ( pid == null )
            {
                throw new ResourceNotFoundException("Page not found");
            }
            
            outty = prepareForPageExecution(ctx, rreq, response, pd);
        }
        catch( Exception e )
        {
	        pageException = e;
            response.setStatus( HttpServletResponse.SC_INTERNAL_SERVER_ERROR);
        }
        if (pageException != null)
        {
            mLogger.error("EXCEPTION: in RollerServlet", pageException);
            request.setAttribute("DisplayException", pageException);
        }
        return outty;
    }

    //------------------------------------------------------------------------
    /**
     * Try to load user-specified Decorator (if specified).  Failing that
     * see if user has a _decorator Page, if not check for a _decorator
     * in the Preview resource loader.  Finally, if none of those can
     * be found fall back to the no-op decorator.
     * @param object
     * @return
     */
    private Template findDecorator(String decoratorName, UserManager userMgr, WebsiteData wd) 
        throws ResourceNotFoundException, ParseErrorException, RollerException, Exception
    {
        Template decorator = null;
        PageData decoratorPage = null;
        String decoratorId = null;
        
        // check for user-specified decorator
        if (decoratorName != null)
        {    
            decoratorPage = userMgr.getPageByName(wd, decoratorName);
            if (decoratorPage != null) 
            {
                decoratorId = decoratorPage.getId();
            }
        }
        
        // if no user-specified decorator try default page-name
        if (decoratorPage == null)
        {
            decoratorPage = userMgr.getPageByName(wd, "_decorator");
            if (decoratorPage != null) 
            {
                decoratorId = decoratorPage.getId();
            }
            else
            {
                // could be in PreviewResourceLoader
                decoratorId = "_decorator";
            }
        }

        // try loading Template
        if (decoratorId != null) 
        {
            try
            {
                decorator = getTemplate(decoratorId, "UTF-8");
            }
            catch (Exception e)
            {
                // it may not exist, so this is okay
            }
        }
        
        // couldn't find Template, load default "no-op" decorator
        if (decorator == null) 
        {
            decorator = getTemplate("/themes/noop_decorator.vm", "UTF-8");
        }
        return decorator;
    }

    /** 
     * Prepare for page execution be setting content type, populating context,
     * and processing the page decorator if needed.
     */
    protected Template prepareForPageExecution(Context ctx, RollerRequest rreq, 
        HttpServletResponse response, PageData pd) throws Exception
    {                    
        Template outty = null;
        UserManager userMgr = rreq.getRoller().getUserManager();
        WebsiteData wd = pd.getWebsite();
        
        // if page has an extension - use that to set the contentType
        String pageLink = pd.getLink();
        String mimeType = getServletConfig().getServletContext().getMimeType(pageLink);
        if(mimeType != null) {
            // we found a match ... set the content type
            response.setContentType(mimeType);
        }
        
        /* old way ... not as flexible -- Allen G
        int period = pd.getLink().indexOf('.');
        if (period > -1) 
        {
            String extension = pd.getLink().substring(period+1);
            if ("js".equals(extension)) 
            {
                extension = "javascript";
            }
            response.setContentType("text/" + extension);
        }
        */
    
        // Made it this far, populate the Context
        ContextLoader.setupContext( ctx, rreq, response );

        // Get the page
        outty =  getTemplate( pd.getId(), "UTF-8" );

        /**
         * User can define a Decorator Template.
         */
        if (wd != null)
        {
            // parse/merge Page template
            StringWriter sw = new StringWriter();
            outty.merge(ctx, sw);
            ctx.put("decorator_body", sw.toString());

            // replace outty with decorator Template
            outty = findDecorator((String)ctx.get("decorator"), userMgr, wd);                
        }
        return outty;
    }
    
    //------------------------------------------------------------------------
    /**
     * Handle error in Velocity processing.
     */
    protected void error( HttpServletRequest req, HttpServletResponse res,
        Exception e) throws ServletException, IOException
    {
        mLogger.warn("ERROR in VelocityServlet",e);
    }
   
    /** 
     * Override to prevent Velocity from putting "req" and "res" into the context.
     * Allowing users access to the underlying Servlet objects is a security risk.
     * If need access to request parameters, use $requestParameters.
     */
    protected Context createContext(
            HttpServletRequest req,
            HttpServletResponse res) {
        
        VelocityContext context = new VelocityContext();
        context.put(REQUEST, new RequestWrapper(req.getParameterMap()));
        return context;
        
    }
    
    /** Provide access to request params only, not actual request */
    public static class RequestWrapper
    {
        Map params = null;
        public RequestWrapper(Map params) 
        {
            this.params = params;
        }
        public String getParameter(String key)
        {
            String ret = null;
            String[] array = (String[])params.get(key);
            if (array != null && array.length > 0)
            {
                ret = array[0];
            }
            return ret;
        }
    }
}