Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.jxpath.servlet; import javax.servlet.ServletContext; import javax.servlet.ServletRequest; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpSession; import javax.servlet.jsp.PageContext; import org.apache.commons.jxpath.JXPathContext; import org.apache.commons.jxpath.JXPathContextFactory; import org.apache.commons.jxpath.JXPathIntrospector; /** * Static methods that allocate and cache JXPathContexts bound to * {@link PageContext}, {@link ServletRequest}, {@link HttpSession} * and {@link ServletContext}. * <p> * The {@link JXPathContext} returned by {@link #getPageContext getPageContext()} * provides access to all scopes via the PageContext.findAttribute() * method. Thus, an expression like "foo" will first look for the attribute * named "foo" in the "page" context, then the "request" context, then * the "session" one and finally in the "application" context. * <p> * If you need to limit the attibute lookup to just one scope, you can use the * pre-definded variables "page", "request", "session" and "application". * For example, the expression "$session/foo" extracts the value of the * session attribute named "foo". * <p> * Following are some implementation details. There is a separate JXPathContext * for each of the four scopes. These contexts are chained according to the * nesting of the scopes. So, the parent of the "page" JXPathContext is a * "request" JXPathContext, whose parent is a "session" JXPathContext (that is * if there is a session), whose parent is an "application" context. * <p> * The XPath context node for each context is the corresponding object: * PageContext, ServletRequest, HttpSession or ServletContext. This feature can * be used by servlets. A servlet can use one of the methods declared by this * class and work with a specific JXPathContext for any scope. * <p> * Since JXPath chains lookups for variables and extension functions, variables * and extension function declared in the outer scopes are also available in * the inner scopes. * <p> * Each of the four context declares exactly one variable, the value of which * is the corresponding object: PageContext, etc. * <p> * The "session" variable will be undefined if there is no session for this * servlet. JXPath does not automatically create sessions. * * @author Dmitri Plotnikov * @version $Revision: 652845 $ $Date: 2008-05-02 12:46:46 -0500 (Fri, 02 May 2008) $ */ public final class JXPathServletContexts { private static JXPathContextFactory factory; static { JXPathIntrospector.registerDynamicClass(PageScopeContext.class, PageScopeContextHandler.class); JXPathIntrospector.registerDynamicClass(PageContext.class, PageContextHandler.class); JXPathIntrospector.registerDynamicClass(ServletContext.class, ServletContextHandler.class); JXPathIntrospector.registerDynamicClass(ServletRequestAndContext.class, ServletRequestHandler.class); JXPathIntrospector.registerDynamicClass(HttpSessionAndServletContext.class, HttpSessionHandler.class); factory = JXPathContextFactory.newInstance(); } /** * Returns a JXPathContext bound to the "page" scope. Caches that context * within the PageContext itself. * @param pageContext as described * @return JXPathContext */ public static JXPathContext getPageContext(PageContext pageContext) { JXPathContext context = (JXPathContext) pageContext.getAttribute(Constants.JXPATH_CONTEXT); if (context == null) { JXPathContext parentContext = getRequestContext(pageContext.getRequest(), pageContext.getServletContext()); context = factory.newContext(parentContext, pageContext); context.setVariables(new KeywordVariables(Constants.PAGE_SCOPE, new PageScopeContext(pageContext))); pageContext.setAttribute(Constants.JXPATH_CONTEXT, context); } return context; } /** * Returns a JXPathContext bound to the "request" scope. Caches that context * within the request itself. * @param request as described * @param servletContext operative * @return JXPathContext */ public static JXPathContext getRequestContext(ServletRequest request, ServletContext servletContext) { JXPathContext context = (JXPathContext) request.getAttribute(Constants.JXPATH_CONTEXT); // If we are in an included JSP or Servlet, the request parameter // will represent the included URL, but the JXPathContext we have // just acquired will represent the outer request. if (context != null) { ServletRequestAndContext handle = (ServletRequestAndContext) context.getContextBean(); if (handle.getServletRequest() == request) { return context; } } JXPathContext parentContext = null; if (request instanceof HttpServletRequest) { HttpSession session = ((HttpServletRequest) request).getSession(false); if (session != null) { parentContext = getSessionContext(session, servletContext); } else { parentContext = getApplicationContext(servletContext); } } ServletRequestAndContext handle = new ServletRequestAndContext(request, servletContext); context = factory.newContext(parentContext, handle); context.setVariables(new KeywordVariables(Constants.REQUEST_SCOPE, handle)); request.setAttribute(Constants.JXPATH_CONTEXT, context); return context; } /** * Returns a JXPathContext bound to the "session" scope. Caches that context * within the session itself. * @param session as described * @param servletContext operative * @return JXPathContext */ public static JXPathContext getSessionContext(HttpSession session, ServletContext servletContext) { JXPathContext context = (JXPathContext) session.getAttribute(Constants.JXPATH_CONTEXT); if (context == null) { JXPathContext parentContext = getApplicationContext(servletContext); HttpSessionAndServletContext handle = new HttpSessionAndServletContext(session, servletContext); context = factory.newContext(parentContext, handle); context.setVariables(new KeywordVariables(Constants.SESSION_SCOPE, handle)); session.setAttribute(Constants.JXPATH_CONTEXT, context); } return context; } /** * Returns a JXPathContext bound to the "application" scope. Caches that * context within the servlet context itself. * @param servletContext operative * @return JXPathContext */ public static JXPathContext getApplicationContext(ServletContext servletContext) { JXPathContext context = (JXPathContext) servletContext.getAttribute(Constants.JXPATH_CONTEXT); if (context == null) { context = factory.newContext(null, servletContext); context.setVariables(new KeywordVariables(Constants.APPLICATION_SCOPE, servletContext)); servletContext.setAttribute(Constants.JXPATH_CONTEXT, context); } return context; } }