001 /** 002 * 003 * Copyright 2003-2004 The Apache Software Foundation 004 * 005 * Licensed under the Apache License, Version 2.0 (the "License"); 006 * you may not use this file except in compliance with the License. 007 * You may obtain a copy of the License at 008 * 009 * http://www.apache.org/licenses/LICENSE-2.0 010 * 011 * Unless required by applicable law or agreed to in writing, software 012 * distributed under the License is distributed on an "AS IS" BASIS, 013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 014 * See the License for the specific language governing permissions and 015 * limitations under the License. 016 */ 017 018 // 019 // This source code implements specifications defined by the Java 020 // Community Process. In order to remain compliant with the specification 021 // DO NOT add / change / or delete method signatures! 022 // 023 024 package javax.servlet.jsp; 025 026 import java.util.Enumeration; 027 028 import javax.servlet.jsp.el.ExpressionEvaluator; 029 import javax.servlet.jsp.el.VariableResolver; 030 031 /** 032 * <p> 033 * <code>JspContext</code> serves as the base class for the 034 * PageContext class and abstracts all information that is not specific 035 * to servlets. This allows for Simple Tag Extensions to be used 036 * outside of the context of a request/response Servlet. 037 * <p> 038 * The JspContext provides a number of facilities to the 039 * page/component author and page implementor, including: 040 * <ul> 041 * <li>a single API to manage the various scoped namespaces 042 * <li>a mechanism to obtain the JspWriter for output 043 * <li>a mechanism to expose page directive attributes to the 044 * scripting environment 045 * </ul> 046 * 047 * <p><B>Methods Intended for Container Generated Code</B> 048 * <p> 049 * The following methods enable the <B>management of nested</B> JspWriter 050 * streams to implement Tag Extensions: <code>pushBody()</code> and 051 * <code>popBody()</code> 052 * 053 * <p><B>Methods Intended for JSP authors</B> 054 * <p> 055 * Some methods provide <B>uniform access</B> to the diverse objects 056 * representing scopes. 057 * The implementation must use the underlying machinery 058 * corresponding to that scope, so information can be passed back and 059 * forth between the underlying environment (e.g. Servlets) and JSP pages. 060 * The methods are: 061 * <code>setAttribute()</code>, <code>getAttribute()</code>, 062 * <code>findAttribute()</code>, <code>removeAttribute()</code>, 063 * <code>getAttributesScope()</code> and 064 * <code>getAttributeNamesInScope()</code>. 065 * 066 * <p> 067 * The following methods provide <B>convenient access</B> to implicit objects: 068 * <code>getOut()</code> 069 * 070 * <p> 071 * The following methods provide <B>programmatic access</b> to the 072 * Expression Language evaluator: 073 * <code>getExpressionEvaluator()</code>, <code>getVariableResolver()</code> 074 * 075 * @since 2.0 076 */ 077 078 public abstract class JspContext { 079 080 /** 081 * Sole constructor. (For invocation by subclass constructors, 082 * typically implicit.) 083 */ 084 public JspContext() { 085 } 086 087 /** 088 * Register the name and value specified with page scope semantics. 089 * If the value passed in is <code>null</code>, this has the same 090 * effect as calling 091 * <code>removeAttribute( name, PageContext.PAGE_SCOPE )</code>. 092 * 093 * @param name the name of the attribute to set 094 * @param value the value to associate with the name, or null if the 095 * attribute is to be removed from the page scope. 096 * @throws NullPointerException if the name is null 097 */ 098 099 abstract public void setAttribute(String name, Object value); 100 101 /** 102 * Register the name and value specified with appropriate 103 * scope semantics. If the value passed in is <code>null</code>, 104 * this has the same effect as calling 105 * <code>removeAttribute( name, scope )</code>. 106 * 107 * @param name the name of the attribute to set 108 * @param value the object to associate with the name, or null if 109 * the attribute is to be removed from the specified scope. 110 * @param scope the scope with which to associate the name/object 111 * 112 * @throws NullPointerException if the name is null 113 * @throws IllegalArgumentException if the scope is invalid 114 * @throws IllegalStateException if the scope is 115 * PageContext.SESSION_SCOPE but the page that was requested 116 * does not participate in a session or the session has been 117 * invalidated. 118 */ 119 120 abstract public void setAttribute(String name, Object value, int scope); 121 122 /** 123 * Returns the object associated with the name in the page scope or null 124 * if not found. 125 * 126 * @param name the name of the attribute to get 127 * @return the object associated with the name in the page scope 128 * or null if not found. 129 * 130 * @throws NullPointerException if the name is null 131 */ 132 133 abstract public Object getAttribute(String name); 134 135 /** 136 * Return the object associated with the name in the specified 137 * scope or null if not found. 138 * 139 * @param name the name of the attribute to set 140 * @param scope the scope with which to associate the name/object 141 * @return the object associated with the name in the specified 142 * scope or null if not found. 143 * 144 * @throws NullPointerException if the name is null 145 * @throws IllegalArgumentException if the scope is invalid 146 * @throws IllegalStateException if the scope is 147 * PageContext.SESSION_SCOPE but the page that was requested 148 * does not participate in a session or the session has been 149 * invalidated. 150 */ 151 152 abstract public Object getAttribute(String name, int scope); 153 154 /** 155 * Searches for the named attribute in page, request, session (if valid), 156 * and application scope(s) in order and returns the value associated or 157 * null. 158 * 159 * @param name the name of the attribute to search for 160 * @return the value associated or null 161 * @throws NullPointerException if the name is null 162 */ 163 164 abstract public Object findAttribute(String name); 165 166 /** 167 * Remove the object reference associated with the given name 168 * from all scopes. Does nothing if there is no such object. 169 * 170 * @param name The name of the object to remove. 171 * @throws NullPointerException if the name is null 172 */ 173 174 abstract public void removeAttribute(String name); 175 176 /** 177 * Remove the object reference associated with the specified name 178 * in the given scope. Does nothing if there is no such object. 179 * 180 * @param name The name of the object to remove. 181 * @param scope The scope where to look. 182 * @throws IllegalArgumentException if the scope is invalid 183 * @throws IllegalStateException if the scope is 184 * PageContext.SESSION_SCOPE but the page that was requested 185 * does not participate in a session or the session has been 186 * invalidated. 187 * @throws NullPointerException if the name is null 188 */ 189 190 abstract public void removeAttribute(String name, int scope); 191 192 /** 193 * Get the scope where a given attribute is defined. 194 * 195 * @param name the name of the attribute to return the scope for 196 * @return the scope of the object associated with the name specified or 0 197 * @throws NullPointerException if the name is null 198 */ 199 200 abstract public int getAttributesScope(String name); 201 202 /** 203 * Enumerate all the attributes in a given scope. 204 * 205 * @param scope the scope to enumerate all the attributes for 206 * @return an enumeration of names (java.lang.String) of all the 207 * attributes the specified scope 208 * @throws IllegalArgumentException if the scope is invalid 209 * @throws IllegalStateException if the scope is 210 * PageContext.SESSION_SCOPE but the page that was requested 211 * does not participate in a session or the session has been 212 * invalidated. 213 */ 214 215 abstract public Enumeration getAttributeNamesInScope(int scope); 216 217 /** 218 * The current value of the out object (a JspWriter). 219 * 220 * @return the current JspWriter stream being used for client response 221 */ 222 abstract public JspWriter getOut(); 223 224 /** 225 * Provides programmatic access to the ExpressionEvaluator. 226 * The JSP Container must return a valid instance of an 227 * ExpressionEvaluator that can parse EL expressions. 228 * 229 * @return A valid instance of an ExpressionEvaluator. 230 * @since 2.0 231 */ 232 public abstract ExpressionEvaluator getExpressionEvaluator(); 233 234 /** 235 * Returns an instance of a VariableResolver that provides access to the 236 * implicit objects specified in the JSP specification using this JspContext 237 * as the context object. 238 * 239 * @return A valid instance of a VariableResolver. 240 * @since 2.0 241 */ 242 public abstract VariableResolver getVariableResolver(); 243 244 /** 245 * Return a new JspWriter object that sends output to the 246 * provided Writer. Saves the current "out" JspWriter, 247 * and updates the value of the "out" attribute in the 248 * page scope attribute namespace of the JspContext. 249 * <p>The returned JspWriter must implement all methods and 250 * behave as though it were unbuffered. More specifically: 251 * <ul> 252 * <li>clear() must throw an IOException</li> 253 * <li>clearBuffer() does nothing</li> 254 * <li>getBufferSize() always returns 0</li> 255 * <li>getRemaining() always returns 0</li> 256 * </ul> 257 * </p> 258 * 259 * @param writer The Writer for the returned JspWriter to send 260 * output to. 261 * @return a new JspWriter that writes to the given Writer. 262 * @since 2.0 263 */ 264 public JspWriter pushBody( java.io.Writer writer ) { 265 return null; // XXX to implement 266 } 267 268 /** 269 * Return the previous JspWriter "out" saved by the matching 270 * pushBody(), and update the value of the "out" attribute in 271 * the page scope attribute namespace of the JspContext. 272 * 273 * @return the saved JspWriter. 274 */ 275 public JspWriter popBody() { 276 return null; // XXX to implement 277 } 278 }