1 /**
2 *
3 * Copyright 2003-2004 The Apache Software Foundation
4 *
5 * Licensed under the Apache License, Version 2.0 (the "License");
6 * you may not use this file except in compliance with the License.
7 * You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17
18
19
20
21
22
23
24 package javax.servlet.jsp;
25
26 import java.util.Enumeration;
27
28 import javax.servlet.jsp.el.ExpressionEvaluator;
29 import javax.servlet.jsp.el.VariableResolver;
30
31 /**
32 * <p>
33 * <code>JspContext</code> serves as the base class for the
34 * PageContext class and abstracts all information that is not specific
35 * to servlets. This allows for Simple Tag Extensions to be used
36 * outside of the context of a request/response Servlet.
37 * <p>
38 * The JspContext provides a number of facilities to the
39 * page/component author and page implementor, including:
40 * <ul>
41 * <li>a single API to manage the various scoped namespaces
42 * <li>a mechanism to obtain the JspWriter for output
43 * <li>a mechanism to expose page directive attributes to the
44 * scripting environment
45 * </ul>
46 *
47 * <p><B>Methods Intended for Container Generated Code</B>
48 * <p>
49 * The following methods enable the <B>management of nested</B> JspWriter
50 * streams to implement Tag Extensions: <code>pushBody()</code> and
51 * <code>popBody()</code>
52 *
53 * <p><B>Methods Intended for JSP authors</B>
54 * <p>
55 * Some methods provide <B>uniform access</B> to the diverse objects
56 * representing scopes.
57 * The implementation must use the underlying machinery
58 * corresponding to that scope, so information can be passed back and
59 * forth between the underlying environment (e.g. Servlets) and JSP pages.
60 * The methods are:
61 * <code>setAttribute()</code>, <code>getAttribute()</code>,
62 * <code>findAttribute()</code>, <code>removeAttribute()</code>,
63 * <code>getAttributesScope()</code> and
64 * <code>getAttributeNamesInScope()</code>.
65 *
66 * <p>
67 * The following methods provide <B>convenient access</B> to implicit objects:
68 * <code>getOut()</code>
69 *
70 * <p>
71 * The following methods provide <B>programmatic access</b> to the
72 * Expression Language evaluator:
73 * <code>getExpressionEvaluator()</code>, <code>getVariableResolver()</code>
74 *
75 * @since 2.0
76 */
77
78 public abstract class JspContext {
79
80 /**
81 * Sole constructor. (For invocation by subclass constructors,
82 * typically implicit.)
83 */
84 public JspContext() {
85 }
86
87 /**
88 * Register the name and value specified with page scope semantics.
89 * If the value passed in is <code>null</code>, this has the same
90 * effect as calling
91 * <code>removeAttribute( name, PageContext.PAGE_SCOPE )</code>.
92 *
93 * @param name the name of the attribute to set
94 * @param value the value to associate with the name, or null if the
95 * attribute is to be removed from the page scope.
96 * @throws NullPointerException if the name is null
97 */
98
99 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;
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;
277 }
278 }