1 /*
2 * $Header: /home/cvs/jakarta-commons/betwixt/src/java/org/apache/commons/betwixt/expression/Context.java,v 1.4 2003/01/12 13:52:03 rdonkin Exp $
3 * $Revision: 1.4 $
4 * $Date: 2003/01/12 13:52:03 $
5 *
6 * ====================================================================
7 *
8 * The Apache Software License, Version 1.1
9 *
10 * Copyright (c) 1999-2002 The Apache Software Foundation. All rights
11 * reserved.
12 *
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
15 * are met:
16 *
17 * 1. Redistributions of source code must retain the above copyright
18 * notice, this list of conditions and the following disclaimer.
19 *
20 * 2. Redistributions in binary form must reproduce the above copyright
21 * notice, this list of conditions and the following disclaimer in
22 * the documentation and/or other materials provided with the
23 * distribution.
24 *
25 * 3. The end-user documentation included with the redistribution, if
26 * any, must include the following acknowlegement:
27 * "This product includes software developed by the
28 * Apache Software Foundation (http://www.apache.org/)."
29 * Alternately, this acknowlegement may appear in the software itself,
30 * if and wherever such third-party acknowlegements normally appear.
31 *
32 * 4. The names "The Jakarta Project", "Commons", and "Apache Software
33 * Foundation" must not be used to endorse or promote products derived
34 * from this software without prior written permission. For written
35 * permission, please contact apache@apache.org.
36 *
37 * 5. Products derived from this software may not be called "Apache"
38 * nor may "Apache" appear in their names without prior written
39 * permission of the Apache Group.
40 *
41 * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
42 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
43 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
44 * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
45 * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
46 * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
47 * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
48 * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
49 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
50 * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
51 * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
52 * SUCH DAMAGE.
53 * ====================================================================
54 *
55 * This software consists of voluntary contributions made by many
56 * individuals on behalf of the Apache Software Foundation. For more
57 * information on the Apache Software Foundation, please see
58 * <http://www.apache.org/>.
59 * $Id: Context.java,v 1.4 2003/01/12 13:52:03 rdonkin Exp $
60 */
61 package org.apache.commons.betwixt.expression;
62
63 import java.util.HashMap;
64 import java.util.Map;
65
66 import org.apache.commons.logging.Log;
67 import org.apache.commons.logging.LogFactory;
68
69 /*** <p><code>Context</code> describes the context used to evaluate
70 * bean expressions.
71 * This is mostly a bean together with a number of context variables.
72 * Context variables are named objects.
73 * In other words,
74 * a context variable associates an object with a string.</p>
75 *
76 * <p> Logging during expression evaluation is done through the logging
77 * instance held by this class.
78 * The object initiating the evaluation should control this logging
79 * and so passing a <code>Log</code> instance is enforced by the constructors.</p>
80 *
81 * <p><code>Context</code> is a natural place to include shared evaluation code.
82 * One of the problems that you get with object graphs is that they can be cyclic.
83 * Xml cannot (directly) include cycles.
84 * Therefore <code>betwixt</code> needs to find and deal properly with cycles.
85 * The algorithm used is to check the parentage of a new child.
86 * If the child is a parent then that operation fails. </p>
87 *
88 * @author <a href="mailto:jstrachan@apache.org">James Strachan</a>
89 * @version $Revision: 1.4 $
90 */
91 public class Context {
92
93 /*** Evaluate this bean */
94 private Object bean;
95 /*** Variables map */
96 private Map variables = new HashMap();
97 /***
98 * Logging uses commons-logging <code>Log</code>
99 * named <code>org.apache.commons.betwixt</code>
100 */
101 private Log log;
102
103 /*** Construct context with default log */
104 public Context() {
105 this.log = LogFactory.getLog( getClass() );
106 }
107
108 /*** Convenience constructor sets evaluted bean and log.
109 *
110 * @param bean evaluate expressions against this bean
111 * @param log log to this logger
112 */
113 public Context(Object bean, Log log) {
114 this.bean = bean;
115 this.log = log;
116 }
117
118 /*** Convenience constructor sets evaluted bean, context variables and log.
119 *
120 * @param bean evaluate expressions against this bean
121 * @param variables context variables
122 * @param log log to this logger
123 */
124 public Context(Object bean, Map variables, Log log) {
125 this.bean = bean;
126 this.variables = variables;
127 this.log = log;
128 }
129
130 /*** Returns a new child context with the given bean but the same log and variables.
131 *
132 * @param newBean create a child context for this bean
133 * @return new Context with new bean but shared variables
134 */
135 public Context newContext(Object newBean) {
136 return new Context(newBean, variables, log);
137 }
138
139 /***
140 * Gets the current bean.
141 * @return the bean against which expressions are evaluated
142 */
143 public Object getBean() {
144 return bean;
145 }
146
147 /***
148 * Set the current bean.
149 * @param bean the Object against which expressions will be evaluated
150 */
151 public void setBean(Object bean) {
152 this.bean = bean;
153 }
154
155 /***
156 * Gets context variables.
157 * @return map containing variable values keyed by variable name
158 */
159 public Map getVariables() {
160 return variables;
161 }
162
163 /***
164 * Sets context variables.
165 * @param variables map containing variable values indexed by varibable name Strings
166 */
167 public void setVariables(Map variables) {
168 this.variables = variables;
169 }
170
171 /***
172 * Gets the value of a particular context variable.
173 * @param name the name of the variable whose value is to be returned
174 * @return the variable value or null if the variable isn't set
175 */
176 public Object getVariable(String name) {
177 return variables.get( name );
178 }
179
180 /***
181 * Sets the value of a particular context variable.
182 * @param name the name of the variable
183 * @param value the value of the variable
184 */
185 public void setVariable(String name, Object value) {
186 variables.put( name, value );
187 }
188
189 /***
190 * Gets the current log.
191 *
192 * @return the implementation to which this class logs
193 */
194 public Log getLog() {
195 return log;
196 }
197
198 /***
199 * Set the log implementation to which this class logs
200 *
201 * @param log the implemetation that this class should log to
202 */
203 public void setLog(Log log) {
204 this.log = log;
205 }
206 }
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