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Java > Open Source Codes > org > apache > commons > jexl > ScriptFactory


1 /*
2  * Copyright 2002-2006 The Apache Software Foundation.
3  *
4  * Licensed under the Apache License, Version 2.0 (the "License");
5  * you may not use this file except in compliance with the License.
6  * You may obtain a copy of the License at
7  *
8  * http://www.apache.org/licenses/LICENSE-2.0
9  *
10  * Unless required by applicable law or agreed to in writing, software
11  * distributed under the License is distributed on an "AS IS" BASIS,
12  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13  * See the License for the specific language governing permissions and
14  * limitations under the License.
15  */
16 package org.apache.commons.jexl;
17
18 import java.io.BufferedReader JavaDoc;
19 import java.io.File JavaDoc;
20 import java.io.FileReader JavaDoc;
21 import java.io.IOException JavaDoc;
22 import java.io.InputStreamReader JavaDoc;
23 import java.io.StringReader JavaDoc;
24 import java.net.URL JavaDoc;
25 import java.net.URLConnection JavaDoc;
26
27 import org.apache.commons.jexl.parser.ASTJexlScript;
28 import org.apache.commons.jexl.parser.ParseException;
29 import org.apache.commons.jexl.parser.Parser;
30 import org.apache.commons.jexl.parser.SimpleNode;
31 import org.apache.commons.jexl.parser.TokenMgrError;
32 import org.apache.commons.logging.Log;
33 import org.apache.commons.logging.LogFactory;
34
35 /**
36  * <p>
37  * Creates {@link Script}s. To create a JEXL Script, pass
38  * valid JEXL syntax to the static createScript() method:
39  * </p>
40  *
41  * <pre>
42  * String jexl = "y = x * 12 + 44; y = y * 4;";
43  * Script script = ScriptFactory.createScript( jexl );
44  * </pre>
45  *
46  * <p>
47  * When an {@link Script} is created, the JEXL syntax is
48  * parsed and verified.
49  * </p>
50  * @since 1.1
51  * @version $Id: ScriptFactory.java 429175 2006-08-06 12:05:23 -0700 (Sun, 06 Aug 2006) rahul $
52  */
53 public class ScriptFactory {
54
55     /** The Log to which all ScriptFactory messages will be logged.*/
56     protected static Log log =
57         LogFactory.getLog("org.apache.commons.jexl.ScriptFactory");
58
59     /**
60      * The singleton ScriptFactory also holds a single instance of
61      * {@link Parser}. When parsing expressions, ScriptFactory
62      * synchronizes on Parser.
63      */
64     protected static Parser parser = new Parser(new StringReader JavaDoc(";"));
65
66     /**
67      * ScriptFactory is a singleton and this is the private
68      * instance fufilling that pattern.
69      */
70     protected static ScriptFactory factory = new ScriptFactory();
71
72     /**
73      * Private constructor, the single instance is always obtained
74      * with a call to getInstance().
75      */
76     private ScriptFactory() {
77
78     }
79
80     /**
81      * Returns the single instance of ScriptFactory.
82      * @return the instance of ScriptFactory.
83      */
84     protected static ScriptFactory getInstance() {
85         return factory;
86     }
87
88     /**
89      * Creates a Script from a String containing valid JEXL syntax.
90      * This method parses the script which validates the syntax.
91      *
92      * @param scriptText A String containing valid JEXL syntax
93      * @return A {@link Script} which can be executed with a
94      * {@link JexlContext}.
95      * @throws Exception An exception can be thrown if there is a
96      * problem parsing the script.
97      */
98     public static Script createScript(String JavaDoc scriptText) throws Exception JavaDoc {
99         return getInstance().createNewScript(scriptText);
100     }
101
102     /**
103      * Creates a Script from a {@link File} containing valid JEXL syntax.
104      * This method parses the script and validates the syntax.
105      *
106      * @param scriptFile A {@link File} containing valid JEXL syntax.
107      * Must not be null. Must be a readable file.
108      * @return A {@link Script} which can be executed with a
109      * {@link JexlContext}.
110      * @throws Exception An exception can be thrown if there is a problem
111      * parsing the script.
112      */
113     public static Script createScript(File JavaDoc scriptFile) throws Exception JavaDoc {
114         if (scriptFile == null) {
115             throw new NullPointerException JavaDoc("scriptFile is null");
116         }
117         if (!scriptFile.canRead()) {
118             throw new IOException JavaDoc("Can't read scriptFile ("
119                 + scriptFile.getCanonicalPath() + ")");
120         }
121         BufferedReader JavaDoc reader = new BufferedReader JavaDoc(new FileReader JavaDoc(scriptFile));
122         return createScript(readerToString(reader));
123             
124     }
125
126     /**
127      * Creates a Script from a {@link URL} containing valid JEXL syntax.
128      * This method parses the script and validates the syntax.
129      *
130      * @param scriptUrl A {@link URL} containing valid JEXL syntax.
131      * Must not be null. Must be a readable file.
132      * @return A {@link Script} which can be executed with a
133      * {@link JexlContext}.
134      * @throws Exception An exception can be thrown if there is a problem
135      * parsing the script.
136      */
137     public static Script createScript(URL JavaDoc scriptUrl) throws Exception JavaDoc {
138         if (scriptUrl == null) {
139             throw new NullPointerException JavaDoc("scriptUrl is null");
140         }
141         URLConnection JavaDoc connection = scriptUrl.openConnection();
142         
143         BufferedReader JavaDoc reader = new BufferedReader JavaDoc(
144             new InputStreamReader JavaDoc(connection.getInputStream()));
145         return createScript(readerToString(reader));
146     }
147
148     /**
149      * Creates a new Script based on the string.
150      *
151      * @param scriptText valid Jexl script
152      * @return Script a new script
153      * @throws Exception for a variety of reasons - mostly malformed scripts
154      */
155     protected Script createNewScript(String JavaDoc scriptText) throws Exception JavaDoc {
156         String JavaDoc cleanText = cleanScript(scriptText);
157         SimpleNode script;
158         // Parse the Expression
159 synchronized (parser) {
160             log.debug("Parsing script: " + cleanText);
161             try {
162                 script = parser.parse(new StringReader JavaDoc(cleanText));
163             } catch (TokenMgrError tme) {
164                 throw new ParseException(tme.getMessage());
165             }
166         }
167         if (script instanceof ASTJexlScript) {
168             return new ScriptImpl(cleanText, (ASTJexlScript) script);
169         } else {
170             throw new IllegalStateException JavaDoc("Parsed script is not "
171                 + "an ASTJexlScript");
172         }
173     }
174
175     /**
176      * @todo move to ParseUtils?
177      * Trims the expression and adds a semi-colon if missing.
178      * @param script to clean
179      * @return trimmed expression ending in a semi-colon
180      */
181     private String JavaDoc cleanScript(String JavaDoc script) {
182         String JavaDoc expr = script.trim();
183         if (!expr.endsWith(";")) {
184             expr += ";";
185         }
186         return expr;
187     }
188     
189     /**
190      * Read a buffered reader into a StringBuffer and return a String with
191      * the contents of the reader.
192      * @param reader to be read.
193      * @return the contents of the reader as a String.
194      * @throws IOException on any error reading the reader.
195      */
196     private static String JavaDoc readerToString(BufferedReader JavaDoc reader)
197         throws IOException JavaDoc {
198         StringBuffer JavaDoc buffer = new StringBuffer JavaDoc();
199         try {
200             String JavaDoc line = null;
201             while ((line = reader.readLine()) != null) {
202                 buffer.append(line).append('\n');
203             }
204             return buffer.toString();
205         } finally {
206             reader.close();
207         }
208
209     }
210
211 }
212
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