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Java > Open Source Codes > org > apache > commons > codec > net > RFC1522Codec


1 /*
2  * Copyright 2001-2004 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
17 package org.apache.commons.codec.net;
18
19 import java.io.UnsupportedEncodingException JavaDoc;
20
21 import org.apache.commons.codec.DecoderException;
22 import org.apache.commons.codec.EncoderException;
23
24 /**
25  * <p>
26  * Implements methods common to all codecs defined in RFC 1522.
27  * </p>
28  *
29  * <p>
30  * <a HREF="http://www.ietf.org/rfc/rfc1522.txt">RFC 1522</a>
31  * describes techniques to allow the encoding of non-ASCII text in
32  * various portions of a RFC 822 [2] message header, in a manner which
33  * is unlikely to confuse existing message handling software.
34  * </p>
35
36  * @see <a HREF="http://www.ietf.org/rfc/rfc1522.txt">
37  * MIME (Multipurpose Internet Mail Extensions) Part Two:
38  * Message Header Extensions for Non-ASCII Text</a>
39  * </p>
40  *
41  * @author Apache Software Foundation
42  * @since 1.3
43  * @version $Id: RFC1522Codec.java,v 1.2 2004/04/09 22:21:43 ggregory Exp $
44  */
45 abstract class RFC1522Codec {
46     
47     /**
48      * Applies an RFC 1522 compliant encoding scheme to the given string of text with the
49      * given charset. This method constructs the "encoded-word" header common to all the
50      * RFC 1522 codecs and then invokes {@link #doEncoding(byte [])} method of a concrete
51      * class to perform the specific enconding.
52      *
53      * @param text a string to encode
54      * @param charset a charset to be used
55      *
56      * @return RFC 1522 compliant "encoded-word"
57      *
58      * @throws EncoderException thrown if there is an error conidition during the Encoding
59      * process.
60      * @throws UnsupportedEncodingException thrown if charset is not supported
61      *
62      * @see <a HREF="http://java.sun.com/j2se/1.3/docs/api/java/lang/package-summary.html#charenc">JRE character
63      * encoding names</a>
64      */
65     protected String JavaDoc encodeText(final String JavaDoc text, final String JavaDoc charset)
66      throws EncoderException, UnsupportedEncodingException JavaDoc
67     {
68         if (text == null) {
69             return null;
70         }
71         StringBuffer JavaDoc buffer = new StringBuffer JavaDoc();
72         buffer.append("=?");
73         buffer.append(charset);
74         buffer.append('?');
75         buffer.append(getEncoding());
76         buffer.append('?');
77         byte [] rawdata = doEncoding(text.getBytes(charset));
78         buffer.append(new String JavaDoc(rawdata, StringEncodings.US_ASCII));
79         buffer.append("?=");
80         return buffer.toString();
81     }
82     
83     /**
84      * Applies an RFC 1522 compliant decoding scheme to the given string of text. This method
85      * processes the "encoded-word" header common to all the RFC 1522 codecs and then invokes
86      * {@link #doEncoding(byte [])} method of a concrete class to perform the specific deconding.
87      *
88      * @param text a string to decode
89      *
90      * @throws DecoderException thrown if there is an error conidition during the Decoding
91      * process.
92      * @throws UnsupportedEncodingException thrown if charset specified in the "encoded-word"
93      * header is not supported
94      */
95     protected String JavaDoc decodeText(final String JavaDoc text)
96      throws DecoderException, UnsupportedEncodingException JavaDoc
97     {
98         if (text == null) {
99             return null;
100         }
101         if ((!text.startsWith("=?")) || (!text.endsWith("?="))) {
102             throw new DecoderException("RFC 1522 violation: malformed encoded content");
103         }
104         int termnator = text.length() - 2;
105         int from = 2;
106         int to = text.indexOf("?", from);
107         if ((to == -1) || (to == termnator)) {
108             throw new DecoderException("RFC 1522 violation: charset token not found");
109         }
110         String JavaDoc charset = text.substring(from, to);
111         if (charset.equals("")) {
112             throw new DecoderException("RFC 1522 violation: charset not specified");
113         }
114         from = to + 1;
115         to = text.indexOf("?", from);
116         if ((to == -1) || (to == termnator)) {
117             throw new DecoderException("RFC 1522 violation: encoding token not found");
118         }
119         String JavaDoc encoding = text.substring(from, to);
120         if (!getEncoding().equalsIgnoreCase(encoding)) {
121             throw new DecoderException("This codec cannot decode " +
122                 encoding + " encoded content");
123         }
124         from = to + 1;
125         to = text.indexOf("?", from);
126         byte[] data = text.substring(from, to).getBytes(StringEncodings.US_ASCII);
127         data = doDecoding(data);
128         return new String JavaDoc(data, charset);
129     }
130
131     /**
132      * Returns the codec name (referred to as encoding in the RFC 1522)
133      *
134      * @return name of the codec
135      */
136     protected abstract String JavaDoc getEncoding();
137
138     /**
139      * Encodes an array of bytes using the defined encoding scheme
140      *
141      * @param bytes Data to be encoded
142      *
143      * @return A byte array containing the encoded data
144      *
145      * @throws EncoderException thrown if the Encoder encounters a failure condition
146      * during the encoding process.
147      */
148     protected abstract byte[] doEncoding(byte[] bytes) throws EncoderException;
149
150     /**
151      * Decodes an array of bytes using the defined encoding scheme
152      *
153      * @param bytes Data to be decoded
154      *
155      * @return a byte array that contains decoded data
156      *
157      * @throws DecoderException A decoder exception is thrown if a Decoder encounters a
158      * failure condition during the decode process.
159      */
160     protected abstract byte[] doDecoding(byte[] bytes) throws DecoderException;
161 }
162
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