Java tutorial
/* * $Id: XmlReader.java,v 1.1 2004/08/19 05:30:22 aslom Exp $ * * The Apache Software License, Version 1.1 * * * Copyright (c) 2000 The Apache Software Foundation. All rights * reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * * 3. The end-user documentation included with the redistribution, * if any, must include the following acknowledgment: * "This product includes software developed by the * Apache Software Foundation (http://www.apache.org/)." * Alternately, this acknowledgment may appear in the software itself, * if and wherever such third-party acknowledgments normally appear. * * 4. The names "Crimson" and "Apache Software Foundation" must * not be used to endorse or promote products derived from this * software without prior written permission. For written * permission, please contact apache@apache.org. * * 5. Products derived from this software may not be called "Apache", * nor may "Apache" appear in their name, without prior written * permission of the Apache Software Foundation. * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE * DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR * ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF * USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, * OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT * OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF * SUCH DAMAGE. * * * This software consists of voluntary contributions made by many * individuals on behalf of the Apache Software Foundation and was * originally based on software copyright (c) 1999, Sun Microsystems, Inc., * http://www.sun.com. For more information on the Apache Software * Foundation, please see <http://www.apache.org/>. */ import java.io.*; import java.util.Hashtable; /** * This handles several XML-related tasks that normal java.io Readers * don't support, inluding use of IETF standard encoding names and * automatic detection of most XML encodings. The former is needed * for interoperability; the latter is needed to conform with the XML * spec. This class also optimizes reading some common encodings by * providing low-overhead unsynchronized Reader support. * * <P> Note that the autodetection facility should be used only on * data streams which have an unknown character encoding. For example, * it should never be used on MIME text/xml entities. * * <P> Note that XML processors are only required to support UTF-8 and * UTF-16 character encodings. Autodetection permits the underlying Java * implementation to provide support for many other encodings, such as * US-ASCII, ISO-8859-5, Shift_JIS, EUC-JP, and ISO-2022-JP. * * @author David Brownell * @version $Revision: 1.1 $ */ final public class XmlReader extends Reader { private static final int MAXPUSHBACK = 512; private Reader in; private String assignedEncoding; private boolean closed; // // This class always delegates I/O to a reader, which gets // its data from the very beginning of the XML text. It needs // to use a pushback stream since (a) autodetection can read // partial UTF-8 characters which need to be fully processed, // (b) the "Unicode" readers swallow characters that they think // are byte order marks, so tests fail if they don't see the // real byte order mark. // // It's got do this efficiently: character I/O is solidly on the // critical path. (So keep buffer length over 2 Kbytes to avoid // excess buffering. Many URL handlers stuff a BufferedInputStream // between here and the real data source, and larger buffers keep // that from slowing you down.) // /** * Constructs the reader from an input stream, autodetecting * the encoding to use according to the heuristic specified * in the XML 1.0 recommendation. * * @param in the input stream from which the reader is constructed * @exception IOException on error, such as unrecognized encoding */ public static Reader createReader(InputStream in) throws IOException { return new XmlReader(in); } /** * Creates a reader supporting the given encoding, mapping * from standard encoding names to ones that understood by * Java where necessary. * * @param in the input stream from which the reader is constructed * @param encoding the IETF standard name of the encoding to use; * if null, autodetection is used. * @exception IOException on error, including unrecognized encoding */ public static Reader createReader(InputStream in, String encoding) throws IOException { if (encoding == null) { return new XmlReader(in); } if ("UTF-8".equalsIgnoreCase(encoding) || "UTF8".equalsIgnoreCase(encoding)) { return new Utf8Reader(in); } if ("US-ASCII".equalsIgnoreCase(encoding) || "ASCII".equalsIgnoreCase(encoding)) { return new AsciiReader(in); } if ("ISO-8859-1".equalsIgnoreCase(encoding) // plus numerous aliases ... ) { return new Iso8859_1Reader(in); } // What we really want is an administerable resource mapping // encoding names/aliases to classnames. For example a property // file resource, "readers/mapping.props", holding and a set // of readers in that (sub)package... defaulting to this call // only if no better choice is available. // return new InputStreamReader(in, std2java(encoding)); } // JDK doesn't know all of the standard encoding names, and // in particular none of the EBCDIC ones IANA defines (and // which IBM encourages). static private final Hashtable charsets = new Hashtable(31); static { charsets.put("UTF-16", "Unicode"); charsets.put("ISO-10646-UCS-2", "Unicode"); // NOTE: no support for ISO-10646-UCS-4 yet. charsets.put("EBCDIC-CP-US", "cp037"); charsets.put("EBCDIC-CP-CA", "cp037"); charsets.put("EBCDIC-CP-NL", "cp037"); charsets.put("EBCDIC-CP-WT", "cp037"); charsets.put("EBCDIC-CP-DK", "cp277"); charsets.put("EBCDIC-CP-NO", "cp277"); charsets.put("EBCDIC-CP-FI", "cp278"); charsets.put("EBCDIC-CP-SE", "cp278"); charsets.put("EBCDIC-CP-IT", "cp280"); charsets.put("EBCDIC-CP-ES", "cp284"); charsets.put("EBCDIC-CP-GB", "cp285"); charsets.put("EBCDIC-CP-FR", "cp297"); charsets.put("EBCDIC-CP-AR1", "cp420"); charsets.put("EBCDIC-CP-HE", "cp424"); charsets.put("EBCDIC-CP-BE", "cp500"); charsets.put("EBCDIC-CP-CH", "cp500"); charsets.put("EBCDIC-CP-ROECE", "cp870"); charsets.put("EBCDIC-CP-YU", "cp870"); charsets.put("EBCDIC-CP-IS", "cp871"); charsets.put("EBCDIC-CP-AR2", "cp918"); // IANA also defines two that JDK 1.2 doesn't handle: // EBCDIC-CP-GR --> CP423 // EBCDIC-CP-TR --> CP905 } // returns an encoding name supported by JDK >= 1.1.6 // for some cases required by the XML spec private static String std2java(String encoding) { String temp = encoding.toUpperCase(); temp = (String) charsets.get(temp); return (temp != null) ? temp : encoding; } /** Returns the standard name of the encoding in use */ public String getEncoding() { return assignedEncoding; } private XmlReader(InputStream stream) throws IOException { super(stream); PushbackInputStream pb; byte buf[]; int len; /*if (stream instanceof PushbackInputStream) pb = (PushbackInputStream) stream; else*/ /** * Commented out the above code to make sure it works when the * document is accessed using http. URL connection in the code uses * a PushbackInputStream with size 7 and when we try to push back * MAX which default value is set to 512 we get and exception. So * that's why we need to wrap the stream irrespective of what type * of stream we start off with. */ pb = new PushbackInputStream(stream, MAXPUSHBACK); // // See if we can figure out the character encoding used // in this file by peeking at the first few bytes. // buf = new byte[4]; len = pb.read(buf); if (len > 0) pb.unread(buf, 0, len); if (len == 4) switch (buf[0] & 0x0ff) { case 0: // 00 3c 00 3f == illegal UTF-16 big-endian if (buf[1] == 0x3c && buf[2] == 0x00 && buf[3] == 0x3f) { setEncoding(pb, "UnicodeBig"); return; } // else it's probably UCS-4 break; case '<': // 0x3c: the most common cases! switch (buf[1] & 0x0ff) { // First character is '<'; could be XML without // an XML directive such as "<hello>", "<!-- ...", // and so on. default: break; // 3c 00 3f 00 == illegal UTF-16 little endian case 0x00: if (buf[2] == 0x3f && buf[3] == 0x00) { setEncoding(pb, "UnicodeLittle"); return; } // else probably UCS-4 break; // 3c 3f 78 6d == ASCII and supersets '<?xm' case '?': if (buf[2] != 'x' || buf[3] != 'm') break; // // One of several encodings could be used: // Shift-JIS, ASCII, UTF-8, ISO-8859-*, etc // useEncodingDecl(pb, "UTF8"); return; } break; // 4c 6f a7 94 ... some EBCDIC code page case 0x4c: if (buf[1] == 0x6f && (0x0ff & buf[2]) == 0x0a7 && (0x0ff & buf[3]) == 0x094) { useEncodingDecl(pb, "CP037"); return; } // whoops, treat as UTF-8 break; // UTF-16 big-endian case 0xfe: if ((buf[1] & 0x0ff) != 0xff) break; setEncoding(pb, "UTF-16"); return; // UTF-16 little-endian case 0xff: if ((buf[1] & 0x0ff) != 0xfe) break; setEncoding(pb, "UTF-16"); return; // default ... no XML declaration default: break; } // // If all else fails, assume XML without a declaration, and // using UTF-8 encoding. // setEncoding(pb, "UTF-8"); } /* * Read the encoding decl on the stream, knowing that it should * be readable using the specified encoding (basically, ASCII or * EBCDIC). The body of the document may use a wider range of * characters than the XML/Text decl itself, so we switch to use * the specified encoding as soon as we can. (ASCII is a subset * of UTF-8, ISO-8859-*, ISO-2022-JP, EUC-JP, and more; EBCDIC * has a variety of "code pages" that have these characters as * a common subset.) */ private void useEncodingDecl(PushbackInputStream pb, String encoding) throws IOException { byte buffer[] = new byte[MAXPUSHBACK]; int len; Reader r; int c; // // Buffer up a bunch of input, and set up to read it in // the specified encoding ... we can skip the first four // bytes since we know that "<?xm" was read to determine // what encoding to use! // len = pb.read(buffer, 0, buffer.length); pb.unread(buffer, 0, len); r = new InputStreamReader(new ByteArrayInputStream(buffer, 4, len), encoding); // // Next must be "l" (and whitespace) else we conclude // error and choose UTF-8. // if ((c = r.read()) != 'l') { setEncoding(pb, "UTF-8"); return; } // // Then, we'll skip any // S version="..." [or single quotes] // bit and get any subsequent // S encoding="..." [or single quotes] // // We put an arbitrary size limit on how far we read; lots // of space will break this algorithm. // StringBuffer buf = new StringBuffer(); StringBuffer keyBuf = null; String key = null; boolean sawEq = false; char quoteChar = 0; boolean sawQuestion = false; XmlDecl: for (int i = 0; i < MAXPUSHBACK - 5; ++i) { if ((c = r.read()) == -1) break; // ignore whitespace before/between "key = 'value'" if (c == ' ' || c == '\t' || c == '\n' || c == '\r') continue; // ... but require at least a little! if (i == 0) break; // terminate the loop ASAP if (c == '?') sawQuestion = true; else if (sawQuestion) { if (c == '>') break; sawQuestion = false; } // did we get the "key =" bit yet? if (key == null || !sawEq) { if (keyBuf == null) { if (Character.isWhitespace((char) c)) continue; keyBuf = buf; buf.setLength(0); buf.append((char) c); sawEq = false; } else if (Character.isWhitespace((char) c)) { key = keyBuf.toString(); } else if (c == '=') { if (key == null) key = keyBuf.toString(); sawEq = true; keyBuf = null; quoteChar = 0; } else keyBuf.append((char) c); continue; } // space before quoted value if (Character.isWhitespace((char) c)) continue; if (c == '"' || c == '\'') { if (quoteChar == 0) { quoteChar = (char) c; buf.setLength(0); continue; } else if (c == quoteChar) { if ("encoding".equals(key)) { assignedEncoding = buf.toString(); // [81] Encname ::= [A-Za-z] ([A-Za-z0-9._]|'-')* for (i = 0; i < assignedEncoding.length(); i++) { c = assignedEncoding.charAt(i); if ((c >= 'A' && c <= 'Z') || (c >= 'a' && c <= 'z')) continue; if (i == 0) break XmlDecl; if (i > 0 && (c == '-' || (c >= '0' && c <= '9') || c == '.' || c == '_')) continue; // map illegal names to UTF-8 default break XmlDecl; } setEncoding(pb, assignedEncoding); return; } else { key = null; continue; } } } buf.append((char) c); } setEncoding(pb, "UTF-8"); } private void setEncoding(InputStream stream, String encoding) throws IOException { assignedEncoding = encoding; in = createReader(stream, encoding); } /** * Reads the number of characters read into the buffer, or -1 on EOF. */ public int read(char buf[], int off, int len) throws IOException { int val; if (closed) return -1; // throw new IOException ("closed"); val = in.read(buf, off, len); if (val == -1) close(); return val; } /** * Reads a single character. */ public int read() throws IOException { int val; if (closed) { throw new IOException("Stream closed"); } val = in.read(); if (val == -1) { close(); } return val; } /** * Returns true iff the reader supports mark/reset. */ public boolean markSupported() { return in == null ? false : in.markSupported(); } /** * Sets a mark allowing a limited number of characters to * be "peeked", by reading and then resetting. * @param value how many characters may be "peeked". */ public void mark(int value) throws IOException { if (in != null) in.mark(value); } /** * Resets the current position to the last marked position. */ public void reset() throws IOException { if (in != null) in.reset(); } /** * Skips a specified number of characters. */ public long skip(long value) throws IOException { return in == null ? 0 : in.skip(value); } /** * Returns true iff input characters are known to be ready. */ public boolean ready() throws IOException { return in == null ? false : in.ready(); } /** * Closes the reader. */ public void close() throws IOException { if (closed) return; in.close(); in = null; closed = true; } // // Delegating to a converter module will always be slower than // direct conversion. Use a similar approach for any other // readers that need to be particularly fast; only block I/O // speed matters to this package. For UTF-16, separate readers // for big and little endian streams make a difference, too; // fewer conditionals in the critical path! // public static abstract class BaseReader extends Reader { protected InputStream instream; protected byte buffer[]; protected int start, finish; BaseReader(InputStream stream) { super(stream); instream = stream; buffer = new byte[8192]; } public abstract String getEncoding(); public boolean ready() throws IOException { return instream == null || (finish - start) > 0 || instream.available() != 0; } // caller shouldn't read again public void close() throws IOException { if (instream != null) { instream.close(); start = finish = 0; buffer = null; instream = null; } } } // // We want this reader, to make the default encoding be as fast // as we can make it. JDK's "UTF8" (not "UTF-8" till JDK 1.2) // InputStreamReader works, but 20+% slower speed isn't OK for // the default/primary encoding. // static final class Utf8Reader extends BaseReader { // 2nd half of UTF-8 surrogate pair private char nextChar; Utf8Reader(InputStream stream) { super(stream); } public String getEncoding() { return "UTF-8"; } public int read(char buf[], int offset, int len) throws IOException { int i = 0, c = 0; if (len <= 0) return 0; // avoid many runtime bounds checks ... a good optimizer // (static or JIT) will now remove checks from the loop. if ((offset + len) > buf.length || offset < 0) throw new ArrayIndexOutOfBoundsException(); // Consume remaining half of any surrogate pair immediately if (nextChar != 0) { buf[offset + i++] = nextChar; nextChar = 0; } while (i < len) { // stop or read data if needed if (finish <= start) { if (instream == null) { c = -1; break; } start = 0; finish = instream.read(buffer, 0, buffer.length); if (finish <= 0) { this.close(); c = -1; break; } } // RFC 2279 describes UTF-8; there are six encodings. // Each encoding takes a fixed number of characters // (1-6 bytes) and is flagged by a bit pattern in the // first byte. The five and six byte-per-character // encodings address characters which are disallowed // in XML documents, as do some four byte ones. // Single byte == ASCII. Common; optimize. // c = buffer[start] & 0x0ff; if ((c & 0x80) == 0x00) { // 0x0000 <= c <= 0x007f start++; buf[offset + i++] = (char) c; continue; } // // Multibyte chars -- check offsets optimistically, // ditto the "10xx xxxx" format for subsequent bytes // int off = start; try { // 2 bytes if ((buffer[off] & 0x0E0) == 0x0C0) { c = (buffer[off++] & 0x1f) << 6; c += buffer[off++] & 0x3f; // 0x0080 <= c <= 0x07ff // 3 bytes } else if ((buffer[off] & 0x0F0) == 0x0E0) { c = (buffer[off++] & 0x0f) << 12; c += (buffer[off++] & 0x3f) << 6; c += buffer[off++] & 0x3f; // 0x0800 <= c <= 0xffff // 4 bytes } else if ((buffer[off] & 0x0f8) == 0x0F0) { c = (buffer[off++] & 0x07) << 18; c += (buffer[off++] & 0x3f) << 12; c += (buffer[off++] & 0x3f) << 6; c += buffer[off++] & 0x3f; // 0x0001 0000 <= c <= 0x001f ffff // Unicode supports c <= 0x0010 ffff ... if (c > 0x0010ffff) throw new CharConversionException("UTF-8 encoding of character 0x00" + Integer.toHexString(c) + " can't be converted to Unicode."); else if (c > 0xffff) { // Convert UCS-4 char to surrogate pair (UTF-16) c -= 0x10000; nextChar = (char) (0xDC00 + (c & 0x03ff)); c = 0xD800 + (c >> 10); } // 5 and 6 byte versions are XML WF errors, but // typically come from mislabeled encodings } else throw new CharConversionException("Unconvertible UTF-8 character" + " beginning with 0x" + Integer.toHexString(buffer[start] & 0xff)); } catch (ArrayIndexOutOfBoundsException e) { // off > length && length >= buffer.length c = 0; } // // if the buffer held only a partial character, // compact it and try to read the rest of the // character. worst case involves three // single-byte reads -- quite rare. // if (off > finish) { System.arraycopy(buffer, start, buffer, 0, finish - start); finish -= start; start = 0; off = instream.read(buffer, finish, buffer.length - finish); if (off < 0) { this.close(); throw new CharConversionException("Partial UTF-8 char"); } finish += off; continue; } // // check the format of the non-initial bytes // for (start++; start < off; start++) { if ((buffer[start] & 0xC0) != 0x80) { this.close(); throw new CharConversionException( "Malformed UTF-8 char -- " + "is an XML encoding declaration missing?"); } } // // If this needed a surrogate pair, consume ASAP // buf[offset + i++] = (char) c; if (nextChar != 0 && i < len) { buf[offset + i++] = nextChar; nextChar = 0; } } if (i > 0) return i; return (c == -1) ? -1 : 0; } } // // We want ASCII and ISO-8859 Readers since they're the most common // encodings in the US and Europe, and we don't want performance // regressions for them. They're also easy to implement efficiently, // since they're bitmask subsets of UNICODE. // // XXX haven't benchmarked these readers vs what we get out of JDK. // static final class AsciiReader extends BaseReader { AsciiReader(InputStream in) { super(in); } public String getEncoding() { return "US-ASCII"; } public int read(char buf[], int offset, int len) throws IOException { if (instream == null) { return -1; } // avoid many runtime bounds checks ... a good optimizer // (static or JIT) will now remove checks from the loop. if ((offset + len) > buf.length || offset < 0) throw new ArrayIndexOutOfBoundsException(); /* 07-Mar-2006, TSa: Actually, it's bad idea to try to fill the * whole buffer -- if this is a blocking source (network socket * for example), we may be blocking too early. */ // So, do we need to try to read more? int avail = (finish - start); if (avail < 1) { start = 0; finish = instream.read(buffer, 0, buffer.length); if (finish <= 0) { this.close(); return -1; } if (len > finish) { len = finish; } } else { if (len > avail) { len = avail; } } for (int i = 0; i < len; i++) { int c = buffer[start++]; if (c < 0) { throw new CharConversionException( "Illegal ASCII character, 0x" + Integer.toHexString(c & 0xff)); } buf[offset + i] = (char) c; } return len; } } static final class Iso8859_1Reader extends BaseReader { Iso8859_1Reader(InputStream in) { super(in); } public String getEncoding() { return "ISO-8859-1"; } public int read(char buf[], int offset, int len) throws IOException { if (instream == null) return -1; // avoid many runtime bounds checks ... a good optimizer // (static or JIT) will now remove checks from the loop. if ((offset + len) > buf.length || offset < 0) throw new ArrayIndexOutOfBoundsException(); /* 07-Mar-2006, TSa: Actually, it's bad idea to try to fill the * whole buffer -- if this is a blocking source (network socket * for example), we may be blocking too early. */ // So, do we need to try to read more? int avail = (finish - start); if (avail < 1) { start = 0; finish = instream.read(buffer, 0, buffer.length); if (finish <= 0) { this.close(); return -1; } if (len > finish) { len = finish; } } else { if (len > avail) { len = avail; } } for (int i = 0; i < len; i++) { buf[offset + i] = (char) (buffer[start++] & 0xFF); } return len; } } }