Java tutorial
package com.fasterxml.jackson.core.json; import java.io.*; import com.fasterxml.jackson.core.*; import com.fasterxml.jackson.core.format.InputAccessor; import com.fasterxml.jackson.core.format.MatchStrength; import com.fasterxml.jackson.core.io.*; import com.fasterxml.jackson.core.sym.BytesToNameCanonicalizer; import com.fasterxml.jackson.core.sym.CharsToNameCanonicalizer; /** * This class is used to determine the encoding of byte stream * that is to contain JSON content. Rules are fairly simple, and * defined in JSON specification (RFC-4627 or newer), except * for BOM handling, which is a property of underlying * streams. */ public final class ByteSourceJsonBootstrapper { final static byte UTF8_BOM_1 = (byte) 0xEF; final static byte UTF8_BOM_2 = (byte) 0xBB; final static byte UTF8_BOM_3 = (byte) 0xBF; /* /********************************************************** /* Configuration /********************************************************** */ protected final IOContext _context; protected final InputStream _in; /* /********************************************************** /* Input buffering /********************************************************** */ protected final byte[] _inputBuffer; private int _inputPtr; private int _inputEnd; /** * Flag that indicates whether buffer above is to be recycled * after being used or not. */ private final boolean _bufferRecyclable; /* /********************************************************** /* Input location /********************************************************** */ /** * Current number of input units (bytes or chars) that were processed in * previous blocks, * before contents of current input buffer. *<p> * Note: includes possible BOMs, if those were part of the input. */ protected int _inputProcessed; /* /********************************************************** /* Data gathered /********************************************************** */ protected boolean _bigEndian = true; protected int _bytesPerChar = 0; // 0 means "dunno yet" /* /********************************************************** /* Life-cycle /********************************************************** */ public ByteSourceJsonBootstrapper(IOContext ctxt, InputStream in) { _context = ctxt; _in = in; _inputBuffer = ctxt.allocReadIOBuffer(); _inputEnd = _inputPtr = 0; _inputProcessed = 0; _bufferRecyclable = true; } public ByteSourceJsonBootstrapper(IOContext ctxt, byte[] inputBuffer, int inputStart, int inputLen) { _context = ctxt; _in = null; _inputBuffer = inputBuffer; _inputPtr = inputStart; _inputEnd = (inputStart + inputLen); // Need to offset this for correct location info _inputProcessed = -inputStart; _bufferRecyclable = false; } /* /********************************************************** /* Encoding detection during bootstrapping /********************************************************** */ /** * Method that should be called after constructing an instace. * It will figure out encoding that content uses, to allow * for instantiating a proper scanner object. */ public JsonEncoding detectEncoding() throws IOException, JsonParseException { boolean foundEncoding = false; // First things first: BOM handling /* Note: we can require 4 bytes to be read, since no * combination of BOM + valid JSON content can have * shorter length (shortest valid JSON content is single * digit char, but BOMs are chosen such that combination * is always at least 4 chars long) */ if (ensureLoaded(4)) { int quad = (_inputBuffer[_inputPtr] << 24) | ((_inputBuffer[_inputPtr + 1] & 0xFF) << 16) | ((_inputBuffer[_inputPtr + 2] & 0xFF) << 8) | (_inputBuffer[_inputPtr + 3] & 0xFF); if (handleBOM(quad)) { foundEncoding = true; } else { /* If no BOM, need to auto-detect based on first char; * this works since it must be 7-bit ascii (wrt. unicode * compatible encodings, only ones JSON can be transferred * over) */ // UTF-32? if (checkUTF32(quad)) { foundEncoding = true; } else if (checkUTF16(quad >>> 16)) { foundEncoding = true; } } } else if (ensureLoaded(2)) { int i16 = ((_inputBuffer[_inputPtr] & 0xFF) << 8) | (_inputBuffer[_inputPtr + 1] & 0xFF); if (checkUTF16(i16)) { foundEncoding = true; } } JsonEncoding enc; /* Not found yet? As per specs, this means it must be UTF-8. */ if (!foundEncoding) { enc = JsonEncoding.UTF8; } else { switch (_bytesPerChar) { case 1: enc = JsonEncoding.UTF8; break; case 2: enc = _bigEndian ? JsonEncoding.UTF16_BE : JsonEncoding.UTF16_LE; break; case 4: enc = _bigEndian ? JsonEncoding.UTF32_BE : JsonEncoding.UTF32_LE; break; default: throw new RuntimeException("Internal error"); // should never get here } } _context.setEncoding(enc); return enc; } /* /********************************************************** /* Constructing a Reader /********************************************************** */ @SuppressWarnings("resource") public Reader constructReader() throws IOException { JsonEncoding enc = _context.getEncoding(); switch (enc) { case UTF32_BE: case UTF32_LE: return new UTF32Reader(_context, _in, _inputBuffer, _inputPtr, _inputEnd, _context.getEncoding().isBigEndian()); case UTF16_BE: case UTF16_LE: case UTF8: // only in non-common case where we don't want to do direct mapping { // First: do we have a Stream? If not, need to create one: InputStream in = _in; if (in == null) { in = new ByteArrayInputStream(_inputBuffer, _inputPtr, _inputEnd); } else { /* Also, if we have any read but unused input (usually true), * need to merge that input in: */ if (_inputPtr < _inputEnd) { in = new MergedStream(_context, in, _inputBuffer, _inputPtr, _inputEnd); } } return new InputStreamReader(in, enc.getJavaName()); } } throw new RuntimeException("Internal error"); // should never get here } public JsonParser constructParser(int parserFeatures, ObjectCodec codec, BytesToNameCanonicalizer rootByteSymbols, CharsToNameCanonicalizer rootCharSymbols, boolean canonicalize, boolean intern) throws IOException, JsonParseException { JsonEncoding enc = detectEncoding(); if (enc == JsonEncoding.UTF8) { /* and without canonicalization, byte-based approach is not performance; just use std UTF-8 reader * (which is ok for larger input; not so hot for smaller; but this is not a common case) */ if (canonicalize) { BytesToNameCanonicalizer can = rootByteSymbols.makeChild(canonicalize, intern); return new UTF8StreamJsonParser(_context, parserFeatures, _in, codec, can, _inputBuffer, _inputPtr, _inputEnd, _bufferRecyclable); } } return new ReaderBasedJsonParser(_context, parserFeatures, constructReader(), codec, rootCharSymbols.makeChild(canonicalize, intern)); } /* /********************************************************** /* Encoding detection for data format auto-detection /********************************************************** */ /** * Current implementation is not as thorough as other functionality * ({@link com.fasterxml.jackson.core.json.ByteSourceJsonBootstrapper}); * supports UTF-8, for example. But it should work, for now, and can * be improved as necessary. */ public static MatchStrength hasJSONFormat(InputAccessor acc) throws IOException { // Ideally we should see "[" or "{"; but if not, we'll accept double-quote (String) // in future could also consider accepting non-standard matches? if (!acc.hasMoreBytes()) { return MatchStrength.INCONCLUSIVE; } byte b = acc.nextByte(); // Very first thing, a UTF-8 BOM? if (b == UTF8_BOM_1) { // yes, looks like UTF-8 BOM if (!acc.hasMoreBytes()) { return MatchStrength.INCONCLUSIVE; } if (acc.nextByte() != UTF8_BOM_2) { return MatchStrength.NO_MATCH; } if (!acc.hasMoreBytes()) { return MatchStrength.INCONCLUSIVE; } if (acc.nextByte() != UTF8_BOM_3) { return MatchStrength.NO_MATCH; } if (!acc.hasMoreBytes()) { return MatchStrength.INCONCLUSIVE; } b = acc.nextByte(); } // Then possible leading space int ch = skipSpace(acc, b); if (ch < 0) { return MatchStrength.INCONCLUSIVE; } // First, let's see if it looks like a structured type: if (ch == '{') { // JSON object? // Ideally we need to find either double-quote or closing bracket ch = skipSpace(acc); if (ch < 0) { return MatchStrength.INCONCLUSIVE; } if (ch == '"' || ch == '}') { return MatchStrength.SOLID_MATCH; } // ... should we allow non-standard? Let's not yet... can add if need be return MatchStrength.NO_MATCH; } MatchStrength strength; if (ch == '[') { ch = skipSpace(acc); if (ch < 0) { return MatchStrength.INCONCLUSIVE; } // closing brackets is easy; but for now, let's also accept opening... if (ch == ']' || ch == '[') { return MatchStrength.SOLID_MATCH; } return MatchStrength.SOLID_MATCH; } else { // plain old value is not very convincing... strength = MatchStrength.WEAK_MATCH; } if (ch == '"') { // string value return strength; } if (ch <= '9' && ch >= '0') { // number return strength; } if (ch == '-') { // negative number ch = skipSpace(acc); if (ch < 0) { return MatchStrength.INCONCLUSIVE; } return (ch <= '9' && ch >= '0') ? strength : MatchStrength.NO_MATCH; } // or one of literals if (ch == 'n') { // null return tryMatch(acc, "ull", strength); } if (ch == 't') { // true return tryMatch(acc, "rue", strength); } if (ch == 'f') { // false return tryMatch(acc, "alse", strength); } return MatchStrength.NO_MATCH; } private static MatchStrength tryMatch(InputAccessor acc, String matchStr, MatchStrength fullMatchStrength) throws IOException { for (int i = 0, len = matchStr.length(); i < len; ++i) { if (!acc.hasMoreBytes()) { return MatchStrength.INCONCLUSIVE; } if (acc.nextByte() != matchStr.charAt(i)) { return MatchStrength.NO_MATCH; } } return fullMatchStrength; } private static int skipSpace(InputAccessor acc) throws IOException { if (!acc.hasMoreBytes()) { return -1; } return skipSpace(acc, acc.nextByte()); } private static int skipSpace(InputAccessor acc, byte b) throws IOException { while (true) { int ch = (int) b & 0xFF; if (!(ch == ' ' || ch == '\r' || ch == '\n' || ch == '\t')) { return ch; } if (!acc.hasMoreBytes()) { return -1; } b = acc.nextByte(); ch = (int) b & 0xFF; } } /* /********************************************************** /* Internal methods, parsing /********************************************************** */ /** * @return True if a BOM was succesfully found, and encoding * thereby recognized. */ private boolean handleBOM(int quad) throws IOException { /* Handling of (usually) optional BOM (required for * multi-byte formats); first 32-bit charsets: */ switch (quad) { case 0x0000FEFF: _bigEndian = true; _inputPtr += 4; _bytesPerChar = 4; return true; case 0xFFFE0000: // UCS-4, LE? _inputPtr += 4; _bytesPerChar = 4; _bigEndian = false; return true; case 0x0000FFFE: // UCS-4, in-order... reportWeirdUCS4("2143"); // throws exception case 0xFEFF0000: // UCS-4, in-order... reportWeirdUCS4("3412"); // throws exception } // Ok, if not, how about 16-bit encoding BOMs? int msw = quad >>> 16; if (msw == 0xFEFF) { // UTF-16, BE _inputPtr += 2; _bytesPerChar = 2; _bigEndian = true; return true; } if (msw == 0xFFFE) { // UTF-16, LE _inputPtr += 2; _bytesPerChar = 2; _bigEndian = false; return true; } // And if not, then UTF-8 BOM? if ((quad >>> 8) == 0xEFBBBF) { // UTF-8 _inputPtr += 3; _bytesPerChar = 1; _bigEndian = true; // doesn't really matter return true; } return false; } private boolean checkUTF32(int quad) throws IOException { /* Handling of (usually) optional BOM (required for * multi-byte formats); first 32-bit charsets: */ if ((quad >> 8) == 0) { // 0x000000?? -> UTF32-BE _bigEndian = true; } else if ((quad & 0x00FFFFFF) == 0) { // 0x??000000 -> UTF32-LE _bigEndian = false; } else if ((quad & ~0x00FF0000) == 0) { // 0x00??0000 -> UTF32-in-order reportWeirdUCS4("3412"); } else if ((quad & ~0x0000FF00) == 0) { // 0x0000??00 -> UTF32-in-order reportWeirdUCS4("2143"); } else { // Can not be valid UTF-32 encoded JSON... return false; } // Not BOM (just regular content), nothing to skip past: //_inputPtr += 4; _bytesPerChar = 4; return true; } private boolean checkUTF16(int i16) { if ((i16 & 0xFF00) == 0) { // UTF-16BE _bigEndian = true; } else if ((i16 & 0x00FF) == 0) { // UTF-16LE _bigEndian = false; } else { // nope, not UTF-16 return false; } // Not BOM (just regular content), nothing to skip past: //_inputPtr += 2; _bytesPerChar = 2; return true; } /* /********************************************************** /* Internal methods, problem reporting /********************************************************** */ private void reportWeirdUCS4(String type) throws IOException { throw new CharConversionException("Unsupported UCS-4 endianness (" + type + ") detected"); } /* /********************************************************** /* Internal methods, raw input access /********************************************************** */ protected boolean ensureLoaded(int minimum) throws IOException { /* Let's assume here buffer has enough room -- this will always * be true for the limited used this method gets */ int gotten = (_inputEnd - _inputPtr); while (gotten < minimum) { int count; if (_in == null) { // block source count = -1; } else { count = _in.read(_inputBuffer, _inputEnd, _inputBuffer.length - _inputEnd); } if (count < 1) { return false; } _inputEnd += count; gotten += count; } return true; } }