StringDecode 类源码分析
package java.lang;
class StringCoding {
private StringCoding() { }
// 缓存在ThreadLocal中，软引用包装，解码
private final static ThreadLocal<SoftReference<StringDecoder>> decoder =
new ThreadLocal<>();
private final static ThreadLocal<SoftReference<StringEncoder>> encoder =
new ThreadLocal<>();
// 警告不支持的字符集开关，默认打开true
private static boolean warnUnsupportedCharset = true;
// 解码软引用获取对象
private static <T> T deref(ThreadLocal<SoftReference<T>> tl) {
SoftReference<T> sr = tl.get();
if (sr == null)
return null;
return sr.get();
}
private static <T> void set(ThreadLocal<SoftReference<T>> tl, T ob) {
tl.set(new SoftReference<T>(ob));
}
// 截取byte数组，从0到len
private static byte[] safeTrim(byte[] ba, int len, Charset cs, boolean isTrusted) {
if (len == ba.length && (isTrusted || System.getSecurityManager() == null))
return ba;
else
return Arrays.copyOf(ba, len);
}
// 截取char数组，从0到len
private static char[] safeTrim(char[] ca, int len,
Charset cs, boolean isTrusted) {
if (len == ca.length && (isTrusted || System.getSecurityManager() == null))
return ca;
else
return Arrays.copyOf(ca, len);
}
private static int scale(int len, float expansionFactor) {
// We need to perform double, not float, arithmetic; otherwise
// we lose low order bits when len is larger than 2**24.
return (int)(len * (double)expansionFactor);
}
// 查找编码字符集
private static Charset lookupCharset(String csn) {
if (Charset.isSupported(csn)) {
try {
return Charset.forName(csn);
} catch (UnsupportedCharsetException x) {
throw new Error(x);
}
}
return null;
}
// 警告不支持当前的字符集并关闭开关
private static void warnUnsupportedCharset(String csn) {
if (warnUnsupportedCharset) {
// 因为在vm初始化就有可能调用此方法，所以不用log api，用messageUtils类
MessageUtils.err("WARNING: Default charset " + csn +
" not supported, using ISO-8859-1 instead");
warnUnsupportedCharset = false;
}
}
// decoding内部静态类
private static class StringDecoder {
private final String requestedCharsetName;
private final Charset cs;
private final CharsetDecoder cd;
private final boolean isTrusted;
private StringDecoder(Charset cs, String rcn) {
this.requestedCharsetName = rcn;
this.cs = cs;
this.cd = cs.newDecoder()
.onMalformedInput(CodingErrorAction.REPLACE)
.onUnmappableCharacter(CodingErrorAction.REPLACE);
this.isTrusted = (cs.getClass().getClassLoader0() == null);
}
String charsetName() {
if (cs instanceof HistoricallyNamedCharset)
return ((HistoricallyNamedCharset)cs).historicalName();
return cs.name();
}
final String requestedCharsetName() {
return requestedCharsetName;
}
// 通过charsetDecoder来decode输入bb得到输出cb
char[] decode(byte[] ba, int off, int len) {
int en = scale(len, cd.maxCharsPerByte());
char[] ca = new char[en];
if (len == 0)
return ca;
if (cd instanceof ArrayDecoder) {
int clen = ((ArrayDecoder)cd).decode(ba, off, len, ca);
return safeTrim(ca, clen, cs, isTrusted);
} else {
cd.reset();
ByteBuffer bb = ByteBuffer.wrap(ba, off, len);
CharBuffer cb = CharBuffer.wrap(ca);
try {
CoderResult cr = cd.decode(bb, cb, true);
if (!cr.isUnderflow())
cr.throwException();
cr = cd.flush(cb);
if (!cr.isUnderflow())
cr.throwException();
} catch (CharacterCodingException x) {
// Substitution is always enabled,
// so this shouldn't happen
throw new Error(x);
}
return safeTrim(ca, cb.position(), cs, isTrusted);
}
}
}
// 搞了个静态方法，默认StringDecoder
static char[] decode(String charsetName, byte[] ba, int off, int len)
throws UnsupportedEncodingException
{
StringDecoder sd = deref(decoder);
String csn = (charsetName == null) ? "ISO-8859-1" : charsetName;
if ((sd == null) || !(csn.equals(sd.requestedCharsetName())
|| csn.equals(sd.charsetName()))) {
sd = null;
try {
Charset cs = lookupCharset(csn);
if (cs != null)
sd = new StringDecoder(cs, csn);
} catch (IllegalCharsetNameException x) {}
if (sd == null)
throw new UnsupportedEncodingException(csn);
set(decoder, sd);
}
return sd.decode(ba, off, len);
}
static char[] decode(Charset cs, byte[] ba, int off, int len) {
CharsetDecoder cd = cs.newDecoder();
int en = scale(len, cd.maxCharsPerByte());
char[] ca = new char[en];
if (len == 0)
return ca;
boolean isTrusted = false;
if (System.getSecurityManager() != null) {
if (!(isTrusted = (cs.getClass().getClassLoader0() == null))) {
ba = Arrays.copyOfRange(ba, off, off + len);
off = 0;
}
}
cd.onMalformedInput(CodingErrorAction.REPLACE)
.onUnmappableCharacter(CodingErrorAction.REPLACE)
.reset();
if (cd instanceof ArrayDecoder) {
int clen = ((ArrayDecoder)cd).decode(ba, off, len, ca);
return safeTrim(ca, clen, cs, isTrusted);
} else {
// 内部默认是new了一个HeapByteBuffer，分配内存为len，分配在jvm的堆上
ByteBuffer bb = ByteBuffer.wrap(ba, off, len);
// 内部默认是new了一个HeapCharBuffer，分配内存为len，分配在jvm的堆上
CharBuffer cb = CharBuffer.wrap(ca);
try {
CoderResult cr = cd.decode(bb, cb, true);
if (!cr.isUnderflow())
cr.throwException();
cr = cd.flush(cb);
if (!cr.isUnderflow())
cr.throwException();
} catch (CharacterCodingException x) {
// Substitution is always enabled,
// so this shouldn't happen
throw new Error(x);
}
return safeTrim(ca, cb.position(), cs, isTrusted);
}
}
// 报错用ISO编码集在世一遍
static char[] decode(byte[] ba, int off, int len) {
String csn = Charset.defaultCharset().name();
try {
// use charset name decode() variant which provides caching.
return decode(csn, ba, off, len);
} catch (UnsupportedEncodingException x) {
warnUnsupportedCharset(csn);
}
try {
return decode("ISO-8859-1", ba, off, len);
} catch (UnsupportedEncodingException x) {
// If this code is hit during VM initialization, MessageUtils is
// the only way we will be able to get any kind of error message.
MessageUtils.err("ISO-8859-1 charset not available: "
+ x.toString());
// If we can not find ISO-8859-1 (a required encoding) then things
// are seriously wrong with the installation.
System.exit(1);
return null;
}
}
// -- Encoding --
private static class StringEncoder {
private Charset cs;
private CharsetEncoder ce;
private final String requestedCharsetName;
private final boolean isTrusted;
private StringEncoder(Charset cs, String rcn) {
this.requestedCharsetName = rcn;
this.cs = cs;
this.ce = cs.newEncoder()
.onMalformedInput(CodingErrorAction.REPLACE)
.onUnmappableCharacter(CodingErrorAction.REPLACE);
this.isTrusted = (cs.getClass().getClassLoader0() == null);
}
String charsetName() {
if (cs instanceof HistoricallyNamedCharset)
return ((HistoricallyNamedCharset)cs).historicalName();
return cs.name();
}
final String requestedCharsetName() {
return requestedCharsetName;
}
byte[] encode(char[] ca, int off, int len) {
int en = scale(len, ce.maxBytesPerChar());
byte[] ba = new byte[en];
if (len == 0)
return ba;
if (ce instanceof ArrayEncoder) {
int blen = ((ArrayEncoder)ce).encode(ca, off, len, ba);
return safeTrim(ba, blen, cs, isTrusted);
} else {
ce.reset();
ByteBuffer bb = ByteBuffer.wrap(ba);
CharBuffer cb = CharBuffer.wrap(ca, off, len);
try {
CoderResult cr = ce.encode(cb, bb, true);
if (!cr.isUnderflow())
cr.throwException();
cr = ce.flush(bb);
if (!cr.isUnderflow())
cr.throwException();
} catch (CharacterCodingException x) {
// Substitution is always enabled,
// so this shouldn't happen
throw new Error(x);
}
return safeTrim(ba, bb.position(), cs, isTrusted);
}
}
}
static byte[] encode(String charsetName, char[] ca, int off, int len)
throws UnsupportedEncodingException
{
StringEncoder se = deref(encoder);
String csn = (charsetName == null) ? "ISO-8859-1" : charsetName;
if ((se == null) || !(csn.equals(se.requestedCharsetName())
|| csn.equals(se.charsetName()))) {
se = null;
try {
Charset cs = lookupCharset(csn);
if (cs != null)
se = new StringEncoder(cs, csn);
} catch (IllegalCharsetNameException x) {}
if (se == null)
throw new UnsupportedEncodingException (csn);
set(encoder, se);
}
return se.encode(ca, off, len);
}
static byte[] encode(Charset cs, char[] ca, int off, int len) {
CharsetEncoder ce = cs.newEncoder();
int en = scale(len, ce.maxBytesPerChar());
byte[] ba = new byte[en];
if (len == 0)
return ba;
boolean isTrusted = false;
if (System.getSecurityManager() != null) {
if (!(isTrusted = (cs.getClass().getClassLoader0() == null))) {
ca = Arrays.copyOfRange(ca, off, off + len);
off = 0;
}
}
ce.onMalformedInput(CodingErrorAction.REPLACE)
.onUnmappableCharacter(CodingErrorAction.REPLACE)
.reset();
if (ce instanceof ArrayEncoder) {
int blen = ((ArrayEncoder)ce).encode(ca, off, len, ba);
return safeTrim(ba, blen, cs, isTrusted);
} else {
ByteBuffer bb = ByteBuffer.wrap(ba);
CharBuffer cb = CharBuffer.wrap(ca, off, len);
try {
CoderResult cr = ce.encode(cb, bb, true);
if (!cr.isUnderflow())
cr.throwException();
cr = ce.flush(bb);
if (!cr.isUnderflow())
cr.throwException();
} catch (CharacterCodingException x) {
throw new Error(x);
}
return safeTrim(ba, bb.position(), cs, isTrusted);
}
}
static byte[] encode(char[] ca, int off, int len) {
String csn = Charset.defaultCharset().name();
try {
// use charset name encode() variant which provides caching.
return encode(csn, ca, off, len);
} catch (UnsupportedEncodingException x) {
warnUnsupportedCharset(csn);
}
try {
return encode("ISO-8859-1", ca, off, len);
} catch (UnsupportedEncodingException x) {
// If this code is hit during VM initialization, MessageUtils is
// the only way we will be able to get any kind of error message.
MessageUtils.err("ISO-8859-1 charset not available: "
+ x.toString());
// If we can not find ISO-8859-1 (a required encoding) then things
// are seriously wrong with the installation.
System.exit(1);
return null;
}
}
}
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