Properties 源码分析

package java.util;

import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.io.PrintStream;
import java.io.PrintWriter;
import java.io.Reader;
import java.io.StreamCorruptedException;
import java.io.UnsupportedEncodingException;
import java.io.Writer;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;
import java.util.concurrent.ConcurrentHashMap;
import java.util.function.BiConsumer;
import java.util.function.BiFunction;
import java.util.function.Function;

import jdk.internal.misc.SharedSecrets;
import jdk.internal.util.xml.PropertiesDefaultHandler;

/**
* 1）Properties 文件表示一个持久的属性集，Properties 实例可以被保存到流中或从流加载。
* 2）Properties 实例可以包含一个默认的 Properties 对象，当属性在当前 Properties 中不存在时，
* 会尝试从默认的 Properties 中读取。
* 3）put 和 putAll 允许插入 Object 对象，不建议使用，建议通过 setProperties 方法添加属性。
* 4）集合视图 entrySet、keySet、values 返回的迭代器都是快速失败的。
* 5）Properties 继承了 Hashtable，Hashtable 继承了 Dictionary，键和值都不能为 null
*/
public
class Properties extends Hashtable<Object,Object> {
 /**
 * use serialVersionUID from JDK 1.1.X for interoperability
 */
 private static final long serialVersionUID = 4112578634029874840L;

 /**
 * A property list that contains default values for any keys not
 * found in this property list.
 * 当键不存在时，默认查找的 Properties 对象
 */
 protected Properties defaults;

 /**
 * Properties does not store values in its inherited Hashtable, but instead
 * in an internal ConcurrentHashMap. Synchronization is omitted from
 * simple read operations. Writes and bulk operations remain synchronized,
 * as in Hashtable.
 * 存储键值对的 ConcurrentHashMap 实例
 */
 private transient ConcurrentHashMap<Object, Object> map;

 /**
 * Creates an empty property list with no default values.
 * 创建一个容量为 8 的空 Properties 对象，没有默认的 Properties
 */
 public Properties() {
 this(null, 8);
 }

 /**
 * Creates an empty property list with no default values, and with an
 * initial size accommodating the specified number of elements without the
 * need to dynamically resize.
 * 创建一个容量为 initialCapacity 的空 Properties 对象，没有默认的 Properties
 */
 public Properties(int initialCapacity) {
 this(null, initialCapacity);
 }

 /**
 * Creates an empty property list with the specified defaults.
 * 创建一个容量为 8 的空 Properties 对象，并有默认的 Properties
 */
 public Properties(Properties defaults) {
 this(defaults, 8);
 }

 private Properties(Properties defaults, int initialCapacity) {
 super((Void) null);
 map = new ConcurrentHashMap<>(initialCapacity);
 this.defaults = defaults;
 }

 /**
 * Calls the {@code Hashtable} method {@code put}. Provided for
 * parallelism with the {@code getProperty} method. Enforces use of
 * strings for property keys and values. The value returned is the
 * result of the {@code Hashtable} call to {@code put}.
 * 通过 setProperty 方法设置新的键值对
 */
 public synchronized Object setProperty(String key, String value) {
 return put(key, value);
 }

 /**
 * Reads a property list (key and element pairs) from the input
 * character stream in a simple line-oriented format.
 *
 * A natural line that contains only white space characters is
 * considered blank and is ignored. A comment line has an ASCII
 * {@code '#'} or {@code '!'} as its first non-white
 * space character; comment lines are also ignored and do not
 * encode key-element information. In addition to line
 * terminators, this format considers the characters space
 * ({@code ' '}, {@code '\u005Cu0020'}), tab
 * ({@code '\t'}, {@code '\u005Cu0009'}), and form feed
 * ({@code '\f'}, {@code '\u005Cu000C'}) to be white
 * space.
 * 只有空格的行和以 # 或 ! 作为第一个非空字符的行都被忽略。
 * 属性文件的格式可以是
 * name=kristy
 * name:kristy
 * name kristy
 * 从 Reader 中加载属性
 */
 public synchronized void load(Reader reader) throws IOException {
 Objects.requireNonNull(reader, "reader parameter is null");
 load0(new LineReader(reader));
 }

 /**
 * Reads a property list (key and element pairs) from the input
 * byte stream. The input stream is in a simple line-oriented
 * format as specified in
 * {@link #load(java.io.Reader) load(Reader)} and is assumed to use
 * the ISO 8859-1 character encoding.
 * 从 InputStream 中加载属性
 */
 public synchronized void load(InputStream inStream) throws IOException {
 Objects.requireNonNull(inStream, "inStream parameter is null");
 load0(new LineReader(inStream));
 }

 private void load0 (LineReader lr) throws IOException {
 char[] convtBuf = new char[1024];
 int limit;
 int keyLen;
 int valueStart;
 char c;
 boolean hasSep;
 boolean precedingBackslash;

 while ((limit = lr.readLine()) >= 0) {
 c = 0;
 keyLen = 0;
 valueStart = limit;
 hasSep = false;

 //System.out.println("line=<" + new String(lineBuf, 0, limit) + ">");
 precedingBackslash = false;
 while (keyLen < limit) {
 c = lr.lineBuf[keyLen];
 //need check if escaped.
 if ((c == '=' || c == ':') && !precedingBackslash) {
 valueStart = keyLen + 1;
 hasSep = true;
 break;
 } else if ((c == ' ' || c == '\t' || c == '\f') && !precedingBackslash) {
 valueStart = keyLen + 1;
 break;
 }
 if (c == '\\') {
 precedingBackslash = !precedingBackslash;
 } else {
 precedingBackslash = false;
 }
 keyLen++;
 }
 while (valueStart < limit) {
 c = lr.lineBuf[valueStart];
 if (c != ' ' && c != '\t' && c != '\f') {
 if (!hasSep && (c == '=' || c == ':')) {
 hasSep = true;
 } else {
 break;
 }
 }
 valueStart++;
 }
 String key = loadConvert(lr.lineBuf, 0, keyLen, convtBuf);
 String value = loadConvert(lr.lineBuf, valueStart, limit - valueStart, convtBuf);
 put(key, value);
 }
 }

 /* Read in a "logical line" from an InputStream/Reader, skip all comment
 * and blank lines and filter out those leading whitespace characters
 * (\u0020, \u0009 and \u000c) from the beginning of a "natural line".
 * Method returns the char length of the "logical line" and stores
 * the line in "lineBuf".
 */
 class LineReader {
 public LineReader(InputStream inStream) {
 this.inStream = inStream;
 inByteBuf = new byte[8192];
 }

 public LineReader(Reader reader) {
 this.reader = reader;
 inCharBuf = new char[8192];
 }

 byte[] inByteBuf;
 char[] inCharBuf;
 char[] lineBuf = new char[1024];
 int inLimit = 0;
 int inOff = 0;
 InputStream inStream;
 Reader reader;

 int readLine() throws IOException {
 int len = 0;
 char c = 0;

 boolean skipWhiteSpace = true;
 boolean isCommentLine = false;
 boolean isNewLine = true;
 boolean appendedLineBegin = false;
 boolean precedingBackslash = false;
 boolean skipLF = false;

 while (true) {
 if (inOff >= inLimit) {
 inLimit = (inStream==null)?reader.read(inCharBuf)
 :inStream.read(inByteBuf);
 inOff = 0;
 if (inLimit <= 0) {
 if (len == 0 || isCommentLine) {
 return -1;
 }
 if (precedingBackslash) {
 len--;
 }
 return len;
 }
 }
 if (inStream != null) {
 //The line below is equivalent to calling a
 //ISO8859-1 decoder.
 c = (char)(inByteBuf[inOff++] & 0xFF);
 } else {
 c = inCharBuf[inOff++];
 }
 if (skipLF) {
 skipLF = false;
 if (c == '\n') {
 continue;
 }
 }
 if (skipWhiteSpace) {
 if (c == ' ' || c == '\t' || c == '\f') {
 continue;
 }
 if (!appendedLineBegin && (c == '\r' || c == '\n')) {
 continue;
 }
 skipWhiteSpace = false;
 appendedLineBegin = false;
 }
 if (isNewLine) {
 isNewLine = false;
 if (c == '#' || c == '!') {
 // Comment, quickly consume the rest of the line,
 // resume on line-break and backslash.
 if (inStream != null) {
 while (inOff < inLimit) {
 byte b = inByteBuf[inOff++];
 if (b == '\n' || b == '\r' || b == '\\') {
 c = (char)(b & 0xFF);
 break;
 }
 }
 } else {
 while (inOff < inLimit) {
 c = inCharBuf[inOff++];
 if (c == '\n' || c == '\r' || c == '\\') {
 break;
 }
 }
 }
 isCommentLine = true;
 }
 }

 if (c != '\n' && c != '\r') {
 lineBuf[len++] = c;
 if (len == lineBuf.length) {
 int newLength = lineBuf.length * 2;
 if (newLength < 0) {
 newLength = Integer.MAX_VALUE;
 }
 char[] buf = new char[newLength];
 System.arraycopy(lineBuf, 0, buf, 0, lineBuf.length);
 lineBuf = buf;
 }
 //flip the preceding backslash flag
 if (c == '\\') {
 precedingBackslash = !precedingBackslash;
 } else {
 precedingBackslash = false;
 }
 }
 else {
 // reached EOL
 if (isCommentLine || len == 0) {
 isCommentLine = false;
 isNewLine = true;
 skipWhiteSpace = true;
 len = 0;
 continue;
 }
 if (inOff >= inLimit) {
 inLimit = (inStream==null)
 ?reader.read(inCharBuf)
 :inStream.read(inByteBuf);
 inOff = 0;
 if (inLimit <= 0) {
 if (precedingBackslash) {
 len--;
 }
 return len;
 }
 }
 if (precedingBackslash) {
 len -= 1;
 //skip the leading whitespace characters in following line
 skipWhiteSpace = true;
 appendedLineBegin = true;
 precedingBackslash = false;
 if (c == '\r') {
 skipLF = true;
 }
 } else {
 return len;
 }
 }
 }
 }
 }

 /*
 * Converts encoded \uxxxx to unicode chars
 * and changes special saved chars to their original forms
 */
 private String loadConvert (char[] in, int off, int len, char[] convtBuf) {
 if (convtBuf.length < len) {
 int newLen = len * 2;
 if (newLen < 0) {
 newLen = Integer.MAX_VALUE;
 }
 convtBuf = new char[newLen];
 }
 char aChar;
 char[] out = convtBuf;
 int outLen = 0;
 int end = off + len;

 while (off < end) {
 aChar = in[off++];
 if (aChar == '\\') {
 aChar = in[off++];
 if(aChar == 'u') {
 // Read the xxxx
 int value=0;
 for (int i=0; i<4; i++) {
 aChar = in[off++];
 switch (aChar) {
 case '0': case '1': case '2': case '3': case '4':
 case '5': case '6': case '7': case '8': case '9':
 value = (value << 4) + aChar - '0';
 break;
 case 'a': case 'b': case 'c':
 case 'd': case 'e': case 'f':
 value = (value << 4) + 10 + aChar - 'a';
 break;
 case 'A': case 'B': case 'C':
 case 'D': case 'E': case 'F':
 value = (value << 4) + 10 + aChar - 'A';
 break;
 default:
 throw new IllegalArgumentException(
 "Malformed \\uxxxx encoding.");
 }
 }
 out[outLen++] = (char)value;
 } else {
 if (aChar == 't') aChar = '\t';
 else if (aChar == 'r') aChar = '\r';
 else if (aChar == 'n') aChar = '\n';
 else if (aChar == 'f') aChar = '\f';
 out[outLen++] = aChar;
 }
 } else {
 out[outLen++] = aChar;
 }
 }
 return new String (out, 0, outLen);
 }

 /*
 * Converts unicodes to encoded \uxxxx and escapes
 * special characters with a preceding slash
 */
 private String saveConvert(String theString,
 boolean escapeSpace,
 boolean escapeUnicode) {
 int len = theString.length();
 int bufLen = len * 2;
 if (bufLen < 0) {
 bufLen = Integer.MAX_VALUE;
 }
 StringBuilder outBuffer = new StringBuilder(bufLen);

 for(int x=0; x<len; x++) {
 char aChar = theString.charAt(x);
 // Handle common case first, selecting largest block that
 // avoids the specials below
 if ((aChar > 61) && (aChar < 127)) {
 if (aChar == '\\') {
 outBuffer.append('\\'); outBuffer.append('\\');
 continue;
 }
 outBuffer.append(aChar);
 continue;
 }
 switch(aChar) {
 case ' ':
 if (x == 0 || escapeSpace)
 outBuffer.append('\\');
 outBuffer.append(' ');
 break;
 case '\t':outBuffer.append('\\'); outBuffer.append('t');
 break;
 case '\n':outBuffer.append('\\'); outBuffer.append('n');
 break;
 case '\r':outBuffer.append('\\'); outBuffer.append('r');
 break;
 case '\f':outBuffer.append('\\'); outBuffer.append('f');
 break;
 case '=': // Fall through
 case ':': // Fall through
 case '#': // Fall through
 case '!':
 outBuffer.append('\\'); outBuffer.append(aChar);
 break;
 default:
 if (((aChar < 0x0020) || (aChar > 0x007e)) & escapeUnicode ) {
 outBuffer.append('\\');
 outBuffer.append('u');
 outBuffer.append(toHex((aChar >> 12) & 0xF));
 outBuffer.append(toHex((aChar >> 8) & 0xF));
 outBuffer.append(toHex((aChar >> 4) & 0xF));
 outBuffer.append(toHex( aChar & 0xF));
 } else {
 outBuffer.append(aChar);
 }
 }
 }
 return outBuffer.toString();
 }

 private static void writeComments(BufferedWriter bw, String comments)
 throws IOException {
 bw.write("#");
 int len = comments.length();
 int current = 0;
 int last = 0;
 char[] uu = new char[6];
 uu[0] = '\\';
 uu[1] = 'u';
 while (current < len) {
 char c = comments.charAt(current);
 if (c > '\u00ff' || c == '\n' || c == '\r') {
 if (last != current)
 bw.write(comments.substring(last, current));
 if (c > '\u00ff') {
 uu[2] = toHex((c >> 12) & 0xf);
 uu[3] = toHex((c >> 8) & 0xf);
 uu[4] = toHex((c >> 4) & 0xf);
 uu[5] = toHex( c & 0xf);
 bw.write(new String(uu));
 } else {
 bw.newLine();
 if (c == '\r' &&
 current != len - 1 &&
 comments.charAt(current + 1) == '\n') {
 current++;
 }
 if (current == len - 1 ||
 (comments.charAt(current + 1) != '#' &&
 comments.charAt(current + 1) != '!'))
 bw.write("#");
 }
 last = current + 1;
 }
 current++;
 }
 if (last != current)
 bw.write(comments.substring(last, current));
 bw.newLine();
 }

 /**
 * Calls the {@code store(OutputStream out, String comments)} method
 * and suppresses IOExceptions that were thrown.
 *
 * @deprecated This method does not throw an IOException if an I/O error
 * occurs while saving the property list. The preferred way to save a
 * properties list is via the {@code store(OutputStream out,
 * String comments)} method or the
 * {@code storeToXML(OutputStream os, String comment)} method.
 *
 * @param out an output stream.
 * @param comments a description of the property list.
 * @exception ClassCastException if this {@code Properties} object
 * contains any keys or values that are not
 * {@code Strings}.
 */
 @Deprecated
 public void save(OutputStream out, String comments) {
 try {
 store(out, comments);
 } catch (IOException e) {
 }
 }

 /**
 * Writes this property list (key and element pairs) in this
 * {@code Properties} table to the output character stream in a
 * format suitable for using the {@link #load(java.io.Reader) load(Reader)}
 * method.
 * 
 * Properties from the defaults table of this {@code Properties}
 * table (if any) are not written out by this method.
 * 
 * If the comments argument is not null, then an ASCII {@code #}
 * character, the comments string, and a line separator are first written
 * to the output stream. Thus, the {@code comments} can serve as an
 * identifying comment. Any one of a line feed ('\n'), a carriage
 * return ('\r'), or a carriage return followed immediately by a line feed
 * in comments is replaced by a line separator generated by the {@code Writer}
 * and if the next character in comments is not character {@code #} or
 * character {@code !} then an ASCII {@code #} is written out
 * after that line separator.
 * 
 * Next, a comment line is always written, consisting of an ASCII
 * {@code #} character, the current date and time (as if produced
 * by the {@code toString} method of {@code Date} for the
 * current time), and a line separator as generated by the {@code Writer}.
 * 
 * Then every entry in this {@code Properties} table is
 * written out, one per line. For each entry the key string is
 * written, then an ASCII {@code =}, then the associated
 * element string. For the key, all space characters are
 * written with a preceding {@code \} character. For the
 * element, leading space characters, but not embedded or trailing
 * space characters, are written with a preceding {@code \}
 * character. The key and element characters {@code #},
 * {@code !}, {@code =}, and {@code :} are written
 * with a preceding backslash to ensure that they are properly loaded.
 * 
 * After the entries have been written, the output stream is flushed.
 * The output stream remains open after this method returns.
 * 将属性列表存储到 Writer 中，并添加相关注释
 */
 public void store(Writer writer, String comments)
 throws IOException
 {
 store0((writer instanceof BufferedWriter)?(BufferedWriter)writer
 : new BufferedWriter(writer),
 comments,
 false);
 }

 /**
 * Writes this property list (key and element pairs) in this
 * {@code Properties} table to the output stream in a format suitable
 * for loading into a {@code Properties} table using the
 * {@link #load(InputStream) load(InputStream)} method.
 * 
 * Properties from the defaults table of this {@code Properties}
 * table (if any) are not written out by this method.
 * 
 * This method outputs the comments, properties keys and values in
 * the same format as specified in
 * {@link #store(java.io.Writer, java.lang.String) store(Writer)},
 * with the following differences:
 * <ul>
 * <li>The stream is written using the ISO 8859-1 character encoding.
 *
 * <li>Characters not in Latin-1 in the comments are written as
 * {@code \u005Cu}xxxx for their appropriate unicode
 * hexadecimal value xxxx.
 *
 * <li>Characters less than {@code \u005Cu0020} and characters greater
 * than {@code \u005Cu007E} in property keys or values are written
 * as {@code \u005Cu}xxxx for the appropriate hexadecimal
 * value xxxx.
 * </ul>
 * 
 * After the entries have been written, the output stream is flushed.
 * The output stream remains open after this method returns.
 * 将属性列表存储到 OutputStream 中，并添加相关注释
 */
 public void store(OutputStream out, String comments)
 throws IOException
 {
 store0(new BufferedWriter(new OutputStreamWriter(out, "8859_1")),
 comments,
 true);
 }

 private void store0(BufferedWriter bw, String comments, boolean escUnicode)
 throws IOException
 {
 if (comments != null) {
 writeComments(bw, comments);
 }
 bw.write("#" + new Date().toString());
 bw.newLine();
 synchronized (this) {
 for (Map.Entry<Object, Object> e : entrySet()) {
 String key = (String)e.getKey();
 String val = (String)e.getValue();
 key = saveConvert(key, true, escUnicode);
 /* No need to escape embedded and trailing spaces for value, hence
 * pass false to flag.
 */
 val = saveConvert(val, false, escUnicode);
 bw.write(key + "=" + val);
 bw.newLine();
 }
 }
 bw.flush();
 }

 /**
 * Loads all of the properties represented by the XML document on the
 * specified input stream into this properties table.
 *
 * The XML document must have the following DOCTYPE declaration:
 * <pre>
 * <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
 * </pre>
 * Furthermore, the document must satisfy the properties DTD described
 * above.
 *
 * An implementation is required to read XML documents that use the
 * "{@code UTF-8}" or "{@code UTF-16}" encoding. An implementation may
 * support additional encodings.
 *
 * The specified stream is closed after this method returns.
 * 从 XML 文件中加载属性列表
 */
 public synchronized void loadFromXML(InputStream in)
 throws IOException, InvalidPropertiesFormatException
 {
 Objects.requireNonNull(in);
 PropertiesDefaultHandler handler = new PropertiesDefaultHandler();
 handler.load(this, in);
 in.close();
 }

 /**
 * Emits an XML document representing all of the properties contained
 * in this table.
 *
 * An invocation of this method of the form {@code props.storeToXML(os,
 * comment)} behaves in exactly the same way as the invocation
 * {@code props.storeToXML(os, comment, "UTF-8");}.
 *
 * @param os the output stream on which to emit the XML document.
 * @param comment a description of the property list, or {@code null}
 * if no comment is desired.
 * @throws IOException if writing to the specified output stream
 * results in an {@code IOException}.
 * @throws NullPointerException if {@code os} is null.
 * @throws ClassCastException if this {@code Properties} object
 * contains any keys or values that are not
 * {@code Strings}.
 * 将属性列表存储到 XML 文件中，并添加相关注释
 */
 public void storeToXML(OutputStream os, String comment)
 throws IOException
 {
 storeToXML(os, comment, "UTF-8");
 }

 /**
 * Emits an XML document representing all of the properties contained
 * in this table, using the specified encoding.
 *
 * The XML document will have the following DOCTYPE declaration:
 * <pre>
 * <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
 * </pre>
 *
 * If the specified comment is {@code null} then no comment
 * will be stored in the document.
 *
 * An implementation is required to support writing of XML documents
 * that use the "{@code UTF-8}" or "{@code UTF-16}" encoding. An
 * implementation may support additional encodings.
 *
 * The specified stream remains open after this method returns.
 *
 * This method behaves the same as
 * {@linkplain #storeToXML(OutputStream os, String comment, Charset charset)}
 * except that it will {@linkplain java.nio.charset.Charset#forName look up the charset}
 * using the given encoding name.
 * 将属性列表存储到 XML 文件中，并添加相关注释，可以指定文件编码
 */
 public void storeToXML(OutputStream os, String comment, String encoding)
 throws IOException {
 Objects.requireNonNull(os);
 Objects.requireNonNull(encoding);

 try {
 Charset charset = Charset.forName(encoding);
 storeToXML(os, comment, charset);
 } catch (IllegalCharsetNameException | UnsupportedCharsetException e) {
 throw new UnsupportedEncodingException(encoding);
 }
 }

 /**
 * Emits an XML document representing all of the properties contained
 * in this table, using the specified encoding.
 *
 * The XML document will have the following DOCTYPE declaration:
 * <pre>
 * <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd">
 * </pre>
 *
 * If the specified comment is {@code null} then no comment
 * will be stored in the document.
 *
 * An implementation is required to support writing of XML documents
 * that use the "{@code UTF-8}" or "{@code UTF-16}" encoding. An
 * implementation may support additional encodings.
 *
 * Unmappable characters for the specified charset will be encoded as
 * numeric character references.
 *
 * The specified stream remains open after this method returns.
 * 将属性列表存储到 XML 文件中，并添加相关注释，可以指定字符集
 * @since 10
 */
 public void storeToXML(OutputStream os, String comment, Charset charset)
 throws IOException {
 Objects.requireNonNull(os, "OutputStream");
 Objects.requireNonNull(charset, "Charset");
 PropertiesDefaultHandler handler = new PropertiesDefaultHandler();
 handler.store(this, os, comment, charset);
 }

 /**
 * Searches for the property with the specified key in this property list.
 * If the key is not found in this property list, the default property list,
 * and its defaults, recursively, are then checked. The method returns
 * {@code null} if the property is not found.
 * 根据指定的键读取属性值
 */
 public String getProperty(String key) {
 Object oval = map.get(key); // 从当前 Properties 中读取
 String sval = (oval instanceof String) ? (String)oval : null; // 非字符串都返回 null
 // 返回值为 null，则尝试从默认属性中读取
 return ((sval == null) && (defaults != null)) ? defaults.getProperty(key) : sval;
 }

 /**
 * Searches for the property with the specified key in this property list.
 * If the key is not found in this property list, the default property list,
 * and its defaults, recursively, are then checked. The method returns the
 * default value argument if the property is not found.
 * 根据指定的键读取值，如果键不存在或值为 null，则返回 defaultValue
 */
 public String getProperty(String key, String defaultValue) {
 String val = getProperty(key);
 return (val == null) ? defaultValue : val;
 }

 /**
 * Returns an enumeration of all the keys in this property list,
 * including distinct keys in the default property list if a key
 * of the same name has not already been found from the main
 * properties list.
 * 获取所有的属性名称
 */
 public Enumeration<?> propertyNames() {
 Hashtable<String,Object> h = new Hashtable<>();
 enumerate(h);
 return h.keys();
 }

 /**
 * Returns an unmodifiable set of keys from this property list
 * where the key and its corresponding value are strings,
 * including distinct keys in the default property list if a key
 * of the same name has not already been found from the main
 * properties list. Properties whose key or value is not
 * of type {@code String} are omitted.
 * 
 * The returned set is not backed by this {@code Properties} object.
 * Changes to this {@code Properties} object are not reflected in the
 * returned set.
 * 获取所有的字符串属性名称
 */
 public Set<String> stringPropertyNames() {
 Map<String, String> h = new HashMap<>();
 enumerateStringProperties(h);
 return Collections.unmodifiableSet(h.keySet());
 }

 /**
 * Prints this property list out to the specified output stream.
 * This method is useful for debugging.
 */
 public void list(PrintStream out) {
 out.println("-- listing properties --");
 Map<String, Object> h = new HashMap<>();
 enumerate(h);
 for (Map.Entry<String, Object> e : h.entrySet()) {
 String key = e.getKey();
 String val = (String)e.getValue();
 if (val.length() > 40) {
 val = val.substring(0, 37) + "...";
 }
 out.println(key + "=" + val);
 }
 }

 /**
 * Prints this property list out to the specified output stream.
 * This method is useful for debugging.
 */
 public void list(PrintWriter out) {
 out.println("-- listing properties --");
 Map<String, Object> h = new HashMap<>();
 enumerate(h);
 for (Map.Entry<String, Object> e : h.entrySet()) {
 String key = e.getKey();
 String val = (String)e.getValue();
 if (val.length() > 40) {
 val = val.substring(0, 37) + "...";
 }
 out.println(key + "=" + val);
 }
 }

 /**
 * Enumerates all key/value pairs into the specified Map.
 */
 private void enumerate(Map<String, Object> h) {
 if (defaults != null) {
 defaults.enumerate(h);
 }
 for (Map.Entry<Object, Object> e : entrySet()) {
 String key = (String)e.getKey();
 h.put(key, e.getValue());
 }
 }

 /**
 * Enumerates all key/value pairs into the specified Map
 * and omits the property if the key or value is not a string.
 */
 private void enumerateStringProperties(Map<String, String> h) {
 if (defaults != null) {
 defaults.enumerateStringProperties(h);
 }
 for (Map.Entry<Object, Object> e : entrySet()) {
 Object k = e.getKey();
 Object v = e.getValue();
 if (k instanceof String && v instanceof String) {
 h.put((String) k, (String) v);
 }
 }
 }

 /**
 * Convert a nibble to a hex character
 * 将整数转换为十六进制字符
 */
 private static char toHex(int nibble) {
 return hexDigit[(nibble & 0xF)];
 }

 /** A table of hex digits */
 private static final char[] hexDigit = {
 '0','1','2','3','4','5','6','7','8','9','A','B','C','D','E','F'
 };

 // Hashtable methods overridden and delegated to a ConcurrentHashMap instance
 @Override
 public int size() {
 return map.size();
 }

 @Override
 public boolean isEmpty() {
 return map.isEmpty();
 }

 @Override
 public Enumeration<Object> keys() {
 // CHM.keys() returns Iterator w/ remove() - instead wrap keySet()
 return Collections.enumeration(map.keySet());
 }

 @Override
 public Enumeration<Object> elements() {
 // CHM.elements() returns Iterator w/ remove() - instead wrap values()
 return Collections.enumeration(map.values());
 }

 @Override
 public boolean contains(Object value) {
 return map.contains(value);
 }

 @Override
 public boolean containsValue(Object value) {
 return map.containsValue(value);
 }

 @Override
 public boolean containsKey(Object key) {
 return map.containsKey(key);
 }

 @Override
 public Object get(Object key) {
 return map.get(key);
 }

 @Override
 public synchronized Object put(Object key, Object value) {
 return map.put(key, value);
 }

 @Override
 public synchronized Object remove(Object key) {
 return map.remove(key);
 }

 @Override
 public synchronized void putAll(Map<?, ?> t) {
 map.putAll(t);
 }

 @Override
 public synchronized void clear() {
 map.clear();
 }

 @Override
 public synchronized String toString() {
 return map.toString();
 }

 @Override
 public Set<Object> keySet() {
 return Collections.synchronizedSet(map.keySet(), this);
 }

 @Override
 public Collection<Object> values() {
 return Collections.synchronizedCollection(map.values(), this);
 }

 @Override
 public Set<Map.Entry<Object, Object>> entrySet() {
 return Collections.synchronizedSet(new EntrySet(map.entrySet()), this);
 }

 /*
 * Properties.entrySet() should not support add/addAll, however
 * ConcurrentHashMap.entrySet() provides add/addAll. This class wraps the
 * Set returned from CHM, changing add/addAll to throw UOE.
 */
 private static class EntrySet implements Set<Map.Entry<Object, Object>> {
 private Set<Map.Entry<Object,Object>> entrySet;

 private EntrySet(Set<Map.Entry<Object, Object>> entrySet) {
 this.entrySet = entrySet;
 }

 @Override public int size() { return entrySet.size(); }
 @Override public boolean isEmpty() { return entrySet.isEmpty(); }
 @Override public boolean contains(Object o) { return entrySet.contains(o); }
 @Override public Object[] toArray() { return entrySet.toArray(); }
 @Override public <T> T[] toArray(T[] a) { return entrySet.toArray(a); }
 @Override public void clear() { entrySet.clear(); }
 @Override public boolean remove(Object o) { return entrySet.remove(o); }

 @Override
 public boolean add(Map.Entry<Object, Object> e) {
 throw new UnsupportedOperationException();
 }

 @Override
 public boolean addAll(Collection<? extends Map.Entry<Object, Object>> c) {
 throw new UnsupportedOperationException();
 }

 @Override
 public boolean containsAll(Collection<?> c) {
 return entrySet.containsAll(c);
 }

 @Override
 public boolean removeAll(Collection<?> c) {
 return entrySet.removeAll(c);
 }

 @Override
 public boolean retainAll(Collection<?> c) {
 return entrySet.retainAll(c);
 }

 @Override
 public Iterator<Map.Entry<Object, Object>> iterator() {
 return entrySet.iterator();
 }
 }

 @Override
 public synchronized boolean equals(Object o) {
 return map.equals(o);
 }

 @Override
 public synchronized int hashCode() {
 return map.hashCode();
 }

 @Override
 public Object getOrDefault(Object key, Object defaultValue) {
 return map.getOrDefault(key, defaultValue);
 }

 @Override
 public synchronized void forEach(BiConsumer<? super Object, ? super Object> action) {
 map.forEach(action);
 }

 @Override
 public synchronized void replaceAll(BiFunction<? super Object, ? super Object, ?> function) {
 map.replaceAll(function);
 }

 @Override
 public synchronized Object putIfAbsent(Object key, Object value) {
 return map.putIfAbsent(key, value);
 }

 @Override
 public synchronized boolean remove(Object key, Object value) {
 return map.remove(key, value);
 }

 @Override
 public synchronized boolean replace(Object key, Object oldValue, Object newValue) {
 return map.replace(key, oldValue, newValue);
 }

 @Override
 public synchronized Object replace(Object key, Object value) {
 return map.replace(key, value);
 }

 @Override
 public synchronized Object computeIfAbsent(Object key,
 Function<? super Object, ?> mappingFunction) {
 return map.computeIfAbsent(key, mappingFunction);
 }

 @Override
 public synchronized Object computeIfPresent(Object key,
 BiFunction<? super Object, ? super Object, ?> remappingFunction) {
 return map.computeIfPresent(key, remappingFunction);
 }

 @Override
 public synchronized Object compute(Object key,
 BiFunction<? super Object, ? super Object, ?> remappingFunction) {
 return map.compute(key, remappingFunction);
 }

 @Override
 public synchronized Object merge(Object key, Object value,
 BiFunction<? super Object, ? super Object, ?> remappingFunction) {
 return map.merge(key, value, remappingFunction);
 }

 //
 // Special Hashtable methods
 @Override
 protected void rehash() { /* no-op */ }

 @Override
 public synchronized Object clone() {
 Properties clone = (Properties) cloneHashtable();
 clone.map = new ConcurrentHashMap<>(map);
 return clone;
 }

 // Hashtable serialization overrides
 // (these should emit and consume Hashtable-compatible stream)
 @Override
 void writeHashtable(ObjectOutputStream s) throws IOException {
 List<Object> entryStack = new ArrayList<>(map.size() * 2); // an estimate

 for (Map.Entry<Object, Object> entry : map.entrySet()) {
 entryStack.add(entry.getValue());
 entryStack.add(entry.getKey());
 }

 // Write out the simulated threshold, loadfactor
 float loadFactor = 0.75f;
 int count = entryStack.size() / 2;
 int length = (int)(count / loadFactor) + (count / 20) + 3;
 if (length > count && (length & 1) == 0) {
 length--;
 }
 synchronized (map) { // in case of multiple concurrent serializations
 defaultWriteHashtable(s, length, loadFactor);
 }

 // Write out simulated length and real count of elements
 s.writeInt(length);
 s.writeInt(count);

 // Write out the key/value objects from the stacked entries
 for (int i = entryStack.size() - 1; i >= 0; i--) {
 s.writeObject(entryStack.get(i));
 }
 }

 @Override
 void readHashtable(ObjectInputStream s) throws IOException,
 ClassNotFoundException {
 // Read in the threshold and loadfactor
 s.defaultReadObject();

 // Read the original length of the array and number of elements
 int origlength = s.readInt();
 int elements = s.readInt();

 // Validate # of elements
 if (elements < 0) {
 throw new StreamCorruptedException("Illegal # of Elements: " + elements);
 }

 // Constructing the backing map will lazily create an array when the first element is
 // added, so check it before construction. Note that CHM's constructor takes a size
 // that is the number of elements to be stored -- not the table size -- so it must be
 // inflated by the default load factor of 0.75, then inflated to the next power of two.
 // (CHM uses the same power-of-two computation as HashMap, and HashMap.tableSizeFor is
 // accessible here.) Check Map.Entry[].class since it's the nearest public type to
 // what is actually created.
 SharedSecrets.getJavaObjectInputStreamAccess()
 .checkArray(s, Map.Entry[].class, HashMap.tableSizeFor((int)(elements / 0.75)));

 // create CHM of appropriate capacity
 map = new ConcurrentHashMap<>(elements);

 // Read all the key/value objects
 for (; elements > 0; elements--) {
 Object key = s.readObject();
 Object value = s.readObject();
 map.put(key, value);
 }
 }
}

Properties 源码分析

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