java.util.Properties说明。
该类主要是读取属性配置文件，两种文件类型：普通文件格式为key = value；xml文件。
1）key = value示例如下：
public class TestProperties {
public static void main(String[] args) {
Properties properties = new Properties();
FileInputStream fileInputStream;
try {
fileInputStream = new FileInputStream(new File("D:/testProperties.txt"));
// properties.loadFromXML(fileInputStream);
properties.load(fileInputStream);
for (Object pro : properties.keySet()) {
System.out.println(pro + "==" + properties.get(pro));
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}配置文件为：
name = hello value = good
结果为：
name==hello value==good
2）读取xml文件，代码如下：
public class TestProperties {
public static void main(String[] args) {
Properties properties = new Properties();
FileInputStream fileInputStream;
try {
fileInputStream = new FileInputStream(new File("D:/testProperties.xml"));
properties.loadFromXML(fileInputStream);
// properties.load(fileInputStream);
for (Object pro : properties.keySet()) {
System.out.println(pro + "==" + properties.get(pro));
}
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}配置文件为：
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"> <properties> <comment>Hi</comment> <entry key="foo">bar</entry> <entry key="fu">baz</entry> <entry key="feee">baeee</entry> </properties>
运行结果为：
feee==baeee fu==baz foo==bar
2.源码分析：
该类继承自HashTable，结构为key-value，如下：
public class Properties extends Hashtable<Object,Object>
1）load（InputStream）方法，该方法主要作用是读取配置文件内的相关配置，并且将信息用key-value结构存放到Properties中。源码为：
public synchronized void load(InputStream inStream) throws IOException {
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;
//1.按行读取配置文件，返回值为该行的长度
while ((limit = lr.readLine()) >= 0) {
c = 0;
keyLen = 0;
valueStart = limit;
hasSep = false;
//System.out.println("line=<" + new String(lineBuf, 0, limit) + ">");
precedingBackslash = false;
//1.1对该行每个字符进行遍历，找到=或者：符号的位置
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++;
}
//keyLen为符号之前不为空的最终位置，valueStart为符号之后的第一个不为空的位置
String key = loadConvert(lr.lineBuf, 0, keyLen, convtBuf);
String value = loadConvert(lr.lineBuf, valueStart, limit - valueStart, convtBuf);
//将解析出的key和value存放到hashTable中
put(key, value);
}
}2）store（OutputStream out, String comments）方法，out为输出的文档，comments为配置文件的说明，在key-value时为注释信息，在xml文件格式下为<comments>标签内容。源代码如下：
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 (Enumeration<?> e = keys(); e.hasMoreElements();) {
String key = (String)e.nextElement();
String val = (String)get(key);
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();
}
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();
}JDK源码学习（9）- java.util.Properties实例与源码
原文：http://yinyueml.blog.51cto.com/4841237/1831684