JDK1.5（代号Tiger）中更新了java.util.Properties类，提供了从XML文件中读写key-value对属性的简单方法：loadFromXML()和storeToXML()
1、基本加载属性的方法
l Sample属性文件：sample.properties
l 加载属性的Sample程序
import java.io.FileInputStream; import java.util.Properties; public class LoadSampleProperties { public static void main(String[] args) throws Exception { Properties prop = new Properties(); FileInputStream fis = new FileInputStream("props/sample.properties"); prop.load(fis); prop.list(System.out); System.out.println("\nThe foo property: " + prop.getProperty("foo")); } } l 输出结果如下：
-- listing properties -- fu=baz foo=bar The foo property: bar
2、从XML中加载属性
l 下面是Properties DTD清单：
<?xml version="1.0" encoding="UTF-8"?> <!-- DTD for properties --> <!ELEMENT properties ( comment?, entry* ) > <!ATTLIST properties version CDATA #FIXED "1.0"> <!ELEMENT comment (#PCDATA) > <!ELEMENT entry (#PCDATA) > <!ATTLIST entry key CDATA #REQUIRED> l Sample XML属性文件：sample.xml（符合上面的Properties DTD）
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"> <properties> <comment>Hello</comment> <entry key="foo">bar</entry> <entry key="fu">baz</entry> </properties> l <entry>标记指定具体一个属性，由key属性指定属性名，而<entry>标记的内容指定属性值
l <comment>标记可以用来指定注释
l 从XML文件加载属性的Sample程序
import java.io.FileInputStream; import java.util.Properties; public class LoadSampleXML { public static void main(String[] args) throws Exception { Properties prop = new Properties(); FileInputStream fis = new FileInputStream("props/sample.xml"); prop.loadFromXML(fis); prop.list(System.out); System.out.println("\nThe foo property: " + prop.getProperty("foo")); } } l 输出的结果是一样的
l 可以看出方法很简单：使用XML文件来保存属性，使用loadFromXML()方法替代原来的load()方法来加载XML文件中属性
3、更新XML文件中的属性值
l Sample程序
import java.io.FileInputStream; import java.io.FileOutputStream; import java.util.Properties; public class UpdateSampleXml { public static void main(String[] args) throws Exception { Properties prop = new Properties(); FileInputStream fis = new FileInputStream("props/sample.xml"); prop.loadFromXML(fis); prop.list(System.out); System.out.println("\nThe foo property: " + prop.getProperty("foo")); prop.setProperty("foo", "Hello World!"); prop.setProperty("new-name", "new-value"); FileOutputStream fos = new FileOutputStream("props/sample.xml"); prop.storeToXML(fos, "Store Sample"); fos.close(); fis = new FileInputStream("props/sample.xml"); prop.loadFromXML(fis); prop.list(System.out); System.out.println("\nThe foo property: " + prop.getProperty("foo")); } } l 上面的例子加载了sample.xml中的属性，更新了foo属性的值，并新加了new-name属性，调用storeToXML()方法保存到原文件中，并改变注释内容为Store Sample
l 程序执行后的sample.xml的内容如下：
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE properties SYSTEM "http://java.sun.com/dtd/properties.dtd"> <properties> <comment>Store Sample</comment> <entry key="new-name">new-value</entry> <entry key="fu">baz</entry> <entry key="foo">Hello World!</entry> </properties> 
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