Tiger系列一：从XML中加载属性

xml|加载

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

foo=bar
fu=baz
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>