Tiger系列一:从XML中加载属性

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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>

 

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