XML文件解析示例

从所周知，XML文件解析有SAX和DOM

其中DOM需要一次性将xml文件读入内存，构建DOM树

SAX无须在一开始将xml文件读入内存，采用事件驱动，文件读入的过程，即解析的过程。

除了优秀的Dom4j解析，本文介绍下apche里的解析器。

XPath使用路径表达式识别XML文档里的节点
http://www.cnblogs.com/skyblue/archive/2008/06/19/900187.html
示例：

package com.zte.sunquan.demo.xml;

import org.apache.commons.configuration.ConfigurationException;
import org.apache.commons.configuration.EnvironmentConfiguration;
import org.apache.commons.configuration.HierarchicalConfiguration;
import org.apache.commons.configuration.XMLConfiguration;
import org.apache.commons.configuration.event.ConfigurationEvent;
import org.apache.commons.configuration.event.ConfigurationListener;
import org.apache.commons.configuration.reloading.FileChangedReloadingStrategy;
import org.apache.commons.configuration.reloading.ReloadingStrategy;
import org.apache.commons.configuration.tree.xpath.XPathExpressionEngine;
import org.junit.Assert;
import org.junit.Before;
import org.junit.Test;

import java.util.concurrent.TimeUnit;

/**
* Created by 10184538 on 2017/6/25.
*/
public class XmlRead {
private String configFile = "/config.xml";
private String rootElementName = "properties";
private XMLConfiguration cfg;

public void loadCfg(Class cls) {
cfg = new XMLConfiguration();
cfg.setRootElementName(rootElementName);
cfg.setAttributeSplittingDisabled(true);
try {
cfg.load(cls.getResourceAsStream(configFile));
FileChangedReloadingStrategy strategy = new FileChangedReloadingStrategy();
strategy.setRefreshDelay(1);
cfg.setFileName("config.xml");//如果设置了reloading-strategy则必须设置文件
cfg.setReloadingStrategy(strategy);
} catch (ConfigurationException e) {
e.printStackTrace();
}
}

private void loadConfig(XMLConfiguration rootCfg) {
for (HierarchicalConfiguration cfg : rootCfg.configurationsAt("property")) {
System.out.println(cfg.getString("[@name]"));
}
}

@Before
public void init() {
loadCfg(XmlRead.class);
}

@Test
public void getCommonConfig() {
Assert.assertEquals("default-topic", cfg.getString("property.[@name]"));
Assert.assertEquals("China", cfg.getString("property.country"));
Assert.assertEquals("China", cfg.getString("property(0).country"));
Assert.assertEquals("Japan", cfg.getString("property(1).country"));
}

@Test
public void getConfigByXPath() throws ConfigurationException {
cfg.setExpressionEngine(new XPathExpressionEngine());
Assert.assertEquals("China", cfg.getString("property[@name = 'default-topic']/country"));
Assert.assertEquals("Japan", cfg.getString("property[num>11]/country"));
Assert.assertEquals("Japan", cfg.getString("property[last()]/country"));
}

@Test
public void getEnvironmentConfig() {
EnvironmentConfiguration config = new EnvironmentConfiguration();
Assert.assertEquals("C:\\Program Files\\Java\\jdk1.8.0_91", config.getString("JAVA_HOME"));
}

@Test
public void whenConfigChange() throws InterruptedException, ConfigurationException {
cfg = new XMLConfiguration("config.xml");
FileChangedReloadingStrategy strategy = new FileChangedReloadingStrategy();
strategy.setRefreshDelay(1);
cfg.setReloadingStrategy(strategy);
while (true) {
System.out.println(cfg.getString("property.country"));
TimeUnit.SECONDS.sleep(2);
}
}

@Test
public void whenConfigChangeListener() throws InterruptedException, ConfigurationException {
cfg = new XMLConfiguration("config.xml");
FileChangedReloadingStrategy strategy = new FileChangedReloadingStrategy();
strategy.setRefreshDelay(1);
cfg.setReloadingStrategy(strategy);
cfg.addConfigurationListener(new ConfigurationListener() {
@Override
public void configurationChanged(ConfigurationEvent event) {
if (!event.isBeforeUpdate())
{
// only display events after the modification was done
System.out.println("Received event!");
System.out.println("Type = " + event.getType());
if (event.getPropertyName() != null)
{
System.out.println("Property name = " + event.getPropertyName());
}
if (event.getPropertyValue() != null)
{
System.out.println("Property value = " + event.getPropertyValue());
}
}
}
});
while (true) {
System.out.println(cfg.getString("property.country"));
TimeUnit.SECONDS.sleep(2);
}
}

}