读取 jpa 的配置文件.添加自己的属性.

package com.freewebsys.sns.common;

import java.io.IOException;
import java.io.InputStream;
import java.net.MalformedURLException;
import java.net.URL;
import java.util.Enumeration;
import java.util.Iterator;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;

import org.dom4j.Document;
import org.dom4j.DocumentFactory;
import org.dom4j.Element;
import org.dom4j.io.SAXReader;
import org.xml.sax.SAXNotRecognizedException;
import org.xml.sax.SAXNotSupportedException;

public class SysConfUtil {

/**
* @param args
* @throws MalformedURLException
*/
public static void main(String[] args) throws MalformedURLException {
// TODO Auto-generated method stub
System.out.println(getConfigValue("mail.host"));
// System.out.println(getConfigValue("mail.username"));
}

private static Document document = null;

static {
Enumeration<URL> xmls;
SAXReader reader = new SAXReader(DocumentFactory.getInstance());
try {
xmls = Thread.currentThread().getContextClassLoader()
.getResources("META-INF/persistence.xml");
if (xmls.hasMoreElements()) {
URL configURL = xmls.nextElement();
document = reader.read(configURL.openStream());
}
} catch (Exception e) {
System.out.println("加载配置失败：" + e.getMessage());
}
// System.out.println(document.selectSingleNode("@name=mail.host"));
}

@SuppressWarnings("unchecked")
public static String getConfigValue(String name) {
System.out.println(document.getRootElement().getName());
// /*[name()='persistence']/*[name()='persistence-unit']/*[name()='properties']/*[name()='property']
// 得到根节点
Element root = document.getRootElement();
// 得到persistenceUnit
Element persistenceUnit = root.element("persistence-unit");
// 得到下面的属性
Element properties = persistenceUnit.element("properties");
// 对属性进行循环，找到自定义的配置
for (Iterator<Element> i = properties.elementIterator("property"); i
.hasNext();) {
Element property = i.next();
if (property.attributeValue("name") != null
&& property.attributeValue("name").equals(name)) {
// 如果有这个属性返回value
return property.attributeValue("value");
}
}
return "";
}
}