Java解析XML文件开源库DOM4J

	private volatile static SystemConfig config = null;
	public static SystemConfig newInstance() {
        if (config == null) {
            synchronized (config) {
                if (config == null) {
                    config = new SystemConfig();
                    SAXReader reader = new SAXReader();
                    try {
                        document = reader.read(configPath);
                        root = document.getRootElement();
                    } catch (DocumentException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
        return config;
    }

//獲取節點
root.element(key);
//獲取節點內容
root.element(key).getText();
root.element(key).getTextTrim();
root.element(key).getStringValue();

Element element = root.addElement(key);
element.setText(value);
//將創建的節點添加進編譯後配置文件中
OutputFormat format = OutputFormat.createPrettyPrint();
format.setEncoding("UTF-8");
try {
      XMLWriter writer = new XMLWriter(new FileOutputStream(configPath.getPath()), format);
      writer.write(document);
} catch (IOException e) {
      e.printStackTrace();
}

package com.lmc.util;
import org.apache.log4j.Logger;
import org.dom4j.Document;
import org.dom4j.DocumentException;
import org.dom4j.Element;
import org.dom4j.io.OutputFormat;
import org.dom4j.io.SAXReader;
import org.dom4j.io.XMLWriter;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import java.util.List;
public class SystemConfig {
    private volatile static SystemConfig config = null;
    private static URL configPath = SystemConfig.class.getClassLoader().getResource("SystemConfig.xml");
    private static Document document;
    private static Element root;
    private static final Logger LOGGER = Logger.getLogger(SystemConfig.class);
    /**
     * 單例模式，只對外創建一個LoadConfig
     * @return
     */
    public static SystemConfig newInstance() {
        if (config == null) {
            synchronized (SystemConfig.class) {
                if (config == null) {
                    config = new SystemConfig();
                    SAXReader reader = new SAXReader();
                    try {
                        document = reader.read(configPath);
                        root = document.getRootElement();
                    } catch (DocumentException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
        return config;
    }
    /**
     * 通过key返回value
     * @param key
     * @return
     */
    public String getValueByKey(String key) {
        String resultvalue = null;
        if (root.element(key) == null) {
            LOGGER.error("The key is not exist!! key: " + key);
            return null;
        } else {
            resultvalue = root.element(key).getStringValue();
            if (resultvalue == null) {
                LOGGER.error("get value by key FAIL!! key: " + key);
                return null;
            }
        }
        return resultvalue;
    }
    /**
     * 通過key來設置value如果key不存在,創建新的key。
     * @param value
     * @param key
     */
    public void setValueByKey(String value, String key) {
        Element element = root.addElement(key);
        element.setText(value);
        OutputFormat format = OutputFormat.createPrettyPrint();
        format.setEncoding("UTF-8");
        try {
            XMLWriter writer = new XMLWriter(new FileOutputStream(configPath.getPath()), format);
            writer.write(document);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    public void str(String key) {
        Element element = root.element(key);
        System.out.println(element.getText());
        System.out.println(element.getStringValue());
        System.out.println(element.getTextTrim());
    }
}