缓存机制读取xml

一 、首先实现一个Cache类，里面有读取对象的方法get()，如果文件没有被修改则直接从HashMap里面将对象取出，如果文件被修改则调用readObject()方法实现从文件中读出数据，并同时将读出的数据放入HashMap里，将原来的对象覆盖。这样下次再读数据的时候就可以从缓存中直接读到，并且保证是最新的数据。还有一个判断文件是否被修改的方法getModified()；

import java.io.File;
import java.util.HashMap;
public class Cache {
    private static Cache instance;
    
    HashMap mapLastModified = new HashMap();
    HashMap mapValues = new HashMap();
    private  Cache() {
        super();
    }    
     public static Cache getInstance()
    {
       if (instance == null)           
                instance = new Cache();
       return instance;
           
        }
    public Object get(String name, String path, Class clsParser, Class clsInstantiator, Class clsObj) {
        Object obj = null;
        String absPath = getClass().getResource(path).getPath();        
        Long modified = getModified(name, absPath);
        if (modified != null) {
            obj = readObject(absPath, clsParser, clsInstantiator, clsObj);
            
            mapLastModified.put(name, modified);
            mapValues.put(name, obj);
            System.out.println("get object from file");
        } else {
            obj = mapValues.get(name);
            System.out.println("get object from cache");
        }       
        return obj;
    }
    
    private Long getModified(String name, String path) {
        Long modified = new Long(new File(path).lastModified());
        Long saveModified = (Long) mapLastModified.get(name);
        if ((saveModified != null) && (saveModified.longValue() >= modified.longValue())) {
            modified = null;
        }        
        return modified;
    }
    
    private Object readObject(String path, Class clsParser, Class clsInstantiator, Class clsObj) {
        try {
            FileParser parser = (FileParser) clsParser.newInstance();
            Instantiator instantiator = (Instantiator) clsInstantiator.newInstance();
            Object config = parser.parse(path);            
            return instantiator.instantiate(clsObj, config);
            
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }       
        return null;
    }
}

 

二、 解析XML文件的类XmlFileParser，
为了方便处理不同文件的解析，在这里先定义一个接口FileParser，XmlFileParser实现了它，如果还有诸如对其他种类文件的解析也可以实现它。
//FileParser.java
public interface FileParser {
Object parse(String path);
}

//XmlFileParser.java
//采用Jdom的解析方式

import java.io.FileInputStream;
import java.io.IOException;
import org.jdom.Document;
import org.jdom.Element;
import org.jdom.input.SAXBuilder;
public class XmlFileParser implements FileParser {
 public XmlFileParser() {
  super();
 }
 public Object parse(String path) {
  Element root=null;
  FileInputStream fi = null;
  try {
   fi = new FileInputStream(path);
   SAXBuilder sb = new SAXBuilder();
   Document doc = sb.build(fi);
    root= doc.getRootElement();
   
  } catch (Exception e) {
   e.printStackTrace();
  } finally {
   try {
    fi.close();
   } catch (IOException e1) {   }
  }
  return root.getChildren();
 }
}

 

三 接下来是一个实例化处理的类ListTypeInstantiator，同样为了方便处理不同文件的实例化，在这里先定义一个接口Instantiator，ListTypeInstantiator实现了它。

//Instantiator.java
public interface Instantiator {
Object instantiate(Class clazz, Object configuration);
}

//ListTypeInstantiator.java

import java.util.ArrayList;
import java.util.List;
import org.apache.commons.beanutils.BeanUtils;
import org.jdom.Element;
public class ListTypeInstantiator implements Instantiator {
 public ListTypeInstantiator() {
  super();
 }
 public Object instantiate(Class clazz, Object configuration) {
  List arr = new ArrayList();
  Object bean = null;
    
  List children = (List) configuration;
  Element child = null;
  List attributes = null;
  Element attribute = null;
  
  try { 
   for(int i=0; i< children.size(); i++) {
    child = (Element) children.get(i);
    bean = clazz.newInstance();   
    attributes = child.getChildren();
    for(int j=0; j< attributes.size(); j++) {
     attribute = (Element) attributes.get(j);
     BeanUtils.setProperty(bean, attribute.getName(), attribute.getText());
    }   
    arr.add(bean);
   }
  } catch(Exception e) {
   e.printStackTrace();
  }  
  return arr;
 }
}

 

四 另外还需要一个封装我想要数据形式的JavaBean，这里设为NewsBean{}.
//NewsBean.java

public class NewsBean {
 private Long id;
 private String newsTitle;
 private String newsContent;
 private String newsType;
 private String deployDate;
 private String cancelDate;
    
 public Long getId() {
  return id;
 }
 public void setId(Long id) {
  this.id = id;
 }   
 public String getNewsTitle() {
  return newsTitle;
 }
 public void setNewsTitle(String newsTitle) {
  this.newsTitle = newsTitle;
 }
 public String getNewsContent() {
  return newsContent;
 }
 public void setNewsContent(String newsContent) {
  this.newsContent = newsContent;
 }
 public String getNewsType() {
  return newsType;
 }
 public void setNewsType(String newsType) {
  this.newsType = newsType;
 }
 public String getDeployDate() {
  return deployDate;
 }
 public void setDeployDate(String deployDate) {
  this.deployDate = deployDate;
 }
 public String getCancelDate() {
  return cancelDate;
 }
 public void setCancelDate(String cancelDate) {
  this.cancelDate = cancelDate;
 } 
}

五 最后一步测试结果，将news.xml文件放到classes目录下。
//MainClass.java

 

import java.util.List;
public class MainClass{
 public static void main(String[] args) throws Exception {
  List news1 = null;
  List news2 = null;
  NewsBean bean = null;
  news1 = (List)Cache.getInstance().get("news", "/news.xml", XmlFileParser.class, ListTypeInstantiator.class, NewsBean.class);  
  for (int i = 0; i < news1.size(); i++) {
   bean = (NewsBean) news1.get(i);
   System.out.println(bean.getId());
   System.out.println(bean.getNewsTitle());
   System.out.println(bean.getNewsContent());
   System.out.println(bean.getNewsType());
   System.out.println(bean.getDeployDate());
   System.out.println(bean.getCancelDate());
  } 
  System.out.println("Ok");
  news2 = (List)Cache.getInstance().get("news", "/news.xml", XmlFileParser.class, ListTypeInstantiator.class, NewsBean.class);  
  for (int i = 0; i < news2.size(); i++) {
   bean = (NewsBean) news2.get(i);
   System.out.println(bean.getId());
   System.out.println(bean.getNewsTitle());
   System.out.println(bean.getNewsContent());
   System.out.println(bean.getNewsType());
   System.out.println(bean.getDeployDate());
   System.out.println(bean.getCancelDate());
  }
}
}

第一次会从文件中读出数据，第二次就会从缓存中读取了，试着多读几次速度明显快很多。

测试的news.xml文件

<?xml version="1.0" encoding="gb2312"?>
<javanews>
<news>
<id>1</id>
<newsTitle>jdk1.5 API 中文版</newsTitle>
<newsContent>赶快下载</newsContent>
<newsType>news</newsType>
<deployDate>2005-11-30</deployDate>
<cancelDate>2006-1-30</cancelDate>
</news>
<news>
<id>2</id>
<newsTitle>java RPG 游戏</newsTitle>
<newsContent>赶快下载</newsContent>
<newsType>news</newsType>
<deployDate>2005-11-30</deployDate>
<cancelDate>2006-1-30</cancelDate>

</news>
</javanews>

运行结果：

C:\java>java MainClass

get object from file
news
1
jdk1.5 API 中文版
赶快下载
2005-11-30
2006-1-30
news
2
java RPG 游戏
赶快下载
2005-11-30
2006-1-30
Ok

news
get object from cache
1
jdk1.5 API 中文版
赶快下载
2005-11-30
2006-1-30
news
2
java RPG 游戏
赶快下载
2005-11-30
2006-1-30

C:\java>