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缓存机制高速读取XML文件

2012-10-28 
缓存机制快速读取XML文件利用缓存机制快速读取XML文件数据    下面把简单实现的几个Class说一说。    一 首

缓存机制快速读取XML文件
利用缓存机制快速读取XML文件数据
  
  下面把简单实现的几个Class说一说。
  
  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();
  
  代码实现如下:
  
  import java.io.File;
  import java.util.HashMap;
  
  public class Cache {
  
  HashMap mapLastModified = new HashMap();
  HashMap mapValues = new HashMap();
  public Cache() {
  super();
  }
  public Object get(String name, String path, Class clsParser, Class clsInstantiator, Class clsObj) {
  Object obj = ;
  String absPath = getClass().getResource(path).getPath();
  Long modified = getModified(name, absPath);
  if (modified != ) {
  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 != ) && (saveModified.longValue() >= modified.longValue())) {
  modified = ;
  }
  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 ;
  }
  }
  
  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) {
  
  FileInputStream fi = ;
  try {
  fi = new FileInputStream(path);
  SAXBuilder sb = new SAXBuilder();
  Document doc = sb.build(fi);
  Element root = doc.getRootElement();
  return root.getChildren();
  } catch (Exception e) {
  e.printStackTrace();
  } finally {
  try {
  fi.close();
  } catch (IOException e1) {
  }
  }
  }
  }
  
  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 = ;
  
  List children = (List) configuration;
  Element child = ;
  
  List attributes = ;
  Element attribute = ;
  
  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 = ;
  List news2 = ;
  NewsBean bean = ;
  
  news1 = (List)Cache.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());
  }
  news2 = (List)Cache.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。



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