WEB应用通过Spring注入实现类

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众所周知Spring实现了控制反转和依赖注入

下面以一简单Web应用来说明如何通过Spring注入实现类代码如下

代码1:IDateFormat
//接口定义
package com.doit8.common.util;
public interface IDateFormat {
public String getNowDate();
}

代码2:DateFormatImpl
//实现类,该实现类作用只是取得当前日期并格式化它.
package com.doit8.common.util;
import java.text.SimpleDateFormat;
import java.util.Date;
public class DateFormatImpl implements IDateFormat{
public String getNowDate() {
  Date date=new Date();
  SimpleDateFormat formatter = new SimpleDateFormat("yyyy-MM-dd");
  String dateString = formatter.format(date);
  return dateString;
}
}

代码3:MyBeanFactory
//Bean工产通过Spring取得注入的实现类方法,通过传入的request取得Web应用的上下文环境
package com.doit8.common.util;

import javax.servlet.ServletContext;
import javax.servlet.http.HttpServletRequest;
import org.springframework.beans.factory.BeanFactory;
import org.springframework.web.context.support.WebApplicationContextUtils;
import org.springframework.web.servlet.support.RequestContextUtils;

public class MyBeanFactory {
private static BeanFactory overrideFactory = null;
private static BeanFactory factory = null;
/**
* 获取spring实例
* @return
* @throws InstantiationException
*/
public static Object getInstance(HttpServletRequest request,String beanName) throws InstantiationException {
  try {
   if (overrideFactory != null) {
    Object reply = overrideFactory.getBean(beanName);
    return reply;
   }
   if (factory == null) {
    factory = getBeanFactory(request);
    overrideFactory = factory;
   }
   Object reply = factory.getBean(beanName);
   return reply;
  } catch (RuntimeException ex) {
   throw ex;
  } catch (Exception ex) {
   throw new InstantiationException(ex.toString());
  }
}
/**
* 获取spring bean工厂
*
* @return
*/
private static BeanFactory getBeanFactory(HttpServletRequest request) {
  ServletContext srvCtx = request.getSession().getServletContext();
  if (request != null) {
   return RequestContextUtils.getWebApplicationContext(request, srvCtx);
  } else {
   return WebApplicationContextUtils.getWebApplicationContext(srvCtx);
  }
}
}

代码4:TestLoadClass
//取得注入实现类的JAVABEAN
package test;
import javax.servlet.http.HttpServletRequest;
import com.doit8.common.util.DateFormatImpl;
import com.doit8.common.util.IDateFormat;
import com.doit8.common.util.MyBeanFactory;
public class TestLoadClass {
IDateFormat datefomat;
private String datestr;
public TestLoadClass(HttpServletRequest request)
{
  try {
   //根据Spring配置的BeanName取得实现类(Spring配置见下配置文件)
   datefomat=(DateFormatImpl)MyBeanFactory.getInstance(request,"DateFormat");
   datestr=datefomat.getNowDate();
  } catch (InstantiationException e) {
   // TODO Auto-generated catch block
   e.printStackTrace();
  }
}
public String getDate()
{
  return datestr;
}
}

配置文件1:web.xml
需要在web.xml文件中指定Spring的配置文件侦听类
<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
   <context-param>
  <param-name>contextConfigLocation</param-name>
  <param-value>/WEB-INF/applicationContext.xml</param-value>
</context-param>
<listener>
  <listener-class>
   org.springframework.web.context.ContextLoaderListener
  </listener-class>
</listener>
</web-app>

配置文件2:applicationContext.xml
该配置文件指定实现类
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
<bean id="DateFormat" class="com.doit8.common.util.DateFormatImpl">
</bean>
</beans>

完成以上配置后就可以在Web应用中用到Spring配置中配置的实现类了。见下JSP代码
<%@ page language="java" pageEncoding="UTF-8"%>
<%@ page import="test.TestLoadClass"%>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
    <base href="<%=basePath%>">
    <title>My JSP 'testjsp.jsp' starting page</title>
    <meta http-equiv="pragma" content="no-cache">
    <meta http-equiv="cache-control" content="no-cache">
    <meta http-equiv="expires" content="0">
    <meta http-equiv="keywords" content="keyword1,keyword2,keyword3">
    <meta http-equiv="description" content="This is my page">
</head>

运行结果在页面上显示当前格式化后的日期