使用spring 4.0 + maven 构建超简单的web项目

2022-09-22 15:28:18

一.需求

使用spring去管理web项目,是目前非常流行的一种思路,本文将介绍使用maven+spring 4.0.2 来构建一个简单的web项目.

二.实现

1.新建一个maven项目,如下图所示:

这里因为是构建web项目,所以,选择的是webapp.

项目的架构图:

2.在pom.xml中添加所依赖的jar包,如下所示:

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"

    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.amos</groupId>

    <artifactId>ssh_integrated</artifactId>

    <packaging>war</packaging>

    <version>0.0.1-SNAPSHOT</version>

    <name>ssh_integrated Maven Webapp</name>

    <url>http://maven.apache.org</url>

    <dependencies>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-web</artifactId>

            <version>4.0.2.RELEASE</version>

        </dependency>

        <dependency>

            <groupId>junit</groupId>

            <artifactId>junit</artifactId>

            <version>3.8.1</version>

            <scope>test</scope>

        </dependency>

        <dependency>

            <groupId>org.springframework</groupId>

            <artifactId>spring-context</artifactId>

            <version>4.0.2.RELEASE</version>

        </dependency>

    </dependencies>

    <build>

        <finalName>ssh_integrated_spring</finalName>

    </build>

</project>

3.新建一个接口com.amos.service.IHello.java,并实现接口.

package com.amos.service;

public interface IHello {

    public String sayHi();

}

com.amos.service.HelloImpl.java

package com.amos.service;

import java.util.Date;

public class HelloImpl implements IHello{

    private String msg;

    public void setMsg(String msg) {

        this.msg = msg;

    }

    public String sayHi() {

        return "当前时间:"+new Date()+" msg:"+msg;

    }

}

4.新建一个Servlet,并实现此Servlet

com.amos.web.HelloServlet

package com.amos.web;

import java.io.IOException;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import org.springframework.context.ApplicationContext;

import org.springframework.web.context.support.WebApplicationContextUtils;

import com.amos.service.IHello;

@WebServlet(name="HelloServlet",urlPatterns={"/hello"})

public class HelloServlet extends HttpServlet {

    private static final long serialVersionUID = 2801654413247618244L;

    private IHello hello;

    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {

        //方法1,使用传统方式去加载beans.xml,每次请求时加载

        //ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");

        //方法2,使用监听器的方式加载beans.xml,在一启动的时候就加载监听器,避免多次加载,提高效率

        //ApplicationContext applicationContext  = (ApplicationContext) this.getServletContext().getAttribute("SpringApplicationContext");

        //方法3,使用spring自带的监听器去加载beans.xml

        //ApplicationContext applicationContext  = (ApplicationContext) this.getServletContext().getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);

        //使用webapplicationcontextutils这个工具类可以很方便的获取ApplicationContext,只需要传入servletContext

        ApplicationContext applicationContext = WebApplicationContextUtils.getRequiredWebApplicationContext(this.getServletContext());

        hello = applicationContext.getBean(IHello.class);

        String sayHi = hello.sayHi();

        System.err.println("sayHi:" + sayHi);

        resp.setContentType("text/html;charset=utf-8");

        resp.getWriter().write("<h2>" + sayHi + "</h2>");

    }

}

注:这里要注意的是实现spring管理Bean的三种方式.

第一种:最传统的方式,同时也是效率最低的一种,因为,每次发一个请求都要重新加载一次,而且对于不同的Servlet的要每个都去加载,会大大降低效率.

第二种:使用监听器来实现加载beans.xml,每次项目启动的时候加载一次就可以了.这样大提高了效率.

com.amos.web.InitSpringFactoryListener.java

package com.amos.web;

import javax.servlet.ServletContextEvent;

import javax.servlet.ServletContextListener;

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class InitSpringFactoryListener implements ServletContextListener {

    public InitSpringFactoryListener() {

    }

    public void contextInitialized(ServletContextEvent arg0) {

        //这里将加载beans.xml加载到内存中,放到servletcontext中,名称可以随便取,这里取为SpringApplicationContext,

        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("beans.xml");

        arg0.getServletContext().setAttribute("SpringApplicationContext", applicationContext);

    }

    public void contextDestroyed(ServletContextEvent arg0) {

    }

}

同时,web.xml中要定义一个listener属性.

<!-- 自己去写一个监听器来实现加载beans.xml,进而启动spring容器 -->

    <!--

    <listener>

        <listener-class>com.amos.web.InitSpringFactoryListener</listener-class>

    </listener> -->

第三种:针对第二种方法,其实spring中已经封装好了一种监听器,人工去配置即可,原理和第二种方法一致.

只需要在web.xml中加入如下代码即可.

<!-- 使用spring自带的监听器,其默认加载的是WEB-INF下的applicationContext.xml -->

    <listener>

        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>

    </listener>

但运行进会报如下错误:

org.springframework.beans.factory.BeanDefinitionStoreException: IOException parsing XML document from ServletContext resource [/WEB-INF/applicationContext.xml]; nested exception is java.io.FileNotFoundException: Could not open ServletContext resource [/WEB-INF/applicationContext.xml]

    at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:343)

    at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:303)

    at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:180)

    at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:216)

    at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions(AbstractBeanDefinitionReader.java:187)

    at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:125)

    at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions(XmlWebApplicationContext.java:94)

    at org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory(AbstractRefreshableApplicationContext.java:129)

    at org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory(AbstractApplicationContext.java:540)

    ........

    Caused by: java.io.FileNotFoundException: Could not open ServletContext resource [/WEB-INF/applicationContext.xml]

    at org.springframework.web.context.support.ServletContextResource.getInputStream(ServletContextResource.java:141)

    at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions(XmlBeanDefinitionReader.java:329)

    ... 22 more

说找不到applicationContext.xml文件,那么如何解决这个问题呢?

他说找不到,那就在WIB-INF目录下建一个即可.

然后引入自定义的beans.xml即可.

<?xml version="1.0" encoding="UTF-8"?>

<beans xmlns="http://www.springframework.org/schema/beans"

    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"

    xmlns:tx="http://www.springframework.org/schema/tx" xmlns:aop="http://www.springframework.org/schema/aop"

    xsi:schemaLocation="http://www.springframework.org/schema/beans

               http://www.springframework.org/schema/beans/spring-beans-4.0.xsd

               http://www.springframework.org/schema/context

               http://www.springframework.org/schema/context/spring-context-4.0.xsd

               http://www.springframework.org/schema/tx

               http://www.springframework.org/schema/tx/spring-tx-4.0.xsd

               http://www.springframework.org/schema/aop

               http://www.springframework.org/schema/aop/spring-aop-4.0.xsd

               ">
   <import resource="classpath:beans.xml"/>

</beans>

这个时候问题解决.

这里HelloSerlvet中如何获取对应的ApplicationContext呢?

//方法3,使用spring自带的监听器去加载beans.xml

        //ApplicationContext applicationContext  = (ApplicationContext) this.getServletContext().getAttribute(WebApplicationContext.ROOT_WEB_APPLICATION_CONTEXT_ATTRIBUTE);

这个是需要查看源码才能发现其属性名称,所以比较麻烦.这里还有一种较简便的方法,如下所示:

//使用webapplicationcontextutils这个工具类可以很方便的获取ApplicationContext,只需要传入servletContext

        ApplicationContext applicationContext = WebApplicationContextUtils.getRequiredWebApplicationContext(this.getServletContext());

第三种方法,基本上配置完毕,但还会感觉很不爽,因为还要新建一个applicationContext.xml去专门import bean.xml,是相当讨厌的.

其实还可以在web.xml中配置自定义的xml文件名称,如下所示:

    <!-- 配置spring的加载文件路径及文件名称 -->

    <context-param>

        <param-name>contextConfigLocation</param-name>

        <param-value>classpath:beans.xml</param-value>

    </context-param>

org.springframework.web.context.ContextLoaderListener中有这样一段说明:

<p>Processes a {@link #CONFIG_LOCATION_PARAM "contextConfigLocation"}

* context-param and passes its value to the context instance, parsing it into

* potentially multiple file paths which can be separated by any number of

* commas and spaces, e.g. "WEB-INF/applicationContext1.xml,

* WEB-INF/applicationContext2.xml". Ant-style path patterns are supported as well,

* e.g. "WEB-INF/*Context.xml,WEB-INF/spring*.xml" or "WEB-INF/**/*Context.xml".

* If not explicitly specified, the context implementation is supposed to use a

* default location (with XmlWebApplicationContext: "/WEB-INF/applicationContext.xml").

*

可以自定义spring默认加载的xml文件的名称,可以以逗号和空格进行分隔,也可以使用Ant类型的去标记.xml如,WEB-INF/spring*.xml

否则默认的加载的就是applicationContext.xml.
可以在web.xml中进行配置其参数.

所以,最终的web.xml如下:

<!DOCTYPE web-app PUBLIC

 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"

 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>

    <display-name>Archetype Created Web Application</display-name>

    <!-- 配置spring的加载文件路径及文件名称 -->

    <context-param>

        <param-name>contextConfigLocation</param-name>

        <param-value>classpath:beans.xml</param-value>

    </context-param>

    <!-- 使用spring自带的监听器,其默认加载的是WEB-INF下的applicationContext.xml -->

    <listener>

        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>

    </listener>

    <!-- 自己去写一个监听器来实现加载beans.xml,进而启动spring容器 -->

    <!--

    <listener>

        <listener-class>com.amos.web.InitSpringFactoryListener</listener-class>

    </listener> -->

</web-app>

5.运行效果

6.本文源码

https://github.com/amosli/ssh_integrated_spring

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