spring in action 学习笔记十四：用纯注解的方式实现spring mvc

　　　　在讲用纯注解的方式实现springmvc之前先介绍一个类：AbstractAnnotationDispatcherServletInitializer.这个类的作用是：任何一个类继承AbstractAnnotationDispatcherServletInitializer,将会自动的被用为配置DispatcherServlet,以及在DispatcherServlet中的的spring容器（如：spring-servlet.xml）文件。

spring in action的描述是：any class that extends AbstractAnnotationDispatcherServletInitializer will automatically be used to configure DispatcherServlet and the Spring Application context in the application's servlet context.

AbstractAnnotationDispatcherServlet的代码如下：

/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.springframework.web.servlet.support;

import org.springframework.util.ObjectUtils;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;

/**
 * Base class for {@link org.springframework.web.WebApplicationInitializer}
 * implementations that register a
 * {@link org.springframework.web.servlet.DispatcherServlet DispatcherServlet}
 * configured with annotated classes, e.g. Spring's
 * {@link org.springframework.context.annotation.Configuration @Configuration} classes.
 *
 * <p>Concrete implementations are required to implement {@link #getRootConfigClasses()}
 * and {@link #getServletConfigClasses()} as well as {@link #getServletMappings()}.
 * Further template and customization methods are provided by
 * {@link AbstractDispatcherServletInitializer}.
 *
 * <p>This is the preferred approach for applications that use Java-based
 * Spring configuration.
 *
 * @author Arjen Poutsma
 * @author Chris Beams
 * @since 3.2
 */
public abstract class AbstractAnnotationConfigDispatcherServletInitializer
        extends AbstractDispatcherServletInitializer {

    /**
     * {@inheritDoc}
     * <p>This implementation creates an {@link AnnotationConfigWebApplicationContext},
     * providing it the annotated classes returned by {@link #getRootConfigClasses()}.
     * Returns {@code null} if {@link #getRootConfigClasses()} returns {@code null}.
     */
    @Override
    protected WebApplicationContext createRootApplicationContext() {
        Class<?>[] configClasses = getRootConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            AnnotationConfigWebApplicationContext rootAppContext = new AnnotationConfigWebApplicationContext();
            rootAppContext.register(configClasses);
            return rootAppContext;
        }
        else {
            return null;
        }
    }

    /**
     * {@inheritDoc}
     * <p>This implementation creates an {@link AnnotationConfigWebApplicationContext},
     * providing it the annotated classes returned by {@link #getServletConfigClasses()}.
     */
    @Override
    protected WebApplicationContext createServletApplicationContext() {
        AnnotationConfigWebApplicationContext servletAppContext = new AnnotationConfigWebApplicationContext();
        Class<?>[] configClasses = getServletConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            servletAppContext.register(configClasses);
        }
        return servletAppContext;
    }

    /**
     * Specify {@link org.springframework.context.annotation.Configuration @Configuration}
     * and/or {@link org.springframework.stereotype.Component @Component} classes to be
     * provided to the {@linkplain #createRootApplicationContext() root application context}.
     * @return the configuration classes for the root application context, or {@code null}
     * if creation and registration of a root context is not desired
     */
    protected abstract Class<?>[] getRootConfigClasses();

    /**
     * Specify {@link org.springframework.context.annotation.Configuration @Configuration}
     * and/or {@link org.springframework.stereotype.Component @Component} classes to be
     * provided to the {@linkplain #createServletApplicationContext() dispatcher servlet
     * application context}.
     * @return the configuration classes for the dispatcher servlet application context or
     * {@code null} if all configuration is specified through root config classes.
     */
    protected abstract Class<?>[] getServletConfigClasses();

}

案例的目录结构如下图所示：

RootConfig的代码如下：

package spittr.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;

/**
 * Created by ${秦林森} on 2017/6/12.
 */
@Configuration
/**
 * excludeFilters是指明不被@ComponentScan扫描的类型
 */
@ComponentScan(basePackages = {"spittr"},excludeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION,value = EnableWebMvc.class)})

public class RootConfig {

}

WebConfig的代码如下：

package spittr.config;

import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.ViewResolver;
import org.springframework.web.servlet.config.annotation.DefaultServletHandlerConfigurer;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
import org.springframework.web.servlet.view.BeanNameViewResolver;
import org.springframework.web.servlet.view.InternalResourceViewResolver;
import spittr.web.HomeController;

/**
 * Created by ${秦林森} on 2017/6/12.
 */
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = {"spittr.web"})
public class WebConfig extends WebMvcConfigurerAdapter{
    @Bean
    public ViewResolver viewResolver(){
        InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
        //设置前缀
        viewResolver.setPrefix("/WEB-INF/views/");
        //设置后缀
        viewResolver.setSuffix(".jsp");
        viewResolver.setExposeContextBeansAsAttributes(true);
        return  viewResolver;
    }
    @Override
    public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
        configurer.enable();//configure static content handling.
    }

}

package spittr.config;

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

/**
 * Created by ${秦林森} on 2017/6/12.
 */
public class SpittrWebApplicationInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {

    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class<?>[]{RootConfig.class};
    }

    @Override
    protected Class<?>[] getServletConfigClasses() {
        //specifiy configuration class
        return new Class<?>[]{WebConfig.class};
    }

    @Override
    protected String[] getServletMappings() {
        return new String[]{"*.do"};//Map DispatcherServlet to
    }
}

HomeController的代码如下：

package spittr.web;

import org.springframework.stereotype.Controller;
import org.springframework.web.WebApplicationInitializer;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

/**
 * Created by ${秦林森} on 2017/6/12.
 */
@Controller
@RequestMapping(value = "/people")
public class HomeController {
    @RequestMapping(value = "/home.do",method = RequestMethod.GET)
    public  String home(){
        return  "home";
    }
}

home.jsp的代码如下：

<%--
  Created by IntelliJ IDEA.
  User: Administrator
  Date: 2017/6/12
  Time: 16:25
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<head>
    <title>spittr</title>
</head>
<body>
    welcome to china ,one of the ancient civilized countries.
</body>
</html>

注意我这个项目的web应用名设置为该项目名。

启动tomcat 输入：http://localhost:8090/spring20170602/people/home.do

访问结果如下图所示: