allen0818 的部落格

在Spring MVC的運作機制中，主要有兩個地方會用到XML配置，

1. 在web.xml中設置DispatcherServlet，讓前端所有Request都先經過這支Servlet才決定要交由哪個控制器處理
2. Spring本身的配置文件 xxx-servlet.xml

而這兩個XML都可以用Annotation標記的方式來取代其功能，底下簡單以一個範例來記錄如何改寫:
改寫後的專案配置會是這樣:

1. 在POM中加入下列的dependency:

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>4.2.5.RELEASE</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>javax.servlet.jsp-api</artifactId>
            <version>2.3.1</version>
        </dependency>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>jstl</artifactId>
            <version>1.2</version>
        </dependency>

2. 在原先NetBeans所建好的Maven專案中，預設已經在POM的build標籤內導入下列的Plugin:

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.1</version>
                <configuration>
                    <source>1.7</source>
                    <target>1.7</target>
                    <compilerArguments>
                        <endorseddirs>${endorsed.dir}</endorseddirs>
                    </compilerArguments>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>2.3</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>

其中，maven-war-plugin是為了讓maven在沒有web.xml的環境下也可以順利build Web專案
而maven-compiler-plugin則是用來指定建置前後的JDK版本
3. 建立Initialization Class HelloWorldInitializer.java

package allen0818.springmvcprojwithoutxml.configuration;

import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;
 
import org.springframework.web.WebApplicationInitializer;
import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;
import org.springframework.web.servlet.DispatcherServlet;
 
public class HelloWorldInitializer implements WebApplicationInitializer {
 
    public void onStartup(ServletContext container) throws ServletException {
 
        AnnotationConfigWebApplicationContext ctx = new AnnotationConfigWebApplicationContext();
        ctx.register(HelloWorldConfiguration.class);
        ctx.setServletContext(container);
 
        ServletRegistration.Dynamic servlet = container.addServlet("dispatcher", new DispatcherServlet(ctx));
 
        servlet.setLoadOnStartup(1);
        servlet.addMapping("/");
    }
}

這邊是用來取代原先在web.xml註冊DispatcherServlet的動作
4. 建立Configuration Class HelloWorldConfiguration.java

package allen0818.springmvcprojwithoutxml.configuration;

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.EnableWebMvc;
import org.springframework.web.servlet.view.InternalResourceViewResolver;
import org.springframework.web.servlet.view.JstlView;

/**
 *
 * @author allen0818
 */
@Configuration
@EnableWebMvc
@ComponentScan(basePackages = "allen0818.springmvcprojwithoutxml")
public class HelloWorldConfiguration {
  @Bean
  public ViewResolver viewResolver() {
    InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
    viewResolver.setViewClass(JstlView.class);
    viewResolver.setPrefix("/WEB-INF/views/");
    viewResolver.setSuffix(".jsp");
    
    return viewResolver;
  }
}

這邊則是用來取代原先Spring的配置文件，其中有幾個地方要注意:
(1) @Configuration 是為了告知Spring Container這個Class中含有Spring配置會用到的Bean(ex: viewResolver)
(2) @EnableWebMvc 是用來取代原先XML中所定義的 mvc:annotation-driven，表示我們將用Annotation來配置Spring
(3) @ComponentScan(basePackages = "allen0818.springmvcprojwithoutxml")告知Spring需要搜尋哪個範圍內的Annotation標記
5. 建立Controller HelloWorldController

package allen0818.springmvcprojwithoutxml.controller;

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

/**
 *
 * @author allen0818
 */
 
@Controller
@RequestMapping("/")
public class HelloWorldController {
 
    @RequestMapping(method = RequestMethod.GET)
    public String sayHello(ModelMap model) {
        model.addAttribute("greeting", "Hello World from Spring 4 MVC");
        return "welcome";
    }
 
    @RequestMapping(value = "/helloagain", method = RequestMethod.GET)
    public String sayHelloAgain(ModelMap model) {
        model.addAttribute("greeting", "Hello World Again, from Spring 4 MVC");
        return "welcome";
    }
}

6. 建立view welcome.jsp

<%-- 
    Document   : welcome
    Created on : 2016/5/9, 上午 11:33:07
    Author     : allen0818
--%>

<%@page contentType="text/html" pageEncoding="UTF-8"%>
<!DOCTYPE html>
<html>
    <head>
        <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
        <title>Welcome Page</title>
    </head>
    <body>
        Greeting : ${greeting}
    </body>
</html>

呈現效果如下:

參考資料:
1. http://websystique.com/springmvc/spring-4-mvc-helloworld-tutorial-annotation-javaconfig-full-example/
2. http://docs.spring.io/spring/docs/4.0.x/spring-framework-reference/html/mvc.html