Spring MVC 核心流程

如今的java web開發，大致和以往我們在學校學習的SSH已經大不一樣了，現在基本成熟的大公司都使用Spring MVC 快速開發WEB應用。當然小編我也是**Spring MVC**的長期實踐者。
首先想和大家普及下我眼中的Spring mcv整個流程過程

Spring MVC 的 restFul風格

說實話自己用了這個久的Spring mvc 只知道他請求的連結格式是和restful風格一致的，但是並沒有想過它同時也和resteasy，支援標準的JAX，接下來就帶大家體會下，並且指出可能存在的坑哈

1. 搭建SpringMVC框架
   本系統採用的是開發工具是idea 同時使用的是springmvc +maven的方式實現的簡單demo
   廢話不多說，先給大家看看專案結構
   
   
   專案和大多是專案一樣，java下放類，resources放一些配置檔案和資源，webapp下存放靜態資源
   當然這裡需要和大家強調下web.xml的配置

<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">
 


    <display-name>Spring MVC Application</display-name>

    <servlet>
        <servlet-name>springServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name
 
>contextConfigLocation</param-name>
            <param-value>classpath*:mvc-dispatcher-servlet.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>
<!--配置/和/*的區別在於是否會攔截靜態資源 例如.jsp-->
    <servlet-mapping>
        <servlet-name>springServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>
</web-app>

pom檔案也有需要注意的地方，如果要支援json格式的restful，需要匯入jackson的相關的包，後面再說實現原理的時候會進一步說明

<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.springapp</groupId>
    <artifactId>SpringWebFlow</artifactId>
    <packaging>war</packaging>
    <version>1.0-SNAPSHOT</version>
    <name>SpringWebFlow</name>

    <properties>
        <spring.version>4.1.1.RELEASE</spring.version>
        <jackson.version>2.1.4</jackson.version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-core</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>servlet-api</artifactId>
            <version>2.5</version>
        </dependency>

        <dependency>
            <groupId>javax.servlet.jsp</groupId>
            <artifactId>jsp-api</artifactId>
            <version>2.1</version>
            <scope>provided</scope>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>${spring.version}</version>
        </dependency>

        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-test</artifactId>
            <version>${spring.version}</version>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-core</artifactId>
            <version>${jackson.version}</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>${jackson.version}</version>
        </dependency>

        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-annotations</artifactId>
            <version>${jackson.version}</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.module</groupId>
            <artifactId>jackson-module-jaxb-annotations</artifactId>
            <version>${jackson.version}</version>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.jaxrs</groupId>
            <artifactId>jackson-jaxrs-json-provider</artifactId>
            <version>${jackson.version}</version>
            <!-- Jackson2.2.0 版本對於 CXF2.7.3 不支援 -->
            <!-- http://www.marshut.com/krrqx/fasterxml-jackson-2-2-provider-no-longer-works-with-cxf-jax-rs.pdf -->
            <!-- http://cxf.547215.n5.nabble.com/Creating-input-values-on-WADL-td5728910.html -->
        </dependency>

        <!-- Spring WebMVC 3.1.2 用到 -->
        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-mapper-asl</artifactId>
            <version>1.9.0</version>
        </dependency>
        <dependency>
            <groupId>org.codehaus.jackson</groupId>
            <artifactId>jackson-core-asl</artifactId>
            <version>1.9.0</version>
        </dependency>


        <dependency>
            <groupId>junit</groupId>
            <artifactId>junit</artifactId>
            <version>4.11</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <finalName>SpringWebFlow</finalName>
        <plugins>
            <plugin>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <source>1.6</source>
                    <target>1.6</target>
                </configuration>
            </plugin>
            <plugin>
                <artifactId>maven-surefire-plugin</artifactId>
                <configuration>
                    <includes>
                        <include>**/*Tests.java</include>
                    </includes>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

最後一個需要注意的是spring的配置檔案，裡面需要加下mvc的自動驅動註解，不然後面有些註解沒法用

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:util="http://www.springframework.org/schema/util"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd
       http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util.xsd">

    <mvc:annotation-driven/>

    <context:component-scan base-package="com.springapp.mvc"/>

    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/pages/"/>
        <property name="suffix" value=".jsp"/>
    </bean>

</beans>

最後就是Controller的程式碼了

package com.springapp.mvc;

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

@Controller
@RequestMapping("/test")
public class HelloController {

    @RequestMapping(value = "/hello",method = RequestMethod.GET)
    public String printWelcome(ModelMap model) {
        model.addAttribute("message", "Hello world!");
        return "hello";
    }

    @RequestMapping(value = "userInfo",method = RequestMethod.POST)
    @ResponseBody
    public  Person userInfo(@RequestBody Person person){

        System.out.println("人的姓名:"+person.getName()+"，人的年齡"+person.getAge());

        return person;
    }
}

這裡可以看到使用了@RequestBody 表明接受的請求會先進過訊息轉化器(http conversion),訊息轉化器根據請求過來的請求做解析，當然也可以通過consumes進行指定值解析哪種格式contest-type格式
這也是為什麼需要匯入上文中說的jackson的包，內部訊息轉化器使用的jackson的方式轉化的

最後當然是用postman進行呼叫了哈哈