一个最基础的 Spring 4 MVC Maven 项目 | 隔叶黄莺 Yanbin Blog

2018-04-30 | 阅读(611)

这是一个最基本的 Spring 4 MVC 的 Maven 项目，非 SpringBoot 的，SpringBoot 由于有许多自动化配置特性，会更简单些。本例全部用 Java 代码作为配置，免除了创建 web.xml 和如 dispatcher-servlet.xml 这样的文件。本人更倾向于 Java 配置，它的优势在于能进行编译期检查，逻辑性也强，配置文件只是改动无需重新编译，都是要重启服务的; 关于使用 XML 配置文件的方式可参考文后的链接。

本文侧重于 Spring MVC 项目提供 RESTful JSON API, 因而静态 Web 内容提及较少。创建一个 Maven 项目的方式，可以直接创建一个 pom.xml 文件，然后编辑它的内容，使用 IntelliJ IDEA 的话只需要选择导入为一个 Maven 项目就成，Eclipse 的话可能还要事先运行 mvn eclipse:eclipse 初始化一下。

项目结构布局

就是一个普通的 Maven 项目，稍稍不同的是 src/main 目录中除了 java 和 resources 之外，还有 webapp 目录，用于存放 web 静态文件或模板文件的。

pom.xml 文件内容

<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>demo</groupId>
    <artifactId>springmvc</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>war</packaging>

    <properties>
        <jdk.version>1.8</jdk.version>
        <maven-compiler-plugin.version>3.1</maven-compiler-plugin.version>

        <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
        <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>

        <spring.version>4.3.16.RELEASE</spring.version>
        <maven-war-plugin.version>2.4</maven-war-plugin.version>
        <tomcat7.version>2.2</tomcat7.version>
        <servlet.version>3.0.1</servlet.version>
        <jackson.version>2.9.5</jackson.version>
        <logback.version>1.2.3</logback.version>
        <guava.version>25.0-jre</guava.version>
    </properties>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>org.springframework</groupId>
                <artifactId>spring-framework-bom</artifactId>
                <version>${spring.version}</version>
                <scope>import</scope>
                <type>pom</type>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>${servlet.version}</version>
            <scope>provided</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>${jackson.version}</version>
        </dependency>
        <dependency>
            <groupId>ch.qos.logback</groupId>
            <artifactId>logback-classic</artifactId>
            <version>${logback.version}</version>
        </dependency>
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>${guava.version}</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${maven-compiler-plugin.version}</version>
                <configuration>
                    <encoding>UTF-8</encoding>
                    <source>${jdk.version}</source>
                    <target>${jdk.version}</target>
                </configuration>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <version>${maven-war-plugin.version}</version>
                <configuration>
                    <failOnMissingWebXml>false</failOnMissingWebXml>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.tomcat.maven</groupId>
                <artifactId>tomcat7-maven-plugin</artifactId>
                <version>${tomcat7.version}</version>
                <configuration>
                    <path>/springmvc</path>
                    <contextReloadable>true</contextReloadable>
                </configuration>
            </plugin>

        </plugins>
    </build>
</project>

<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">

<artifactId>springmvc</artifactId>

<version>1.0-SNAPSHOT</version>

<jdk.version>1.8</jdk.version>

<maven-compiler-plugin.version>3.1</maven-compiler-plugin.version>

<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>

<project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>

<spring.version>4.3.16.RELEASE</spring.version>

<maven-war-plugin.version>2.4</maven-war-plugin.version>

<tomcat7.version>2.2</tomcat7.version>

<servlet.version>3.0.1</servlet.version>

<jackson.version>2.9.5</jackson.version>

<logback.version>1.2.3</logback.version>

<guava.version>25.0-jre</guava.version>

</properties>

<groupId>org.springframework</groupId>

<artifactId>spring-framework-bom</artifactId>

<version>${spring.version}</version>

<scope>import</scope>

</dependency>

</dependencies>

</dependencyManagement>

<groupId>javax.servlet</groupId>

<artifactId>javax.servlet-api</artifactId>

<version>${servlet.version}</version>

<scope>provided</scope>

</dependency>

<groupId>org.springframework</groupId>

<artifactId>spring-webmvc</artifactId>

</dependency>

<groupId>com.fasterxml.jackson.core</groupId>

<artifactId>jackson-databind</artifactId>

<version>${jackson.version}</version>

</dependency>

<groupId>ch.qos.logback</groupId>

<artifactId>logback-classic</artifactId>

<version>${logback.version}</version>

</dependency>

<groupId>com.google.guava</groupId>

<artifactId>guava</artifactId>

<version>${guava.version}</version>

</dependency>

</dependencies>

<build>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-compiler-plugin</artifactId>

<version>${maven-compiler-plugin.version}</version>

<source>${jdk.version}</source>

<target>${jdk.version}</target>

</configuration>

</plugin>

<groupId>org.apache.maven.plugins</groupId>

<artifactId>maven-war-plugin</artifactId>

<version>${maven-war-plugin.version}</version>

<failOnMissingWebXml>false</failOnMissingWebXml>

</configuration>

</plugin>

<groupId>org.apache.tomcat.maven</groupId>

<artifactId>tomcat7-maven-plugin</artifactId>

<version>${tomcat7.version}</version>

<path>/springmvc</path>

</configuration>

</plugin>

</plugins>

</build>

</project>

本例使用了 slfj + logback 作为日志框架与实现，并且引入非常常用的 Google Guava 通用库。

maven-war-plugin 用于创建可发布的 war 包
tomcat7-maven-plugin 用于测试项目，它的 contextReloadable 属性可在类改动重新编译后使 Spring 重新启动

在 IntelliJ IDEA 中如果想要修改 Java 类后自动重启 Spring 上下文的话，有两种方式

1. 启用自动编译功能，Preferences/Build, Execution, Deployment/Compiler, 勾选上 Build project automatically
2. 类修改后，从 Build 菜单中，选 Recompile..., Build Project, Build Module, Rebuild Project 都会触发 Spring 上下文重启。

WebInitializer 类

package config;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.web.WebApplicationInitializer;
import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;
import org.springframework.web.filter.CharacterEncodingFilter;
import org.springframework.web.servlet.DispatcherServlet;

import javax.servlet.DispatcherType;
import javax.servlet.FilterRegistration;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.ServletRegistration;
import java.util.EnumSet;

public class WebInitializer implements WebApplicationInitializer {

    private static final Logger logger = LoggerFactory.getLogger(WebInitializer.class);

    @Override
    public void onStartup(ServletContext container) throws ServletException {
        logger.info("Starting container......");

        AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
        context.register(WebAppConfig.class);
        context.setServletContext(container);
        context.refresh();

        ServletRegistration.Dynamic dispatcher = container.addServlet("dispatcher", new DispatcherServlet(context));
        dispatcher.setLoadOnStartup(1);
        dispatcher.addMapping("/");

        FilterRegistration.Dynamic filter = container.addFilter("encoding", CharacterEncodingFilter.class);
        filter.setInitParameter("encoding", "UTF-8");
        filter.addMappingForServletNames(EnumSet.allOf(DispatcherType.class), true, "dispatcher");
    }
}

package config;

import org.slf4j.Logger;

import org.slf4j.LoggerFactory;

import org.springframework.web.WebApplicationInitializer;

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

import org.springframework.web.filter.CharacterEncodingFilter;

import org.springframework.web.servlet.DispatcherServlet;

import javax.servlet.DispatcherType;

import javax.servlet.FilterRegistration;

import javax.servlet.ServletContext;

import javax.servlet.ServletException;

import javax.servlet.ServletRegistration;

import java.util.EnumSet;

public class WebInitializer implements WebApplicationInitializer {

private static final Logger logger = LoggerFactory.getLogger(WebInitializer.class);

@Override

public void onStartup(ServletContext container) throws ServletException {

logger.info("Starting container......");

AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();

context.register(WebAppConfig.class);

context.setServletContext(container);

context.refresh();

ServletRegistration.Dynamic dispatcher = container.addServlet("dispatcher", new DispatcherServlet(context));

dispatcher.setLoadOnStartup(1);

dispatcher.addMapping("/");

FilterRegistration.Dynamic filter = container.addFilter("encoding", CharacterEncodingFilter.class);

filter.setInitParameter("encoding", "UTF-8");

filter.addMappingForServletNames(EnumSet.allOf(DispatcherType.class), true, "dispatcher");

}

这是 Seervlet 3 才有的特性，在 Spring-Web 项目中有一个实现了 Servlet3 ServletContainerInitializer 接口的类 SpringServletContainerInitializer, 它会在 Spring 容器启动时扫描 WebApplicationInitializer 的所有实现类，并调用它们的 onStartup 文件。由此才实现了免 web.xml 文件配置 servlet 的方式。

SpringServletContainerInitializer 是以 SPI 的方式加载的，定义在 spring-web 包中，见下图

并且这个 WebInitializer 把 Spring 的上下文 AnnotationConfigWebApplicationContext 与 Servlet 容器上下文 ServletContext 关联起来了。注册了 Spring 本身的 Java 配置 WebAppConfig 类。创建了 / 到 dispatcher servlet 的映射。

WebAppConfig 类

package config;

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

@EnableWebMvc
@ComponentScan(basePackages = {"controller"})
public class WebAppConfig {

}

package config;

import org.springframework.context.annotation.ComponentScan;

import org.springframework.web.servlet.config.annotation.EnableWebMvc;

@EnableWebMvc

@ComponentScan(basePackages = {"controller"})

public class WebAppConfig {

}

这个类对于当前实例来说没多少内容，主要就是 EnableWebMvc 启用 SpringMVC 特性，并指示 Spring 上下文扫描 controller 包。因为该例只用一个 controller 来进行演示，未涉及到 service, model 等内容。

UserController 类

package controller;

import com.google.common.collect.ImmutableMap;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import java.util.Map;

@RestController
@RequestMapping("/users")
public class UserController {

    @RequestMapping(value="/{userId}", method= RequestMethod.GET)
    public Map<String, Object> getUserInfo(@PathVariable("userId") Integer userId) {
        return ImmutableMap.of("UserId", userId, "Name", "Yanbin");
    }
}

package controller;

import com.google.common.collect.ImmutableMap;

import org.springframework.web.bind.annotation.PathVariable;

import org.springframework.web.bind.annotation.RequestMapping;

import org.springframework.web.bind.annotation.RequestMethod;

import org.springframework.web.bind.annotation.RestController;

import java.util.Map;

@RestController

@RequestMapping("/users")

public class UserController {

@RequestMapping(value="/{userId}", method= RequestMethod.GET)

public Map<String, Object> getUserInfo(@PathVariable("userId") Integer userId) {

return ImmutableMap.of("UserId", userId, "Name", "Yanbin");

}

此处注解没什么好说的，普通的 Spring RESTful 的 controller 的注解

测试运行 tomcat

在项目目录下，执行 mvn tomcat7:run 命令

[INFO] --- tomcat7-maven-plugin:2.2:run (default-cli) @ springmvc ---
[INFO] Running war on http://localhost:8080/springmvc
[INFO] Creating Tomcat server configuration at /Users/yanbin/workspace/springmvc/target/tomcat
[INFO] create webapp with contextPath: /springmvc
Apr 30, 2018 7:54:04 AM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8080"]
Apr 30, 2018 7:54:04 AM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Tomcat
Apr 30, 2018 7:54:04 AM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.47
Apr 30, 2018 7:54:06 AM org.apache.catalina.core.ApplicationContext log
INFO: 1 Spring WebApplicationInitializers detected on classpath
2018-04-30 07:54:06 [localhost-startStop-1] INFO WebInitializer - Starting container......
2018-04-30 07:54:06 [localhost-startStop-1] INFO AnnotationConfigWebApplicationContext - Refreshing Root WebApplicationContext: startup date [Mon Apr 30 07:54:06 CDT 2018]; root of context hierarchy
2018-04-30 07:54:06 [localhost-startStop-1] INFO AnnotationConfigWebApplicationContext - Registering annotated classes: [class config.WebAppConfig]
2018-04-30 07:54:06 [localhost-startStop-1] INFO AutowiredAnnotationBeanPostProcessor - JSR-330 'javax.inject.Inject' annotation found and supported for autowiring
2018-04-30 07:54:07 [localhost-startStop-1] INFO RequestMappingHandlerMapping - Mapped "{[/users/{userId}],methods=[GET]}" onto public java.util.Map<java.lang.String, java.lang.Object> controller.UserController.getUserInfo(java.lang.Integer)
2018-04-30 07:54:07 [localhost-startStop-1] INFO RequestMappingHandlerAdapter - Looking for @ControllerAdvice: Root WebApplicationContext: startup date [Mon Apr 30 07:54:06 CDT 2018]; root of context hierarchy
Apr 30, 2018 7:54:07 AM org.apache.catalina.core.ApplicationContext log
INFO: Initializing Spring FrameworkServlet 'dispatcher'
2018-04-30 07:54:07 [localhost-startStop-1] INFO DispatcherServlet - FrameworkServlet 'dispatcher': initialization started
2018-04-30 07:54:07 [localhost-startStop-1] INFO DispatcherServlet - FrameworkServlet 'dispatcher': initialization completed in 19 ms
Apr 30, 2018 7:54:07 AM org.apache.coyote.AbstractProtocol start
INFO: Starting ProtocolHandler ["http-bio-8080"]

这样就启动了我们的 SpringMVC 项目，可以测试 http://localhost:8080/springmvc/users/1234

➜ / curl -v http://localhost:8080/springmvc/users/1234
* Trying ::1...
* TCP_NODELAY set
* Connected to localhost (::1) port 8080 (#0)
> GET /springmvc/users/1234 HTTP/1.1
> Host: localhost:8080
> User-Agent: curl/7.54.0
> Accept: */*
>
< HTTP/1.1 200 OK
< Server: Apache-Coyote/1.1
< Content-Type: application/json;charset=UTF-8
< Transfer-Encoding: chunked
< Date: Mon, 30 Apr 2018 13:04:52 GMT
<
* Connection #0 to host localhost left intact
{"UserId":1234,"Name":"Yanbin"}

因为我们在 pom.xml 中引入了 jackson, 所以 Controller 方法返回的对象被自动转换为 JSON 格式的数据

http://localhost:8080/springmvc/ 将会访问到 src/webapp/index.jsp 的内容，如果文件存在的话。

关于响应格式

如果在项目中还引入了 Jackson 的另一个 xml 包

<dependency>
    <groupId>com.fasterxml.jackson.dataformat</groupId>
    <artifactId>jackson-dataformat-xml</artifactId>
    <version>${jackson.version}</version>
</dependency>

<groupId>com.fasterxml.jackson.dataformat</groupId>

<artifactId>jackson-dataformat-xml</artifactId>

<version>${jackson.version}</version>

</dependency>

mvn tomcat7:run 重启 Tomcat, 访问 http://localhost:8080/springmvc/users/1234, 这时候看到输出的是 xml 格式

➜ / curl -v http://localhost:8080/springmvc/users/1234
.......
>
< HTTP/1.1 200 OK
< Server: Apache-Coyote/1.1
< Content-Type: application/xml;charset=UTF-8
< Transfer-Encoding: chunked
< Date: Mon, 30 Apr 2018 13:06:47 GMT
<
* Connection #0 to host localhost left intact
<Map><UserId>1234</UserId><Name>Yanbin</Name></Map>

那么在这种情况下如何再次获得 JSON 的响应数据呢？有三种办法

请求时指定响应头

➜ / curl -H "Accept:application/json" http://localhost:8080/springmvc/users/1234
{"UserId":1234,"Name":"Yanbin"}

@RequestMapping 指定 produces

Controller 类或方法上指定 @RequestMapping 的 produces 属性为 json, 例如

@RequestMapping(value = "/users", produces = "application/json")
//或
@RequestMapping(value="/{userId}", method=RequestMethod.GET, produces = "application/json")

这时候不带 Accept 头默认的响应就是 JSON 了

借助于 WebMvcConfigurerAdapter 设置默认的响应类型

修改前面的 WebAppConfig 类的内容如下

@EnableWebMvc
@ComponentScan(basePackages = {"controller"})
public class WebAppConfig extends WebMvcConfigurerAdapter {

    @Override
    public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
        configurer.defaultContentType(MediaType.APPLICATION_JSON_UTF8);
    }

}

@EnableWebMvc

@ComponentScan(basePackages = {"controller"})

public class WebAppConfig extends WebMvcConfigurerAdapter {

@Override

public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {

configurer.defaultContentType(MediaType.APPLICATION_JSON_UTF8);

}

如果在 Controller 或请求头中没有特别说明默认输出 JSON 格式响应。也就是说这时候请求头中如果要求得到 XML 格式的数据还是没问题的。

➜ / curl -H "Accept:text/xml" http://localhost:8080/springmvc/users/1234
<Map><UserId>1234</UserId><Name>Yanbin</Name></Map>

链接：

Spring MVC Hello World 例子(web.xml 和 dispatcher-servlet.xml 方式)
Spring 4 MVC Tutorial Maven Example - Spring Java Configuration

本文链接 https://yanbin.blog/basic-spring-4-mvc-maven-project/, 来自隔叶黄莺 Yanbin Blog

1 Comment

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zhangwugui

6 years ago

老哥的文章总是浅显易懂，佩服，希望老哥多多更博，已加入书签。

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