一起學JAVA之《spring boot》02-開發您的第一個Spring Boot應用程序

一、導航

本節內容簡介：
1. 開發之前環境檢查
2. 創建pom.xml並導入依賴
3. 編寫代碼
4. 代碼解釋
5. 運行代碼
6. 創建可執行的jar

二、開發之前環境檢查

讓我們在Java中開發一個簡單的 Hello World 的Web應用程序，來介紹Spring Boot一些主要的功能。
這裏將使用Maven構建該項目。

在開始之前，打開終端（windwos cmd）來驗證java版本和maven版本

C:\Users\SEELE>java -version
java version "1.8.0_121"
Java(TM) SE Runtime Environment (build 1.8.0_121-b13)
Java HotSpot(TM) 64-Bit Server VM (build 25.121-b13, mixed mode)

這裏要注意檢查maven版本不是maven -v,而是mvn -v

C:\Users\SEELE>mvn -v
Apache Maven 3.2.5 (12a6b3acb947671f09b81f49094c53f426d8cea1...

三、創建pom.xml並導入依賴

使用idea創建一個maven項目，並添加maven 父類依賴

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.likeoak</groupId>
    <artifactId>springboot</artifactId>
    <version>1.0.0</version>

    <!--添加父類依賴-->
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.2.RELEASE</version>
    </parent>

</project>

添加web依賴


 <!--web依賴-->
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
    </dependencies>

四、編寫代碼

默認情況下，Maven將從src/main/java編譯源代碼，因此您需要創建該文件夾結構，然後添加一個名爲src/main/java/Example.java的文件：
注意：官方建議不要使用默認的default包來創建啓動類，這樣會導致所有的包都會被掃描，包括jar


package com.likeoak;


import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

/**
 * The type Spring boot example.
 */
RestController
@EnableAutoConfiguration
public class SpringBootExample {

    @RequestMapping("/")
    String home() {
        return "Hello World!";
    }
    public static void main(String[] args) throws Exception {
        SpringApplication.run(SpringBootExample.class, args);
    }


}

五、代碼解釋

儘管以上代碼不多，但是卻發生很多事情，讓我們一步一步來解釋吧

1. 註解解釋
上面一共用了三個註解 @RestController ,@RequestMapping, @EnableAutoConfiguration

@RestController是一個被稱爲構造性（stereotype）的註解，它表示的意思是是一個REST風格的Controller
@RequestMapping 這個註解是提供路由信息，所有HTTP的 “/”這個請求都會被這個home方法捕獲，這個和@RestController一起的意思是，當訪問”/”這個路徑的時候，就以字符串的形式返回”Hello World!”

@EnableAutoConfiguration 這個註解的意思是告訴spring boot 根據你配置的jar來猜測你想如何配置spring
這裏我們配置了spring-boot-starter-web這個jar,spring boot 就會爲我們自動配置tomcat和SprngMVC的相關配置
,可以參考下面spring-boot-starter-web依賴包,看到裏面有springMVC和tomcat的引用

附spring-boot-starter-web依賴包

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starters</artifactId>
        <version>1.5.2.RELEASE</version>
    </parent>
    <artifactId>spring-boot-starter-web</artifactId>
    <name>Spring Boot Web Starter</name>
    <description>Starter for building web, including RESTful, applications using Spring
        MVC. Uses Tomcat as the default embedded container</description>
    <url>http://projects.spring.io/spring-boot/</url>
    <organization>
        <name>Pivotal Software, Inc.</name>
        <url>http://www.spring.io</url>
    </organization>
    <properties>
        <main.basedir>${basedir}/../..</main.basedir>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-tomcat</artifactId>
        </dependency>
        <dependency>
            <groupId>org.hibernate</groupId>
            <artifactId>hibernate-validator</artifactId>
        </dependency>
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
        </dependency>
    </dependencies>
</project>

附spring-boot-starter-tomcat依賴

<?xml version="1.0" encoding="UTF-8"?>
<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/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starters</artifactId>
        <version>1.5.2.RELEASE</version>
    </parent>
    <artifactId>spring-boot-starter-tomcat</artifactId>
    <name>Spring Boot Tomcat Starter</name>
    <description>Starter for using Tomcat as the embedded servlet container. Default
        servlet container starter used by spring-boot-starter-web</description>
    <url>http://projects.spring.io/spring-boot/</url>
    <organization>
        <name>Pivotal Software, Inc.</name>
        <url>http://www.spring.io</url>
    </organization>
    <properties>
        <main.basedir>${basedir}/../..</main.basedir>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-core</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-el</artifactId>
        </dependency>
        <dependency>
            <groupId>org.apache.tomcat.embed</groupId>
            <artifactId>tomcat-embed-websocket</artifactId>
        </dependency>
    </dependencies>
</project>

2. main方法
main方法是一個java標準入口方法。這裏main方法通過調用runm,將業務委託給了 Spring Boot的 SpringApplication 類。SpringApplication將引導我們啓動spring,相應的啓動被自動配置的tomcat web服務器，這裏我們需要將主類 SpringBootExample作爲參數傳給run方法，告訴spring boot 那個是主類，並傳遞args參數給 spring boot,對於這個args參數，我們後續會講解.

六、運行代碼

直接運行main方法

運行結果：

                     .__  .__ __                       __
__  _  ____  _  ____  _  __  |  | |__|  | __ ____  _________  |  | __     ____  ____   _____
\ \/ \/ /\ \/ \/ /\ \/ \/ /  |  | |  |  |/ // __ \/  _ \__  \ |  |/ /   _/ ___\/  _ \ /     \
 \     /  \     /  \     /   |  |_|  |    <\  ___(  <_> ) __ \|    <    \  \__(  <_> )  Y Y  \
  \/\_/    \/\_/    \/\_/ /\ |____/__|__|_ \\___  >____(____  /__|_ \ /\ \___  >____/|__|_|  /
                          \/              \/    \/          \/     \/ \/     \/            \/
2017-06-25 18:58:59.061  INFO 10640 --- [           main] com.likeoak.SpringBootExample            : Starting SpringBootExample on SEELE-PC with PID 10640 (G:\Mybook\springBoot\target\classes started by SEELE in G:\Mybook\springBoot)
2017-06-25 18:58:59.065  INFO 10640 --- [           main] com.likeoak.SpringBootExample            : No active profile set, falling back to default profiles: default
2017-06-25 18:58:59.107  INFO 10640 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@6b8ca3c8: startup date [Sun Jun 25 18:58:59 CST 2017]; root of context hierarchy
2017-06-25 18:59:00.581  INFO 10640 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2017-06-25 18:59:00.597  INFO 10640 --- [           main] o.apache.catalina.core.StandardService   : Starting service Tomcat
2017-06-25 18:59:00.598  INFO 10640 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.11
2017-06-25 18:59:00.748  INFO 10640 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2017-06-25 18:59:00.748  INFO 10640 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1645 ms
2017-06-25 18:59:00.900  INFO 10640 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Mapping servlet: 'dispatcherServlet' to [/]
2017-06-25 18:59:00.904  INFO 10640 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2017-06-25 18:59:00.905  INFO 10640 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2017-06-25 18:59:00.905  INFO 10640 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2017-06-25 18:59:00.906  INFO 10640 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2017-06-25 18:59:01.247  INFO 10640 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@6b8ca3c8: startup date [Sun Jun 25 18:58:59 CST 2017]; root of context hierarchy
2017-06-25 18:59:01.337  INFO 10640 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/]}" onto java.lang.String com.likeoak.SpringBootExample.home()
2017-06-25 18:59:01.342  INFO 10640 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error]}" onto public org.springframework.http.ResponseEntity<java.util.Map<java.lang.String, java.lang.Object>> org.springframework.boot.autoconfigure.web.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2017-06-25 18:59:01.342  INFO 10640 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/error],produces=[text/html]}" onto public org.springframework.web.servlet.ModelAndView org.springframework.boot.autoconfigure.web.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse)
2017-06-25 18:59:01.376  INFO 10640 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-06-25 18:59:01.376  INFO 10640 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-06-25 18:59:01.452  INFO 10640 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-06-25 18:59:01.669  INFO 10640 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2017-06-25 18:59:01.760  INFO 10640 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2017-06-25 18:59:01.764  INFO 10640 --- [           main] com.likeoak.SpringBootExample            : Started SpringBootExample in 3.182 seconds (JVM running for 3.816)

然後訪問 http://localhost:8080/
結果：
Hello World!

七、創建可執行的jar

這裏通過maven插件來實現，在pom.xml中引入spring-boot-maven-plugin

  <!-- 可執行jar-->
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

執行mvn package

[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building springboot 1.0.0
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-resources-plugin:2.6:resources (default-resources) @ springboot ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] Copying 0 resource
[INFO] Copying 1 resource
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:compile (default-compile) @ springboot ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-resources-plugin:2.6:testResources (default-testResources) @ springboot ---
[INFO] Using 'UTF-8' encoding to copy filtered resources.
[INFO] skip non existing resourceDirectory G:\Mybook\springBoot\src\test\resources
[INFO] 
[INFO] --- maven-compiler-plugin:3.1:testCompile (default-testCompile) @ springboot ---
[INFO] Nothing to compile - all classes are up to date
[INFO] 
[INFO] --- maven-surefire-plugin:2.18.1:test (default-test) @ springboot ---
[INFO] No tests to run.
[INFO] 
[INFO] --- maven-jar-plugin:2.6:jar (default-jar) @ springboot ---
[INFO] 
[INFO] --- spring-boot-maven-plugin:1.5.2.RELEASE:repackage (default) @ springboot ---
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 1.790 s
[INFO] Finished at: 2017-06-25T19:47:08+08:00
[INFO] Final Memory: 19M/226M
[INFO] ------------------------------------------------------------------------

打包之後，再target下面會出現spring-1.0.0.jar包

運行：
java -jar spring-1.0.0.jar

後續會繼續推出這一系列spring boot的文章

本人網站：一起學JAVA

一起學JAVA之《spring boot》02-開發您的第一個Spring Boot應用程序

一、導航

二、開發之前環境檢查

三、創建pom.xml並導入依賴

四、編寫代碼

五、代碼解釋

六、運行代碼

七、創建可執行的jar

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一起學JAVA之《spring boot》02-開發您的第一個Spring Boot應用程序

一、導航

二、開發之前環境檢查

三、創建pom.xml並導入依賴

四、編寫代碼

五、代碼解釋

六、運行代碼

七、 創建可執行的jar

七、創建可執行的jar