springboot学习之HelloWorld

springboot是一个全新的框架，被设计用来简化spring的配置。我们知道，以前我们使用spring来做开发时，需要做很多模板化的配置来完成基础功能的搭建，就算是一个很小的项目，也需要进行很多必需的配置才能使用spring的功能，显然这受到很多spring使用者的吐槽！！！那springboot的出现就是用来解决这个问题的，springboot框架使用自己独特的方式进行配置，使开发人员不再需要做模板化的配置，将所有的关注点全部集中在功能开发，所有的配置都交给springboot来完成。
下面我们来完成一个springboot版的hellowold
1.引入springboot相关依赖

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.0.0.RELEASE</version>
    <relativePath/> 
</parent>

开发Web程序需要用到spring-boot-starter-web包

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

下面是Java代码：

package com.example.demo;

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

@RestController
@EnableAutoConfiguration
public class SpringbootexampleApplication {

    @RequestMapping("/")
    String index(){
        return "HelloWorld!";
    }

    public static void main(String[] args) {
        SpringApplication.run(SpringbootexampleApplication.class, args);
    }
}

@RestController 表示该类是一个Web Controller，可以用来接收Web请求
@EnableAutoConfiguration 表示开启springboot的自动配置功能，springboot会“猜测”你可能会用到哪些jar包，并且自动引入。比如，本例中加入spring-boot-starter-web依赖包，springboot就会自动引入tomcat、springMVC相关的jar包，并自动进行Web项目相关配置

本例中有main方法，可以像运行普通的Java main方法一样运行springboot，springboot提供SpringApplication.run()方法来启动应用程序

运行结果如下:

  .   ____          _            __ _ _
 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.0.RELEASE)

2018-03-21 21:22:31.310  INFO 11596 --- [           main] c.e.demo.SpringbootexampleApplication    : Starting SpringbootexampleApplication on PC-PZJ with PID 11596 (E:\workspace\springbootexample\target\classes started by arno.peng in E:\workspace\springbootexample)
2018-03-21 21:22:31.326  INFO 11596 --- [           main] c.e.demo.SpringbootexampleApplication    : No active profile set, falling back to default profiles: default
2018-03-21 21:22:31.451  INFO 11596 --- [           main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@b7f23d9: startup date [Wed Mar 21 21:22:31 CST 2018]; root of context hierarchy
2018-03-21 21:22:33.263  INFO 11596 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2018-03-21 21:22:33.295  INFO 11596 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
....
...中间部分省略
...
org.springframework.boot.autoconfigure.web.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest)
2018-03-21 21:22:33.935  INFO 11596 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Started SpringbootexampleApplication in 3.547 seconds (JVM running for 5.034)
2018-03-21 21:22:47.758  INFO 11596 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring FrameworkServlet 'dispatcherServlet'
2018-03-21 21:22:47.758  INFO 11596 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization started
2018-03-21 21:22:47.778  INFO 11596 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization completed in 20 ms

从启动信息中，我们可以看到，springboot会默认帮我们启动内置的tomcat容器，端口号是8080
访问：http://localhost:8080/
这里写图片描述

可以看到，我们并没有进行任何的配置，就可以完整的运行起来，这就是springboot的零配置！

springboot还支持java -jar的方式来运行，一般生产环境会使用这种方式来运行
首先在pom.xml文件中加入maven插件的支持

<build>
    <plugins>
        <plugin>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-maven-plugin</artifactId>
        </plugin>
    </plugins>
</build>

然后在命令行执行打包命令

$ mvn package

打包成功后，会显示如下的信息：

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[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building springbootexample 0.0.1-SNAPSHOT
[INFO] ------------------------------------------------------------------------

......中间部分省略

[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 3:58.358s
[INFO] Finished at: Thu Mar 22 21:31:43 CST 2018
[INFO] Final Memory: 24M/88M
[INFO] ------------------------------------------------------------------------

此时，在你项目的target目录下会生成对应的jar文件，这就是可以直接运行的jar文件，里面包含项目所有的依赖以及内嵌的tomcat容器
执行命令

java -jar springbootexample-0.0.1-SNAPSHOT.jar

会出现跟我们之前直接运行一样的输出：

 /\\ / ___'_ __ _ _(_)_ __  __ _ \ \ \ \
( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
 \\/  ___)| |_)| | | | | || (_| |  ) ) ) )
  '  |____| .__|_| |_|_| |_\__, | / / / /
 =========|_|==============|___/=/_/_/_/
 :: Spring Boot ::        (v2.0.0.RELEASE)

2018-03-22 21:38:25.026  INFO 2268 --- [           main] c.e.demo.SpringbootexampleApplication    : Starting SpringbootexampleApplication v0.0.1-SNAPSHOT on PC-PZJ with PID 2268 (E:\workspace\springbootexample\target\springbootexample-0.0.1-SNAPSHOT.jar started by arno.peng in E:\workspace\springbootexample\target)
2018-03-22 21:38:25.032  INFO 2268 --- [           main] c.e.demo.SpringbootexampleApplication    : No active profile set, falling back to default profiles: default
2018-03-22 21:38:25.148  INFO 2268 --- [           main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@75828a0f: startup date [Thu Mar 22 21:38:25 CST 2018]; root of context hierarchy
2018-03-22 21:38:27.725  INFO 2268 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat initialized with port(s): 8080 (http)
2018-03-22 21:38:27.776  INFO 2268 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2018-03-22 21:38:27.776  INFO 2268 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.28
.....
中间部分省略
.....
2018-03-22 21:38:29.188  INFO 2268 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-22 21:38:29.189  INFO 2268 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-22 21:38:29.262  INFO 2268 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2018-03-22 21:38:29.530  INFO 2268 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2018-03-22 21:38:29.623  INFO 2268 --- [           main] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2018-03-22 21:38:29.629  INFO 2268 --- [           main] c.e.demo.SpringbootexampleApplication    : Started SpringbootexampleApplication in 5.29 seconds (JVM running for 6.002)

此时，在浏览器输入 http://localhost:8080 会得到同样的输出

springboot学习之HelloWorld

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