SpringBoot入门1—简介及helloworld

Spring Boot简介

Spring Boot让我们的Spring应用变的更轻量化。比如：你可以仅仅依靠一个Java类来运行一个Spring引用。你也可以打包你的应用为jar并通过使用java -jar来运行你的Spring Web应用。

Spring Boot的主要优点：

• 为所有Spring开发者更快的入门
• 开箱即用，提供各种默认配置来简化项目配置
• 内嵌式容器简化Web项目
• 没有冗余代码生成和XML配置的要求

用Spring Boot编写helloworld

1.首先创建一个maven项目

2.添加Spring Boot依赖

通常，让你的Maven POM文件继承 spring-boot-starter-parent，并声明一个或多个 Starter POMs依赖即可。

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.5.4.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
  </parent>

  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding>
    <java.version>1.8</java.version>
  </properties>

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

    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-test</artifactId>
      <scope>test</scope>
    </dependency>

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

3.创建java类，编写helloworld代码

package com.xzh.demo;

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

@RestController
@SpringBootApplication
public class DemoApplication {

    @RequestMapping("/hello")
    public String index() {
        return "Hello World!!!";
    }

    public static void main(String[] args) {
        SpringApplication.run(com.xzh.demo.DemoApplication.class, args);
    }
}

核心注解类说明

@RestController

就是@Controller+@ResponseBody组合，支持RESTful访问方式，返回结果都是json字符串

@SpringBootApplication

就是@SpringBootConfiguration+@EnableAutoConfiguration+ @ComponentScan等组合在一起，非常简单，使用也方便

@EnableAutoConfiguration注解

这个注解告诉Spring Boot“猜测”将如何配置Spring。@EnableAutoConfiguration是借助@Import的帮助，将所有符合自动配置条件的bean定义加载到IoC容器。

@ComponentScan

用注解配置实现自动扫描，默认会扫描当前包和所有子包,并加载符合条件的组件(比如@Component和@Repository等)，和xml配置自动扫描效果一样

@SpringBootConfiguration

说明这是一个配置文件类(SpringBoot社区推荐使用基于JavaConfig的配置形式)

4.运行创建的java类

2017-07-21 16:18:35.787  INFO 19984 --- [           main] com.xzh.demo.DemoApplication             : Starting DemoApplication on LAPTOP-T56QDVQ2 with PID 19984 (F:workspaceIDEAhelloworld	argetclasses started by lenovo in F:workspaceIDEAhelloworld)
2017-07-21 16:18:35.789  INFO 19984 --- [           main] com.xzh.demo.DemoApplication             : No active profile set, falling back to default profiles: default
2017-07-21 16:18:35.837  INFO 19984 --- [           main] ationConfigEmbeddedWebApplicationContext : Refreshing org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@8646db9: startup date [Fri Jul 21 16:18:35 CST 2017]; root of context hierarchy
2017-07-21 16:18:37.293  INFO 19984 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat initialized with port(s): 8080 (http)
2017-07-21 16:18:37.305  INFO 19984 --- [           main] o.apache.catalina.core.StandardService   : Starting service [Tomcat]
2017-07-21 16:18:37.306  INFO 19984 --- [           main] org.apache.catalina.core.StandardEngine  : Starting Servlet Engine: Apache Tomcat/8.5.15
2017-07-21 16:18:37.375  INFO 19984 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring embedded WebApplicationContext
2017-07-21 16:18:37.375  INFO 19984 --- [ost-startStop-1] o.s.web.context.ContextLoader            : Root WebApplicationContext: initialization completed in 1542 ms
2017-07-21 16:18:37.477  INFO 19984 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean  : Mapping servlet: 'dispatcherServlet' to [/]
2017-07-21 16:18:37.481  INFO 19984 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'characterEncodingFilter' to: [/*]
2017-07-21 16:18:37.481  INFO 19984 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'hiddenHttpMethodFilter' to: [/*]
2017-07-21 16:18:37.481  INFO 19984 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'httpPutFormContentFilter' to: [/*]
2017-07-21 16:18:37.481  INFO 19984 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean   : Mapping filter: 'requestContextFilter' to: [/*]
2017-07-21 16:18:37.735  INFO 19984 --- [           main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext@8646db9: startup date [Fri Jul 21 16:18:35 CST 2017]; root of context hierarchy
2017-07-21 16:18:37.769  INFO 19984 --- [           main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/hello]}" onto public java.lang.String com.xzh.demo.DemoApplication.index()
2017-07-21 16:18:37.772  INFO 19984 --- [           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)
2017-07-21 16:18:37.772  INFO 19984 --- [           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)
2017-07-21 16:18:37.789  INFO 19984 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-07-21 16:18:37.789  INFO 19984 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-07-21 16:18:37.810  INFO 19984 --- [           main] o.s.w.s.handler.SimpleUrlHandlerMapping  : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler]
2017-07-21 16:18:37.887  INFO 19984 --- [           main] o.s.j.e.a.AnnotationMBeanExporter        : Registering beans for JMX exposure on startup
2017-07-21 16:18:37.916  INFO 19984 --- [           main] s.b.c.e.t.TomcatEmbeddedServletContainer : Tomcat started on port(s): 8080 (http)
2017-07-21 16:18:37.919  INFO 19984 --- [           main] com.xzh.demo.DemoApplication             : Started DemoApplication in 2.324 seconds (JVM running for 2.719)
2017-07-21 16:18:41.874  INFO 19984 --- [nio-8080-exec-1] o.a.c.c.C.[Tomcat].[localhost].[/]       : Initializing Spring FrameworkServlet 'dispatcherServlet'
2017-07-21 16:18:41.874  INFO 19984 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization started
2017-07-21 16:18:41.883  INFO 19984 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet        : FrameworkServlet 'dispatcherServlet': initialization completed in 9 ms

5.访问http://localhost:8080/hello

参考：

Spring Boot 官方文档学习（一）入门及使用

Spring Boot学习

Spring Boot应用程序开发入门

Spring Boot快速入门

Spring Boot参考指南