Springboot(一)------springboot入门

xiaoxiao2021-02-28 29

一、springboot简介

1.1springboot介绍

springboot的目的在于创建和启动新的基于spring框架的项目。springboot会选择最适合spring子项目和第三方开源库进行整合。大部分springboot应用只需要非常少的配置就可以快速运行起来。

springboot是伴随spring4诞生的，它提供了一种快速使用spring的方式。

1.2 spring特点

（1）为基于spring的开发提供更快的入门体验

（2）创建可以独立运行的spring应用

（3）可以嵌入tomcat或jetty服务器，不需要打包成war文件

（4）提供推荐的基础pom文件（start）来简化Apache Maven的配置

（5）竟可能的根据项目依赖来自动配置spring框架

（6）提供可以直接在生产环境中使用的功能如性能指标应用信息和应用健康检查

（7）开箱即用，没有代码生产也无需xml配置，同时也可以修改默认值来满足特定的需求

（8）其他大量的项目都是基于springboot之上，如springcloud

1.3springboot缺点

（1）依赖太多，随便的一个springboot应用都有好几十M

（2）缺少服务的注册和发现等解决方案

（3）缺少监控集成方案，安全管理方案

1.4 spring应用场景

（1）spring能应用场景

（2）Javaweb应用

（3）微服务

二 spring 的Java配置Demo

从Spring3.x开始提供了Java配置方式，使用Java配置方式可以更好的理解你配置的Bean，现在我们就处于这个时代，并且Spring4.x和Spring boot都推荐使用java配置的方式.

Java配置是Spring4.x推荐的配置方式，可以完全替代xml配置。

2.1 创建一个maveng工程springboot-demo-01，选择war类型（web应用）

2.2 导入依赖pom文件如下

<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.itcast.springboot</groupId> <artifactId>springboot-demo-01</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>war</packaging> <dependencies>  <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>5.0.4.RELEASE</version> </dependency>  <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>5.0.4.RELEASE</version> </dependency>     <dependency> <groupId>com.alibaba</groupId> <artifactId>druid</artifactId> <version>1.1.9</version> </dependency> </dependencies> <build> <finalName>${project.artifactId}</finalName> <plugins>  <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-resources-plugin</artifactId> <configuration> <source>${jdk.version}</source> <target>${jdk.version}</target> <encode>${project.build.sourceEncoding}</encode> </configuration> </plugin>  <plugin> <groupId>org.apache.maven.plugins</groupId> <artifactId>maven-compiler-plugin</artifactId> <version>3.7.0</version> <configuration> <source>${jdk.version}</source> <target>${jdk.version}</target> <encode>${project.build.sourceEncoding}</encode> </configuration> </plugin> </plugins> </build> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> </properties> </project>

2.3创建一个User对象

package com.itcast.springboot.javaconfig; public class User { private String username; private String password; private Integer age; public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public Integer getAge() { return age; } public void setAge(Integer age) { this.age = age; } @Override public String toString() { return "User [username=" + username + ", password=" + password + ", age=" + age + "]"; } }

2.4 编写UserDAO用于模拟与数据库的交互

package com.itcast.springboot.javaconfig; import java.util.ArrayList; import java.util.List; public class UserDAO { public List<User> queryUserList(){ List<User> list=new ArrayList<User>(); for(int i=0;i<10;i++){ User user=new User(); user.setUsername("username_"+(i+1)); user.setPassword("password_"+(i+1)); user.setAge(i+1); list.add(user); } return list; } }

2.5 编写UserService

package com.itcast.springboot.javaconfig; import java.util.List; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.stereotype.Service; //import org.springframework.beans.factory.annotation.Autowired; @Service public class UserService { //注入spring容器的bean对象 @Autowired private UserDAO dao; public List<User> queryUserList(){ return dao.queryUserList(); } }

2.6编写springConfig用于实例化spring容器

package com.itcast.springboot.javaconfig; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.Configuration; /** * * @author jack * */ @Configuration//通过该注解来表明该类是一个spring的配置，相当于一个xml @ComponentScan(basePackages="com.itcast.springboot.javaconfig") public class SpringConfig { //通过该注解来表明是一个bean对象相当于xml中的bean @Bean public UserDAO getUserDAO(){ return new UserDAO(); } }

2.7编写测试类

package com.itcast.springboot.javaconfig; import java.util.List; import org.springframework.context.annotation.AnnotationConfigApplicationContext; /** * spring的Java配置方式 * @author jack * */ public class Test { public static void main(String[] args) { //通过Java配置来实例化spring容器 AnnotationConfigApplicationContext context=new AnnotationConfigApplicationContext(SpringConfig.class); //获取spring容器中的bean对象 UserService userService=context.getBean(UserService.class); //调用对象中的方法 List<User> list=userService.queryUserList(); for(User user:list){ System.out.println(user); } //销毁容器 context.destroy(); } }

测试结果：

User [username=username_1, password=password_1, age=1] User [username=username_2, password=password_2, age=2] User [username=username_3, password=password_3, age=3] User [username=username_4, password=password_4, age=4] User [username=username_5, password=password_5, age=5] User [username=username_6, password=password_6, age=6] User [username=username_7, password=password_7, age=7] User [username=username_8, password=password_8, age=8] User [username=username_9, password=password_9, age=9] User [username=username_10, password=password_10, age=10]

三 springBoot快速入门

3.1 新建一个springboot-primary-02的maven项目

类型选择war，后面以这个为模板做web.

遇到问题：

使用maven创建web项目时，可能会出现如下错误：

web.xml is missing and <failOnMissingWebXml> is set to true此问题的解决办法：a. 右键点击Project Explorer中的Deployment Descriptorb. 选择Generate Deployment Descriptor Stub,这样就能生成src/main/webapp/WEB_INF/web.xml文件了。

3.2 导入依赖pom文件

<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.itcast</groupId> <artifactId>springboot-primary-02</artifactId> <version>0.0.1-SNAPSHOT</version> <packaging>war</packaging>   <parent> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-parent</artifactId> <version>2.0.1.RELEASE</version> <relativePath />  </parent> <dependencies>   <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency>   <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>5.0.4.RELEASE</version> </dependency>  <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>5.0.4.RELEASE</version> </dependency>  <dependency> <groupId>com.alibaba</groupId> <artifactId>druid</artifactId> <version>1.1.9</version> </dependency>  <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> </dependency> </dependencies> <properties> <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding> <project.reporting.outputEncoding>UTF-8</project.reporting.outputEncoding> <java.version>1.8</java.version> </properties> <build> <plugins>  <plugin> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-maven-plugin</artifactId> <configuration> <source>${jdk.version}</source> <target>${jdk.version}</target> <encode>${project.build.sourceEncoding}</encode> </configuration> </plugin> </plugins> </build> </project>

3.3建立app入口类

package com.itcast; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.context.annotation.Configuration; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.ResponseBody; @Controller @SpringBootApplication @Configuration public class HelloApplication { @RequestMapping("/hello") @ResponseBody public String hello(){ return "hello springBoot!"; } public static void main(String[] args) { SpringApplication.run(HelloApplication.class, args); } }

代码说明：

1、@SpringBootApplication：Spring Boot项目的核心注解，主要目的是开启自动配置。；

2、@Configuration：这是一个配置Spring的配置类；

3、@Controller：标明这是一个SpringMVC的Controller控制器；

4、main方法：在main方法中启动一个应用，即：这个应用的入口；

测试类运行结果：

. ____ _ __ _ _ /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \ ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \ \\/ ___)| |_)| | | | | || (_| | ) ) ) ) ' |____| .__|_| |_|_| |_\__, | / / / / =========|_|==============|___/=/_/_/_/ :: Spring Boot :: (v2.0.1.RELEASE) 2018-05-19 15:58:09.431 INFO 12208 --- [ main] com.itcast.HelloApplication : Starting HelloApplication on jack-PC with PID 12208 (D:\workSpaces\EclipseWorkspace\SpringBoot\springboot-primary-02\target\classes started by jack in D:\workSpaces\EclipseWorkspace\SpringBoot\springboot-primary-02) 2018-05-19 15:58:09.456 INFO 12208 --- [ main] com.itcast.HelloApplication : No active profile set, falling back to default profiles: default 2018-05-19 15:58:09.878 INFO 12208 --- [ main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@55040f2f: startup date [Sat May 19 15:58:09 CST 2018]; root of context hierarchy 2018-05-19 15:58:18.016 INFO 12208 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat initialized with port(s): 8080 (http) 2018-05-19 15:58:18.221 INFO 12208 --- [ main] o.apache.catalina.core.StandardService : Starting service [Tomcat] 2018-05-19 15:58:18.221 INFO 12208 --- [ main] org.apache.catalina.core.StandardEngine : Starting Servlet Engine: Apache Tomcat/8.5.29 2018-05-19 15:58:18.253 INFO 12208 --- [ost-startStop-1] o.a.catalina.core.AprLifecycleListener : The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: [E:\Program Files\Java\jre1.8.0_112\bin;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;E:/Program Files/Java/jre1.8.0_112/bin/server;E:/Program Files/Java/jre1.8.0_112/bin;E:/Program Files/Java/jre1.8.0_112/lib/amd64;D:\orcle\orcle12c\12.1.0\dbhome_1\bin;C:\ProgramData\Oracle\Java\javapath;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;E:\Program Files\Java\jdk1.8.0_112\bin;E:\Program Files\Java\jdk1.8.0_112\jre\bin;E:\Program Files\MySQL\mysql-5.7.16-winx64\bin;E:\Program Files\apache-maven\apache-maven-3.5.3\bin;E:\Program Files\Git\cmd;E:\Program Files\Gradle\gradle-4.7\bin;E:\Program Files\TortoiseGit\bin;E:\Program Files\eclipse;;.] 2018-05-19 15:58:19.048 INFO 12208 --- [ost-startStop-1] o.a.c.c.C.[Tomcat].[localhost].[/] : Initializing Spring embedded WebApplicationContext 2018-05-19 15:58:19.048 INFO 12208 --- [ost-startStop-1] o.s.web.context.ContextLoader : Root WebApplicationContext: initialization completed in 9225 ms 2018-05-19 15:58:19.623 INFO 12208 --- [ost-startStop-1] o.s.b.w.servlet.ServletRegistrationBean : Servlet dispatcherServlet mapped to [/] 2018-05-19 15:58:19.656 INFO 12208 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'characterEncodingFilter' to: [/*] 2018-05-19 15:58:19.657 INFO 12208 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'hiddenHttpMethodFilter' to: [/*] 2018-05-19 15:58:19.657 INFO 12208 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'httpPutFormContentFilter' to: [/*] 2018-05-19 15:58:19.658 INFO 12208 --- [ost-startStop-1] o.s.b.w.servlet.FilterRegistrationBean : Mapping filter: 'requestContextFilter' to: [/*] 2018-05-19 15:58:20.190 INFO 12208 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**/favicon.ico] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler] 2018-05-19 15:58:21.325 INFO 12208 --- [ main] s.w.s.m.m.a.RequestMappingHandlerAdapter : Looking for @ControllerAdvice: org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@55040f2f: startup date [Sat May 19 15:58:09 CST 2018]; root of context hierarchy 2018-05-19 15:58:21.558 INFO 12208 --- [ main] s.w.s.m.m.a.RequestMappingHandlerMapping : Mapped "{[/hello]}" onto public java.lang.String com.itcast.HelloApplication.hello() 2018-05-19 15:58:21.574 INFO 12208 --- [ 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.servlet.error.BasicErrorController.error(javax.servlet.http.HttpServletRequest) 2018-05-19 15:58:21.576 INFO 12208 --- [ 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.servlet.error.BasicErrorController.errorHtml(javax.servlet.http.HttpServletRequest,javax.servlet.http.HttpServletResponse) 2018-05-19 15:58:21.637 INFO 12208 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/webjars/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler] 2018-05-19 15:58:21.637 INFO 12208 --- [ main] o.s.w.s.handler.SimpleUrlHandlerMapping : Mapped URL path [/**] onto handler of type [class org.springframework.web.servlet.resource.ResourceHttpRequestHandler] 2018-05-19 15:58:22.069 INFO 12208 --- [ main] o.s.j.e.a.AnnotationMBeanExporter : Registering beans for JMX exposure on startup 2018-05-19 15:58:22.310 INFO 12208 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8080 (http) with context path '' 2018-05-19 15:58:22.334 INFO 12208 --- [ main] com.itcast.HelloApplication : Started HelloApplication in 14.969 seconds (JVM running for 18.124)

在Spring Boot项目中，启动的方式有两种，一种是直接run Java Application另外一种是通过Spring Boot的Maven插件运行。

第一种：run as Java Application

第二种：

这个是插件启动

4 springboot的核心

4.1 springboot 入口类和@springbootApplication

Spring Boot的项目一般都会有*Application的入口类，入口类中会有main方法，这是一个标准的Java应用程序的入口方法。

@SpringBootApplication注解是Spring Boot的核心注解，它其实是一个组合注解：

* Copyright 2012-2017 the original author or authors. package org.springframework.boot.autoconfigure; import java.lang.annotation.Documented; import java.lang.annotation.ElementType; import java.lang.annotation.Inherited; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; import org.springframework.boot.SpringBootConfiguration; import org.springframework.boot.context.TypeExcludeFilter; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.ComponentScan; import org.springframework.context.annotation.ComponentScan.Filter; import org.springframework.context.annotation.Configuration; import org.springframework.context.annotation.FilterType; import org.springframework.core.annotation.AliasFor; /** * Indicates a {@link Configuration configuration} class that declares one or more * {@link Bean @Bean} methods and also triggers {@link EnableAutoConfiguration * auto-configuration} and {@link ComponentScan component scanning}. This is a convenience * annotation that is equivalent to declaring {@code @Configuration}, * {@code @EnableAutoConfiguration} and {@code @ComponentScan}. * * @author Phillip Webb * @author Stephane Nicoll * @since 1.2.0 */ @Target(ElementType.TYPE) @Retention(RetentionPolicy.RUNTIME) @Documented @Inherited @SpringBootConfiguration @EnableAutoConfiguration @ComponentScan(excludeFilters = { @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class), @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) }) public @interface SpringBootApplication { /** * Exclude specific auto-configuration classes such that they will never be applied. * @return the classes to exclude */ @AliasFor(annotation = EnableAutoConfiguration.class) Class<?>[] exclude() default {}; /** * Exclude specific auto-configuration class names such that they will never be * applied. * @return the class names to exclude * @since 1.3.0 */ @AliasFor(annotation = EnableAutoConfiguration.class) String[] excludeName() default {}; /** * Base packages to scan for annotated components. Use {@link #scanBasePackageClasses} * for a type-safe alternative to String-based package names. * @return base packages to scan * @since 1.3.0 */ @AliasFor(annotation = ComponentScan.class, attribute = "basePackages") String[] scanBasePackages() default {}; /** * Type-safe alternative to {@link #scanBasePackages} for specifying the packages to * scan for annotated components. The package of each class specified will be scanned. * <p> * Consider creating a special no-op marker class or interface in each package that * serves no purpose other than being referenced by this attribute. * @return base packages to scan * @since 1.3.0 */ @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses") Class<?>[] scanBasePackageClasses() default {}; }

a. @SpringBootConfiguration：这是Spring Boot项目的配置注解，这也是一个组合注解

在Spring Boot项目中推荐使用@ SpringBootConfiguration替代@Configuration

b. @EnableAutoConfiguration：启用自动配置，该注解会使SpringBoot根据项目中依赖的jar包自动配置项目的配置项：

如：我们添加了spring-boot-starter-web的依赖，项目中也就会引入SpringMVC的依赖，Spring Boot就会自动配置tomcat和SpringMVC

C. @ComponentScan：默认扫描@SpringBootApplication所在类的同级目录以及它的子目录。

4.2 关闭自动配置

通过上述，我们得知，Spring Boot会根据项目中的jar包依赖，自动做出配置，Spring Boot支持的自动配置如下（非常多）：

如果我们不需要Spring Boot自动配置，想关闭某一项的自动配置，该如何设置呢？

比如：我们不想自动配置solr，想手动配置。

@SpringBootApplication(exclude={SolrAutoConfiguration.class})

package com.itcast; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration; import org.springframework.context.annotation.Configuration; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.ResponseBody; @Controller @SpringBootApplication(exclude={SolrAutoConfiguration.class}) @Configuration public class HelloApplication { @RequestMapping("/hello") @ResponseBody public String hello(){ return "hello springBoot!"; } public static void main(String[] args) { SpringApplication.run(HelloApplication.class, args); } }

4.3自定义Banner

启动Spring Boot项目后会看到这样的图案：

这个图片其实是可以自定义的

a)打开网站： http://patorjk.com/software/taag/#p=display&h=3&v=3&f=4Max&t=itcast Spring Boot

b)拷贝生成的字符到一个文本文件中，并且将该文件命名为banner.txt

c)将banner.txt拷贝到项目的resources目录中

d)重新启动程序，查看效果：

如果不想看到这个banner,也可以关闭

package com.itcast; import org.springframework.boot.Banner; import org.springframework.boot.SpringApplication; import org.springframework.boot.autoconfigure.SpringBootApplication; import org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration; import org.springframework.context.annotation.Configuration; import org.springframework.stereotype.Controller; import org.springframework.web.bind.annotation.RequestMapping; import org.springframework.web.bind.annotation.ResponseBody; @Controller @SpringBootApplication(exclude={SolrAutoConfiguration.class}) @Configuration public class HelloApplication { @RequestMapping("/hello") @ResponseBody public String hello(){ return "hello springBoot!"; } public static void main(String[] args) { SpringApplication app=new SpringApplication(HelloApplication.class); app.setBannerMode(Banner.Mode.OFF); app.run(args); } }

4.4 全局配置文件

Spring Boot项目使用一个全局的配置文件application.properties或者是application.yml，在resources目录下或者类路径下的/config下，一般我们放到resources下。

注意：在相同目录下，application.properties的配置级别高于application.yml。即当同时存在是application.yml是个摆设

a)修改tomcat的端口

application.properties文件中

server.port=8081 application.yml文件中 server: port: 8088

运行结果：

2018-05-19 17:12:30.533 INFO 11936 --- [ main] o.s.b.w.embedded.tomcat.TomcatWebServer : Tomcat started on port(s): 8081 (http) with context path ''b)修改进入DispatcherServlet的规则为：*.html

application.properties文件中

server.port=8081 server.servlet-path=*.html application.yml文件中 server: port: 8088 servlet-path: /*.jspc)SpringBoot对各种日志框架都做了支持，我们可以通过配置来修改默认的日志的配置 application.properties文件中 logging.level.org.springframework=DEBUGapplication.yml文件中

日志级别从低到高分为TRACE < DEBUG < INFO < WARN < ERROR < FATAL，如果设置为WARN，则低于WARN的信息都不会输出。

Spring Boot中默认配置ERROR、WARN和INFO级别的日志输出到控制台。

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