SpringBoot学习（一）----第一个Helloworld程序

Spring Boot 简介

Spring Boot 是由 Pivotal 团队提供用来简化 Spring 的搭建和开发过程的全新框架。随着近些年来微服务技术的流行，Spring Boot 也成了时下炙手可热的热点技术。

Spring Boot 去除了大量的 xml 配置文件，简化了复杂的依赖管理，配合各种 starter 使用，基本上可以做到自动化配置。Spring 可以做的事情，现在用 Spring boot 都可以做。

Spring Boot 它使用“习惯优于配置”（项目中存在大量的配置，此外还内置一个习惯性的配置，让你无须手动进行配置）的理念让你的项目快速运行起来。

使用 Spring Boot 很容易创建一个独立运行（运行 jar，内嵌 Servlet 容器）、准生产级别的基于 Spring 框架的项目，使用 Spring Boot 你可以不用或者只需要很少的 Spring 配置。

SpringBoot来简化Spring应用开发，约定大约配置，去繁从简，just run就能创建一个独立的产品级别的应用。

SpringBoot的优点

1、快速创建独立运行的Spring项目以及与主流框架集成

2、使用嵌入式的Servlet容器，应用无需打成WAR包

3、starters自动依赖与版本控制

4、大量的自动配置，简化开发，也可修改默认值

5、无需配置XML，无代码生成，开箱即用

6、准生产环境的运行时应用监控

7、与云计算的天然集成

 Spring Boot 核心功能

1）独立运行的 Spring 项目

Spring Boot 可以以 jar 包的形式独立运行，运行一个 Spring Boot 项目只需通过 java–jar xx.jar 来运行。

2）内嵌 Servlet 容器

Spring Boot 可选择内嵌 Tomcat、Jetty 或者 Undertow，这样我们无须以 war 包形式部署项目。

3）提供 starter 简化 Maven 配置

Spring 提供了一系列的 starter pom 来简化 Maven 的依赖加载。

4）自动配置 Spring

Spring Boot 会根据在类路径中的 jar 包、类，为 jar 包里的类自动配置 Bean，这样会极大地减少我们要使用的配置。当然，Spring Boot 只是考虑了大多数的开发场景，并不是所有的场景，若在实际开发中我们需要自动配置 Bean，而 Spring Boot 没有提供支持，则可以自定义自动配置。

5）准生产的应用监控

Spring Boot 提供基于 http、ssh、telnet 对运行时的项目进行监控。

6）无代码生成和 xml 配置

Spring Boot 的神奇的不是借助于代码生成来实现的，而是通过条件注解来实现的，这是 Spring 4.x 提供的新特性。Spring 4.x 提倡使用 Java 配置和注解配置组合，而 Spring Boot 不需要任何 xml 配置即可实现 Spring 的所有配置。

SpringBoot快速搭建

SpringBoot是Spring框架对“约定优先于配置（Convention Over Configuration）”理念的最佳实践的产物，一个典型的 SpringBoot 应用本质上其实就是一个基于 Spring 框架的应用。

下面动手使用Maven写第一个SpringBoot程序。

第一步，使用Maven创建一个SpringBoot项目，具体maven程序如何创建，看maven模块内容。

第二步，导入SpringBoot所需要的jar包，使用Maven的pom.xml文件写依赖。

pom.xml

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<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>com.zk.myspringboot_002</groupId>
    <artifactId>myspringboot_002</artifactId>
    <packaging>war</packaging>
    <version>0.0.1-SNAPSHOT</version>
    <name>myspringboot_002 Maven Webapp</name>
    <url>http://maven.apache.org</url>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <!-- 继承父包 -->
    </dependencies>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.4.3.RELEASE</version>
    </parent>
    <build>
        <finalName>myspringboot_002</finalName>
    </build>
</project>

第三步，创建SpringBootApplicationFirst.java和TestController.java

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package com.zk.myspringboot;
 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
 
@SpringBootApplication
public class SpringBootApplicationFirst {
     
    public static void main(String[]args){
        SpringApplication.run(SpringBootApplicationFirst.class, args);
    }
    public static void run(String...arg0) {
        System.out.println("Hello world from Command Line Runner");
    }
}
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package com.zk.myspringboot;
 
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class TestController {  
    @RequestMapping("/demo")
    public String home() {
        return "Hello,world";
    }  
}

第四步，执行SpringBootApplicationFirst.java,run as->spring boot app,myeclipse中显示的执行结果如下：

 

可以看到，默认端口为8080。

第五步，在浏览器中输入localhost:8080/demo，根据RequestMapping的url名称访问。

成功。

看一下SpringBootApplication注解里面的具体的内容

SpringBootApplication.java

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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))
public @interface SpringBootApplication {
 
    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return the classes to exclude
     */
    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
     */
    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 {};
 
}

其中标注的三个注解，这三种注解的主要功能如下：

一.@SpringBootConfiguration 并能够在他们的 “Application” 类上定义额外的配置

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/*
 * Copyright 2012-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
package org.springframework.boot;
 
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
 
import org.springframework.context.annotation.Configuration;
 
/**
 * Indicates that a class provides Spring Boot application
 * {@link Configuration @Configuration}. Can be used as an alternative to the Spring's
 * standard {@code @Configuration} annotation so that configuration can be found
 * automatically (for example in tests).
 * <p>
 * Application should only ever include <em>one</em> {@code @SpringBootConfiguration} and
 * most idiomatic Spring Boot applications will inherit it from
 * {@code @SpringBootApplication}.
 *
 * @author Phillip Webb
 * @since 1.4.0
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Configuration
public @interface SpringBootConfiguration {
 
}

@SpringBootConfiguration继承自@Configuration，二者功能也一致，标注当前类是配置类，并会将当前类内声明的一个或多个以@Bean注解标记的方法的实例纳入到srping容器中，并且实例名就是方法名。

二.@EnableAutoConfiguration的作用启动自动的配置，@EnableAutoConfiguration注解的意思就是Springboot根据你添加的 jar 包来配置你项目的默认配置，比如根据spring-boot-starter-web ，来判断你的项目是否需要添加了webmvc和tomcat，就会自动的帮你配置 web 项目中所需要的默认配置。简单点说就是它会根据定义在 classpath 下的类，自动的给你生成一些 Bean，并加载到 Spring 的 Context 中。

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/*
 * Copyright 2012-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
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.autoconfigure.condition.ConditionalOnBean;
import org.springframework.boot.autoconfigure.condition.ConditionalOnClass;
import org.springframework.boot.autoconfigure.condition.ConditionalOnMissingBean;
import org.springframework.boot.context.embedded.EmbeddedServletContainerFactory;
import org.springframework.boot.context.embedded.tomcat.TomcatEmbeddedServletContainerFactory;
import org.springframework.context.annotation.Conditional;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.Import;
import org.springframework.core.io.support.SpringFactoriesLoader;
 
/**
 * Enable auto-configuration of the Spring Application Context, attempting to guess and
 * configure beans that you are likely to need. Auto-configuration classes are usually
 * applied based on your classpath and what beans you have defined. For example, If you
 * have {@code tomcat-embedded.jar} on your classpath you are likely to want a
 * {@link TomcatEmbeddedServletContainerFactory} (unless you have defined your own
 * {@link EmbeddedServletContainerFactory} bean).
 * <p>
 * Auto-configuration tries to be as intelligent as possible and will back-away as you
 * define more of your own configuration. You can always manually {@link #exclude()} any
 * configuration that you never want to apply (use {@link #excludeName()} if you don't
 * have access to them). You can also exclude them via the
 * {@code spring.autoconfigure.exclude} property. Auto-configuration is always applied
 * after user-defined beans have been registered.
 * <p>
 * The package of the class that is annotated with {@code @EnableAutoConfiguration} has
 * specific significance and is often used as a 'default'. For example, it will be used
 * when scanning for {@code @Entity} classes. It is generally recommended that you place
 * {@code @EnableAutoConfiguration} in a root package so that all sub-packages and classes
 * can be searched.
 * <p>
 * Auto-configuration classes are regular Spring {@link Configuration} beans. They are
 * located using the {@link SpringFactoriesLoader} mechanism (keyed against this class).
 * Generally auto-configuration beans are {@link Conditional @Conditional} beans (most
 * often using {@link ConditionalOnClass @ConditionalOnClass} and
 * {@link ConditionalOnMissingBean @ConditionalOnMissingBean} annotations).
 *
 * @author Phillip Webb
 * @author Stephane Nicoll
 * @see ConditionalOnBean
 * @see ConditionalOnMissingBean
 * @see ConditionalOnClass
 * @see AutoConfigureAfter
 */
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
    String ENABLED_OVERRIDE_PROPERTY = "spring.boot.enableautoconfiguration";
 
    /**
     * Exclude specific auto-configuration classes such that they will never be applied.
     * @return the classes to exclude
     */
    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
     */
    String[] excludeName() default {};
}

三、@ComponentScan  组件扫描

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/*
 * Copyright 2002-2016 the original author or authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
 
package org.springframework.context.annotation;
 
import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Repeatable;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;
 
import org.springframework.beans.factory.support.BeanNameGenerator;
import org.springframework.core.annotation.AliasFor;
import org.springframework.core.type.filter.TypeFilter;
 
/**
 * Configures component scanning directives for use with @{@link Configuration} classes.
 * Provides support parallel with Spring XML's {@code <context:component-scan>} element.
 *
 * <p>Either {@link #basePackageClasses} or {@link #basePackages} (or its alias
 * {@link #value}) may be specified to define specific packages to scan. If specific
 * packages are not defined, scanning will occur from the package of the
 * class that declares this annotation.
 *
 * <p>Note that the {@code <context:component-scan>} element has an
 * {@code annotation-config} attribute; however, this annotation does not. This is because
 * in almost all cases when using {@code @ComponentScan}, default annotation config
 * processing (e.g. processing {@code @Autowired} and friends) is assumed. Furthermore,
 * when using {@link AnnotationConfigApplicationContext}, annotation config processors are
 * always registered, meaning that any attempt to disable them at the
 * {@code @ComponentScan} level would be ignored.
 *
 * <p>See {@link Configuration @Configuration}'s Javadoc for usage examples.
 *
 * @author Chris Beams
 * @author Juergen Hoeller
 * @author Sam Brannen
 * @since 3.1
 * @see Configuration
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Repeatable(ComponentScans.class)
public @interface ComponentScan {
 
    /**
     * Alias for {@link #basePackages}.
     * <p>Allows for more concise annotation declarations if no other attributes
     * are needed — for example, {@code @ComponentScan("org.my.pkg")}
     * instead of {@code @ComponentScan(basePackages = "org.my.pkg")}.
     */
    @AliasFor("basePackages")
    String[] value() default {};
 
    /**
     * Base packages to scan for annotated components.
     * <p>{@link #value} is an alias for (and mutually exclusive with) this
     * attribute.
     * <p>Use {@link #basePackageClasses} for a type-safe alternative to
     * String-based package names.
     */
    @AliasFor("value")
    String[] basePackages() default {};
 
    /**
     * Type-safe alternative to {@link #basePackages} 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.
     */
    Class<?>[] basePackageClasses() default {};
 
    /**
     * The {@link BeanNameGenerator} class to be used for naming detected components
     * within the Spring container.
     * <p>The default value of the {@link BeanNameGenerator} interface itself indicates
     * that the scanner used to process this {@code @ComponentScan} annotation should
     * use its inherited bean name generator, e.g. the default
     * {@link AnnotationBeanNameGenerator} or any custom instance supplied to the
     * application context at bootstrap time.
     * @see AnnotationConfigApplicationContext#setBeanNameGenerator(BeanNameGenerator)
     */
    Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class;
 
    /**
     * The {@link ScopeMetadataResolver} to be used for resolving the scope of detected components.
     */
    Class<? extends ScopeMetadataResolver> scopeResolver() default AnnotationScopeMetadataResolver.class;
 
    /**
     * Indicates whether proxies should be generated for detected components, which may be
     * necessary when using scopes in a proxy-style fashion.
     * <p>The default is defer to the default behavior of the component scanner used to
     * execute the actual scan.
     * <p>Note that setting this attribute overrides any value set for {@link #scopeResolver}.
     * @see ClassPathBeanDefinitionScanner#setScopedProxyMode(ScopedProxyMode)
     */
    ScopedProxyMode scopedProxy() default ScopedProxyMode.DEFAULT;
 
    /**
     * Controls the class files eligible for component detection.
     * <p>Consider use of {@link #includeFilters} and {@link #excludeFilters}
     * for a more flexible approach.
     */
    String resourcePattern() default ClassPathScanningCandidateComponentProvider.DEFAULT_RESOURCE_PATTERN;
 
    /**
     * Indicates whether automatic detection of classes annotated with {@code @Component}
     * {@code @Repository}, {@code @Service}, or {@code @Controller} should be enabled.
     */
    boolean useDefaultFilters() default true;
 
    /**
     * Specifies which types are eligible for component scanning.
     * <p>Further narrows the set of candidate components from everything in {@link #basePackages}
     * to everything in the base packages that matches the given filter or filters.
     * <p>Note that these filters will be applied in addition to the default filters, if specified.
     * Any type under the specified base packages which matches a given filter will be included,
     * even if it does not match the default filters (i.e. is not annotated with {@code @Component}).
     * @see #resourcePattern()
     * @see #useDefaultFilters()
     */
    Filter[] includeFilters() default {};
 
    /**
     * Specifies which types are not eligible for component scanning.
     * @see #resourcePattern
     */
    Filter[] excludeFilters() default {};
 
    /**
     * Specify whether scanned beans should be registered for lazy initialization.
     * <p>Default is {@code false}; switch this to {@code true} when desired.
     * @since 4.1
     */
    boolean lazyInit() default false;
 
 
    /**
     * Declares the type filter to be used as an {@linkplain ComponentScan#includeFilters
     * include filter} or {@linkplain ComponentScan#excludeFilters exclude filter}.
     */
    @Retention(RetentionPolicy.RUNTIME)
    @Target({})
    @interface Filter {
 
        /**
         * The type of filter to use.
         * <p>Default is {@link FilterType#ANNOTATION}.
         * @see #classes
         * @see #pattern
         */
        FilterType type() default FilterType.ANNOTATION;
 
        /**
         * Alias for {@link #classes}.
         * @see #classes
         */
        @AliasFor("classes")
        Class<?>[] value() default {};
 
        /**
         * The class or classes to use as the filter.
         * <p>The following table explains how the classes will be interpreted
         * based on the configured value of the {@link #type} attribute.
         * <table border="1">
         * <tr><th>{@code FilterType}</th><th>Class Interpreted As</th></tr>
         * <tr><td>{@link FilterType#ANNOTATION ANNOTATION}</td>
         * <td>the annotation itself</td></tr>
         * <tr><td>{@link FilterType#ASSIGNABLE_TYPE ASSIGNABLE_TYPE}</td>
         * <td>the type that detected components should be assignable to</td></tr>
         * <tr><td>{@link FilterType#CUSTOM CUSTOM}</td>
         * <td>an implementation of {@link TypeFilter}</td></tr>
         * </table>
         * <p>When multiple classes are specified, <em>OR</em> logic is applied
         * — for example, "include types annotated with {@code @Foo} OR {@code @Bar}".
         * <p>Custom {@link TypeFilter TypeFilters} may optionally implement any of the
         * following {@link org.springframework.beans.factory.Aware Aware} interfaces, and
         * their respective methods will be called prior to {@link TypeFilter#match match}:
         * <ul>
         * <li>{@link org.springframework.context.EnvironmentAware EnvironmentAware}</li>
         * <li>{@link org.springframework.beans.factory.BeanFactoryAware BeanFactoryAware}
         * <li>{@link org.springframework.beans.factory.BeanClassLoaderAware BeanClassLoaderAware}
         * <li>{@link org.springframework.context.ResourceLoaderAware ResourceLoaderAware}
         * </ul>
         * <p>Specifying zero classes is permitted but will have no effect on component
         * scanning.
         * @since 4.2
         * @see #value
         * @see #type
         */
        @AliasFor("value")
        Class<?>[] classes() default {};
 
        /**
         * The pattern (or patterns) to use for the filter, as an alternative
         * to specifying a Class {@link #value}.
         * <p>If {@link #type} is set to {@link FilterType#ASPECTJ ASPECTJ},
         * this is an AspectJ type pattern expression. If {@link #type} is
         * set to {@link FilterType#REGEX REGEX}, this is a regex pattern
         * for the fully-qualified class names to match.
         * @see #type
         * @see #classes
         */
        String[] pattern() default {};
    }
}

可以通过该注解指定扫描某些包下包含如下注解的均自动注册为 spring beans：@Component、@Service、 @Repository、 @Controller、@Entity 等等。

除了这三种注解外：

还有四个方法

1.Class[] exclude() default {}:
根据 class 来排除，排除特定的类加入 spring 容器，传入参数 value 类型是 class 类型。

2.String[] excludeName() default {}:

根据 class name 来排除，排除特定的类加入 spring 容器，传入参数 value 类型是 class 的全类名字符串数组。

3.String[] scanBasePackages() default {}:
指定扫描包，参数是包名的字符串数组。

4.Class[] scanBasePackageClasses() default {}:
扫描特定的包，参数类似是 Class 类型数组。

使用ideal编写第一个springboot helloworld程序

首先创建一个maven工程

建好工程后，再建项目下的java目录和resources目录

pom.xml 

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<?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>org.zk</groupId>
  <artifactId>springboot_001</artifactId>
  <version>1.0-SNAPSHOT</version>
  <packaging>war</packaging>
 
  <name>springboot_001 Maven Webapp</name>
  <!-- FIXME change it to the project's website -->
  <url>http://www.example.com</url>
 
  <properties>
    <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
    <maven.compiler.source>1.7</maven.compiler.source>
    <maven.compiler.target>1.7</maven.compiler.target>
  </properties>
  <parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.5.9.RELEASE</version>
  </parent>
  <dependencies>
    <dependency>
      <groupId>junit</groupId>
      <artifactId>junit</artifactId>
      <version>4.11</version>
      <scope>test</scope>
    </dependency>
    <dependency>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-starter-web</artifactId>
      <version>2.5.4</version>
    </dependency>
  </dependencies>
 
  <build>
    <finalName>springboot_001</finalName>
    <pluginManagement><!-- lock down plugins versions to avoid using Maven defaults (may be moved to parent pom) -->
      <plugins>
        <plugin>
          <artifactId>maven-clean-plugin</artifactId>
          <version>3.1.0</version>
        </plugin>
        <!-- see http://maven.apache.org/ref/current/maven-core/default-bindings.html#Plugin_bindings_for_war_packaging -->
        <plugin>
          <artifactId>maven-resources-plugin</artifactId>
          <version>3.0.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-compiler-plugin</artifactId>
          <version>3.8.0</version>
        </plugin>
        <plugin>
          <artifactId>maven-surefire-plugin</artifactId>
          <version>2.22.1</version>
        </plugin>
        <plugin>
          <artifactId>maven-war-plugin</artifactId>
          <version>3.2.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-install-plugin</artifactId>
          <version>2.5.2</version>
        </plugin>
        <plugin>
          <artifactId>maven-deploy-plugin</artifactId>
          <version>2.8.2</version>
        </plugin>
      </plugins>
    </pluginManagement>
  </build>
</project>

HelloController.java

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package com.zk.controller;
 
 
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
 
@RestController
public class HelloController {
 
    @RequestMapping("/hello")
    public String hello(){
        return "hello";
    }
}
SpringBootTestApplication.java
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package com.zk.controller;
 
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
 
@SpringBootApplication
public class SpringBootTestApplication {
    public static void main(String[] args){
        SpringApplication.run(SpringBootTestApplication.class);
    }
}　

 启动springBoot项目

 访问http://localhost:8080/hello

 　

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