由Spring MVC到Spring Boot

披荆斩棘的小哥哥
464 阅读4分钟

传统的SpringMVC开发我们要做哪些准备

1、maven依赖

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>5.2.7.RELEASE</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>5.2.7.RELEASE</version>
    </dependency>

2.web.xml

    <servlet>
        <servlet-name>springmvc</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>classpath:dispatch-servle.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

    <servlet-mapping>
        <servlet-name>springmvc</servlet-name>        
        <url-pattern>/</url-pattern>
    </servlet-mapping>

3、dispatch-servlet.xml

<context:component-scan: base-package = "com.xxx.xxx.xxx"/>扫描的包路径
Spring通过<context:component-scan/>标签的配置，会自动将扫描到的该路径下带有
@Component，@Controller，@Service，@Repository等注解标记的组件注册到工厂中，来处理我们的请求

<mvc:annotation-driven/>启用注解驱动

<!-- 视图解析器-->
<bean id = "" class = "xxx.xxx.xxx.xxx">
    <property name = "" value = ""/>
    <property name = "" value = ""/>
</bean>

4、如果要整合Spring的话还需要application-context.xml 如端口号等

5、配置Tomcat

现在到Spring Boot开发

1、添加依赖

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

2、启动程序入口

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

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

我们只做了2件事情，添加依赖和一个程序启动入口，其实这就是SpringBoot的2个特性

起步依赖：

       Spring Boot通过起步依赖为项目的依赖管理提供帮助，起步依赖其实就是特殊的maven依赖，利用传递依赖解析把常用的库聚合在一起，组成了为特定功能定制的依赖

自动装配：

       创建Bean并把Bean注入到Ioc容器的过程。这就是自动装配。通过@SpringBootApplication注解完成。我们来看一下这个注解

@SpringBootApplication
     @Configuration
     @ComponentScan
     @EnableAutoConfiguration
           Import({AutoconfigurationImportSelector.class})

核心的实现在AutoconfiguratuionImportSelector类里，该类实现了ImportSelector接口，重写了selectImports方法，跟踪下这个类

最终我们会看到他是读取META-INF下spring.factories文件配置，看下这个配置文件

看一下Spring Boot帮我们装配了什么，倒数第6行是mvc相关配置
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\
org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\
org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\
org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\
org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\
org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\
org.springframework.boot.autoconfigure.cloud.CloudServiceConnectorsAutoConfiguration,\
org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\
org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\
org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\
org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveElasticsearchRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.elasticsearch.ReactiveRestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jdbc.JdbcRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoReactiveRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\
org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\
org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\
org.springframework.boot.autoconfigure.elasticsearch.rest.RestClientAutoConfiguration,\
org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\
org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\
org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\
org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\
org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\
org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\
org.springframework.boot.autoconfigure.http.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.http.codec.CodecsAutoConfiguration,\
org.springframework.boot.autoconfigure.influx.InfluxDbAutoConfiguration,\
org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\
org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\
org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\
org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\
org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\
org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\
org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\
org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\
org.springframework.boot.autoconfigure.jsonb.JsonbAutoConfiguration,\
org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\
org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\
org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\
org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\
org.springframework.boot.autoconfigure.mongo.MongoReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\
org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\
org.springframework.boot.autoconfigure.quartz.QuartzAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketRequesterAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketServerAutoConfiguration,\
org.springframework.boot.autoconfigure.rsocket.RSocketStrategiesAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.UserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.servlet.SecurityFilterAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.reactive.ReactiveUserDetailsServiceAutoConfiguration,\
org.springframework.boot.autoconfigure.security.rsocket.RSocketSecurityAutoConfiguration,\
org.springframework.boot.autoconfigure.security.saml2.Saml2RelyingPartyAutoConfiguration,\
org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\
org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.servlet.OAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.client.reactive.ReactiveOAuth2ClientAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.servlet.OAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.security.oauth2.resource.reactive.ReactiveOAuth2ResourceServerAutoConfiguration,\
org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskExecutionAutoConfiguration,\
org.springframework.boot.autoconfigure.task.TaskSchedulingAutoConfiguration,\
org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\
org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.client.RestTemplateAutoConfiguration,\
org.springframework.boot.autoconfigure.web.embedded.EmbeddedWebServerFactoryCustomizerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.ReactiveWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.WebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.error.ErrorWebFluxAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.ClientHttpConnectorAutoConfiguration,\
org.springframework.boot.autoconfigure.web.reactive.function.client.WebClientAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.ServletWebServerFactoryAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.error.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.servlet.WebMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.reactive.WebSocketReactiveAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketServletAutoConfiguration,\
org.springframework.boot.autoconfigure.websocket.servlet.WebSocketMessagingAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration,\
org.springframework.boot.autoconfigure.webservices.client.WebServiceTemplateAutoConfiguration

当然这些SpringBooot肯定不会都帮我们自动装配，Spring中有条件注解，会有选择的帮我们去自动装配

@ConditionalOnBean // 当给定的在bean存在时,则实例化当前Bean @ConditionalOnMissingBean // 当给定的在bean不存在时,则实例化当前Bean @ConditionalOnClass // 当给定的类名在类路径上存在，则实例化当前Bean @ConditionalOnMissingClass // 当给定的类名在类路径上不存在，则实例化当前Bean

如果我们pom.xm文件中没有添加web依赖，那么SpringBooot肯定不会帮我们自动装配MVC相关配置

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

Spring注解驱动

没有注解之前如果实现io容器，通过xml是这么配置

<beans>
    <bean id = "userService" class="com.user.UserService">
        <property name="userDAO" ref = "userDAO"></property>
    </bean>
    <bean id = "userDAO" class="com.user.UserDAO"></bean>
</beans>

public class UserService implements UserServiceInter {
 
    private UserDAO userDAO;

    get/set方法
}

后面Spring不断演进在2.5版本出现了注解例如

@Controller、@Service、@Component、@Responsity等有了这些标签Spring就会帮助我们管理这些类

@Service
public class UserService implements UserServiceInter{
    @Autowired
    private UserDAO userDAO;
}

@Responsity
public class UserDAO implements UserDAOInter{
}

有了以上注解，还要加上下面的配置表示扫描某个包下面带有注解的类
<context:component-scan: base-package:"com.xxx.xxx.xxx"/>

经过上面的演进，描述bean的xml文件没有了，但是我们还是要依赖一个

<context:component-scan: base-package:"com.xxx.xxx.xxx"/>

Spring继续演进在3.0版本以后出现@Configuration，Java config

@Configuration
public class Config {

        // 有了这个就不需要在UserService类上加@Service注解
	@Bean 
	public UserService getUserService() {
		UserService userService = new UserService();
		return userService;
	}
       // 有了这个就不需要在UserDAO类上加@Responsity注解
       @Bean 
       public UserDAO getUserDAO() {
	    return new UserDAO();
	}
}

@ComponentScan等价于xml里<context:component-scan: base-package:"com.xxx.xxx.xxx"/>
会自动扫描带有Controller、@Service、@Component、@Responsity注解的类，所以如果一个类有这几个
注解中的一个就不需要在配置类里显示@Bean声明了

如果有很多的配置类需要被扫描到那怎么办呢？

第一种用法
用@Import注解导入其他配置@Import
@Import({ConfigA.class,ConfigB.class})
public class Config {

    public Config(){
        System.out.println("==============init Config===============");
    }
}

public class ConfigA {

    public Config() {
        System.out.println("==============init ConfigA===============");
    }
}
这种写法当然比较简单

第二种用法实现ImportSelector接口这个也是SpringBoot采用的用法
首先自定义一个注解
import org.springframework.context.annotation.Import;
import java.lang.annotation.*;

@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@Import({MySelector.class})
public @interface MyEnableAutoConfig {
}

实现ImportSelector接口
import org.springframework.context.annotation.ImportSelector;
import org.springframework.core.io.support.SpringFactoriesLoader;
import org.springframework.core.type.AnnotationMetadata;
import org.springframework.util.Assert;
import org.springframework.util.StringUtils;

import java.util.List;

public class MySelector implements ImportSelector {

    private Class<?>getSpringFactoriesLoaderFactoryClass(){
        //spring.factories文件里面的key,可以是任何一个普通类
        return MyEnableAutoConfig.class;
    }

    @Override
    public String[] selectImports(AnnotationMetadata annotationMetadata) {
        List<String> configurations = getConditionConfigurations();
        return StringUtils.toStringArray(configurations);
    }

    protected List<String> getConditionConfigurations(){
        List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
              getSpringFactoriesLoaderFactoryClass(),MySelector.class.getClassLoader());
        Assert.notEmpty(configurations,"no config");
        return configurations;
    }

}
写自己的配置类
import com.example.test.dao.UserDao;
import com.example.test.service.UserService;
import org.springframework.context.annotation.Bean;

@Configuration
public class ConfigB { 
   
    public ConfigB() {
        System.out.println("==============init ConfigB===============");
    }

    @Bean("userService")
    public UserService getUserService(){
        return new UserService(getUserDao());    
    }

    @Bean("userDao")
    public UserDao getUserDao(){
        return new UserDao();
    }

}
userDao注入到userService
读取的配置文件resource/META-INF/spring.factories
com.example.test.config.MyEnableAutoConfig=\
com.example.test.config.ConfigB,\
com.example.test.config.ConfigC

现在回过头来看看SpringBoot的三个核心注解，如果你掌握了

@Configuration

@ComponentScan

@Import

@EnableAutoConfiguration

这几个注解，那么SpringBooot的自动装配原理自然也就很容易理解了

avatar
文章
阅读
粉丝