spring boot 启动tomcat 及 mvc过程

关于SpringMvc dispatchServlet配置(spring-boot)

接手过三个不同方式的web项目,spring mvc 配置各有不同，整理一下

• 3.spring boot 启动方式

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3.spring boot 启动方式**

1。首先查看启动方法，找到spring applicontext初始化的地方

ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                    args);
            ConfigurableEnvironment environment = prepareEnvironment(listeners,
                    applicationArguments);
            Banner printedBanner = printBanner(environment);
            context = createApplicationContext();
            analyzers = new FailureAnalyzers(context);
            prepareContext(context, environment, listeners, applicationArguments,
                    printedBanner);

这里会创建applicationContext上下文并且调用refresh方法

2。applicationContext refresh() 过程中会调用所有beanFactoryPostProcessor，
而ConfigurationClassPostProcessor 是扫描@Import 注解的处理类

3。这时候再回到我们的main方法，

1。
@SpringBootApplication
 @EnableEurekaServer
@EnableDiscoveryClient
public class EurekaServerApplication {

2。
@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 {

3。
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {

4。
public class AutoConfigurationImportSelector

一步步点进@SpringBootApplication注解，发现最终调用了
AutoConfigurationImportSelector，接着再看此类selectImport方法

1。  AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
                    .loadMetadata(this.beanClassLoader);
            AnnotationAttributes attributes = getAttributes(annotationMetadata);
            List<String> configurations = getCandidateConfigurations(annotationMetadata,
                    attributes);
2。List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
                getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
        Assert.notEmpty(configurations,
                "No auto configuration classes found in META-INF/spring.factories. If you "
                        + "are using a custom packaging, make sure that file is correct.");

这里注释声明了会扫描所有META-INF/spring.factories中的类,改文件很多spring包中都有，我们主要看spring-boot-autoconfigure中的

org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\
org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\
org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration,\
org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\
org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\
org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\
org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\
org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\
org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\

截取了部分配置，其中最重要的三个,
1.EmbeddedServletContainerAutoConfiguration
注入容器bean，根据当前包扫描，默认tomcat
2.DispatcherServletAutoConfiguration
默认dispatchServlet配置
3.WebMvcAutoConfiguration

其中tomcat 到这里只是创建了tomcatFactory，真正创建并启动还是在refresh()方法中

1.EmbeddedWebApplicationContext中
EmbeddedServletContainer localContainer = this.embeddedServletContainer;
        ServletContext localServletContext = getServletContext();
        if (localContainer == null && localServletContext == null) {
            EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
            this.embeddedServletContainer = containerFactory
                    .getEmbeddedServletContainer(getSelfInitializer());
        }
2.TomcatEmbeddedServletContainerFactory
public EmbeddedServletContainer getEmbeddedServletContainer(
            ServletContextInitializer... initializers) {
        Tomcat tomcat = new Tomcat();
        File baseDir = (this.baseDirectory != null ? this.baseDirectory
                : createTempDir("tomcat"));
        tomcat.setBaseDir(baseDir.getAbsolutePath());
        Connector connector = new Connector(this.protocol);
        tomcat.getService().addConnector(connector);
        customizeConnector(connector);
        tomcat.setConnector(connector);
        tomcat.getHost().setAutoDeploy(false);
        configureEngine(tomcat.getEngine());
        for (Connector additionalConnector : this.additionalTomcatConnectors) {
            tomcat.getService().addConnector(additionalConnector);
        }
        prepareContext(tomcat.getHost(), initializers);
        return getTomcatEmbeddedServletContainer(tomcat);
    }
3.public TomcatEmbeddedServletContainer(Tomcat tomcat, boolean autoStart) {
        Assert.notNull(tomcat, "Tomcat Server must not be null");
        this.tomcat = tomcat;
        this.autoStart = autoStart;
        initialize();
    }
4.initialize();中最终启动web容器