Spring、SpringMVC注解方式整合

1 原理

• Web容器在启动的时候，会扫描每个jar包下的META-INF/services/javax.servlet.ServletContainerInitializer文件。
• 加载META-INF/services/javax.servlet.ServletContainerInitializer这个文件指定的类SpringContainerInitializer。

• Spring的应用一启动就会加载感兴趣的WebApplicationInitializer接口下的所有组件，并且为WebApplicationInitializer组件创建对象（组件不能是接口或者抽象类）。

package org.springframework.web;

import java.lang.reflect.Modifier;
import java.util.LinkedList;
import java.util.List;
import java.util.ServiceLoader;
import java.util.Set;

import javax.servlet.ServletContainerInitializer;
import javax.servlet.ServletContext;
import javax.servlet.ServletException;
import javax.servlet.annotation.HandlesTypes;

import org.springframework.core.annotation.AnnotationAwareOrderComparator;
import org.springframework.lang.Nullable;
import org.springframework.util.ReflectionUtils;

@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {

    @Override
    public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
            throws ServletException {

        List<WebApplicationInitializer> initializers = new LinkedList<>();

        if (webAppInitializerClasses != null) {
            for (Class<?> waiClass : webAppInitializerClasses) {
                // Be defensive: Some servlet containers provide us with invalid classes,
                // no matter what @HandlesTypes says...
                if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
                        WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
                    try {
                        initializers.add((WebApplicationInitializer)
                                ReflectionUtils.accessibleConstructor(waiClass).newInstance());
                    }
                    catch (Throwable ex) {
                        throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
                    }
                }
            }
        }

        if (initializers.isEmpty()) {
            servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
            return;
        }

        servletContext.log(initializers.size() + " Spring WebApplicationInitializers detected on classpath");
        AnnotationAwareOrderComparator.sort(initializers);
        for (WebApplicationInitializer initializer : initializers) {
            initializer.onStartup(servletContext);
        }
    }

}

• 其中：
• AbstractContextLoaderInitializer中有createRootApplicationContext()方法用来创建根容器。
• AbstractDispatcherServletInitializer有createServletApplicationContext()方法用来创建web的IOC容器，有createDispatcherServlet()方法来创建DispatchServlet，然后将创建好的DispatcherServlet添加到ServletContext中，并且创建getServletMappings()方法让用户来创建Servlet的映射。

    protected void registerDispatcherServlet(ServletContext servletContext) {
        String servletName = getServletName();
        Assert.hasLength(servletName, "getServletName() must not return null or empty");

        WebApplicationContext servletAppContext = createServletApplicationContext();
        Assert.notNull(servletAppContext, "createServletApplicationContext() must not return null");

        FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
        Assert.notNull(dispatcherServlet, "createDispatcherServlet(WebApplicationContext) must not return null");
        dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());

        ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
        if (registration == null) {
            throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " +
                    "Check if there is another servlet registered under the same name.");
        }

        registration.setLoadOnStartup(1);
        registration.addMapping(getServletMappings());
        registration.setAsyncSupported(isAsyncSupported());

        Filter[] filters = getServletFilters();
        if (!ObjectUtils.isEmpty(filters)) {
            for (Filter filter : filters) {
                registerServletFilter(servletContext, filter);
            }
        }

        customizeRegistration(registration);
    }

• AbstractAnnotationConfigDispatcherServletInitializer(注解方式配置DispatchServlet初始化器)，使用createRootApplicationContext()方法来创建根容器，其方法调用了一个抽象方法getRootConfigClasses()以便传入配置类；使用createServletApplicationContext()方法创建Web的IOC容器，其方法调用了一个抽象方法getServletConfigClasses()以便传入SpringMVC的配置类。

package org.springframework.web.servlet.support;

import org.springframework.lang.Nullable;
import org.springframework.util.ObjectUtils;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.AnnotationConfigWebApplicationContext;

public abstract class AbstractAnnotationConfigDispatcherServletInitializer
        extends AbstractDispatcherServletInitializer {

    /**
     * {@inheritDoc}
     * <p>This implementation creates an {@link AnnotationConfigWebApplicationContext},
     * providing it the annotated classes returned by {@link #getRootConfigClasses()}.
     * Returns {@code null} if {@link #getRootConfigClasses()} returns {@code null}.
     */
    @Override
    @Nullable
    protected WebApplicationContext createRootApplicationContext() {
        Class<?>[] configClasses = getRootConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
            context.register(configClasses);
            return context;
        }
        else {
            return null;
        }
    }

    /**
     * {@inheritDoc}
     * <p>This implementation creates an {@link AnnotationConfigWebApplicationContext},
     * providing it the annotated classes returned by {@link #getServletConfigClasses()}.
     */
    @Override
    protected WebApplicationContext createServletApplicationContext() {
        AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
        Class<?>[] configClasses = getServletConfigClasses();
        if (!ObjectUtils.isEmpty(configClasses)) {
            context.register(configClasses);
        }
        return context;
    }

    /**
     * Specify {@code @Configuration} and/or {@code @Component} classes for the
     * {@linkplain #createRootApplicationContext() root application context}.
     * @return the configuration for the root application context, or {@code null}
     * if creation and registration of a root context is not desired
     */
    @Nullable
    protected abstract Class<?>[] getRootConfigClasses();

    /**
     * Specify {@code @Configuration} and/or {@code @Component} classes for the
     * {@linkplain #createServletApplicationContext() Servlet application context}.
     * @return the configuration for the Servlet application context, or
     * {@code null} if all configuration is specified through root config classes.
     */
    @Nullable
    protected abstract Class<?>[] getServletConfigClasses();

}

• 总结：以注解方式启动SpringMVC，只需要写一个类继承AbstractAnnotationConfigDispatcherServletInitializer，重写getRootConfigClasses()方法和getServletConfigClasses()方法即可。

2 Spring、SpringMVC整合

2.1 导入所需要jar包的maven坐标

<!-- junit -->
<dependency>
    <groupId>junit</groupId>
    <artifactId>junit</artifactId>
    <version>4.12</version>
    <scope>test</scope>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aop</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-aspects</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-jdbc</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-orm</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-web</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-tx</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-test</artifactId>
    <version>5.2.2.RELEASE</version>
</dependency>
<dependency>
    <groupId>javax.servlet</groupId>
    <artifactId>javax.servlet-api</artifactId>
    <version>4.0.1</version>
    <scope>provided</scope>
</dependency>

2.2 整合

• 示例：
• MyAbstractAnnotationConfigDispatcherServletInitializer.java

package com.sunxiaping.config;

import org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer;

public class MyAbstractAnnotationConfigDispatcherServletInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
    /**
     * 获取根容器的配置类 类似于Spring的配置文件
     * @return
     */
    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class[]{RootConfig.class};
    }

    /**
     * 获取Web容器的配置类 类似于SpringMVC的配置
     * @return
     */
    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class[]{AppConfig.class};
    }

    /**
     * 获取DispatchServlet的映射信息
     * @return
     */
    @Override
    protected String[] getServletMappings() {
        return new String[]{"/"};
    }
}

• RootConfig.java

package com.sunxiaping.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.stereotype.Controller;

//Spring容器不扫描@Controller
@Configuration
@ComponentScan(value = "com.sunxiaping",
        excludeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION, classes = Controller.class)})
public class RootConfig {

}

• AppConfig.java

package com.sunxiaping.config;

import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.annotation.FilterType;
import org.springframework.stereotype.Controller;
import org.springframework.web.servlet.config.annotation.*;
import org.springframework.web.servlet.i18n.LocaleChangeInterceptor;
import org.springframework.web.servlet.theme.ThemeChangeInterceptor;

//Spring容器只扫描@Controller
@Configuration
@ComponentScan(value = "com.sunxiaping",
        includeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION, classes = Controller.class)},
        useDefaultFilters = false)
@EnableWebMvc //相当于<mvc:annotation-drivern>
public class AppConfig extends WebMvcConfigurerAdapter {

    /**
     * 配置视图解析器
     *
     * @param registry
     */
    @Override
    public void configureViewResolvers(ViewResolverRegistry registry) {
        registry.jsp("/WEB-INF/view", ".jsp");
    }

    /**
     * 相当于原来的 <mvc:default-servlet-handler/>
     *
     * @param configurer
     */
    @Override
    public void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
        configurer.enable();
    }

    /**
     * <mvc:view-controller path="/" view-name="home"/>
     *
     * @param registry
     */
    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/").setViewName("home");
    }

    /**
     * <mvc:interceptors>
     *     <bean class="org.springframework.web.servlet.i18n.LocaleChangeInterceptor"/>
     *     <mvc:interceptor>
     *         <mvc:mapping path="/**"/>
     *         <mvc:exclude-mapping path="/admin/**"/>
     *         <bean class="org.springframework.web.servlet.theme.ThemeChangeInterceptor"/>
     *     </mvc:interceptor>
     * </mvc:interceptors>
     * @param registry
     */
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LocaleChangeInterceptor());
        registry.addInterceptor(new ThemeChangeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**");
    }

}