Spring 註解驅動（二）Servlet 3.0 註解驅動在 Spring MVC 中的應用

Spring 註解驅動（二）Servlet 3.0 註解驅動在 Spring MVC 中的應用

Spring 系列目錄(http://www.javashuo.com/article/p-kqecupyl-bm.html)

在 Servlet 3.0 時支持註解啓動，再也不須要 web.xml 配製文件。詳見《Servlet 3.0 規範（二）註解規範》：http://www.javashuo.com/article/p-kktlszqi-dv.html

1、Servlet 3.0 與 Spring MVC 整合

@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) {
                // WebApplicationInitializer 的實現類
                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;
        }

        // 執行 onStartup
        AnnotationAwareOrderComparator.sort(initializers);
        for (WebApplicationInitializer initializer : initializers) {
            initializer.onStartup(servletContext);
        }
    }

}

Spring MVC 啓動時會調用 WebApplicationInitializer 實現類的 onStartup 方法啓動 WEB 容器。WebApplicationInitializer 的繼承關係以下：

WebApplicationInitializer
    |- AbstractContextLoaderInitializer
        |- AbstractDispatcherServletInitializer
            |- AbstractAnnotationConfigDispatcherServletInitializer

• AbstractContextLoaderInitializer 建立 Root 根容器並註冊 ContextLoaderListener，建立根容器由子類實現。核心方法：registerContextLoaderListener

• AbstractDispatcherServletInitializer 建立 Servlet 容器，並註冊 DispatcherServlet 和 Filete，建立根容器由子類實現。核心方法：registerDispatcherServlet

• AbstractAnnotationConfigDispatcherServletInitializer 建立 Root 和 Servlet 容器。核心方法：createRootApplicationContext、createServletApplicationContext

斷點調試，webAppInitializerClasses 有如下類，顯然只有一個實現類 MyAbstractAnnotationConfigDispatcherServletInitializer 執行了 onStartup 方法。

0 = {Class@4467} "class org.springframework.web.servlet.support.AbstractAnnotationConfigDispatcherServletInitializer"
1 = {Class@4468} "class org.springframework.web.servlet.support.AbstractDispatcherServletInitializer"
2 = {Class@4469} "class org.springframework.web.server.adapter.AbstractReactiveWebInitializer"
3 = {Class@4470} "class org.springframework.web.context.AbstractContextLoaderInitializer"
4 = {Class@4471} "class com.github.binarylei.MyAbstractAnnotationConfigDispatcherServletInitializer"

2、WebMvcConfigurer 接管 xml 配置

(1) @EnableWebMvc

開啓 Spring 高級功能，至關於 <mvc:annotation-driven/>

(2) WebMvcConfigurer

對應之前 XML 配置中的每一項，以 interceptors 爲例，其他詳見官方文檔：Spring 註解配置類 WebMvcConfigurer(https://docs.spring.io/spring/docs/5.1.3.RELEASE/spring-framework-reference/web.html#mvc-config)

@Configuration
@EnableWebMvc
public class WebConfig implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(new LocaleChangeInterceptor());
        registry.addInterceptor(new ThemeChangeInterceptor()).addPathPatterns("/**").excludePathPatterns("/admin/**");
        registry.addInterceptor(new SecurityInterceptor()).addPathPatterns("/secure/*");
    }
}

以上代碼至關於以前 XML 中的

<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:interceptor>
        <mvc:mapping path="/secure/*"/>
        <bean class="org.example.SecurityInterceptor"/>
    </mvc:interceptor>
</mvc:interceptors>

3、模擬 Spring Boot 將 WEB 打成 jar 包運行

Spring 官方文檔註解配置

使用 tomcat7-maven-plugin 插件模擬 Spring Boot。

(1) WebApplicationInitializer 實現類

public class MyAbstractAnnotationConfigDispatcherServletInitializer extends
        AbstractAnnotationConfigDispatcherServletInitializer {

    // Root 容器配置
    protected Class<?>[] getRootConfigClasses() {
        return new Class[0];
    }

    // Servlet 容器配置
    protected Class<?>[] getServletConfigClasses() {
        return new Class[]{MyServletConfig.class};
    }

    // Servlet Mapping，取代 web.xml 中的 servlet-mapping 配置
    protected String[] getServletMappings() {
        return new String[]{"/"};
    }

    // Filter 配置，取代 web.xml 中的 filter 配置
    @Override
    protected Filter[] getServletFilters() {
        CharacterEncodingFilter encodingFilter = new CharacterEncodingFilter();
        encodingFilter.setEncoding("utf-8");
        encodingFilter.setForceRequestEncoding(true);
        encodingFilter.setForceResponseEncoding(true);

        return new Filter[]{encodingFilter};
    }
}

// 取代 spring-mvc.xml 配製
@Configuration
@ComponentScan(basePackages = "com.github.binarylei",
        excludeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION, classes = Controller.class)})
public class MyRootConfig {
}

// 取代 spring-context.xml 配製
@Configuration
@ComponentScan(basePackages = "com.github.binarylei",
        includeFilters = {@ComponentScan.Filter(type = FilterType.ANNOTATION, classes = Controller.class)})
public class MyServletConfig {

    @Bean
    public ViewResolver viewResolver(){
        InternalResourceViewResolver viewResolver = new InternalResourceViewResolver();
        viewResolver.setViewClass(JstlView.class);
        viewResolver.setPrefix("/WEB-INF/view/");
        viewResolver.setSuffix(".jsp");
        return viewResolver;
    }
}

(2) tomcat7-maven-plugin 配製

tomcat7-maven-plugin 官網：http://tomcat.apache.org/maven-plugin-2.1/executable-war-jar.html

<packaging>war</packaging>
<properties>
    <spring.version>5.1.0.RELEASE</spring.version>

    <project.build.sourceEncoding>utf-8</project.build.sourceEncoding>
    <maven.compiler.source>1.8</maven.compiler.source>
    <maven.compiler.target>1.8</maven.compiler.target>
</properties>

<dependencies>
    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-webmvc</artifactId>
        <version>${spring.version}</version>
    </dependency>
    <dependency>
        <groupId>javax.servlet</groupId>
        <artifactId>javax.servlet-api</artifactId>
        <version>3.1.0</version>
        <scope>provided</scope>
    </dependency>
    <dependency>
        <groupId>jstl</groupId>
        <artifactId>jstl</artifactId>
        <version>1.2</version>
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-war-plugin</artifactId>
            <version>3.2.0</version>
            <configuration>
                <failOnMissingWebXml>false</failOnMissingWebXml>
            </configuration>
        </plugin>
        <plugin>
            <groupId>org.apache.tomcat.maven</groupId>
            <artifactId>tomcat7-maven-plugin</artifactId>
            <version>2.1</version>
            <executions>
                <execution>
                    <id>tomcat-run</id>
                    <goals>
                        <goal>exec-war-only</goal>
                    </goals>
                    <phase>package</phase>
                    <configuration>
                        <path>/</path>
                    </configuration>
                </execution>
            </executions>
        </plugin>
    </plugins>
</build>

(3) 運行

執行 mvn package 後生成了兩個文件：spring-war-1.0.0.war 和 spring-war-1.0.0-war-exec.jar

# localhost:8080/
java -jar spring-war-1.0.0-war-exec.jar 
# IDEA remote 調試時(suspend=y)
java -jar -agentlib:jdwp=transport=dt_socket,server=y,suspend=y,address=*:5005 spring-war-1.0.0-war-exec.jar

tomcat 啓動遠程時報錯：https://www.aliyun.com/jiaocheng/1443062.html

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天天用心記錄一點點。內容也許不重要，但習慣很重要！