Springboot学习笔记3-Springboot web开发
springboot在开发web项目的时候具备天然的优势，现在的很多企业级开发都是依托于springboot的。
使用springboot的步骤：
1、创建一个SpringBoot应用，选择我们需要的模块，SpringBoot就会默认将我们的需要的模块自动配置好。
2、手动在配置文件中配置部分配置项目就可以运行起来了。
3、专注编写业务代码，不需要考虑以前那样一大堆的配置了。
1、springboot整合servlet
很多同学在刚接触web开发的时候第一个接触的都是servlet，下面我们来使用springboot整合servlet
（1）编写servlet类
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| @WebServlet(name = "myServlet",urlPatterns = "/srv")
public class MyServlet extends HttpServlet {
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
System.out.println("111");
super.doGet(req, resp);
}
}
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（2）在启动类上添加如下配置
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| @SpringBootApplication
@ServletComponentScan
public class ConfigApplication {
public static void main(String[] args) {
SpringApplication.run(ConfigApplication.class, args);
}
}
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（3）编写filter类
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| @WebFilter(filterName = "MyFilter", urlPatterns = "/filter")
public class MyFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("init");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("filter");
chain.doFilter(request,response);
}
@Override
public void destroy() {
System.out.println("destory");
}
}
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（4）编写监听器
listener是servlet规范定义的一种特殊类，用于监听servletContext,HttpSession和ServletRequest等域对象的创建和销毁事件。监听域对象的属性发生修改的事件，用于在事件发生前、发生后做一些必要的处理。可用于以下方面：1、统计在线人数和在线用户2、系统启动时加载初始化信息3、统计网站访问量4、记录用户访问路径。
编写监听器类
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| package com.mashibing.config;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;
public class MyHttpSessionListener implements HttpSessionListener {
public static int online=0;
@Override
public void sessionCreated(HttpSessionEvent se) {
System.out.println("创建session");
online++;
}
@Override
public void sessionDestroyed(HttpSessionEvent se) {
System.out.println("销毁session");
}
}
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添加到配置类
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| package com.mashibing.config;
import org.springframework.boot.web.servlet.ServletListenerRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.LocaleResolver;
import org.springframework.web.servlet.config.annotation.EnableWebMvc;
import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@Configuration
public class MyMvcConfig implements WebMvcConfigurer {
@Bean
public ServletListenerRegistrationBean listenerRegist(){
ServletListenerRegistrationBean srb = new ServletListenerRegistrationBean();
srb.setListener(new MyHttpSessionListener());
System.out.println("listener");
return srb;
}
}
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添加控制层代码
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| package com.mashibing.controller;
import com.mashibing.config.MyHttpSessionListener;
import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.ResponseBody;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
@Controller
public class ThymeleafController {
@RequestMapping("/login")
public String login(HttpServletRequest request){
HttpSession session = request.getSession(true);
return "login";
}
@RequestMapping("online")
@ResponseBody
public String online(){
return "当前在线人数："+MyHttpSessionListener.online +"人";
}
}
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先发送login请求，然后再发送online的请求
2、静态资源的配置
默认情况下，Spring Boot 将在 classpath 或者 ServletContext 根目录下从名为 /static （/public、/resources 或 /META-INF/resources）目录中服务静态内容。它使用了 Spring MVC 的 ResourceHttpRequestHandler，因此您可以通过添加自己的 WebMvcConfigurerAdapter 并重写 addResourceHandlers 方法来修改此行为。
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| @Override
public void addResourceHandlers(ResourceHandlerRegistry registry) {
if (!this.resourceProperties.isAddMappings()) {
logger.debug("Default resource handling disabled");
return;
}
Duration cachePeriod = this.resourceProperties.getCache().getPeriod();
CacheControl cacheControl = this.resourceProperties.getCache().getCachecontrol().toHttpCacheControl();
if (!registry.hasMappingForPattern("/webjars/**")) {
customizeResourceHandlerRegistration(registry.addResourceHandler("/webjars/**")
.addResourceLocations("classpath:/META-INF/resources/webjars/")
.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
}
String staticPathPattern = this.mvcProperties.getStaticPathPattern();
if (!registry.hasMappingForPattern(staticPathPattern)) {
customizeResourceHandlerRegistration(registry.addResourceHandler(staticPathPattern)
.addResourceLocations(getResourceLocations(this.resourceProperties.getStaticLocations()))
.setCachePeriod(getSeconds(cachePeriod)).setCacheControl(cacheControl));
}
}
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（1）加载webjars文件
在pom文件中添加jquery的相关依赖，直接可以通过浏览器访问到http://localhost:8080/webjars/jquery/3.4.1/jquery.js
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| <dependency>
<groupId>org.webjars</groupId>
<artifactId>jquery</artifactId>
<version>3.4.1</version>
</dependency>
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（2）加载静态资源
当查找静态资源的时候能够发现静态资源的路径是/**，会去ResourceProperties这个类，可以看到对应的资源目录。
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| @ConfigurationProperties(prefix = "spring.resources", ignoreUnknownFields = false)
public class ResourceProperties {
private static final String[] CLASSPATH_RESOURCE_LOCATIONS = { "classpath:/META-INF/resources/",
"classpath:/resources/", "classpath:/static/", "classpath:/public/" };
private String[] staticLocations = CLASSPATH_RESOURCE_LOCATIONS;
private String[] appendSlashIfNecessary(String[] staticLocations) {
String[] normalized = new String[staticLocations.length];
for (int i = 0; i < staticLocations.length; i++) {
String location = staticLocations[i];
normalized[i] = location.endsWith("/") ? location : location + "/";
}
return normalized;
}
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可以看到静态资源的目录一共有如下几个：
“classpath:/resources/”
“classpath:/static/”
“classpath:/public/”
（3）首页的配置信息
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| @Bean
public WelcomePageHandlerMapping welcomePageHandlerMapping(ApplicationContext applicationContext,
FormattingConversionService mvcConversionService, ResourceUrlProvider mvcResourceUrlProvider) {
WelcomePageHandlerMapping welcomePageHandlerMapping = new WelcomePageHandlerMapping(
new TemplateAvailabilityProviders(applicationContext), applicationContext, getWelcomePage(),
this.mvcProperties.getStaticPathPattern());
welcomePageHandlerMapping.setInterceptors(getInterceptors(mvcConversionService, mvcResourceUrlProvider));
return welcomePageHandlerMapping;
}
private Optional<Resource> getWelcomePage() {
String[] locations = getResourceLocations(this.resourceProperties.getStaticLocations());
return Arrays.stream(locations).map(this::getIndexHtml).filter(this::isReadable).findFirst();
}
private Resource getIndexHtml(String location) {
return this.resourceLoader.getResource(location + "index.html");
}
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3、springmvc的扩展
springmvc框架是一个mvc的web框架，springmvc允许创建@controller和@RestController bean来处理传入的HTTP请求，控制器种的方法通过@RequestMapping注解映射到HTTP。
Springboot提供了适用于大多数Springmvc应用的自动配置。
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| 引入 ContentNegotiatingViewResolver 和 BeanNameViewResolver bean视图解析器。
支持服务静态资源，包括对 WebJar 的支持。
自动注册 Converter（网页传入的数据封装成对象，完成数据类型的转化）、GenericConverter 和 Formatter bean（将日期转换成规定的格式）。
支持 HttpMessageConverter，用来转换http请求和响应。
自动注册 MessageCodesResolver，定义错误代码生成规则。
支持静态 index.html。
支持自定义 Favicon。
自动使用 ConfigurableWebBindingInitializer bean，将请求树绑定到javaBean中。
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自动配置了ViewResolver，就是我们之前学习的SpringMVC的视图解析器：即根据方法的返回值取得视图对象（View），然后由视图对象决定如何渲染（转发，重定向）。
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|
@Bean
@ConditionalOnBean({ViewResolver.class})
@ConditionalOnMissingBean(
name = {"viewResolver"},
value = {ContentNegotiatingViewResolver.class}
)
public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
resolver.setContentNegotiationManager((ContentNegotiationManager)beanFactory.getBean(ContentNegotiationManager.class));
resolver.setOrder(-2147483648);
return resolver;
}
@Nullable
public View resolveViewName(String viewName, Locale locale) throws Exception {
RequestAttributes attrs = RequestContextHolder.getRequestAttributes();
Assert.state(attrs instanceof ServletRequestAttributes, "No current ServletRequestAttributes");
List<MediaType> requestedMediaTypes = this.getMediaTypes(((ServletRequestAttributes)attrs).getRequest());
if (requestedMediaTypes != null) {
List<View> candidateViews = this.getCandidateViews(viewName, locale, requestedMediaTypes);
View bestView = this.getBestView(candidateViews, requestedMediaTypes, attrs);
if (bestView != null) {
return bestView;
}
}
String mediaTypeInfo = this.logger.isDebugEnabled() && requestedMediaTypes != null ? " given " + requestedMediaTypes.toString() : "";
if (this.useNotAcceptableStatusCode) {
if (this.logger.isDebugEnabled()) {
this.logger.debug("Using 406 NOT_ACCEPTABLE" + mediaTypeInfo);
}
return NOT_ACCEPTABLE_VIEW;
} else {
this.logger.debug("View remains unresolved" + mediaTypeInfo);
return null;
}
}
private List<View> getCandidateViews(String viewName, Locale locale, List<MediaType> requestedMediaTypes)
throws Exception {
List<View> candidateViews = new ArrayList<>();
if (this.viewResolvers != null) {
Assert.state(this.contentNegotiationManager != null, "No ContentNegotiationManager set");
for (ViewResolver viewResolver : this.viewResolvers) {
View view = viewResolver.resolveViewName(viewName, locale);
if (view != null) {
candidateViews.add(view);
}
for (MediaType requestedMediaType : requestedMediaTypes) {
List<String> extensions = this.contentNegotiationManager.resolveFileExtensions(requestedMediaType);
for (String extension : extensions) {
String viewNameWithExtension = viewName + '.' + extension;
view = viewResolver.resolveViewName(viewNameWithExtension, locale);
if (view != null) {
candidateViews.add(view);
}
}
}
}
}
if (!CollectionUtils.isEmpty(this.defaultViews)) {
candidateViews.addAll(this.defaultViews);
}
return candidateViews;
}
@Override
protected void initServletContext(ServletContext servletContext) {
Collection<ViewResolver> matchingBeans =
BeanFactoryUtils.beansOfTypeIncludingAncestors(obtainApplicationContext(), ViewResolver.class).values();
if (this.viewResolvers == null) {
this.viewResolvers = new ArrayList<>(matchingBeans.size());
for (ViewResolver viewResolver : matchingBeans) {
if (this != viewResolver) {
this.viewResolvers.add(viewResolver);
}
}
}
else {
for (int i = 0; i < this.viewResolvers.size(); i++) {
ViewResolver vr = this.viewResolvers.get(i);
if (matchingBeans.contains(vr)) {
continue;
}
String name = vr.getClass().getName() + i;
obtainApplicationContext().getAutowireCapableBeanFactory().initializeBean(vr, name);
}
}
AnnotationAwareOrderComparator.sort(this.viewResolvers);
this.cnmFactoryBean.setServletContext(servletContext);
}
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通过上面的代码分析，我们知道了springboot是在容器中去找视图解析器，因此，我们可以给容器自定义添加视图解析器,这个类会帮我们将他组合起来。
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@Bean
public ViewResolver myViewResolver(){
return new MyViewResolver();
}
private static class MyViewResolver implements ViewResolver{
@Override
public View resolveViewName(String s, Locale locale) throws Exception {
return null;
}
}
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扩展使用springmvc
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package com.mashibing.config;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
@Configuration
public class MyMvcConfig implements WebMvcConfigurer {
@Override
public void addViewControllers(ViewControllerRegistry registry) {
registry.addViewController("/msb").setViewName("success");
}
}
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注意：将html添加到添加到Templates中,需要添加模板引擎。
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| <dependency>
<groupId>org.thymeleaf</groupId>
<artifactId>thymeleaf-spring5</artifactId>
</dependency>
<dependency>
<groupId>org.thymeleaf.extras</groupId>
<artifactId>thymeleaf-extras-java8time</artifactId>
</dependency>
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